ZX rear brakes nightmare
Moderator: RichardW
ZX rear brakes nightmare
My ZX 2.0i has just failed its MOT. The rear brake calipers had seized up and so I sorted them out, gave it some new discs and pads and took it back for another go.
Still no luck.
This time it's "low effort to the nearside rear service brake". The guy at the garage reckoned that the piston might still be seized, but I told him I'd sorted that out. After a bit of uming annd ahing he said, maybe the flexible hose is on its way out.
Does that seem likely?
The pedal doesn't feel spongy as I thought it would if that was going.
Is this guy mad? am I mad? What else could it be?
Any suggestions gratefully received as I've spent far too long underneath the car to give up on it now.
Still no luck.
This time it's "low effort to the nearside rear service brake". The guy at the garage reckoned that the piston might still be seized, but I told him I'd sorted that out. After a bit of uming annd ahing he said, maybe the flexible hose is on its way out.
Does that seem likely?
The pedal doesn't feel spongy as I thought it would if that was going.
Is this guy mad? am I mad? What else could it be?
Any suggestions gratefully received as I've spent far too long underneath the car to give up on it now.
Is the back of the car lightly loaded and the fuel tank nearly empty?
If so the back brakes are not really meant to work. I know that this is a strange statement but there is a valve (or valves) somewhere which are designed to limit the rear brake effort when the car is lightly loaded to prevent rear wheel lock up. From what I remember of the Haynes book for our diesel there are a number of different mechanisms and so I would suggest you find which one is used in your car.
I have known MOT testers keep a load to be used in the back of some cars before tests to make sure this problem doesn't arise. I would suggest in any event that you have the car tested with some weight in it to prevent this problem.
jeremy
If so the back brakes are not really meant to work. I know that this is a strange statement but there is a valve (or valves) somewhere which are designed to limit the rear brake effort when the car is lightly loaded to prevent rear wheel lock up. From what I remember of the Haynes book for our diesel there are a number of different mechanisms and so I would suggest you find which one is used in your car.
I have known MOT testers keep a load to be used in the back of some cars before tests to make sure this problem doesn't arise. I would suggest in any event that you have the car tested with some weight in it to prevent this problem.
jeremy
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These valves can be pressure limiting, or in some cases deceleration cut off, which means a ball bearing inside the valve rolls forward under braking and operates a mechanism that prevents any more pressure reaching the rear brakes.
This type of valve has to be angled upward slightly towards the front to keep the ball bearing at its rearmost position.
This car will not benefit from added weight over the rear axle, the estate version will however, due to a load sensetive pressure limiting setup as it has massive (Iknow we're talking discs here) drums compared to the hatch.
Dave
This type of valve has to be angled upward slightly towards the front to keep the ball bearing at its rearmost position.
This car will not benefit from added weight over the rear axle, the estate version will however, due to a load sensetive pressure limiting setup as it has massive (Iknow we're talking discs here) drums compared to the hatch.
Dave
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Yep pressure limiting, you could swap them over and if the problem then goes to the other wheel, money spent on a new one will be in the right place and will sort it.
My money would be on that valve but I would need confirmation of its condition before forking out.
If there is anything impeeding the progress of fluid along the pipework like a collapsing flexible hose, it may be reasonable to expect the same in the other direction, meaning the brake will not release instantly but will drag for a short while.
Dave
My money would be on that valve but I would need confirmation of its condition before forking out.
If there is anything impeeding the progress of fluid along the pipework like a collapsing flexible hose, it may be reasonable to expect the same in the other direction, meaning the brake will not release instantly but will drag for a short while.
Dave
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Dave Burns</i>
These valves can be pressure limiting, or in some cases deceleration cut off, which means a ball bearing inside the valve rolls forward under braking and operates a mechanism that prevents any more pressure reaching the rear brakes.
This type of valve has to be angled upward slightly towards the front to keep the ball bearing at its rearmost position.
This car will not benefit from added weight over the rear axle, the estate version will however, due to a load sensetive pressure limiting setup as it has massive (Iknow we're talking discs here) drums compared to the hatch.
Dave
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Dave,if you are out there, from the above, can I take it the pressure limiting valves will benefit from extra weight (eg, a tank of fuel) because my near side rear has just failed. Read about 100 on the test where as the other side was near 200. Worked well with handbrake. I have just put new pads in (after the test) as the outer one of the the nearside was very worn. The caliper was not silding very well so perhaps this was partly the issue. I was going to fill up with fuel before I go back on Tuesday anyway as I had read something on the site before. Will it help?
A quick response appreciated from anyone else who knows.
Dave
These valves can be pressure limiting, or in some cases deceleration cut off, which means a ball bearing inside the valve rolls forward under braking and operates a mechanism that prevents any more pressure reaching the rear brakes.
This type of valve has to be angled upward slightly towards the front to keep the ball bearing at its rearmost position.
This car will not benefit from added weight over the rear axle, the estate version will however, due to a load sensetive pressure limiting setup as it has massive (Iknow we're talking discs here) drums compared to the hatch.
Dave
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Dave,if you are out there, from the above, can I take it the pressure limiting valves will benefit from extra weight (eg, a tank of fuel) because my near side rear has just failed. Read about 100 on the test where as the other side was near 200. Worked well with handbrake. I have just put new pads in (after the test) as the outer one of the the nearside was very worn. The caliper was not silding very well so perhaps this was partly the issue. I was going to fill up with fuel before I go back on Tuesday anyway as I had read something on the site before. Will it help?
A quick response appreciated from anyone else who knows.
Dave
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- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
No it wont help at all, the rear disc brake set up is not load compensating.
Its purely hydraulic pressure limiting, the wheels will lock up at a known pressure at various speeds so the valves are there to make sure this pressure is never reached.
When they go wrong however they don't allow enough pressure through and so you end up with reduced brake effort on one of the rear wheels, or both if both valves go bad at the same time, which is rare.
Dave
Its purely hydraulic pressure limiting, the wheels will lock up at a known pressure at various speeds so the valves are there to make sure this pressure is never reached.
When they go wrong however they don't allow enough pressure through and so you end up with reduced brake effort on one of the rear wheels, or both if both valves go bad at the same time, which is rare.
Dave
Dave, thanks for your reply, I wondered how they worked and there is no point me going down that avenue.
NiSK, hoepfully you are right and the caliper will work better now it is sliding better. Both sides of the disc were getting used but the fact that the outer pad was worn substantially more than its eqivalent on the other side (to about 2-3mm) shows somthing was/is wrong.
Thanks all
Dave
NiSK, hoepfully you are right and the caliper will work better now it is sliding better. Both sides of the disc were getting used but the fact that the outer pad was worn substantially more than its eqivalent on the other side (to about 2-3mm) shows somthing was/is wrong.
Thanks all
Dave