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MG MGB Technical - Brake drum skimming

I am renovating a Banjo axle and the brake drums are rusted and pitted. Is there a maximum diameter that the drums can be skimmed to without causing lack of braking efficiency?
Graham Gilmore

Graham,
I think the minimum thickness is actually cast on the drum side, although it may rusted away by now. I'm still at work so I can't look in Haynes, it may well be in there though.
David Smith

David, the minimum thickness for the front discs is quoted but I cannot find anything about the rear drums in either Haynes or the official w'shop manual.
Graham Gilmore

I have seen drums that were marked but I just checked two spares and they are not marked. I just read a brake article in a Bendix Brake Service Manual and the size markings were required beginning in 1971. Original MGB drum diameter was 10". In Motorheads maintenance section I found this note on minimum thickness.
http://motorheadltd.com/Tech%20Tips/T6Blurbs.htm
"The minimum brake drum thickness is .06 inches"
I believe they intended to say the maximum inside diameter is 10.060", I believe that is the figure I have seen on MGB drums. A drum only .060" thick would surely split or crack when the brakes are applied. I would go with 10.060".

If the drums are turned the brake shoes should be ground to match the bigger drum diameter. A good brake or machine shop should be able to do this. Otherwise the shoes will have a very small contact area.

Clifton
Clifton Gordon

I agree Clifton, 60 Thou does seem rather thin!! I am not sure about the need to grind the brake shoes though as the pivot effect of the adjuster/cylinder doesn't put the whole shoe surface in contact anyway and the same effect can probably be achieved by strenuous bedding in of the shoes. Thanks for the info anyway.
Graham Gilmore

I recently had my drums machined and used the 10.06" figure which I think is also quoted in the Bentley manual although I dont have my copy with me at this time. I did have the machine shop check the work with a brake shoe that I gave him with the drums.
pAul

This thread was discussed between 07/11/2007 and 08/11/2007

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