Golf mk3 brake balance (pressure regulator / ABS)?

[mikko.rantalainen]

Hi!

I have a problem with my rear brake balance. The left rear wheel has less stopping power than the right rear wheel (I had the car tested and left rear wheel had 1.0KN of stopping power when the right rear wheel had 1.4KN which means a 40% difference). The front brakes are correctly balanced. All the brakes release correctly after using brakes and the hand brake is also correctly balanced. As such, I believe that the problem is caused by brake fluid pressure applied to rear brakes.

Car details:
Golf mk3 1996
1.9L TDI 81 kW with VNT turbo
ABS brakes with drums in the rear (ABS system seems to be working ok and will activate under heavy braking)

Some questions:

1. Does this car have brake pressure regulator or does the ABS system take care of the brake balance?
2. Where the pressure regulator is located if I have one?
3. Can I somehow verify that it's broken short of replacing it in the first place?
4. The car has old brake fluid in it (more than two years), could this be fixed by only changing the fluid?
5. Anything else? What I should check next?

[Fluid]

Yes. It's probably seized or the caliper is sticking. It's on the rear axle and has a lever. When the car shifts it changes the proportioning. You need a brake specialist to test and adjust it because the pressures are too high. Did you fail inspection?

[mikko.rantalainen]

Originally Posted by Fluid

Yes. It's probably seized or the caliper is sticking. It's on the rear axle and has a lever. When the car shifts it changes the proportioning. You need a brake specialist to test and adjust it because the pressures are too high.

The brake pressure regulator on the rear axle changes the proportioning between front and rear brakes but not between left and right rear brake, right?

Currently, the balance between front and rear is correct but the balance between rear right and rear left are not correct. I'm trying to figure out where the problem is.

Originally Posted by Fluid

Did you fail inspection?

Yeah, I failed yearly inspection because of this issue. The legal limit for rear balance difference is 30% and I got 40%. The difference in balance has been within 5% during previous years, so something has changed during the last year. Within last year, I have replaced right front brake caliber but I wouldn't expect that to change the left rear braking force.

[chittychittybangbang]

I would replace the caliper. It sounds like it's sticking. The proportioning valve is front-rear. The only way I can think of testing it other than by measuring braking force as you've already done, is to remove it and inspect it. If you do that, you might as well rebuild it but it's probably cheaper to buy a rebuilt caliper. As long as it's a good rebuild, it should work. It's possible the metal brake line got crimped. I don't know if they use separate lines for left and right on this year with ABS. I know later models with ABS do but their proportioning valve is at the ABS pump. I don't think changing the fluid will do anything unless there was a massive air bubble in there.

[mikko.rantalainen]

Originally Posted by chittychittybangbang

I would replace the caliper. It sounds like it's sticking. The proportioning valve is front-rear.

I had some time yesterday and checked the brake lines under the car. There's nothing in the brake lines near the rear axle so I guess that there's no proportioning valve in this car. Probably the ABS system takes care of front-rear balance. (Both the left and the right rear metallic brake lines go from front to back side-by-side until near rear axle. Then the lines go through a short rubber brake lines at rear axle linkage and then again continue with metallic brake lines to the drums.)

I think I'll proceed to replace the caliper. It's not sticking very much because the brake releases okay (and there's still some stopping power), but I think that you're right that the problem must be there.

[mikko.rantalainen]

Originally Posted by mikko.rantalainen

I think I'll proceed to replace the caliper. It's not sticking very much because the brake releases okay (and there's still some stopping power), but I think that you're right that the problem must be there.

I replaced the caliber and the front part of it was seized (the caliber has two pistons, one towards the front and an another towards the back). I haven't yet reinspecpected the car but I believe that it's okay now.

Thank you.

[chittychittybangbang]

good to hear.