Brake problem

steveb · 24-08-11, 09:22 AM

I have a problem with the N/S/R Brake not working on a 1993 100 Avant TDI, The handbrake is very good but when tested the footbrake only gives a very low reading, i have changed both hoses in case they where preventing fluid flow but no difference. The pads are good and free in the calipers All the other axle brake performances are good. Any ideas ?

Thanks in advance

Steve

Cuppatea · 24-08-11, 10:17 AM

Did the flow of fluid appear ok when bleeding after replacing the hoses? maybe give it a quick bleed again to be sure its air free. How are you bleeding it?

Id make sure the cable operated lever returns to its stop ok, then double check all sliders are free and wind back the piston, then out again to set the caliper/pad clearance correctly.
Give the pedal a few hard pumps and road test.

baron2211 · 24-08-11, 12:13 PM

I had a similar proble on the 200 last year and it turned out to be an f'ed caliper. Fortunately mine was still under warranty and it was changed foc. If you are getting the fluid through with no bubbles in it and the hand break lever is working corrcetly then this may be the same fault. Interstingly mine went from stuck off and not working to stuck on on the way back from Cornwall!! Mmmmm, blue disc!

Hanuman · 24-08-11, 12:30 PM

Does that car have the brake pressure relief valve at the rear axle? The line from the front goes via a valve that is operated by a lever, linked via a spring/coil to the axle. Under braking, the lever is pulled down, restricting flow to the rear circuit.

It's an alloy block, with a simple piston valve. Mounted probably just ahead of the left side, trailing arm.
On my V8, it was heavily corroded, and the valve was only partially open. Internally, it was heavily corroded.

Phil Payne · 24-08-11, 01:39 PM

Quote:

Originally Posted by The Real MSH!

Does that car have the brake pressure relief valve at the rear axle?

That's really intended to compensate for passenger and luggage loads - MoT cars are usually lightly loaded and it shouldn't have much effect.

steveb · 24-08-11, 01:51 PM

Yes i'm getting a good flow of fluid, the claiper slides etc are free. yes it does have the load sensing valve, as plenty of fluid is coming through i don't think the fault is here it supplys the other side as well so would give a low reading onthe O/S I've ordered a new caliper, fingers crossed this fixes it.

Hanuman · 24-08-11, 02:02 PM

Quote:

Originally Posted by Phil Payne

That's really intended to compensate for passenger and luggage loads - MoT cars are usually lightly loaded and it shouldn't have much effect.

It shouldn't have much effect, true. But once seized, it's seized. As was the case with mine. INternally, it was pretty fouled up with assorted crud, and getting the valve free was difficult. Net result was that the rear circuit was on reduced flow, and differential, until I'd replaced it.
Hence, I mention it. By the looks of it, on VAGCAT, they are different on the C-chassis(?) cars, anyway.

24-08-11, 12:30 PM	#4
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,006	Does that car have the brake pressure relief valve at the rear axle? The line from the front goes via a valve that is operated by a lever, linked via a spring/coil to the axle. Under braking, the lever is pulled down, restricting flow to the rear circuit. It's an alloy block, with a simple piston valve. Mounted probably just ahead of the left side, trailing arm. On my V8, it was heavily corroded, and the valve was only partially open. Internally, it was heavily corroded. __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

24-08-11, 01:51 PM	#6
steveb Senior Member Classic Audi Club Member Join Date: Jul 2008 Location: West Berkshire Posts: 1,155	Yes i'm getting a good flow of fluid, the claiper slides etc are free. yes it does have the load sensing valve, as plenty of fluid is coming through i don't think the fault is here it supplys the other side as well so would give a low reading onthe O/S I've ordered a new caliper, fingers crossed this fixes it. __________________ [FONT] '76 Leyland Princess 2200 HLS '79 Scirocco storm '84 WR '89 coupe quattro '01 A2 1.4 TDI SE '14 A3 1.4 TFSI COD [/color][/size][/font]

24-08-11, 10:17 AM	#2
Cuppatea Grown up member Join Date: Feb 2011 Location: Somerset Posts: 105	Did the flow of fluid appear ok when bleeding after replacing the hoses? maybe give it a quick bleed again to be sure its air free. How are you bleeding it? Id make sure the cable operated lever returns to its stop ok, then double check all sliders are free and wind back the piston, then out again to set the caliper/pad clearance correctly. Give the pedal a few hard pumps and road test.

24-08-11, 12:13 PM	#3
baron2211 Grown up member Classic Audi Club Member Join Date: Aug 2009 Location: Midlands, or North East Posts: 690	I had a similar proble on the 200 last year and it turned out to be an f'ed caliper. Fortunately mine was still under warranty and it was changed foc. If you are getting the fluid through with no bubbles in it and the hand break lever is working corrcetly then this may be the same fault. Interstingly mine went from stuck off and not working to stuck on on the way back from Cornwall!! Mmmmm, blue disc!