Long brake pedal travel with large "dead zone"

[MetalMan]

Hey guys, I've been chasing this problem for a while and hoping for some insight.

My S4's brake pedal travel is long with what feels like a large ~1.5-2 inch "dead zone" (no reaction from brakes). Also with engine off and pedal pumped until stiff, there is still has a pretty large amount of travel (probably the same 1.5-2 inches).
This really doesn't inspire confidence in the car's braking... especially when I switch back to S4 from driving my Corvette, which has ZERO dead zone. At least the S4's brakes work well enough once the dead zone has been surpassed.

When I push the pedal quickly through the dead zone (engine running), there is a noise from the pedal/booster, kinda like an air squishing noise if that makes sense. My wife thinks more of it than I do (my suspicion is it's only a symptom).

Here's what I've done, in chronological order:

• verified brake booster isn't leaking / losing vacuum, also replaced the firewall check valve
• replaced brake fluid reservoir (Genuine part)
• stainless steel brake lines all around (Centric parts). Bled brakes.
• replaced all brake pads with EBC Reds. Lubed all slider pins. Bled front brakes.
• rotors weren't that old when I bought the car, they're fine still
• replaced master cylinder (TRW part)
• bled 5L fluid using 2bar pressure (Motive bleeder) over 2 instances of bleeding (11 days apart). Also bled ABS using VCDS probably 10-15 times (through driver-front caliper bleeder). Have followed Bentley procedures, and then some, including tapping calipers with a rubber mallet. Also used pedal pump method with engine running and Motive bleeder also going @ 20psi. Seemed like I got all the air out. Reservoir never ran low on fluid after replacing MC.
• Last night I played with the rod/nut between master cylinder and brake booster, but learned that only affects brake pedal position.

Any additional ideas? Thanks for reading!

[MetalMan]

These are some of the next steps I am considering:

• Rear calipers: I've read the dead zone issue can be caused by sticking/seized rear calipers; but: the pistons turned in fine when I changed pads, it's a CA car that doesn't have rust, and the parking brake seems to work great. Still I may dismount the rear calipers and see how they individually actuate from depressing the brake pedal.
• Bleeding brakes with 2bar pressure, but pedal pump WITHOUT closing bleeders. Probably would have a slower return stroke on the pedal. Supposedly this helps with moving fluid through faster and may help get out any stubborn air bubbles.
• Vacuum bleeding at the calipers? I have a vacuum bleeder hand pump.
• Brake booster: it's one of the few things I haven't replaced/messed with; it's not a fun one to swap out unless you're already replacing the master cylinder. At least used ones are under $50 shipped.

[MetalMan]

Okay, tried extra-bleeding the rears today... put through 2L of fresh fluid, 1.3L right-rear and 0.7L left-rear. Used the Motive power bleeder @ 20+psi, left the bleeder open, and got in a real leg workout pumping the brake pedal (with slow pedal release on each stroke). At no point did I see ANY air exit the bleeder valves, and unfortunately (fortunately?) it made no difference on pedal feel.

As noted in the first post above, the "air squishing" noise was a little more noticeable with increased pedal travel due to brake bleeding. I could more-so discern the noise during the "dead zone", almost like there's a buffer/damper that is actuated before the master cylinder is actually depressed. Perhaps this points a bit more to something going on with the brake booster?

[rguil]

b5 isnt well known for having the most responsive brakes. Its a "luxury" car after all LOL. The air squishy noise is normal, i think. Its happened on all the vag cars ive owned and worked on.
Did you bleed the abs pump with VCDS?

[MetalMan]

b5 isnt well known for having the most responsive brakes. Its a "luxury" car after all LOL. The air squishy noise is normal, i think. Its happened on all the vag cars ive owned and worked on.
Did you bleed the abs pump with VCDS?

I've had 3 B5s total, my prior [crashed] B5 A4 definitely didn't exhibit this long brake pedal travel situation.

• .... Also bled ABS using VCDS probably 10-15 times (through driver-front caliper bleeder).

[christianb5s4]

Did you bleed your ABS enough times using VCDS? I kid. For what it's worth, on stock calipers I had that same thing but maybe not as severe. I was going to mention tired stock brake lines but you have SS already.

You're welcome to feel my brakes albeit 18Zs up front to see if it feels similar?

[MetalMan]

Did you bleed your ABS enough times using VCDS? I kid. For what it's worth, on stock calipers I had that same thing but maybe not as severe. I was going to mention tired stock brake lines but you have SS already.

You're welcome to feel my brakes albeit 18Zs up front to see if it feels similar?

Seriously, I'm hoping I didn't shorten the ABS pump's life with all that bleeding!

Perhaps we can do a "brake feel swap", you can see how bad mine is and I can see how good yours is? lol

[MacDaddy]

I think you may need to bench bleed your master again, its a bitch to get all the air out.

Buy a master cylinder bleeding kit (it has various plastic adapters to go in the side and hoses that go into the small cap on the reservoir) and pump it till it stops blowing bubbles.

[christianb5s4]

Seriously, I'm hoping I didn't shorten the ABS pump's life with all that bleeding!

Perhaps we can do a "brake feel swap", you can see how bad mine is and I can see how good yours is? lol

Anytime! Just let me know when you're free.

[MetalMan]

Anytime! Just let me know when you're free.

I think you may need to bench bleed your master again, its a bitch to get all the air out.

Buy a master cylinder bleeding kit (it has various plastic adapters to go in the side and hoses that go into the small cap on the reservoir) and pump it till it stops blowing bubbles.

Thanks for chiming in. Frankly I didn't bench bleed the MC because the Bentley manual says nothing about it.
Came across a thread you made 2 years ago on a very similar topic:
https://www.audizine.com/forum/showt...-non-ESP-b5-s4

I bought a bench bleeder kit 6 years ago (also for an old B5 A4 that had squishy pedal after MC replacement...):
https://www.amazon.com/gp/product/B00E6TXW6U/
Never really used it, but would be awesome if I can use it for this.

To be clear, are these the right steps to bench bleed in-car?

1. Jack up the rear end so the MC is at least horizontal
2. Unscrew brake lines from MC, and screw in plastic adapters to the brake line ports
3. Hook up hoses to the plastic adapters, the other ends go into the fluid reservoir
4. Slowly pump brake pedal, until no more air appears in the hoses
5. Unscrew plastic adapters and reattach brake lines
6. Bleed all 4 brakes, following Bentley procedure: RR, LR, RF, LF. Open LF bleeder and run ABS pump a few times

[Maker]

I tried all the above you did including SS brake lines with minimal improvement.
The biggest difference came after checking the clearance between the end of the booster rod
and the master cylinder. In my case, there was .065 clearance. I pulled out the bullnose pin
and installed a .045 thick spacer, reassembled and pressure bled only at the ABS feed lines and
now they feel and work like they should.

[darren p.]

It sounds like you have air in the system somewhere. I recently struggled with this and stumbled upon this thread which fixed my issue.
https://www.audizine.com/forum/showt...ding+procedure

[MacDaddy]

Thanks for chiming in. Frankly I didn't bench bleed the MC because the Bentley manual says nothing about it.
Came across a thread you made 2 years ago on a very similar topic:
https://www.audizine.com/forum/showt...-non-ESP-b5-s4

I bought a bench bleeder kit 6 years ago (also for an old B5 A4 that had squishy pedal after MC replacement...):
https://www.amazon.com/gp/product/B00E6TXW6U/
Never really used it, but would be awesome if I can use it for this.

To be clear, are these the right steps to bench bleed in-car?

1. Jack up the rear end so the MC is at least horizontal
2. Unscrew brake lines from MC, and screw in plastic adapters to the brake line ports
3. Hook up hoses to the plastic adapters, the other ends go into the fluid reservoir
4. Slowly pump brake pedal, until no more air appears in the hoses
5. Unscrew plastic adapters and reattach brake lines
6. Bleed all 4 brakes, following Bentley procedure: RR, LR, RF, LF. Open LF bleeder and run ABS pump a few times

If you didnt bleed your master then i am 100% confident that is your issue, i was chasing a crappy brake pedal for years, you could bench bleed in the car, i dont see why it wouldnt work.

When i bled mine in the vice i found i had to really vary how fast/slow etc to get all the air out. Simply pumping it willy nilly wasnt getting the air out, so id say have a helper to observe untill all the air bubbles are gone

[MetalMan]

If you didnt bleed your master then i am 100% confident that is your issue, i was chasing a crappy brake pedal for years, you could bench bleed in the car, i dont see why it wouldnt work.

When i bled mine in the vice i found i had to really vary how fast/slow etc to get all the air out. Simply pumping it willy nilly wasnt getting the air out, so id say have a helper to observe untill all the air bubbles are gone

I evaluated the potential for in-car bench bleeding last night. Looks like there's poor access to the rear-most brake line without removing the reservoir. And it turns out I don't have the correct MC adapter fittings.
I checked out how level I could get the MC by jacking up the rear end. This was the highest I was willing to lift only the rear:
https://photos.app.goo.gl/yAh9Dv7kqCKgib3h7
https://photos.app.goo.gl/m81NLTuQjZ5boLfA8
The MC was nowhere near level with that angle.

Based on the information posted here (thanks guys!), this is what I tried yesterday:

• Rear end raised up high
• Pressure bleeder filled with fluid and pressurized to <5psi (just to make sure there was a steady supply of fluid into the res)
• Ran ABS pump 25 times for right-rear. Witnessed no air bubbles. Bled ~600mL fluid.
• Ran ABS pump 30 times on left-rear. Noticed not much fluid compared to right side, so loosened bleeder screw a little more. Ran ABS pump another ~25 times, and seemed to get a few bubbles out, certainly more fluid drained this time. Bled ~800mL fluid.
• Decided to try cranking pressure bleeder up to 30psi as well [for "fun"], didn't really make a difference
• Pedal still feels more or less the same, with the dead zone

So one of my next steps will be to again jack up the rear end and try bench bleeding in-car. I'll buy this kit for the adapters (but use clear tubing):
https://www.amazon.com/Dorman-13911-...dp/B001SG8ZC0/

I tried all the above you did including SS brake lines with minimal improvement.
The biggest difference came after checking the clearance between the end of the booster rod
and the master cylinder. In my case, there was .065 clearance. I pulled out the bullnose pin
and installed a .045 thick spacer, reassembled and pressure bled only at the ABS feed lines and
now they feel and work like they should.

I think this is very interesting... the "dead zone" doesn't feel squishy, it just kinda feels like there's no actuation of the master cylinder.
Can you provide a little more description on this "bullnose pin"? How did you remove it from the booster (booster removed from car), and where did you put the .045 spacer?

[Maker]

Remove your master cylinder and you can pull out the bullnose
contact pin from the end of the booster shaft with needle nose pliers.
Take care not to drop it as you pull it out. It has small stem with a light press fit
into the booster shaft.I used 2 small washers 1/4 dia. od .022 thick and placed them
on the stem with a little bit of greese to hold them in place.You want to end up with .02 gap.
Reinstall in the shaft end with needle nose pliers. Reasembled and bleed just the two feed lines at the ABS unit with the
pressure bleeder. I finally have decent brakes.
https://techtalk.mpbrakes.com/how-to...r-cylinder-gap

[MetalMan]

Remove your master cylinder and you can pull out the bullnose
contact pin from the end of the booster shaft with needle nose pliers.
Take care not to drop it as you pull it out. It has small stem with a light press fit
into the booster shaft.I used 2 small washers 1/4 dia. od .022 thick and placed them
on the stem with a little bit of greese to hold them in place.You want to end up with .02 gap.
Reinstall in the shaft end with needle nose pliers. Reasembled and bleed just the two feed lines at the ABS unit with the
pressure bleeder. I finally have decent brakes.
https://techtalk.mpbrakes.com/how-to...r-cylinder-gap

I appreciate your additional explanation! Very interesting stuff, including that article. Definitely looks like it would be worthwhile to check out... perhaps I could pull out the master, take measurements and/or add spacers for the bullnose pin, bench bleed the MC on a vice, reinstall MC and bleed.

Could also design & 3D print a tool similar to the Booster Pin Depth Gauge shown in that article instead of taking a bunch of measurements and doing math (reduce my chance for human error).

As far as bleeding the 2 ABS feed lines, did you use any special tools/fittings or just slip a hose over the flared brake line and use a hose clamp?

[MacDaddy]

That doorman kit is almost exactly what i used, looks like it comes with metric and standard adapters where mine was a “metric kit”.

Pumping up the brake bleeder to 30psi shouldn't be nessisary if you have an ESP car, thas only required for non ESP cars like mine.

[MetalMan]

Figured I'd share an intermediate update:

Made an attempt at in-car MC "bench" bleeding, rear end not lifted (car level).
First off, the Dorman kit only kind-of worked... the M10x1.0 fitting worked just fine, but the M12x1.0 fitting leaked (seemed like it's not long enough to reach the sealing surface inside the MC? that fitting didn't bottom out like the M10 fitting). This was a problem because if my wife released the brake pedal too fast, air would be drawn in through the M12x1.0 fitting.
In the end I had her stop pumping/slowly releasing when I could no longer see air bubbles on the pump stroke.

It's seemingly impossible to prevent fluid from leaking out of the brake lines after detaching them to the MC, so naturally there is air in those lines. Therefore, my next step was to do a full brake bleed. Which I did, mostly using the Motive power bleeder at 25-30psi, but also with ABS module cycling and some pedal pushes. The rear lines eventually put out an extreme amount of air bubbles but it seemed to clear up. The front lines didn't really put out any noticeable air bubbles.

Now the pedal feel is probably worse than before, but the brakes still work at least.

My next steps:

• order more brake fluid (I've gone through 10L now...). Been using Pentosin 1204204 which comes in a 5L jug, for ~$30 from RockAuto
• find a better M12x1.0 fitting, that will actually seal
• detach master cylinder
• measure brake booster pin to MC clearance, and shim if necessary per Maker
• properly bench bleed MC
• reinstall MC
• bleed ABS -> MC hard lines @ ABS module

[darren p.]

I don't envy you. I battled a similar issue to this in my VW a few years ago and bench bleeding the MC didn't solve it. It drove me nuts. Ultimately I figured out that the rear calipers were a little seized up and turning the pistons out a bit freed them both up. This was after the car had been sitting for a while though.

[zatch_303]

ABS output test? Not sure if our cars even have that but on the B8's this has fixed spongy brake pedal feel for most after swapping to the Q5 Brembo's. Random shot in the dark.

[MetalMan]

ABS output test? Not sure if our cars even have that but on the B8's this has fixed spongy brake pedal feel for most after swapping to the Q5 Brembo's. Random shot in the dark.

That's the same thing as where I mention "ran ABS pump" above.

[zatch_303]

Bah sorry, worth a shot. Best of luck.

[MetalMan]

4 month update
The S4 was down for 3.5 of the last 4 months, for a variety of things (plus not much time to work on it).

Got around to playing with the brakes. My plans were:

1. remove brake master cylinder and bench bleed it
2. check brake booster's bullnose pin fit to MC

I felt pretty confident the MC was adequately bench bled. For the record, I realized part-way through a check valve was needed to prevent air bubbles from back-flowing into the MC, so I ordered one.
Also the Dorman bench bleed kit's M12x1.0 fitting isn't long enough to seal in the MC, but I stuffed an O-ring behind it and that seemed to enable an adequate seal.

It was a little challenging measuring the gap between bullnose pin and MC; nonetheless my measurements suggested the gap was about 0.050-0.055". I had a 0.032" thick M4 washer laying around and added that behind the bullnose pin.
(FWIW I found this exercise interesting. Part of my job as a Mechanical Engineer is analyzing tolerances stackups in the design stage. No way would I allow such a large gap to occur)

Afterward I bled the front corners, and subsequently cracked open the brake line between MC and ABS @ the ABS module for the rear brakes and got a little bubble. Then I bled the rears.
I should note that this brake bleeding session wasn't my usual "full" session and I didn't bleed the ABS module.

After 3.5 months of the car being down, I got in a first drive last night. The brakes are still kinda soft (maybe slightly better) but at least they worked.

Thinking I need to do a full bleeding session next... In removing the MC initially, I drained too much fluid from the reservoir (through the front-driver brake caliper) and managed to get air in the line. Fingers crossed that more extensive bleeding including ABS module will resolve the long pedal travel!

[james 408]

brake pad initial bite has a bit of a factor, caliper flex has a bit of a factor, and certainly any gap between the pedal/MC pin would allow play.... but I tend to agree it's air in the lines. What are you using to prevent air from sucking into the back end anyway? if you're just pissing it out the port you're going to suck air in and your brake bleed will be completely ineffective, i don't care how much fluid you flush through it. Usually when I bleed the brakes (and haven't changed something like a master cylinder or sucked a bunch of air into an empty resevoir), you don't need to even remove much fluid at all to restore a tight pedal feel. like a tiny little bottle will do for all 4 corners. you only do the rest to flush the actual fluid to prevent the old fluid from bubble/boil. Are you using a $4 surgical tube from the auto parts store and a submerged container of fluid? if you're good there, then i'd be considering actual master cylinder function. the plungers specifically and them not sealing right allowing pressure to leak, at least initially or a little bit.

I'm not saying it's not possible you've got a bit of air stuck somewhere, but... rebleeding 10 times, might be worth finding a guy to just stupid-check your process. And the only reason they know is because they were stupid first.

I mean one time i was bleeding a clutch, and I didn't realize it didn't share the brake fluid resevoir. 30 minutes in and i'd sucked nothing but air in the system and i was baffled why my brake resevoir was still topped off.

[MetalMan]

brake pad initial bite has a bit of a factor, caliper flex has a bit of a factor, and certainly any gap between the pedal/MC pin would allow play.... but I tend to agree it's air in the lines. What are you using to prevent air from sucking into the back end anyway? if you're just pissing it out the port you're going to suck air in and your brake bleed will be completely ineffective, i don't care how much fluid you flush through it. Usually when I bleed the brakes (and haven't changed something like a master cylinder or sucked a bunch of air into an empty resevoir), you don't need to even remove much fluid at all to restore a tight pedal feel. like a tiny little bottle will do for all 4 corners. you only do the rest to flush the actual fluid to prevent the old fluid from bubble/boil. Are you using a $4 surgical tube from the auto parts store and a submerged container of fluid? if you're good there, then i'd be considering actual master cylinder function. the plungers specifically and them not sealing right allowing pressure to leak, at least initially or a little bit.

I'm not saying it's not possible you've got a bit of air stuck somewhere, but... rebleeding 10 times, might be worth finding a guy to just stupid-check your process. And the only reason they know is because they were stupid first.

I mean one time i was bleeding a clutch, and I didn't realize it didn't share the brake fluid resevoir. 30 minutes in and i'd sucked nothing but air in the system and i was baffled why my brake resevoir was still topped off.

What am I "using to prevent air from sucking into the back end"? Not sure I fully follow, most of my bleeding is with a Motive Power Bleeder. Yesterday I had it set between 15-25psi (varied depending on which wheel I bled).
But when I do the pedal pump method, my wife pumps the brakes and I open/close the bleeder screw to prevent back-flow when she releases the pedal. (it's kinda annoying, I basically use the commands: "pump" and "release" with her)

On my C5 Z06 I installed Russel speed bleeders, though. I think they work okay.

Also I use the Schwaben fluid catch container that ECS sells.

So I did remove/reinstall the MC, and did at one point introduce in air... therefore it may take more than a little fluid to push out the bubbles.

This MC is quite new, originally installed 9.5 months ago and has only seen 3k miles. (granted I didn't bench bleed it before initial installation)

If after this next round of "full" bleeding the pedal still feels bad, it will probably be time to seek a professional... I'm not thrilled about allowing someone else to work on the car since I do everything except tires & alignment, but I can admit my limitations.

[james 408]

There's a long video i didn't watch, but if you see that sprite bottle? https://www.youtube.com/watch?v=ioHjV4d6BWk that's key. you use it to catcht he fluid, but that can be any container. the key is the surgical tubing. not only can you see the tiny air bubble density as the fluid exits the bleeder, but unless you leave it sitting for a minute unattended, you can't suck air back into the system from the bleeder screw, there's the whole tubing filled with fluid with the end sitting in a pool of fluid, in other words, it's almost impossible to suck air back in the bleeder. this is the key to victory. it's basically a cyphon, but instead of actually pulling it out like a vacuum pump, it just prevents air from backflowing. you just get the right diameter surgical tubing, which is sitting in the auto parts store for an overpriced $4, or like 20 cents at a hardware store. Then hit up the recycling bin on the way out for a container. negates the need to shut off the bleeder screw while the brake/pressurebleeder is still going, and a little insurance, and a little extra visibility in what the condition of the fluid is coming out, and the air bubble density.

I don't even stop bleeding until the pedal feels solid at any corner. Even if there are tiny little bubbles in the fluid, that's really not going to cause any problems as long as the pedals firm. Not sure i've ever even seen "no air bubbles coming out", there's almost always some baby bubbles. backing off the brake slowly does like nothing, just sucks air in once the pressure equates at the other end regardless of how slowly you release it. it's more like hold, then shut the valve. But that's what the surgical tube submerged is for, worst case you suck back in some tainted fluid, not a pocket of air.


edit: I glanced at the video, he's using the little hand vacuum pump, just forget that, use your powerbleeder, run the tube from the bleeder screw to a puddle of fluid. That little hand pump is completely worthless, i got so mad when i tried to use that crap. I'm not even kidding, every single seal in the entire kit leaked, 5 minutes in I don't even think i got more than a few drops of the fluid halfway out the line. The "why are you returning this" question was an exercise in self-restraint.

[MetalMan]

There's a long video i didn't watch, but if you see that sprite bottle? https://www.youtube.com/watch?v=ioHjV4d6BWk that's key. you use it to catcht he fluid, but that can be any container. the key is the surgical tubing. not only can you see the tiny air bubble density as the fluid exits the bleeder, but unless you leave it sitting for a minute unattended, you can't suck air back into the system from the bleeder screw, there's the whole tubing filled with fluid with the end sitting in a pool of fluid, in other words, it's almost impossible to suck air back in the bleeder. this is the key to victory. it's basically a cyphon, but instead of actually pulling it out like a vacuum pump, it just prevents air from backflowing. you just get the right diameter surgical tubing, which is sitting in the auto parts store for an overpriced $4, or like 20 cents at a hardware store. Then hit up the recycling bin on the way out for a container. negates the need to shut off the bleeder screw while the brake/pressurebleeder is still going, and a little insurance, and a little extra visibility in what the condition of the fluid is coming out, and the air bubble density.

I don't even stop bleeding until the pedal feels solid at any corner. Even if there are tiny little bubbles in the fluid, that's really not going to cause any problems as long as the pedals firm. Not sure i've ever even seen "no air bubbles coming out", there's almost always some baby bubbles. backing off the brake slowly does like nothing, just sucks air in once the pressure equates at the other end regardless of how slowly you release it. it's more like hold, then shut the valve. But that's what the surgical tube submerged is for, worst case you suck back in some tainted fluid, not a pocket of air.


edit: I glanced at the video, he's using the little hand vacuum pump, just forget that, use your powerbleeder, run the tube from the bleeder screw to a puddle of fluid. That little hand pump is completely worthless, i got so mad when i tried to use that crap. I'm not even kidding, every single seal in the entire kit leaked, 5 minutes in I don't even think i got more than a few drops of the fluid halfway out the line. The "why are you returning this" question was an exercise in self-restraint.

Frankly I have no idea what you're getting at with this post? Does anybody bleed brakes without a clear tube? What risk is there of air bubbles being sucked back into the system with a pressure bleeder? Or with a 2-man brake pump job when the bleeder screw is closed between pumps?

[james 408]

I'm just telling you what works for me, everytime. and what doesn't work for me is not having that tube on exit, squishy squishy.

And i've seen it done right, i've seen it done wrong. Listen as you please.

[fR3ZNO]

You’ve done a pretty thorough job chasing this issue. I went through something similar between my old B5 and my current B6 (both A4s). I’m assuming your S4 has the stock HP2’s? I think that would explain part of the difference between your old A4 and the S4. When I “upgraded” to HP2’s on my B6 I found the dead zone you’re describing to be terrible and not confidence inspiring whatsoever even after multiple power bleeds and ABS bleeds with VCDS. Which was frustrating because when I first bought it, the pedal felt very firm with very little “dead zone”. It had stainless lines all around, stock calipers and IIRC, Hawk pads. I finally attributed this issue to the amount of flex in the HP2 calipers. It was so bad I ended up just going back to stock calipers with stiffening kit and some Stoptech Sport pads. Which for the record is much better overall especially since it’s a daily.

On my B5 A4 I also tried replacing the MC in attempt to get rid of “dead zone” and initially tried replacing it without a bench bleed and having the rear of the car raised. I ended up pulling it and doing a bench bleed which helped, but didn’t solve the issue that I replaced the MC for in the first place. The B5 A4 also had stock calipers F/R. This was a few years back but I believe I also used the Dorman MC bleeder kit, which had the same issue with the fittings not sealing.

[james 408]

pad will change initial bite, still won't cure a bleed issue if present. Try driving a buddy's if you're not sure what the cause is. I can't tell you the number of crappy rubber line all manner of flex rustbuckets i've seen with firm brake pedals after a bleed though, and I don't remember the stock calipers doing that either, but maybe I'm misreading. After a bad bleed sure, all my cars do that. I probably never left the parking spot if I paid for it.

[james 408]

https://www.wagnerbrake.com/technica...es-spongy.html

all I was trying to tell ya on the brake bleed is if you lose continuous flow and the line isn't submerged, you're gonna suck in air, unless you're a god on that bleeder screw in the hubby wifey combo. Just submerge the line and pump the crap outa the brake, hold it on, shut the line, done. If you have any suction gap on the line, like say on a flexible tube on the bleeder screw your torquing around 50 times in a row, I'm just telling you what I've seen.

[MetalMan]

I'm just telling you what works for me, everytime. and what doesn't work for me is not having that tube on exit, squishy squishy.

And i've seen it done right, i've seen it done wrong. Listen as you please.

Although I appreciate you responding, my interpretation of what you've shared doesn't really provide anything I haven't already covered (in this thread or otherwise).

You’ve done a pretty thorough job chasing this issue. I went through something similar between my old B5 and my current B6 (both A4s). I’m assuming your S4 has the stock HP2’s? I think that would explain part of the difference between your old A4 and the S4. When I “upgraded” to HP2’s on my B6 I found the dead zone you’re describing to be terrible and not confidence inspiring whatsoever even after multiple power bleeds and ABS bleeds with VCDS. Which was frustrating because when I first bought it, the pedal felt very firm with very little “dead zone”. It had stainless lines all around, stock calipers and IIRC, Hawk pads. I finally attributed this issue to the amount of flex in the HP2 calipers. It was so bad I ended up just going back to stock calipers with stiffening kit and some Stoptech Sport pads. Which for the record is much better overall especially since it’s a daily.

On my B5 A4 I also tried replacing the MC in attempt to get rid of “dead zone” and initially tried replacing it without a bench bleed and having the rear of the car raised. I ended up pulling it and doing a bench bleed which helped, but didn’t solve the issue that I replaced the MC for in the first place. The B5 A4 also had stock calipers F/R. This was a few years back but I believe I also used the Dorman MC bleeder kit, which had the same issue with the fittings not sealing.

Yeah stock HP2s. Pads are EBC Redstuff and not super old.
Interestingly you're not the first person to comment to me about HP2s having poor feel compared to other brake options, but I also. A buddy upgraded to 18Z which he determined to have vastly improved pedal feel. Unfortunately going with a different brake setup isn't really in the cards at this point.
Perhaps the HP2s are just that much more of a hassle to bleed effectively and air tends to remain trapped somewhere??

One thing I haven't tried is vacuum bleeding.

https://www.wagnerbrake.com/technica...es-spongy.html

all I was trying to tell ya on the brake bleed is if you lose continuous flow and the line isn't submerged, you're gonna suck in air, unless you're a god on that bleeder screw in the hubby wifey combo. Just submerge the line and pump the crap outa the brake, hold it on, shut the line, done.

When I partake in the 2-man bleeding job (husband/wife duo), I am a god lol. Nothing gets past me. I'm actively keeping an eye on the clear tube and can/will see any bubbles. BUT most of the time I bleed with Motive power bleeder.

[james 408]

I see I skim read the first time through and only read your final post, my bad man. The pushrod thing makes perfect sense now that you've sortedish your air pocket. I... just assumed. Can you blame me?

[fR3ZNO]

Although I appreciate you responding, my interpretation of what you've shared doesn't really provide anything I haven't already covered (in this thread or otherwise).



Yeah stock HP2s. Pads are EBC Redstuff and not super old.
Interestingly you're not the first person to comment to me about HP2s having poor feel compared to other brake options, but I also. A buddy upgraded to 18Z which he determined to have vastly improved pedal feel. Unfortunately going with a different brake setup isn't really in the cards at this point.
Perhaps the HP2s are just that much more of a hassle to bleed effectively and air tends to remain trapped somewhere??

One thing I haven't tried is vacuum bleeding.

Yeah, there’s a reason why S4 guys are so happy to get rid of the HP2’s. I don’t think it’s trapped air in the caliper necessarily, it’s the caliper itself flexing during braking events which leads to that “dead zone”. It’s due to the slider design which has more flex compared to a caliper like the 18Z which is much stiffer.

[MetalMan]

Seems pretty gnarly that it can flex so much.

In other news, I drove the S4 a whopping 5 miles last night, to & from the nearest E85 gas station (prior tank of E85 was getting low, and had been nearly 4 months since last fill-up). It seemed to drive a bit better than the night prior and I was able to further evaluate the brakes.

So... I do think the pushrod spacing helped, as the initial pedal travel feels reduced and feels like it's doing something. It still has long travel but I'm optimistic it's just air in the system.

[christianb5s4]

My brake pedal feel improved immensely switching out the HP2 calipers for 18Zs, much more linear and progressive. If the PO used cheap brake pads that will also affect how they feel and perhaps installing higher quality pads could help if you don't want to get new calipers?

[james 408]

That makes sense. This notion that it's all caliper flex sounds like marketing has seeped into diagnosis to me. Never seen it, never heard it, hence why I assumed it was a bad bleed, especially if you can hear it squishing like that, the answer's pretty clear. The pin length is a known issue when changing the booster/master, and it's one of the only things that's going to affect all 4. Pad difference will have more of an impact than the caliper. Everyone agrees on this:

"Monoblocks are all well and good for well-resourced manufacturers and for the precise world of motorsport, but what about for your own ride? Should you go out and buy monoblock calipers immediately, to avoid the dreaded caliper flex?

That’s not a question that can be broadly answered without delving into specific circumstances, but it’s safe to say that any improvements aren’t going to be felt dramatically. If funds are limited, a pad upgrade is much more likely going to make a meaningful difference to the way your brakes feel and operate." -car throttle, me, and everybody else. Same thing with metal lines. It's all marketing dellusion.

If it were pulling or had a stiff pedal, then maybe you look to some of this other stuff. But as it stands, it's the bleed, it's a leak, or its a bad master (assuming you've got the mechanical parts between the pedal and master all snug now). The only other item that I can think of would be like the abs pump.

[fR3ZNO]

Marketing? I’d disagree. Just because you can’t see it doesn’t mean it’s not happening. Sure, there’s a lot of things that can add up to cause a squishy, non reactive pedal. But assuming everything else is fine, caliper flex can definitely be a source of what OP is describing.

Don’t get me wrong, I didn’t go out and buy “monoblock” calipers either. But on my setup, I’m fairly happy but little improvements do add up in overall pedal feel.

-Stainless lines
-Stoptech Sport pads
-Caliper bushing kit

Those 3 things help remove the major sources of possible flex or “squishiness” in the pedal.

[MetalMan]

Alright, did my "full bleed" last night. Here are those details:

Followed Bentley procedure:

• Right rear, 650 mL. Around 350mL in, it released a good number of bubbles. Bubbles stopped ~500mL in.
• Left rear, 450mL. Didn't witness any bubbles.
• Right front, 600mL. Didn't witness any bubbles.
• Left front, 600mL. Didn't witness any bubbles.

For all wheels:

• maintained 27-30psi on the Motive Power Bleeder
• performed 2 sessions of 8-10 full pedal pumps (ensured clear drain hose was submerged in fluid), with power bleeder still going @27-30psi

Then I also ran ABS pump 2x with left front bleeder screw open and power bleeder @ ~25psi

I only saw bubbles from the right rear. It's possible I missed some elsewhere (i.e. during the pedal pumps) but there was definitely no air when the bleeder screws were tightened.

During the test drive I performed 2x ABS stops, or at least tried. The brake switch is still uninstalled from playing with the booster & master cylinder and the ABS module didn't like that.

And the concensus? Pedal feel is maybe marginally improved but still undoubtedly has long travel. Compared to months ago the pedal more-so feels like it's doing something in the earlier part of the travel now (even if just moving the master cylinder), but a good chunk of the initial travel doesn't result in any braking force.

But as it stands, it's the bleed, it's a leak, or its a bad master (assuming you've got the mechanical parts between the pedal and master all snug now). The only other item that I can think of would be like the abs pump.

As mentioned the master cylinder is pretty new, only replaced as a diagnostic step (old one performed the exact same).
Don't think it's a leak since there's no perceivable fluid loss.
Unless you disagree that my above bleeding was inadequate, I'm ruling out air in the system (at least air that can be removed...).
Do ABS pumps go bad and affect brake pedal feel? ABS throws no codes except for last night because brake switch was unplugged, and the pump works just fine when triggered in VCDS or running other output tests.

But assuming everything else is fine, caliper flex can definitely be a source of what OP is describing.

...I’m fairly happy but little improvements do add up in overall pedal feel.

-Stainless lines
-Stoptech Sport pads
-Caliper bushing kit

Those 3 things help remove the major sources of possible flex or “squishiness” in the pedal.

Caliper flex would be an expensive one to diagnose! Assuming the diagnostic step is swapping in different calipers. 18Z would be awesome but I don't think they fit under 17" wheels?
Otherwise I've done SS lines and haven't seen any caliper bushing kits for HP2 calipers.

I suppose trying a different set of pads could be a good idea at this point... also wondering if the EBC Redstuff pads have never fully bedded in because the rotors weren't brand new; the rotors have probably only 15k miles at this point though. Have also come across some posts in general about Redstuff having poor pedal feel for some people even after bedding in, but many people think they're great pads.
But if I try new pads then I may as well buy new rotors too. Ah, the rabbit hole.

[fR3ZNO]

Just do some FEA on them ;)

But in all seriousness, if you’re going to get new pads and rotors, may as well invest that into a 17Z/18Z setup. Especially since HP2 pads are so expensive anyway, (another reason I ditched mine).

Most of the harder, performance oriented pads do recommend longer bed in times in addition to the initial break in procedure. Just takes longer for them to wear in especially if they’re put on used rotors.