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MG MGA - unbalanced brakes

My ZB Magnette failed it's MoT with unbalanced front brakes. Previously I had this problem with my MGA, which I eventually resolved by swapping the brake drums between cars.

Aha I though, and swapped them back. The car pulls to the left when braking, but it is only noticeable at low speeds.

I have checked that all the wheel cylinders are coming out when the brake is pressed. One seems to be a little reluctant to return when the peddle is released.

The garage also suggested backing off the adjustment on one side, but I am pretty dubious as the hydraulic pressures should mean that the system is self-balancing. It doesn't seem to make much difference either.

The new MoT requires a complete retest (so I'm told) and I'm a bit reluctant to keep giving the garage money until it's sorted out.

Can anyone suggest anything else that may be at fault?
Dan Smithers

You probably need new brake hoses, and perhaps wheel cylinders rebuilt.
SF
Dwight
DCM McCullough

If I understand your situation correctly, the problem is under light braking only. Under a hard braking condition the brakes pull evenly.

This would indicate a lazy wheel cylinder. This could be caused by the flex line swelling internally and closing off the fluid passageway. Replacement of the hoses would be warranted.

It could also be weak shoe springs or rusty slides (where the brake shoes rub against the backing plate). Replacing the springs and lubing the backing plate would be the solution here.

Chuck
Chuck Schaefer

Chuck,
It's not really a question of light or heavy braking.
On a quite straight piece of road, travelling in a straight line I release hold of the steering wheel and brake.
The car contues in a straight line until travelling at less than 5 mph when it pulls to the left.

dan
Dan Smithers

Dan

I had the same issue repeatedly on the rear brakes last year when putting my car through the test here. We tried swapping drums over (both were anyway relatively new) adjusting brakes in all ways, and it made no diffeernce (just moved the issue randomly from one side to the other and back!), and in the end I just drove the 2km to the test centre with my foot on the brake pedal all the way, at which point (fourth attempt) it passed with *perfect* brake balance. As the drums were less than a year old, all hoses were less than a year old, no air in the system, the pedal as hard as a rock, shoes were matched and both adjusted to the same level on the snail adjuster, we were all stumped, and my solution was born of desparation!

Dominic
dominic clancy

You could try backing off the adjusters one at a time, this might tell you which cylinder is dragging. If it were me I'd just go ahead and rebuild the wheel cylinders and replace the flex hoses if they seem to be in poor shape. Rebuild kits are cheap and it only takes a short while to do the job.
Mark

Mark, I have already tried backing off adjusters on one side. All it seems to do is increase the pedal travel.

Dominic, perhaps it is just a case that one of the brakes has got out of practice as the cat has not been used for a few months while I was doing some bodywork repairs.


Dan Smithers

Dan

Just a thought...

Have you tried physically blowing through the flexible brake hoses. I found one of mine blocked by the inward expansion of the hose. While you can apply sufficient pressure to apply the brake, the spring return cannot return the fluid and can leave that brake rubbing. This heats up the brake (disc/drum) giving a stronger pull to one side or the other when brakes are applied.

Pete
Pete Tipping

Dan, might be a reach, but have you checked the rear brakes as well? Considering the symptoms you describe I could see where a dragging brake in the rear might not be noticable until most of the weight transfer to the front under braking had been removed when nearly stopped. I had a similar situation on an old truck with a leaking wheel cylinder which had glazed the linings on one rear side. At speed when braking there wasn't a problem, but at lower speeds the rear wheel would grab and cause the car to pull to the side.
Bill Young

The good news is that the car passed the test on Friday. When I was out yesterday, I tried my testbarking with the steering wheel released and the car now stops in a straight line. I guess the brakes needed a good dose of looking at!

The bad news is that I can't tell whether this is a symptom of something else.

Bill, the UK MoT test checks brakes in axle pairs, so the balance was definitely out on the front. This uses an inconveniently large (and presumably) expensive set of rollers that I can't install in my garage.

cheers

dan
Dan Smithers

DAn,
I don't know exactly about Magnette ZB but, you could have a look at the front left suspension condition too and around the lower trunnion bolts housing ovalization in A arms plus the bushes condition.
Renou

Dan, It sounds like the UK uses a Brake dyno. You could set up something if you were inclined to do it, but it would require an I-beam frame with two sets of rolls, one for each wheel. Clayton Dynamometer used to make them, I don't know whether they still do, but yes, they are expensive. You could also set up a pressure gage on each brake line, with a floating needle to stop at the highest pressure attained, which would tell you whether you had a hydraulic problem or a mechanical problem. The straight line test is all you really need.
mike parker

We used to get uneven, quite scary, pulling out of the brakes on Datsun pickup trucks from the 70's. They had 4 wheel drum brakes and the pull was caused by worn king pins and their bushings. The problem was barely apparent with old worn out brakes but once new shoes were installed and drums turned the darn things would change lanes erratically when brakes were applied. These were the last Japanese vehicle with drums on all 4 and the last with king pins. Worn suspension can cause brake pulls.
R J Brown

This thread was discussed between 23/03/2006 and 29/03/2006

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