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MG MGA - Brake drum machining

What is the minimum safe thickness for brake drums? I need mine machined and I want to be able to tell the machine shop a specific thickness to maintain.
Steve Simmons

Steve,
I checked 4 different books, and none show drum or rotor specificatins. I think that this requires somebody in the business. BTW, maybe a brake shop will have the specs; after all, it's only been 40+ years to get them.
mike parker

Steve,
I'm sure I saw a thread on this in the past...did you check the achives? As I recall the wasn't a published spec but the responses suggested a number.
Regards,
GTF
G T Foster

Yes, I remember the thread but for some reason couldn't find it. Anyone know what happens if drums are machined too far?
Steve Simmons

Steve,
A friend bought a 72 Ford in 1980, it made a terrible racket when it moved. He took it home, took off the back wheels, and found the drums literally cut into rings where the rivets cut through. The only reason that the car stopped was the front brakes and the fact that the rings held the brake shoes from expanding too far.
I have heard that the drums can shatter, maybe that's what he had.
mike parker

Steve,

On the early MGB, they are stamped on the drums. So you might check closely for a number. On the TD that I was playing with, I had the same question as you as no printed or internet info was available. The advise I got from the TD guys was that if they are over ground, the adjusters will do a 360. MGA pushrods have similar set up, right? So, if your brakes currently hold on anything less than the last few clicks, perhaps you're ok to grind (turn is the machine shop term). I wouldn't tell them the thickness to maintain, they will only turn to a minimum to make them clean and round. I'd consult with your machine shop. I find when you talk to anyone professional such as machinist, they are intriged by the notion of anything MG and always welcome your input and they proceede with caution.

Paul
Paul Hanley

Thanks for the input. I'll pass the info along when I take the parts in a couple days.
Steve Simmons

I always have the same reaction when people start scrimping on brake parts: BUY A NEW SET. They are NOT expensive, and whatever they cost, it's not going to be a lot more than what your machine shop will charge to do the job.
dominic

Steve:

Noticed this a while ago, from a short thread entitled 'Brake Drums'.

Begins:

Posted 08 November 1998 at 13:34:26 UK time
Don Tremblay,sassawanna@aol.com
The maximum amount of removal for your 1956 MGA is 10.125" on the inside diameter of course. Do not go beyond this point. If your drums are approaching this point (excellent chance)-do not weld "tips" to the shoes as you mentioned unless you have a death wish. You would be better off finding a brake shoe relining shop in your area that will reline your shoes to compensate for the drum wear. Your last option would be to shell out the bucks for a new set of drums. Not a bad option considering that sooner or later these things will be extinct.

Ends.

I cut it out at the time 'cos I'd mislaid the MG Service Memo on this topic, which if I remember correctly, gives sixty thou. as the maximum permissible grind. HTH.

Alex
A. W. Risk

As you remove more material...the heat dissipation is reduced. This leads to brake fade in heavy braking conditions. Cheaper pads (non-riveted) may let go if sufficiently worn and greatly overheated. Normally you can hear the shhishing or grinding sound of rivets making grooves in the drums.
The figures most companies/shops use are rather in the safe limit for liability purposes. Better to be safe than dead, so weigh the risk before going beyond the recommended limits.
Those of you needing the 4-hole type drums...note that the Z-Magnettes come with 4 of them. Cheers
Jon Bachelor

Dominic, it isn't about skimping on brake drums, it's about knowing if they are worn too much or not. No sense in throwing away a perfectly good set of drums just because I'm not sure what the recommended tolerance is!

Alex, that sounds like the number quoted recently in the other thread. I'll keep it in mind for the machine shop. Thanks!
Steve Simmons

I enquired locally about getting my drums turned a few months ago. The labour cost was more than buying new replacements.
Dan Smithers

I agree that safety shouldn't be compromised by turning drums beyond the recommended I.D. I'm puzzled though by advice that new drums are comparable in cost to machining. Turning a drum usually costs around $15 locally - Moss' catalog price for a new one is around $150 in Canadian dollars. If there is a much cheaper alternative I'd appreciate knowing of it since I think my drums have seen their last turning. Thanks
Tom Heath

Had my rear drums machined out years ago, the local brake shop done the job and had specs,and you can in NZ anyway get oversize lining fitted and ground down to fit the drums
Martyn
Martyn Dunn 1

Dan...more than cost of New to turn??
I'm moving to the UK...WooHOO!!! Talk about EASY MONEY!

Best price would be thru a Moss distributor
like Jeff at:
http://www.lbcarco.com/
264-790 (ATB7075)
BRAKE DRUM
MGA REAR, 1500 DISC/WHL FRONT
Retail $119.95 Our Price $101.96

This assumes your model uses the 4-hole type. Cheers
Jon Bachelor

They probably didn't want the work.

New drums approx £60. I guess that's a little more than an hours work at charge rates. No idea what the machinist actually sees of that though.
Dan Smithers

This thread was discussed between 02/11/2004 and 04/11/2004

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.