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MG MGB Technical - Rear Brake Puzzle

In adjusting a rear brake the other day, the adjuster just kept turning in until it went all the way through.

I've driven nothing but MGs since about 1972 and I've never had this happen.

The shoes have about 20,000 miles on them and look very good. The adjuster is a bit worn, but doesn't look too bad. I know that drums shouldn't be more than 10.06", while mine seems to measure 10.1".

I guess the thing to do is to replace the drums and adjusters, although I've never had to replace a drum before.

I'm curious to know if anyone else has had this experience.

Thanks,

Steve Lipofsky


Steve Lipofsky

Is the footbrake working OK? The other end of the shoes pivots on the hydraulic cylinder , maybe thats jammed in . It's also possible that the handbrake mechanism is sticking on inside the drum. Have got the drums off now ?
S Best

S

The foot brake is working fine. A tad moretravel than ideal, but that is because the brake is question is not quite fully adjusted.

The Wheel cylinder is relatively new and appears to be functioning just fine.

Yes, I have pulled the drum twice. The hand brake fully releases.

Steve
Steve Lipofsky

Steve
Has one of the wedges 'disappeared'?
For this to suddenly happen something is not right. Double check the drum.
Dave
Dave Wellings

Hi Steve.

I had the same problem on my daughters midget.

Drums were oversize, and shoes were partly worn.

New drums and shoes cured the problem.

Cheers
Ian F
Ian Fraser

Dave,

Both "wedges" are there. As I said, there is some wear to the adjuster, but not all that much as far I can observe.

Steve
Steve Lipofsky

It's possible that a PO or brake/tire shop
might have had the drum turned
to an excessive diameter, and additional wear has
now made adjusting impossible. Drums are cheap
enough that they're worth replacing if suspect
(used to be about $30 each, probably more now with
the exchange rate.)


Ronald

I wouldn't have thought that 10.1" as opposed to the 10.06 limit would have accounted for this.
Steve Lipofsky

Well the circumference of a drum of 10.06" diameter is 79.485"

Circ of a 10.1" diam drum is 80.118"

Difference is 0.633"

The full range of the adjuster can't be much more than that. Throw in a bit of lining wear and there you go - no adjustment left.

Cheers
Ian F

Ian Fraser

Steve. A couple of things. First, the adjusters seem to be made of mild steel. This means that they will wear over the years as they are adjusted and the range of motion on your old adjusters may not be as wide as a new set of adjusters could provide. Add into this the fact that most of the shoes available are relined and the shoes may have worn at the pivot contact point. Then add in the fact that the adjusters were designed at a time when the common brake shoes were riveted in place (meaning that they could not have to be adjusted as far out as the current bonded shoes can be) and the fact that your drums seem to have been turned over spec and you can see where the tolerances begin to stack and could lead to the problem you describe. By the way, I believe the correct max internal diameter is 10.040" rather than the 10.060" as someone stated. In any event, whether your drums are .040" or .060" over turned, I agree with Ronald. Replace them. Les
Les Bengtson

You could measure the total adjustment available . With the drum off crank the shoes right out and mark where they come to, then wind it right in and measure . This will give you an idea of how much the tolerances can stack up agin u before you cannot adjust your way out of trouble . Since everything else is fine this does seem to be what is happening .
S Best

Your points are logical and most likely are the explanation for this phenomenon.

It's interesting, however, that I've never seen this before, nor, apparently has anyone on the BB.

Are you sure that most shoes are relined? I've never been asked for a core with all the shoes that I've bought.

Did the riveted shoes have a thicker pad? If so, that would seem to be the single greatest contributing factor to this problem. It seems to me that the adjuster screws used to stick out more from the inside of the wheel.

By the way, the Max diameter for my drum is 10.06 as indicated on the inside of the drum.

The brake adjuster wedges are a very hard steel, but the central adjuster seems to be softer.

Thanks for all your good feedback!
Steve Lipofsky

I just ordered drums & adjusters from Bob at Brit-Tek ((800) 255-5883).

He told me that the riveted shoes were remanufatured, but the bonded shoes that we are currently using, are not. To his knowledge, there is no difference in pad thickness between the two.
Steve Lipofsky

Ian F

Assuming Pi is the same down under, I think the two circumferences calculate to 31.604" and 31.730" respectively i.e. a difference of only 0.126".

Regards,

Barry
73B
B.J. Quartermaine

Hi Barry
Oh dear ... My apologies Steve.

Pi is indeed the same.

Except that I used it to calculate the area rather than the circumference....

Cheers
Ian F
Ian Fraser

This thread was discussed between 09/05/2004 and 10/05/2004

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