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MG MGA - Brake Lining Problems?

I built my car up a few years ago, replacing all the brake parts at the time. I had the shoes relined at a reputable local firm that specialises in this sort of thing (by the way, it's a 1959 1500 - one of the last few, I think - so has drums all round). Ever since that time the MoT has brought with it regular 'advisories' or even failures due to 'brakes out of balance'. On the road it has often proved an uncomfortable drive due to its habit of suddenly and unpredictably locking a front wheel under braking. Partly due to this I haven't done a lot of mileage. (Also that a favourite Sprite sits just in front of it on the drive, and is thus easier to get out).
Now that I've retired, and now that another MoT is due, I decided to give some time to this problem, and have obtained an axle set of NOS shoes - riveted ones this time - which I have fitted. I've not driven it much, but already it feels better. On examining the shoes I've taken off, I can see that there are unworn areas dotted around the lining where it must be low. The attached image shows the worst of the four linings (and is thus easier to photograph). Am I grasping at straws, or could I have found the cause of the out-of-balance/snatching problem?


Gus Gander

Gus,
Have you had the brake drums checked for "ovality".
Perhaps the problem lies with the drums rather than the linings ?
David
D C GRAHAME

Gus,

David has a good point.

looking at the picture though it appears to me that the friction material on the shoes is incorrect.

The outer surface of the friction material needs to be accurate in both "roundness" and diameter, yours looks to be neither. It will take some bedding in to ensure that the shoes match the drums. Light abrading of the drums (assuming they are round and free from cracks etc)and friction material during this process can help.

When set up correctly the brakes should work well and inspire confidence and the front drums are quite adequate for normal driving (even if you do need to press pretty hard!).

Check the system again i.e. that the cylinders are operating freely and the shoes are free to move in their retainers. Also check that the hoses are in good condition. Contamination, bits of rubber pipe or seals, in the system can cause restrictions that could intermittently cause brakes not to apply or release properly. That would also cause the symptoms you describe, which may be then compounded by poorly fitting shoes and/or oval drums. You can bleed the system (Eezibleed)to check for even fluid flow or contamination.

Goes without saying you need to trust your brakes and then you should prefer the MGA to the Sprite!

Worst case scenario, drums machined or new drums, 39.95 each from Moss.

Let us know how you get on,

Neil
Neil McGurk

If the drums have been turned several times, the inside radius of the drum can be significantly larger than the radius of the lining on the shoe. Brake shops used to "re-arc" the lining, grinding it to the same radius as the drum for a perfect fit. This seems to be a lost art, judging from my recent experience with a local import repair shop here.

Ken
k v morton

Years ago I had a front drum brake that would lock up at fairly low speed and light pedal pressure. New shoes didn't make any difference. Switching drums from left to right made the problem go to the other side of the car. The drums were standard size, smooth and round within a couple thou, technically within spec, but they had lots of miles and years of hard use including a couple hundred very spirited autocross dates.

The answer turned out to be that lots of heat cycling had "carburized" the friction surface of the drums. That means small carbon nodules were migrating to the grain boundaries causing a very hard surface. The solution was to have the drums machined. Trying a very light cut for minimal material removal resulted in severe chatter of the cutting tool. The cut had to go about 0.015" deep to have a smooth cut with no tool chatter. Brakes have been working fine for another 85,000 miles.
Barney Gaylord

Ken, I had the same problem with a brand new '81 GLC The rear drum brakes would grab and lock, The dealer replaced the shoes to no avail. They also turned the drums which also did not help either. They brought the regional service manager in for a consult. He sent the shoes and drums out to be match ground and the leading edge of the shoes chamfered. No problem ever again, even after replacing the shoes a few years later.

Gus, I assume that your drums are smooth and shiney with no rust pitting. If not you have to start with that. Your brake shoes look like they are (oil?)glazed. Try giving them a rough up with a coarse sandpaper. Then using a file or rotary grinder, make about a 1/8" chamfer on the leading edge of the friction pads on all offending axles.

I would try this before taking more material off the drums. If this doesn't fix the problem then go for the freshen-up on the drums.

Chuck



C Schaefer

Thanks for the responses, but I am fairly sure I'd tried these. The brake drums on the car have all been changed around all corners, and the shoes have certainly been changed side to side on the front at least, and without much change. I'd given the linings a rub down on a previous occasion and managed to convince myself that things were better, and had chamfered the leading edge (which I rather tend to do as a matter of course when fitting new shoes anyway), Everything's good and dry. The drums are getting on a bit and the snails need to be turned up a bit to get the shoes to bite, so perhaps new drums might help, but I don't think the ones I've got are oval (I can't feel wnything at the pedal, either) so I shall present the car for it's MoT next week with it's new NOS riveted shoes fitted and see how things go before incurring any more expense.

G
Gus Gander

Gus, Don't know how relevant this is, but I had bad cadence braking on my TF a few years ago. I got new shoes and some replacement drums, but it made no difference. I eventually got rid of the problem by fitting new rear brake cylinders. Adrian B.
A Bennett

Hi Gus,
I also get this problem most years with my four drum 1500. I managed to improve things by swapping drums with my ZB Magnette which pretty much narrows it down to the drums. I do find that the wheel cylinders have a tendency to stick if the car is left undriven for too long - perhaps he's trying to tell me something ...

I have also had some success with backing off the adjuster on the stronger side. Yes, I know that it shouldn't make any difference, but it does help it get through the MoT test.

dan
Dan Smithers

Gus

I run a 1500 Coupe and had a similar experience last MOT. Despite pulling up perfectly straight it failed on front brake balance. That evening I dismantled everything, found nothing obviously wrong, put it all back together paying particular attention to the adjustment. The car brake performance felt no better and again the car pulled up dead straight. Took it straight back for a re-test the next morning and it passed. I was really surprised when it failed because the car is used frequently and I pay particular attention to brake adjustment. Like you am now apprehensive about next test. I find that the off side rear has a tendency to lock on heavy breaking and tend to agree with the general thread that old, worn drums are the most likely cause of problems.
D J ROUGET

This thread was discussed between 19/03/2008 and 25/03/2008

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