Micra load-sensitive brake valve question

I have a '93 Micra which has just failed it's MOT test. The mechanic told me the braking at the rear wheels is far too low. He said the "brake balance valve" would hardly move and that part alone costs £400ukp! Tomorrow he's going to try some penetrating oil and try to free it up. The other possibilty he said was the rear brake pistons could be stuck.

So, when I got home I put the car up on the ramps and took a look. All the levers I can see on the brake balance vale (which I now know is a load-sensitivce valve) seem perfect free to me. When I bounce the car up and down the valve spring gets compressed ok and moves the lever (which is under the rubber boot). Maybe there is another part of that valve that's stuck? I can't see anything else to "lever" free.

One more thing is that the car has been standing for 4 months over the winter - could this make either the valve or the brake pistons to seize like this?

Is there any way to be be sure it's the valve that's at fault - as it's so expensive.

ps I just called the garage and the mechanic said the valve should be seen to move if **someone presses the brake pedal**. Is this correct? AFAI can see the mechanism operates because, under braking, the rear end starts to lift, the valve operating lever is compressed and operates in turn the internal hydaulic valve. This clearly DOES happen. How on earth it's meant to move/operate simply by pressing the brake pedal with car is stationary is beyond me! (Well many things are I suppose :-) )

Thanks.

Reply to
dave
Loading thread data ...

Low readings on rear brakes are not of themselves a reason for failure (non working is). The failure due to low brake performance is only correct if the braking efficiency from all four wheels added together is below the minimum required. If the two front wheels will lock up on the rollers (and the rears show some braking) then the brakes ARE good enough to pass. The brakes may have faults yet still be good enough to pass.

To test your rear brakes for yourself you need an assistant and a jack or two. Raise a rear wheel by jacking the suspension rather than the body, get the assistant to press the pedal firmly, with a normal amount of strength you should be able to turn the wheel, it should be stiff, showing that the brake is working, but it should still turn, Applying the handbrake should cause the wheel to lock, now rejack the same end of the car so that the suspension hangs down, again get the assistant to press the brake, the same wheel should now be easier to turn. This show that the load limit valve is working. Micras do suffer from faulty stiff handbrake cables and maladjustment, this causes the self adjusters to fail to operate and the braking from the affected wheel gets less and less, and eventually does not operate at all. Winding the adjusters up by hand gives a temporary fix. I have had to do this on several micras.

mrcheerful

Reply to
mrcheerful

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.