THE brake story...continued...HELP!

[imported_brackie]

You can remove the booster, but nope you can't dismantle it. The booster is a sealed, non-servicable item. (Not that I think there's anything wrong with it, anyway.) But I'm prepared to be wrong, How can it be tested? And what could go wrong internally that would cause this problem? It's holding vacuum and when I'm brave enough to test drive it (you should see the roads here!) it's definitely working. The primary piston is easy to remove (circlip) and the secondary is held back with a stop-bolt.

[Sharkey]

Don't know a bunch about the Audi servos/braking system, but here's my few views:

Remember that the servo is simply an assisting device, the push rod of the MC is still mechanically connected to the pedal mechanism, so in theory a hard pedal with the engine off should remain hard with the engine on. Obviously, you've disproven this.

It might be time to fall back to more extreme troubleshooting. I'd think about getting some 10mm bubble flare plugs and remove the brake lines to the wheel calipers one-at-a-time, replacing the lines with the plugs, and trying it with the engine running. If your pedal still plunges to the floor with all the ports plugged, you can bet it's a MC problem. If you get a hard pedal with just one (or more) of the ports plugged, at least you know where to start looking.

Why servo on/off makes a difference is a mystery, but it's just not possible that your depressing the pedal with the vacuum present can allow the push rod into the MC to not be pressed also.

You do have a Bentley service manual for this vehicle, yes? My A2 Bentley states that "vechiles equipped with the rear load-sensing regulator valve must have the load sensing arm held down towards the axle" while bleeding. Is it possible that the ride height of the car changes when the engine is running, making the regulator change the volume or pressure of the brake fluid going to the rear axle? Just freewheeling thoughts here...

[imported_brackie]

Thanks, Sharkey.. We don't get the Bentley manuals here. The one that I have is for the Rabbit diesel and I got that from the US
The Haynes makes no mention of depressing the lever. When bleeding the brakes I had to jack the car in order to get under (I ain't a kid anymore!) so maybe you're right and I need to have it depressed or on the flat. Excellent suggestion about making the blanks. I assume that these go into the MC ports? (The Audi has twin circuit braking on diagonally opposite wheels.)
Will give the "depressed lever" trick a go today.
Great to have you on the board. Call in regularly and add to our knowledge base!

[Sharkey]

Can't get Bentley manuals??? Have you tried http://www.rb.com ?? I find used bentley manuals in the used book stores here for about $12-18US a pop. My A2 manual (which I bought expressly for installing an ABS hydraulic modulator on the EV) cost me $6 at the flea market, and it was still in the plastic wrap. Sorry, just trying to make you jealous.

If you can't find 10mm bubble flare plugs, you can make your own. Go to the auto dismantelers and cop four of the (good, clean, rust-free) ends off of a scrapped-out body. Cut the steel tubing about 1-2" from the flare nut, then crimp the cut end closed in a vise. Use a gas welder to weld up the crimp and you have a DIY plug. I've found them very handy when removing brake components to stop fluid loss and cap off orifices when cleaning in solvent baths. Never hurts to have a few around. I've also made a few caps from injector pressure lines to cap off injection pumps in storage and while cleaning (never cap off an injection pump and then try to rotate the shaft, you'll blow it apart!!!).

Good luck, there's nothing all that mysterious about hydraulic brakes, at least not until they stop working. Another reason my bus had air brakes!

[Golf Loon]

Gday Sharkey. The Electric Rabbit looks great. Would be an ideal delivery vehicle for a business. I reckon.
Wise words on the brake saga, I`m gonna make me some of those brake blankers!
The Bentley manuals are great, I have one for my Saab, so much more detailed than a haynes. Not available in Australia, we have to resort to ebay.

[Anonymous]

Not available in Australia,

Yes they are. Go to any motoring bookshop.

[Golf Loon]

Great thanks, i`ll check it out. How are the brakes going Brackie?

[imported_brackie]

Nuthn's goin' Mate. Definitely not the car as it might go, but it definitely won't stop! Sent my old seals (from the original 12mm bore MC) to Hobart to get new ones. Gonna fix up the old cylinder and put it back in. If that doesn't fix it it can only be the booster. But I can't even imagine how it can be responsible. Then ...THE CRUSHER!! She's been in my shed for 2 weeks now and I can't get anything else in. Pug needs cooling system flush and coolant, blower fan overhaul, Golf should have had rings and bearings done weeks ago. And we start tearing down walls and building kitchens on Wednesday. You got a booster that would fit??

[Golf Loon]

Aaaaaargh Just cut down the shaft on an Audi Booster so that i can fit it to my golf. Only golf ones here now. Is the seal between the MC and the booster ok? Instant Gasket?

[imported_brackie]

Yeah, the seal is leaking slightly. It's an"O" ring. but I've had small vac leaks on other cars and the pedal's been OK. Are you saying that this could be the culprit?