apexmateria

Car: 1999 Audi A4 Quattro 1.8t

Problem: My front right caliper would seize up when hot. If I left the car to cool down for an hour it would unseize until it got hot again.

I got a rebuilt caliper and swapped it with the seized one, I also cleaned up the front left caliper at the same time because it needed some general maintenance (lube pins, cleaning etc).

The problem is I can't bleed the brakes... The fluid refuses to pass through either front caliper. I disconnected the brake line going to each caliper and the fluid doesn't leak on its own. If I push the brake pedal fluid does come out though but possibly more slowly then it should.. (I'm not too experienced)..

I put some paper towel over the end of the disconnected brake line and gave the brake 5 pumps on either side.

The left side seemed to put out a decent amount of fluid.

The right side put out about 1/3rd the amount the left side did.

(I did this test on each line individually, not with them both disconnected

See pics:

Left side: http://s30.postimg.org/jdrwi018g/201..._56_08_346.jpg

Right side: http://s30.postimg.org/kc89kaekg/201..._11_42_152.jpg

Any idea what's causing the fluid to not pass through either caliper?

And why does more fluid come from the left line?

David.Norton

Well, if you pump the brakes with the screw open you will just draw air into the caliper making the issue worse. The reason your rebuilt caliper leaks less fluid is that it came full of air. Anyway, there are a lot of good instructions available, just do a search on "bleeding brakes instructions". I find the easiest to be with two people.

apexmateria

Hi, thanks for the reply!

Just to clarify:

The rebuilt caliper doesn't pass any fluid, neither does the old one I took off to clean. Not one drop passed through the bleeder. I had to unscrew the lines that go into the caliper to test if they were working.

I'm trying to use the 1 man bleeder kit, the bottle with the magnet.

The thing is.. none of the bleeding the brake methods will work if I can't get fluid to come out of the bleeder.

tenspeed

Remove the bleeder and see if the passage is clogged. It just a bolt with a hole in it. See if brake fluid flows out of the caliper with the bleeder removed too.

apexmateria

I took the bleeder out on both sides and no fluid came out. Even if I pump the brakes.

On the left side I can hear gurgling noises like the fluid is in the caliper it just doesn't have the pressure to get out the hole.

apexmateria

UPDATE: I finally got the calipers bleeding out fluid but it's moving out so slow I think the master cylinder is broken.

After about 15-20 presses on the pedal I got the hose filled on the bleeder kit and it didn't even make it to the bottle yet. After I release the pedal it keeps sucking all the fluid back.. it's a real pain in the ***!

tenspeed

Put a small amount of fluid in the bottle so the hose end is submerged. Bubbles will come out - fluid will be sucked back in.

I would try changing the hoses before replacing a master cylinder. Old hoses are known for collapsing internally which prevents flow.

apexmateria

Hi Tenspeed, thanks again for the help

The thing is I did change the plastic flex line on the front right side.

Is there any good diagnostic tests I can attempt to see if my master cylinder is broken? Or any other tests to see if the lines are faulty?

tenspeed

I haven't had any problems with a master cylinder so I haven't had to test one. I have read about the flexible hoses breaking down with age internally. They tend to act as check valves only allowing fluid flow in one direction. The ones I remember are that caliper doesn't release. I mentioned it because it's a whole lot easier and cheaper to install new flexible hoses to the calipers. A internet and YouTube search might show how to test a master cylinder.

The master cylinder also has a safety feature. If you have a leak, there is a slug inside that moves to block off the leaking portion. Yours might have moved and crud is preventing it's movement back into the normal position. That would account for the lower flow. It should trigger a "Brake" warning light on the dash but I don't know how Audi handles it.

Once the calipers are filled and bled, there's not a large quantity of fluid flow. It's pressure transmitted by the fluid that does the work.

apexmateria

Interesting that you mention that brake warning light.. when I start my car I noticed a new 3 beep warning noise but had no idea what it was. There's also an "E" symbol. It's covered by an aftermarket boost gauge so it might have been there for a while or just appeared, not 100% sure.

I appreciate you taking the time to help me figure this out out, will update the thread when I find the exact issue. Cheers!