Brake pedal going to the floor...

[97ss10]

This problem just started today where the pedal goes all the way to the floor. There's no pumping it up and the fluid resivoir appears full. I'm starting to lean towards a master cylinder problem but I really hope I'm wrong. Someone please help ASAP!!! Thanks!

[koolade9]

Yeah, sounds master cylinder related...

-if you can pump it, it's usually air in the line(s)
-if you push the pedal, and it slowly goes to the floor, it's a leaky master cylinder.

[97ss10]

That's the crazy thing though...it's not using any fluid and the pedal doesn't slowly go down, it immediately goes down. Audi Tech said it could be something between the pedal and the MC but a Euro Car mechanic said it's the MC.

[koolade9]

slow is usually because it's a slow leak in the MS. Yours may have completely failed. It's not using any fluid because it's an internal leak. Think of it like compressing a shock absorber that has bad piston seals.

[97ss10]

Which means I'll need a brake booster also right?

[old guy]

Which means I'll need a brake booster also right?

If you are not losing any fluid it sounds like the primary seal in the master cylinder has failed. What happens is that when you press the pedal the fluid flows past the primary seal and the secondary seal at the other end of the piston pushes the fluid back into the intake port to the fluid reservoir. Your brake booster shouldn't need replacing.

Good luck!

[97ss10]

Are there any how-to's on here anywhere on changing the MC and after it's done, will the standard pedal pump brake bleed work to bleed the system? Should I try to bleed the system first to see if that will fix it or is it definitely the MC? Thanks guys!

[97ss10]

Ok so now the damn thing just started working! My parents brought my other car over to drive until I could get the Audi fixed and when they pulled in the driveway and I got out to show my Dad what it was doing it had plenty of pedal and braked fine. WTF?!?

[old guy]

Are there any how-to's on here anywhere on changing the MC and after it's done, will the standard pedal pump brake bleed work to bleed the system? Should I try to bleed the system first to see if that will fix it or is it definitely the MC? Thanks guys!

I would definitely try bleeding first before attempting to remove the master cylinder. i am not aware of any DIY's for removing the MC but I can tell you it is not a quick and easy job. For bleeding the brakes I highly recommend purchasing a pressure bleeder. I picked up a Motive Power Bleeder for under $50. It's really the proper way to do it and the least likely to introduce other problems that can result from improper bleeding.

Good luck!

[97ss10]

Are aftermarket MCs ok or should I stick to Audi? Orielly's can get a reman. for around $150. Also where's a good place to get a set of Bentley manuals, either on CD (MAC compatible) or paper, and a power bleeder? Thanks for everything. I'll keep you updated.

[old guy]

Are aftermarket MCs ok or should I stick to Audi? Orielly's can get a reman. for around $150. Also where's a good place to get a set of Bentley manuals, either on CD (MAC compatible) or paper, and a power bleeder? Thanks for everything. I'll keep you updated.

Considering you can get a new MC for a little more I would suggest going that route: Clicky click I bough my Bentley for $69 through Auto Parts Warehouse but that was a few years ago. To be honest I can't remember where I purchased the Motive Bleeder. I'm sure I just Googled for the best price and bought it from wherever that was at the time. I'm pretty sure it was under $50.

Good luck!

[97ss10]

Well I haven't had a chance to try bleeding yet but there is a new symptom. When you first get in the car and start it, the pedal goes to the floor. If you punch the pedal quickly with your foot once or twice, it starts working normally. With the power bleeder, will that prevent problems with air getting into the ABS system? Thanks!

[old guy]

Well I haven't had a chance to try bleeding yet but there is a new symptom. When you first get in the car and start it, the pedal goes to the floor. If you punch the pedal quickly with your foot once or twice, it starts working normally. With the power bleeder, will that prevent problems with air getting into the ABS system? Thanks!

If you use the power bleeder properly you shouldn't have any problems with air in the system.

[CO AVANT]

I just wrote this up today if you indeed need to replace your Master Cylinder. I would though recommend you re-bleed the system first to see if that resolves the issue...

This was done on a B6 chassis but this procedure will carry over to other models.

1. Drain the brake fluid out of the reservoir with an extractor

2. Disconnect sensor at bottom of reservoir

3. Pull rubber hose off back right lower side of reservoir (have towels ready for brake fluid spilling down)

4. Take torx bolt out that is holding the reservoir in place. It's a T25 and located under reservoir. Pull off vac line to brake booster if needed for more room.

5. At this point you should be able to wiggle the reservoir upward and out of the 2 rubber sealing grommets. (have more towels ready)

6. Take 10mm 12pt bolts out holding on the Master Cylinder and also take off the 24mm nuts behind them. Forgot if you need to take the 10mm off first or the 24mm. You can figure it out once you're doing it.

7. Take off both hard brake lines going into the Master Cylinder with a 13mm wrench. At this point you should be able to wiggle the lines free out of the MC be wiggling/pulling toward the ecu box. If you can't you can always loosen the other end of those hardlines that meet at the ABS control module.

8. Now you should be able to lift the front end out the brake booster up vertical high enough to clear the battery firewall to pull the Master Cylinder off and out. If not you can get more room by taking off the windshield crowling. (this is much easier than trying to take the brake booster off the brake pedal with audi's special tool like shown in the Bentley)

9. Now you can reinstall the new MC in the reverse order. BUT, before you do that you need to bench bleed the new MC and try as best as possible to get all the air out of the MC before you install in the car. Keep the plugs that come with it to cap it off when you reinstall so it doesn't leak the fluid out.

10. When installing the new MC make sure the MC rod seats into the receiver inside the brake booster perfectly. You might also need to wiggle the brake booster back in place to get the hardware back on.

11. Once you have everything installed back in the reverse order you now need to bleed the brake system. I will tell you that a lot of times the motive power bleeder is not good enough at getting air out of the system and you might have to do the good old conventional pumping the pedal way of bleeding to ensure all the air is out. Ask me how I know this. Must have gone through 10gal of fluid with the power bleeder until I did it the old fashioned way and finally got the air out. You can always bleed the lines at the MC and at the ABS control module if the brake bleeding doesn't do it. Just make sure the pump and/or reservoir doesn't run out of fluid. Then you start all over. Lightly tapping a rubber mallet on the end of the MC or ABS module can help air get untrapped if it's being a bitch. Bleed the clutch slave while you are at it on the brakes.

That should be about it IIRC. Happy wrenching

[97ss10]

Cool...Thanks a lot!