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MG MGA - Imbalanced brakes

I have an ongoing problem with the brake balance on my 1500. It has drum brakes all round.

In short, the car frequently fails the MoT test with front brake balance out of tolerance, or at least a warning that they are near the limit. Previously, freeing off the cylinders and adjusting the shoes has got me through.

What can I do to remedy this problem?

So far I have also tried

replacing the wheel cylinders,

replacing the shoes and linings.

This year I tried replacing the flexible brake hoses

I have now swapped the drums from side to side.

I have checked that the cylinders are set up the same on both sides.

I'm about to try swapping the shoes from side to side.


What else can I do to sort this out?

thanks

dan
Dan Smithers

I don't know how the MOT tests for brake imbalance, as I live in the USA. I have found that the point at which the brakes START to make contact can be affected by the shoe retracting springs. If one set is stronger than the other, then it will delay the working of that set of shoes, causing a slight swerve in the car's direction. This will disappear when a higher braking pressure is applied. Perhaps this might be your issue? A full set of new springs should help. Also it might help to polish up and "lightly" grease the backing plate boss where the brake shoes ride to equalize any friction that may occur from paint or rust.

Chuck
Chuck Schaefer

The UK MoT test checks brakes by putting the car with the wheels on a pair of rollers and measuring the point which locks the wheels there is a dual display so each wheel is measured independently. It also show the braking force applied through the tyre.
Dan Smithers

Dan, in my experience, this problem has usually been due to corroded pistons in the slave cylinders. Like you, I have freed them off, but that is usually only a temporary cure, a few months and they are siezed up again. The only real answer seems to be to replace all the slaves with new ones, fitting new seals is a waste of time. Another thing that Iv'e learnt is not to adjust your brakes too tight, see that the drums can turn freely, that allows the slave pistons to move a bit more in their cylinders and seems to keep them clear of corrosion.
Lindsay Sampford

Ahhhh! Since your test is at lockup, then my analysis is not applicable. Most likely, Lindsay's answer is the solution.

One other thought came to mind though. Somtimes, the leading edge of a shoe lining will grab the drum surface and cause the brakes on that side to grab. Again, this is usually a problem at the start of brake action, not at full lockup. Chamfering the leading edge of the lining on both shoes just a bit should eliminate that grabing action. It might be worth a try if you're willing.

To check the action of the dual wheel cylinders, you can remove the drums and wrap some rope or large wire ties around the shoes. This is to prevent the wheel cylinders from losing the pistons. Then lightly press on the brake pedal and watch for smooth action of the pistons. Do not press so hard as to push out the pistons. You may find the one cylinder that is at fault. It should be found on the weaker of the two sides.
Chuck Schaefer

In case anyone is interested, I was inspecting the linings under torchlight (not my favourite time) and noticed that one set had a sparkling granular apearance and felt dlightly rough to the touch (the stronger side) and the other was smooth and took fingerprints.

I replaced the shoes with an old set (a bit naughty) and the problem went away.

They were good enough to pass at the weekend and another car is back on the road.

I couldn't see any obvious leak, so I'll keep this in mind and watch for contaminated linings again.
Dan Smithers

This thread was discussed between 13/09/2010 and 27/09/2010

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