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MG MGA - Binding brakes
I am reading several articles of people working on their (drum) brakes, and want to share the experience I had on that, some time ago.
After working on the rear axle, new oil seals etc, my A showed a strange braking behaviour. Braking was OK, until the last 0.5 meter, (say 2 foot) then, just before reaching a complete stop, sometimes one, sometimes both brakes locked up and I came to a stop with sliding / screaming tires. Once stopped, I heard the brakes to unlock with a click, and everything was normal again. Very disturbing when you approach pedestrians, or so, from behind. I scared them to almost jump out of their pants, and every time, I got lots of very angry eyes.
This puzzled me quit a while, I did R&R and re adjustment of the rear brakes several times, but no results. At some tome, over a couple of beers, I told this to a guy who used to work, as a mechanic in a VW garage, an he asked me: How do you assemble your brakes ? Mount the drum with the brakes backed off, and then you adjust them? I had to agree with him. Well, he started, thats NOT the way we where supposed to do this. You should adjust the brakes with the drum off, until the point you just can slide the drum over the shoes to mount it and then when the drum is mounted, continue your adjustment until OK. This way the brake shoes are well centred inside.
What happened to you is that the shoes are way off centre, When you adjust they touch the drum at some edge when braking being able to move in the rotating direction so they can act as a wedge. At higher speeds, you have no hinder from this, because of the small braking surface, but when the speed decreases, at some point this small surface has enough friction to block the wheel.
I assembled again the way he told me and., problem completely solved.
For some of you, this is portably an obvious (brake mounting) knowledge, every mechanic is supposed to know, but for me it was, although logic afterwards, a surprise, and there must be other MGA novices who sooner or later run into this, and to who this can be a help.
|Rik de Krom|
|Interesting Rik - I always replace my drums as you initially describe - but no problem yet with locking the brakes - but I will try the second "offical" method next time I have the drums off.|
|Indeed as novice I have been doing as you Rik.|
In fact I took the drum off today cos as you may have read on the other thread I have some issues bleeding the brakes.
On the right rear wheel the travel is too much... and in fact I run out of adjustment before the drums bind...
Do you think that if the drums are not centered properly they the travel could be increased?
I had this idea that the brake shoes would be self centering upon braking.
I will look into what you described...
|Thanks for the Info Rik, I have this problem sometimes and will give your method a try.|
|I also have been doing it as you first describe. Usually with new shoes on my '57A and MGB there is not a lot of extra room to put the drum on anyway. I smear a tiny bit of Lithium grease on the parts of the shoe backing that contact the adjusters and cylinder piston to enable them to slide |
freely and centralise themselves. Then put the drum on and tighten the adjusters till the drum is locked and back it off a few clicks just until it turns again. I have never had a problem this way, but what he says makes sense.
I must be missing something here. What difference does it make as to WHEN you mount the drum? The shoes are moving in "air" whether you mount the drum "now" or "later"???
|I am completely bemused by this "practice" too. Why would it make any difference at all. If it were true, the problem would exist with all cars not just classic ones, and no mechanic I have ever seen at work does any more than roughly centre the shoes by eye so he can get the drum on and then apply brake a few times before making adjustments, then checking again.|
The MGA shoes will self centre when the brakes are applied simply by the forces at work when braking. If the shoes are out of adjustment, the main problem is going to be ineffective brakes because the travel is too far, not that they lock up when applied.
Comes into the "old wives tales" for me.
|Rik, don't understand all this stuff about centering the brake shoes by fitting them with the adjusters wound up. As others have suggested, the brake shoes centre themselves the first time you apply them and continue to keep themselves centred as they wear, the 'activated' end of the shoe wearing more than the pivot end. I would say that your trouble was caused by there not being a chamfer on the leading edge of the linings, causing them to 'dig-in' to the drum as the wheel slows down.|
I had my rear brake drums of and on several times before, on my MGA as well as on different other cars before, and never had any problem wit that. Until that time I described above.
The difference with the previous times was that this time everything has been dismantled and cleaned. When I read in Lindsays reply about the activated part of the shoe wearing more than the other end, could be a part of the problem, because the shoes most certainly got mixed up and swapped places.
But, from that moment on the brakes locked up the last 2 foot of the braking path, and came free again with a click the moment the brake pedal was released. (I could hear this sitting behind the steering wheel.) I had the drums off 2or 3 times to inspect what could be wrong, I hooked up the springs on another hole in the shoe to give more spring force, I made sure everything that was supposed to move a bit was free and able to do so, but the problem stayed, and made driving, no, stopping rather unpleasant.
The advice I got to centre the shoes by adjusting the brakes to 80%, then mount the drum and continue adjustment was a complete surprise. I never heard of this before. I expected that the brake shoe assembly was indeed self centring. Probably in is certainly supposed to be self centring.
However, a fact is, that after centring the shoes, The strange lock up behaviour completely disappeared and has never came back the last 2 years. That centring was all I did that time, I took off the drum, wound up the adjusters until I could slide the drum over the shoes and put the drum in place. Then with the drum fixed, I continued the adjustment until OK. Like I always used to do.
The mechanic who told me about this used to work in a V.W. garage from the late 70ths until shortly, and said thats how he learned to mount brake drums.
I dont know if this practice was the solution and the proper way to mount drums, but it sure looked that was afterwards.
If there is another, better, explanation what happened inside my brakes, and why it was solved by this centring, I will be glad to hear and learn again something more about my MGA, because like Mr. Ramos, and probably a lot of others, at some day 10 years ago, I almost innocently stepped into MGA ownership and learned step by step, year after year, the ins. and outs of the MGA and I have certainly still a lot to learn.
|Rik de Krom|
This thread was discussed between 18/04/2010 and 21/04/2010
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