fn_42

Hi

I just picked up a 2001 S8 & unfortunately know nothing of the maintenance history, just that it was sitting in a barn for ~2 years before I got my hands on it

I just managed to get it running but I'm having a weird issue with the brakes, with the engine RUNNING the pedal will sink almost all the way to the floor with no resistance. It does start working in the last 1" of pedal travel

with the engine OFF, the pedal's rock solid. I can stand on it and it won't sink. Engages at the right height & feels exactly like it should

the car does have brand new pads + rotors on it so I'm sure someone messed with the brakes before I got my hands on it. I bled maybe 1L of brake fluid through it yesterday (using the 2 person method) w/ no difference

I got a "pressure sensor low reading" DTC from the ABS computer but that's it -- I haven't bled the ABS pump because I don't have the technologies (yet) but that is my next step

Just wondering if anyone else here has seen this issue? I'm just trying to iron everything out before I try throwing a new master cylinder at it

Kneale Brownson

Two-person method is a good way to ruin an old brake master cylinder. Audi recommends a pressure bleeder, and that's probably what you should use.

123quattro

You don't need to bleed the ABS unit. That is not your problem. When the ABS/TCS/ESP isn't functioning it's valved out of the system.

If you are sure you got all the air out of the system I would suspect a bad master cylinder. The reason the pedal feels stiff when the car is off is because the booster provides assist making it much easier to push the pedal. It offers roughly 6x assist over what the driver is applying.

fn_42

Interesting, thanks for the info re: ABS unit. It just really feels like there's air in the system somewhere unless my master cyl. is just riding the line of good and bad.

I guess I'll have to get a power bleeder too, I just stuck a 2x4 under the pedal so it wouldn't go all the way down, but I think this is the wrong car to take shortcuts with

Kneale Brownson

bleeder

fn_42

Nice thank you, that will certainly come in handy

I pushed a bunch more fluid through it and did the ABS bleed through vcds-lite. No difference. I am going to try to find some plugs that will screw into the master cylinder outputs so that I can test it

fn_42

Well it's a good thing I decided to plug + test the master cylinder, it works perfectly.

The issue was that the back 1/2 of the front calipers had air in them. I feel like an idiot for not even trying to bleed them until now x_x. I'll have to go buy a rebuild kit because that probably means they're leaking

It's nice to have brakes now! I just took the car on a test drive for the first time and I'm very impressed by how it drives. I got a P0022 code out of it afterwards but at least I'm making progress

audinutt

sounds like you have a bad camshaft adjuster, not a good idea to continue running the engine, it is most likely a broken adjuster shoe and if the timing jumps, prepare to spend a bundle.
Mine looked like this when I pulled the valve cover.

fn_42

Thanks for the heads up! I did pull the valve cover but everything's looking normal

the chain has plenty of tension (I was barely able to deflect it) so I guess I have to keep searching. Hopefully it's not the adjuster

I did notice that the timing belt is pretty much brand new, I wonder if bank 2 is off a tooth. I'm gonna ask around to see if anyone I know has that special alignment bar tool

fn_42

Here's a pic of the shoe, it does look a little worn I can't imagine that's enough to throw a code though?

https://i.imgur.com/BMNmwl5.jpg