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MG MGB Technical - rebuilding calipers

I just read where someone thought rebuilding the calipers on front brake are tricky..really?
Isn't it a couple of o-rings and new pistons sitting in the caliper?

I was about to order a rebuild kit.. what's everyone's take?

Frank
Frank

Frank-
Don't remove the bolts that hold the two halves of the caliper together. They're not reusable and aren't available from any of the major suppliers.
Steve S.

If one is experiencing a major problem with the calipers, other than a simple leak, would one not just assume that the bores were wasted (pitted, rusted, etc..). All the ones I've seen on non MG's were completely shot.
I just had a rear wheel cylinder fail on my 73B, so I just assumed that the other one sooner or later was doomed too. And while I was assuming.... could the calipers be far behind (master cylinder is already new)? A call to Brit-Tech solved it all with a complete re-brake kit. While somewhat expensive, it is really cheap insurance. I have piece of mind knowing that the entire system is in good working order (especially when I get a wild hair on these West Virginia mountain roads).
I have kept the old calipers and will dissasemble them shortly to check their condition. If OK, I'll rebuild them and save them for a rainy day. But if any pitting... in the "used up" pile they go!

Mark
Mark Thomas

Steve S

I did not know that the bolts were not reusable. I had always assumed that peoples instructions on to seperate the 2 halves were based on their importance as a saftey item with the implication that ammeters like me should not mess with them.

However, I have always been a messer so on 2 different cars I have split the calipers in the past!

They have then been reassembled using loctite on the threads of the bolts. So far I have not had any problems but now I am worried.

David
David Witham

I can't see why the bolts are not reusable. I disassembled a caliper and the bolts do not appear to be stretch-to-yield bolts nor do the torque values published indicate the same. Probably the best reason is because of the possibility that a leak may occur between the halves, but careful reassembly should eliminate that problem. Or maybe it's just a ploy to get people to buy new calipers. I can't see how a caliper can be thoroughly examined and rebuilt w/o seperating the halves.
Mike MaGee

I recently rebuilt my calipers and first of all, althought the bores weren't bad, all four pistons had pitting, which required replacement. Installing the seals is easy, installing the metal retainers is not. They're thin metal and bend easily. I made up a special tool out of a C clamp to put even pressure all the was around them to install. Still ended up bending a couple. That's why people take them apart. According to everything I have learned...the bolts that hold the caliper sides together are not to be reused, as retorquing them can stretch them beyond their design limitation. The result could be catastrophic failure under high brake loading. I don't want to take any chances when it comes to stopping, so I will not split my caliper housings. Better to spend a few extra bucks on extra parts, just in case.
R. L Carleen

I split the halves, reassembled, and tested the brakes successfully.... and definitely do not regret it. There was 30 years of sludge in the fluid channel between the caliper halves. Cleaning things up made a huge difference in stopping power. One reminder, don't forget to replace the seal between the 2 halves (available from Moss)

Kevin '69B
Kevin Lichterman

I rebuilt my calipers 10 or 11 years ago when I got the car. I read the warning regarding not reusing the bolts, but did it anyway. It doesn't make sense - why would the factory assemble the calipers with bolts that were that moody? I just started driving the car this year after flushing the brake system and have seen no signs of leaking brake fluid. Maybe I'm lucky.

The only reason that I can see not to reuse the bolts is that if they could stretch under use resulting in a loss of fluid and braking ability. If that's the case, they should have used better bolts in the first place.
Glenn

I just had another thought (it happens...)

Maybe the real issue isn't the bolts at all, but the threaded part of the caliper. I know that threaded holes can weaken after being torqued a few times - like in a cylinder block, for example. Perhaps the factory thought that after a few rebuilds on the calipers the female threads would be shot, and maybe that prompted the non-reusable caliper bolt warning.

Just a thought.
Glenn

Well,
I had already taken the left front caliper apart to see what was in there for the rebuild, and tons of sludge was present. I also saw the small black seal around the passage holes at the top.
Then I put it back together awaiting a rebuild kit.
I'm a little concerned, but as a mechanic in the Air Force for 21 years, I feel fairly confident that the probabilty of catastophic failure of the calipers, or having them coming apart is about zero. There ain't that much presure involved, even with weak or slightly damaged threads (which I didn't detect). Leaks may be a different story. Guess I can search for some bolt replacements as well. And I'll be sure to get extra metal rings to replace he ones I screw up trying to install. Thanks every one!

Frank
Frank

Frank, I have violated the shop manual warning about not separating caliper halves several times. The seal between them may leak if not replaced, Moss 180-285, it's not included in the repair kit. If you order a rebuilt caliper I suspect it has been separated and the old bolts reused. The condition of the caliper bores is not critical if the seal groove is good. The condition of the pistons is critical. Some replacement pistons are black and coated with?, The parts number is the same as the chrome piston. I don't like the black pistons but I have used some for a couple of years and brakes are ok. FWIW, Clifton
Clifton Gordon

Clifton,
I bought a set of stainless pistons on e-bay from a fellow in New York and they look great. Trouble is, he couldn't tell me their origin. Have you ever heard of a source?
David
David

David, I did a search and found this source. I know nothing about them. THe prices seem reasonable for stainless.
http://www.fortunecity.com/silverstone/tread/1046/id23.htm
Clifton Gordon

Clifton,
Thank you for the link and, yes, the prices do seem good. It appears that mine were probably purchased here as item number 114712 with the step machined from the lip. I got a really good deal only $42.55 for the set of four on e-bay.
David
David

MGOC have just started selling the stainless pistons at £ 12 each, Along with dire warnings about being necessary for competent mechanics to instal as they are a safety critical item
FWIW
Vic
V Todman

I don't know about anybody else, but I for one will heed Steve S's advice and not reuse the bolts on the calipers. It is not a case of the bolts being moody as somebody said, they are high tensile strength bolts and if installed properly, were torqued to 80% of their yeild strength. Over the years, the pressure exerted on them by brakeing forces cause them to stretch even further and then relax, further fatigueing them. The reused bolts may or may not fail even if they are torqued properly (does anybody know the proper torque value for them?), so reuse if a real iffy proposition. You will never find anybody in the racing comunity reusing high tensile strength bolts once they have been removed, they always throw them away and install new ones. I reused high tensile strength once, in our TD (gudgeon pin pinch bolts) and the results was a disaster. By the time the engine could come to a complete stop after the bolt broke at 4200 RPM, there was not enough left of the engine to rebuild. I would rather that not happen when I hit the brakes hard in an emergency. Cheers - Dave
David DuBois

Chilton's says the torque spec for the bolts which hold the caliper halves together is 34-37 ft lbs.

How hard are these bolts - grade 5, 8, or higher?

Is there anything special about the bolts such as being shoulder bolts?
Glenn

This thread was discussed between 03/09/2003 and 05/09/2003

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