Hi Skoda forum,

I have been struggling a lot with my rear drum brakes on my Mk1 from 2004. They have an imbalance of around 30-40% where
he left side is the weaker one. Front brakes are fine and below 5% of each other.

I tried everything I could think of to fix it, but so far, everything failed. I did the following:

- changed cylinders on both sides
- changed shoes on both sides
- changed drums on both sides
- left side: replaced brake last part of brake pipe (picture shows the copper one I formed next to original)
- left side: changed flexible brake tube going to replaced pipe
- took out ABS fuse to make sure there was no ABS activity

- vented both sides multiple times

All of these actions have nothing to improve the problem. I still have around 40% difference between the two drum brakes.
When braking with the manual parking brake, the force is a lot more equal, the difference drops to around around 15%.
From that, I suspect that the problem must be of hydraulic nature. It looks like there is no brake power regulator or reducer
on my car. It looks like all brake pipes go directly into the ABS control unit under the hood.

Does anyone have any ideas on what else to try to resolve, or even diagnose, this problem?

/ Pascal

Is the auto adjuster working ok? The teeth on the adjuster wedges can become worn causing the wedge to not hold its position.

 

 

Edited 17 October, 20205 yr by TMB

They look fine. If they were the problem, shouldn't the hand brake test show exact same symptoms as when using the pedal?

Just now, Devnn said:

They look fine. If they were the problem, shouldn't the hand brake test show exact same symptoms as when using the pedal?

 

Yeah, you're probably right there. Only other things I can think of is the master cylinder or ABS unit as you have tried pretty much everything else.

So the imbalance has not changed no matter what parts were changed, bleeding etc or did it occur during the work?

 

You could try disconnecting both handbrake cables & manually actuating the adjusters, also swopping the linings from one side to the other, I cannot justify any of these actions logically but sometimes doing things like that make the fault move or change, gives you what may be the key clue.

 

I would also put the wheels in the air and gradually operate the handbrake one notch at a time feeling the resistance of each drum, you might also try it with someone gradually applying the footbrake but they will need to hold rock steady while you go from side to side.

 

I believe it will be either adjustment or air in the system, a partial blockage in the ABS block for instance should equalise if a constant pressure is put on the pedal and both brakes should then be equal.

 

Possibly an ABS valve leaking fluid back to the master cylinder, you could try holding the brakes on for a long time with a constant pressure just enough to lock the rear wheels & see if one releases.

 

As a very last resort you could plumb in any old master cylinder to the rear brakes only and actuate it, if they come on equally then it has to be the ABS valve block.