Weirdness 101

[Bigglezworth]

Parked my one RS6 back in the middle of July when I started driving my S6 Wagon. Was great for summer trips with my daughters and dog. Had a coolant reservoir burst a few days ago and while I waited for new parts to arrive, decided to go out for a haunt in the beast. To my dismay, I started it up and voila - no brakes.... Pedal pushes easily to the floor.:doh: Yes, only so many parts make up the braking system, but it escapes me on how it went from working perfectly when parked to totally kaput while it sat for 2 months....:vhmmm:

Fluid is topped and no fluid on the ground. >sigh< Weird in my books as I've never had anything like that happen to me in all the years owning/driving/fixing cars. Going to chalk this one up to timing for a failed master cylinder.

Was going to pull it apart and overhaul turbos, timing belt, water pump, etc., so I guess now is as good a time as any. :lovl:

[Aronis]

master cylinder can be removed without taking out engineLOL. have to take dash under body down to get at the bolts.

Mike

[Bigglezworth]

Yes indeed.

[SteveKen]

Double check to see if it's not a plastic check valve in the vacuum line.

[Bigglezworth]

Double check to see if it's not a plastic check valve in the vacuum line.I considered something like that, but that would produce a decent vacuum leak and create stumbling for idle. Also, loss of vacuun leads to a hard pedal vs. spongy one no? With me focusing my effort to repair the S6, I haven't looked in to this any further. Will get around to it this weekend at some point.

[SteveKen]

I considered something like that, but that would produce a decent vacuum leak and create stumbling for idle. Also, loss of vacuun leads to a hard pedal vs. spongy one no? With me focusing my effort to repair the S6, I haven't looked in to this any further. Will get around to it this weekend at some point.

Not necessarily. I've seen it happen on the B5 cars. It depends on which side if the check valve the failure occurs.

[Jorisrs6]

I have the exact same problem. After sitting a few weeks it suddenly lost pressure. I havent had time to look at it yet but if you find out what the problem is, then please post.

[tedshred]

my jet valve went and the car had no brakes. That valve under the intake apparently makes a lot of vacuum to run the brake booster. It also had a big vacuum leak that made it run and idle bad.
did all the hoses under the intake as well as the run on coolant pump. Buy your parts from McKinney VW in Texas, they give 40% off list. Best deal I could find for genuine Audi parts. you might be able to get one of those small phone borescopes under the intake to view it.

[Jorisrs6]

okay my rs6 has been sitting in the grass for months now so I cant see if it has leaked brake fluid. however my engine still runs good so I don't think mine has a vacuum leak. it probably just the valve then. this winter im doing an engine pull and trans swap so it will be easy to fix that at the same time. thanks tedshred

[Bigglezworth]

Faulty seal on master cylinder. Swapped out while I switched in some nice SS front lines and high temp Brembo fluid and voila!

[Aronis]

How much work was master cylinder? I know you have to get up under the dash for the bolts.

Mike

[bethridg]

How much work was master cylinder? I know you have to get up under the dash for the bolts.

Mike

You're thinking the brake booster. The brake master cylinder should be a couple of bolts/nuts on the front of the booster and disconnect the brake lines. All under the cowl cover.

[Aronis]

Got it...thanks...

Mike

[Bigglezworth]

You're thinking the brake booster. The brake master cylinder should be a couple of bolts/nuts on the front of the booster and disconnect the brake lines. All under the cowl cover.Incorrect..... In the great wisdom of the engineers at Audi, the brake booster and master cylinder are fastened together with 120mm+ long bolts.... The firewall that separates the engine compartment from the area where the ECU, braker booster, and coolant resevoir are all located is too tight to the booster to permit removal of bolts in order to separate the master cylinder from the booster..... The bottom bolt can't even come out 25mm before it interferes with the strut tower support brace. In fact you can't even get a standard Torx socket or wrench on it due to proximity of the cross bar. This then also requires you fussing with a puller to remove the windshield wipers in order to get access to removing the windshield lower cowl otherwise you can't get the booster out. I resigned myself to the fact that there was no shortcut with this repair (and I know a number of shortcuts on this car) and yanked it al out. There is simply no way around it. Yes, great design.....

I removed the entire booster/cylinder as a full assembly which involves detaching from the pedal yes.

Stupid Audi should have simply had studs that protruded from the booster to which you loosen a pair of nuts from and remove.

At least I didn't have to remove the entire engine just to repair this item. Wait.... I just did that to replace turbos.....

>sigh<

1837918380

[bethridg]

Oh lord, that's what I get for assuming. And I literally have a brand new booster sitting on the shelf for reference but luckily never got around to installing because my loss of power assist issue turned out to be caused by reversing a check valve when I relocated the SJP (following your lead). Thanks for the correction and, as always, a detailed explanation.