My1998 A4 tdi has failed its MOT on brake inbalance on the front.

This suprised me as I thought it would have been the rears, in the cold the brakes were acting up a little bit for the first stop of two down the road, they sounded like they were dragging but only when applied which was odd but after a couple of stops the noise went away. I was going to look into it but it went away totally a couple of weeks ago so didn't get round to it.

So any ideas, I don't have time to muck around with my tin top and like to fix it right the first time and get the MOT sorted quickly.

I'd be temped to get two new front calipers and just change them over, I'd do that for the same price a garage would charge just to look at the problem.

Any other thoughts or ways of diagnosing exactly whats wrong? My usual problem is once in bits I can't drive anywhere to get the parts!
Thanks

M

I would take them apart. lube the sliders and push the pistons back then try them again. My Nissan did it every year.

The noise from the brakes was probably just surface rust on the discs.

Because Audis have negative scrub radius is is difficult to identify which side is at fault by a road test however the failure ticket should tell you.
Did they give you the numbers from the roller test ?

Sounds like you need one recon caliper ( or a rebuild) and set of pads and perhaps a pair of discs and caliper guide pins. Also while you have wheels off carefully examine the toothed rings for the abs looking for splits and missing teeth.

If you clamp the flex hose before you start disconnecting the caliper it will greatly reduce the fluid loss ammount of bleeding required.

assuming you've checked over all the basics and it is just a stick caliper......

you might get away with just freeing off the calipers

mine have been playing up for a while now - so far I've got away with just working them back and forward at each service to keep them moving
(even resorted once to peeling back the dust seal and putting a couple of drips of brake fluid on the wrong side of the piston - but thats really flogging a dead horse)
just about to bite the bullet and change them, but at least it bought me a couple of years


or if the calipers slides / pistons are free - then what state are the flexable hoses in ?

[Edited on 19/1/2011 by mcerd1]

My Mk5 Golf had an MOT advisory for front brake imbalance. It was just the brake pads starting to seize to the slider on one side. Took less than an hour to clean everything up on both front brakes and apply copper grease to the pad/caliper/slider areas. Cost nothing but a bit of my time on a sunny day. Check the easy stuff first before you go and buy any parts.

Oh, and if the Audi brakes are anything like the Golf ones you'll need a 7mm allen key to undo the slider bolts. This is not a size you'll normally find in a set of allen keys.

I had the same issues on a Fiat 127 we had in the family years ago. That needed the sliding calipers removed, pistons cleaned up and all reassembled to stop the brakes binding. It would then be fine until needing the same 4 months later!

Daughters Fiat Bravo needed same labour only work while she ran it over a four year period.

I suggest just clean it all up well and give it a try.

For that reason I still think the sliding caliper design is inferior.

quote:

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Originally posted by Russell
oh, and if the Audi brakes are anything like the Golf ones you'll need a 7mm allen key to undo the slider bolts. This is not a size you'll normally find in a set of allen keys.

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quote:

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Originally posted by martyn1137
for that reason I still think the sliding caliper design is inferior.

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If the pistons are sticking then freeing them of is a waste of time, the problem is the rubber going hard and sticking to the piston, if you free it off it will just stick again. Usual cause is contamination of the seals by mineral oil. Using WD40 on brake components turns seals hard as it contains hydrocarbons.

9 times out of ten it's just a pad siezed/sticking in the carrier or sticking caliper sliders.