citroen zx brake compensator valve

jango · Unread post by **jango** » 15 Nov 2005, 18:41

Hi everyone,
Got a bit of a problem, about a week ago I took my trusty 1992 Citroen ZX 1.9 Diesel Hatch for it's MOT. Well it failed, but only on a couple of small things, one: the handbrake cable and two: the o/s rear brake was only 50% efficient. The examiner thought that it may be due to a leaky brake cylinder. I replaced the handbrake cable and cylinder and took it back for the re-test, but the rear brake was still the same.

Now the shoes are good and the drums are OK too, the other strange thing is that the handbrake works perfectly, in fact slightly better than the near side. The examiner and I were both scratching our heads trying to work out what could be causing the problem. He suggested perhaps fitting some new shoes and then probably new drums too. But then we remembered the handbrake is working perfectly, very puzzling.

I then asked if if air in the braking system would cause this, he said maybe and then he had a eureka moment and said it might be the brake compensator valve.

Has anyone out there experienced a similar problem, or have you got any more ideas what could be causing the problem? Replacing the shoes and drums seems unnecessary as they have plenty of life left in them.

Many thanks in advance
Joe

jeremy · Unread post by **jeremy** » 15 Nov 2005, 20:38

Has this car a separate brake compensator or is it incorporated somehow with the cylinder?

The required efficiency for a handbrake is only 25% (0.25g) across the axle anyway. Does the tester mean that this one is only producing half what it should - ie 6.25% - in which case you can probably turn the wheel by hand with the brake applied!

bxbodger · Unread post by **bxbodger** » 15 Nov 2005, 20:50

I'm pretty sure that ZX wheel cylinders are the same as those on the Pug 205. If so, the load compensators are built into the cylinders so if it was faulty, changing it should have cured it.

Its most likely some air is still in the system or the hose is collapsed internally and not allowing fluid into the cylinder-does it bleed o.k.?.

jango · Unread post by **jango** » 15 Nov 2005, 21:05

Hi, thanks for you replies

I'm not sure if the hatchback has a separate compensator, I've had a look in the Haynes manual and they only seem to mention the compensator for the estates.

The handbrake works great and passed the required tests at the mot station, (strangely, the side I'm having problems with (o/s) works slightly better than the n/s ) but the foot brake for the o/s rear was down 50% compared to the n/s. rear.

I did wonder about the hose but the examiner never mentioned any problems with it the first time the car was tested. The brakes do seem to bleed OK. This has really got me puzzled

any suggestions will be very much appreciated.

Joe

jeremy · Unread post by **jeremy** » 15 Nov 2005, 21:16

Rest assured it has some form of rear brake compensation or restriction. I think the estates (bigger drums) may have the conventional valve with a spring linking it to some part of the suspension, the TD's (discs) have separate valves lying crossways at the back somewhere.

If I read your initial post correctly your problems are confined to the off side rear brake and you have replaced the cable and the cylinder?. I funked doing ours when the cables went last year and had it done for me but I do wonder if for example it is possible to fit the cylinder incorrectly which might caue incorrect operation of the restrictor valve? ) Wrong side even.

jango · Unread post by **jango** » 15 Nov 2005, 21:36

Hi Jeremy,
Mine is not a TD just diesel and it has drums on the back not discs.
The thing is it failed the first time because of the o/s brake being only 50% efficient, so I replaced the cylinder and took it back to the test station and there was no difference, even with a new cylinder, so the problem can't be that.

Joe

sooty · Unread post by **sooty** » 15 Nov 2005, 22:08

I know its abit of work to do. But to prove whether its the shoes or not why not swop them from one side to the other and ask the garage to retest the performance.

But ensure your brake shoe and handbrake cable adjustments are correct.

jango · Unread post by **jango** » 15 Nov 2005, 22:12

I might just do that, thanks for the suggestion

jeremy · Unread post by **jeremy** » 15 Nov 2005, 23:13

Some brake compensators are simple devices for example employing a ball running up a slope and must therefore be mounted at the correct angle. Is it possible that for example you have been supplied with a nearside cylinder?

I had a Renault 21 with essentially the same rear brakes but with a separate brake compensator. I had a leaky cylinder and recall being supplied with the wrong one and ending up having to bend the steel pipe to fit. The point I'm making is that certainly on that car the cylinders were interchangeable.

jeremy

bxbodger · Unread post by **bxbodger** » 16 Nov 2005, 12:27

I don't think that the load compensator is at fault here at all, and is a bit of a wild goose chase- their purpose is to allow more brake fluid pressure to the rear brakes when the car is heavily loaded up in the back, to compensate for the load, hence the name.

Normally when they fail you get the opposite problem to what you are experiencing, i.e. the rear brakes keep locking up under normal braking as although there's no load, far too much braking effort gets diverted to the back end.

BrianM · Unread post by **BrianM** » 16 Nov 2005, 12:52

Could possibly be air - recently had an Astra with poor brake performance on one side (drivers front) - bled the brake pipe at the master cylinder and it was fine then.

Brian
97 Xantia TD

jango · Unread post by **jango** » 16 Nov 2005, 15:13

Hi,
Thanks for the suggestions, I think you may be right about the compensator!
How would I bleed from the master cylinder as there are no bleed nipples, just 2 brake pipes?

Thanks again for your help

jeremy · Unread post by **jeremy** » 16 Nov 2005, 15:50

It is possible to bleed some components by loosening a pipe and letting air out that way.

With a back brake its often necessary to bleed a considerable amount of fluid out to get rid of all the air, especially if the flexi hose hasn't been clamped.

jeremy

jango · Unread post by **jango** » 17 Nov 2005, 20:45

I think it may be air, so I'm going to bleed the brakes at the weekend, I'll let you know how I get on.

Thanks for all your help, it's been very much appreciated

Unread post by **RichardW** » 18 Nov 2005, 08:04

Get yourself a Gunson's EaziBleed kit - allows pressure bleeding of the brakes. Makes it dead easy, set it up, crack open the bleed nipple and watch the fliud (and hopefully air bubbles!) flow. If you're near Glasgow, you can borrow mine...