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MG MGB Technical - Sticking rear brakes

The rear brakes on my 77B were replaced about 200km ago by a workshop....they are now 'sticking' when I come to a halt. I can feel them applied (almost like a mild handbrake), but as soon as I apply a little throttle in first gear and move the car, they unstick and all is fine. There is no brake smell so they dont appear to be sticking or dragging when underway. What do I do to re-adjust the rear brakes?
MF Cody

Replaced? Shoes, springs, adjuster, cylinders backplate, handbrake cable and compensator?? This sounds to me like the cylinder failing to float properly in the backplate.
Stan Best

Stan, I am confused, can you tell mme why the cylinder needs to float in the backplate. Lockheed cylinders rust into the backplate after a short while, unless you mean the pistons are moving properly.
regards John
john wright

I've just noticed that if the handbrakes sticks on on any of my cars I only know because as I drive off after releasing it there is a scary BANG from the back and then normal service is resumed. I think what is happening is that brake drag forces the cylinder to move a bit, that clears the stiction and the springs re-assert their authority. The B brake cylinder is clearly designed not to be mechanicly strapped to the back plate so i always paint the back plate and then copper grease the cylinder where it fits. Until we know exactly what was done to the car in question its speculation, it may be incorrectly re-assembled springs, and if so I will post a pic.
Stan Best

near side cylinder. I have the w/s manual and could scan in the spring fitting as well if you need it. The black gloop is waxoyl.


Stan Best

Stan, thanks for your explanation, I spent 25 years working for a large brake lining manufactuer in Yorkshire as a road test technician, and when we got new brakes from lockheed there was never any grease on the cylinder. Your problem with a bang is because the liners will have been rusted into the drum and they bang as they release.
john wright

I have visited the site where you worked, we sold them some PDP11 chips, which rather shows my age! A very pretty part of the world. I really am not sure that the piston assy needs to float a bit, but you have to ask yourself when you see a fitting like that, why didn't they just bolt it on?
Stan Best

Stan what the hell are PDP11 chips, the local chippy in Cleckheckmondsidge will go wild as they wil not know how to cook them.
With regards to the wheel cylinders, well they are made by Lockheed ( my old company bought AP years ago and got rid of them PDQ) enought said.
You must tell me where you bought your rose tinted glasses because Cleckhechmondsidge is not scenically pretty, talk about Black satanic mills!!!!!
john wright

I would try backing off the adjusters 1/4 turn and see if that clears up the problem. Sometimes simple solutions cure simple problems. Ray
RAY

MF-
It sounds as if one of the trailing shoes is failing to retract. This could most likely be caused by a sticking piston.
Steve S.

Interesting comment re trailing shoe. This design is typical for a disc/drum set up using one leading and one trailing shoe to ensure the handbrake works in either direction. In reverse the shoes swap over and leading becomes trailing. The trailng shoe is the one that has the actuating piston at the end the drum is moving towards, the "trailing end" . As the drum roates this tends to push the piston back the other one gets a self servo effect as the drum to shoe braking force tends to pull it on. When you take your foot off the brakes the springs should pull the shoes back and the drum/shoe forces should stop straight away. Why would the trailing shoe be more susceptible? Also this leads to the thought since it is a one leading one trail setup, would driving the car forwards and then backwards show which set of shoes was the problem?
Stan Best

Is it sticking rear brakes? Or sticking brakes full stop? I ask because I've had both. Suddenly and after many years without a problem I suddenly found that one rear would lock on when I braked in reverse, but not forwards. Took the drum off and fiddled about but it made no difference. Then I backed off the adjuster one click to where I would normally have it, and it was fine. At the next servive interval I readjusted them to my usual way with no problem, and subsequent to that swapped the shoes from side to side to see if it would cure a squeal (it did) and the problem hasn't come back.

The other problem is all the brakes locking on in hotweather because the servo doesn't release, and you can feel that as a very hard and high pedal, tapping it usually clears it. I've tried lubricating the little air valve (it was lubricated anyway) but it didn't make amny difference. Next thing to try is turning the servo over so the air valve is at the bottom.

The cylinder doesn't need to float, any difference in wear characteristics of the shoes are compensated for by the pistons coming out different amounts, so the shoes apply equal pressure to the drum. It's the handbrake lever that floats inside the drum, for the same reason.
Paul Hunt 2

Explain what you mean by "I can feel them applied, almost like a mild handbrake".
1. Check the cylinders, that the pistons are movingfreely and not leaking
2 The pull-off springs are quite complicated, if the brakes were done by non mg specialists.............well!!!
3 When I put new shoes on, I always file a bevel on the leading edge, and if the drums are worn, on the edges as well.
Allan Reeling

ALSO check condition of rear brake hose and metal brake lines....I had a double whammy on my 77 recently...a collapsing rear hose AND a crushed metal brake line where it attaches to the left rear axle that caused your symptoms ...and yes...it was the last thing I checked!
P J KELLY

This thread was discussed between 05/08/2007 and 09/08/2007

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