Soft Brake Pedal - What to do?

[01northernS4]

So, switched out my stock pads and rotors to Hawk HPS and Zimmerman rotors and bled the system at the shop... The pedal is very soft although it stops well. This was approx. a year ago. Bled the system 6 months ago and it feels more or less the same.

Read soo many search results saying its the pads or the bleeding wasn't done right to it wasn't bed in properly to the brake lines suck or pad aren't sitting right.

I just want the same or similar firm pedal feel to stock back.

All else I'm fine with (i.e. brake power and initial bite, etc...)

What's the verdict gentlemen?

Thanks!

[01northernS4]

They are Hawk HPS+ (not the ceramic ones)

If I pump the brake a few times even after warmed up the pedal feel is the same in that it will not firm up, still goes to the floor with firm pressure... was never able to do that on the stockers.

[aroderick56]

When you pump the brakes, the pedal should firm up. My guess is either 1) air in lines or 2) get some SS lines

[WolfS4]

and new fluid if you haven't already

[01northernS4]

It doesn't and that's what I was thinking...

Mechanic seems to think "that's just the way the Hawk pads feel compared to stock"... he's a good mechanic so I really didn't push it and wanted to see if it would get better with time.

So I should ask him to re-bleed the brakes first and check the lines?

Any other possibilities?

Thanks again

[aroderick56]

It doesn't and that's what I was thinking...

Mechanic seems to think "that's just the way the Hawk pads feel compared to stock"... he's a good mechanic so I really didn't push it and wanted to see if it would get better with time.

So I should ask him to re-bleed the brakes first and check the lines?

Any other possibilities?

Thanks again

From my racing experience, changing different pads never changed how my brake pedal felt. I've used hawks, carbotech, and cobalt. I also change compounds depending on track. My pedal stays the same and always pumps up.

I would bleed them again and again until your pedal pumps up. Also try putting new fluid in and bleed out all the old fluid

[dparm]

The reason the pedal feels "soft" is because the HPS pads have a different compound than the stock brakes. The stock pads are very grabby and bite fast. If you don't like the HPS feel, remove the pads and put stock ones back on. Personally I think the HPS is a lousy pad and I don't understand the hype behind it. Is there something wrong with the stock pads? Are you driving in a manner that overwhelms the stock pad?

You can of course re-bleed, but I don't think much will change. You can also try to re-bed the pads: http://www.zeckhausen.com/bedding_in_brakes.htm

[DTMOOOO]

The difference you are feeling i am guessing it due to the pad bite on the HAWKs vs Stock, stocks have a much stronger initial bite where the Hawks are more linear.

When i made the switch I rebled the system 2 times because i thought it felt weird, but when I drove another S4 i realized my pedal travel was shorter and stiffer but the bite of the stock pads made the braking feel better under normal driving conditions. As well Hawk HPS pads seem to get a lot of Hype on this board but im not a fan

[aroderick56]

The reason the pedal feels "soft" is because the HPS pads have a different compound than the stock brakes. The stock pads are very grabby and bite fast. If you don't like the HPS feel, remove the pads and put stock ones back on. Personally I think the HPS is a lousy pad and I don't understand the hype behind it. Is there something wrong with the stock pads? Are you driving in a manner that overwhelms the stock pad?

You can of course re-bleed, but I don't think much will change. You can also try to re-bed the pads: http://www.zeckhausen.com/bedding_in_brakes.htm

Even if the pads caused a soft pedal, wouldn't the pedal firm up if pumped?

[DTMOOOO]

Damn Dparm beat me on the reply, i think you are just used to the pedal and it is getting to your head worrying about it.

If you have any doubts hook up a pressure bleeder, pump the pedal 2 times to firm it, throw some some clear hoses on the bleeder screws and hit the calipers with a rubber mallet when letting them bleed.

If the fluid comes out clear w/ no bubbles you should be good. Dont forget to bleed the clutch line while you are there as well.

[dparm]

Even if the pads caused a soft pedal, wouldn't the pedal firm up if pumped?

Maybe. I don't know the HPS that well, but it's possible they work better with some heat in them.

[Flexicoker]

Even if the pads caused a soft pedal, wouldn't the pedal firm up if pumped?

No. The property you're talking about is the material stiffness of the pad itself. This could change with temperature but not with pumping, and it can be different between pads. (different brake fluids have different stiffnesses as well, AKA bulk modulus) Pumping will only increase pedal stiffness if there is air in the lines or the caliper pistons have retracted too far.

Others have mentioned a perceived stiffness change due to different grabbiness (AKA coefficient of friction). This is different than stiffness but can be perceived as such since you need to apply more force to achieve the same deceleration.

[audi49]

When you say 'soft'... do you mean less bite or that the brake pedal moves further to the floor. The first could be due to the different pads and the second could be due to a faulty master cylinder.

[01northernS4]

When you say 'soft'... do you mean less bite or that the brake pedal moves further to the floor. The first could be due to the different pads and the second could be due to a faulty master cylinder.

feels mushier than stock
pedal doesn't firm up with repeated pumps
can touch the floor without too much pressure

otherwise initial bite and stopping power good

[dparm]

feels mushier than stock
pedal doesn't firm up with repeated pumps
can touch the floor without too much pressure

otherwise initial bite and stopping power good

Are you leaking brake fluid? Is the reservoir still full?

[01northernS4]

No. The property you're talking about is the material stiffness of the pad itself. This could change with temperature but not with pumping, and it can be different between pads. (different brake fluids have different stiffnesses as well, AKA bulk modulus) Pumping will only increase pedal stiffness if there is air in the lines or the caliper pistons have retracted too far.

Others have mentioned a perceived stiffness change due to different grabbiness (AKA coefficient of friction). This is different than stiffness but can be perceived as such since you need to apply more force to achieve the same deceleration.

interesting

[01northernS4]

Are you leaking brake fluid? Is the reservoir still full?

reservoir full, no leaks that I see

the shop changed to new fluid also

[01northernS4]

The difference you are feeling i am guessing it due to the pad bite on the HAWKs vs Stock, stocks have a much stronger initial bite where the Hawks are more linear.

When i made the switch I rebled the system 2 times because i thought it felt weird, but when I drove another S4 i realized my pedal travel was shorter and stiffer but the bite of the stock pads made the braking feel better under normal driving conditions. As well Hawk HPS pads seem to get a lot of Hype on this board but im not a fan

I don't think so... fully aware of the differences between the pads but I feel the opposite is true... on HPS pedal travel is further and can touch the floor on occasion but on stock pedal travel seemed less and don't ever recall hitting floor, ever

[01northernS4]

The reason the pedal feels "soft" is because the HPS pads have a different compound than the stock brakes. The stock pads are very grabby and bite fast. If you don't like the HPS feel, remove the pads and put stock ones back on. Personally I think the HPS is a lousy pad and I don't understand the hype behind it. Is there something wrong with the stock pads? Are you driving in a manner that overwhelms the stock pad?

You can of course re-bleed, but I don't think much will change. You can also try to re-bed the pads: http://www.zeckhausen.com/bedding_in_brakes.htm

Only reason I changed is it was time for brakes and I was getting tired of the brake dust and wanted a little upgrade... had great success on my BMW before with aftermarket dustless brake pads and was hoping for same here.

HPS has delivered on everything but I'm just trying to get to the bottom of the pedal mushy feel

[01northernS4]

From my racing experience, changing different pads never changed how my brake pedal felt. I've used hawks, carbotech, and cobalt. I also change compounds depending on track. My pedal stays the same and always pumps up.

I would bleed them again and again until your pedal pumps up. Also try putting new fluid in and bleed out all the old fluid

Shop said they did put new fluid in and bleed out all the old...

[01northernS4]

When you pump the brakes, the pedal should firm up. My guess is either 1) air in lines or 2) get some SS lines

This is what I thought... some say no...

Is the best way to get the air out of the lines to re-bleed?

[Flexicoker]

It's possible that you have a damaged brake line that isn't leaking, but is expanding with pressure. It's uncommon but not unheard of. Happened to my Dad once. Stainless steel lines are pretty inexpensive.

[01northernS4]

It's possible that you have a damaged brake line that isn't leaking, but is expanding with pressure. It's uncommon but not unheard of. Happened to my Dad once. Stainless steel lines are pretty inexpensive.

great suggestion!

is it fairly simple to find something like this or do I have to ask them to look for it?

[01northernS4]

also noticed shop used motul dot 5.1, 500ml worth

is this enough for a full change/bleed/flush?

if not, is mixing with remaining stock fluid a problem?

[httuner]

Bad brake master cylinder! Replace it ASAP

[01northernS4]

Bad brake master cylinder! Replace it ASAP

Really?!?

from mixing fluids, symptoms I describe or both?

[Flexicoker]

great suggestion!

is it fairly simple to find something like this or do I have to ask them to look for it?

What I would do in this case is put the car on jackstands and take all of the wheels off. I would then crawl over every bit of rubber hose I could find while someone repeatedly pumped the brakes (HARD!). I would also look over each caliper closely to see if it's moving in any weird way while the brakes are pumped.

The bad master cylinder suggestion from httuner is also possible. It could be failing to hold pressure and the fluid leaking past the seal is going right back into the reservoir. Typically some air would get introduced to this system if the master is bad and has been for some time, but it's still possible. For this you would need to remove the master to inspect.

[dparm]

also noticed shop used motul dot 5.1, 500ml worth

is this enough for a full change/bleed/flush?

if not, is mixing with remaining stock fluid a problem?

Yes, I'd say the full bottle is usually enough. I always buy two just in case.

Brake fluids must be mixable with others. It's a DOT requirement. It won't cause a master cylinder to fail.

[01northernS4]

Yes, I'd say the full bottle is usually enough. I always buy two just in case.

Brake fluids must be mixable with others. It's a DOT requirement. It won't cause a master cylinder to fail.

Sick feeling gone... thanks for the clarification dparm.

[01northernS4]

I will suggest this to the shop.

Thanks Flexicoker

[WolfS4]

add some viagra

[mankytron]

I think it is more then just a change in pads. Recheck for air and bad flex lines as others have stated. Pumping the petal should firm up and have less travel....makes me think the master is leaking internally. What kind of bleeding method was used?

[Flexicoker]

Also, for comparison...

My B6 has 111111 miles (sweet, right!?) with worn out stock, or stock appearing replacement components. I have not done any maintenance to the system since I bought the car. I can also easily push the pedal to the stop, and it does not firm up with pumping. I think this is somewhat typical of a modern overboosted system.

That said, when I do my brake maintenance in the spring I will be doing everything I can to end up with a firmer pedal.

[httuner]

Mixing brake fluids doesn't do any harm, I've done this multiple times in a lot of cars that I've worked on. It's not recommended but it doesn't affect anything. Brake fluid is design to absorb water so it will turn a darker color brown/yellow as it ages. This water absorption ability is a good thing and helps keeps moisture from forming too much in your brake system. So looking at the color of yor brake fluid can help you determine whether it needs to be replaced or not.

A soft pedal feel is always an indication of a bad brake master cylinder, if you have taken the correct steps in properly bleeding your brake lines.

When you apply pressure, the pedal is suppose to get firmer and firmer and not allow the pedal to sink to the ground with the engine off. When the engine is on, it's still suppose to give a nice firm touch and if the pedal is sinking to the ground at a stop with the engine running then you are in need of; 1. Rebleeding the entire brake system or 2. Replacing your brake master cylinder if step 1 doesn't fix the pedal issue.