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MG MGB Technical - Brake Caliper Rebuild

Just returned from a road trip to western PA in our '74 B/GT, and had a problem with right front caliper after heavy braking on long down/up hill driving. Caliper was sticking causing power loss, and smoke for a not so 'grand' enterence to Falling Water. I removed the right front wheel, and pried the brake pads apart to compress the calipers and applied the brakes several times. No other problems for the remainder of the trip. The last re-build on the calipers were a dozen years ago at best guess.

Two questions; first, anyone have experience with MOSS (USA) rebuilt units, or best to keep originals and rebuild a second time? Second, anyone switch to synthetic brake fluid in their MGB?

Regards,

Larry C. '74 B/GT, and '69 midget
Larry C '69 Midget

Larry.. I would suggest that you replace all three brake hoses. This usually is the first indication of calipers sticking. The hoses are breaking down internally.
Sandy
conrad sanders

Sandy,

Thanks for the quick response. Because we do drive this car often I replaced the stock type brake hoses with MOSS braided stainless steel/teflon units about five years ago. Same for our MG Midget.

While I do not discount the new hoses as a possible cause, I believe the problem to be in the caliper. Perhaps contaminated fluid, or moisture at the caliper caused the failure under high heat and pressure?

Regards,

Larry C.
Larry C '69 Midget

Larry,

if there are still the original (chromed) pistons used in your callipers, i would renew them. There are Stainless Steel pistons available for this callipers. The caliper itself shold be cleand with break cleaner and compressed air and new seals fitted.

I once bought an exchange caliper for one of the B's and it is as good as the other ones, so i can not say anything against it.
The brake systems of my B's are toped up with silicone brake fluid. I gave it a try 8 years ago and never had a problem with it anymore.

Ralph
Ralph

Larry-
I've been using a synthetic brake fluid, Valvolene SynPower, for several years. It has a wet boiling point of 343 degrees Fahrenheit (172.8 degrees Celsius) and a dry boiling point of 513 degrees Fahrenheit (267.2 degrees Celsius). Considering the fact that DOT3 brake fluid is a poor choice for high performance driving due to its low wet boiling point of 284 degrees Fahrenheit (140 degrees Celsius) and a dry boiling point of 401 degrees Fahrenheit (205 degrees Celsius) and is now generally considered to be obsolete, the synthetic brake fluid is the superior performer. It is also has the advantage of being markedly less hygroscopic than either DOT 3 or DOT 4 petroleum-based brake fluids. This would also be an excellent occasion to flush the hydraulic system with denatured alcohol. If you do, you will be amazed at the crud that will come flushing out of the system. Denatured alcohol can be obtained at any paint store.
Steve S.

Rebuilding MGB calipers are really easy. I installed new seals and new standard pistons to replace those on my 1965 about 12 years ago. Street driven car with no problems since the rebuild.

I did NOT split the caliper. I was able to pop the pistons out using low pressure air. Check archives for other techniques.

I'm sure rebuilt ones will be perfectly fine also.
Robert McCoy

Consider new remanufactured calipers. Autozone sells them for about $50.00. I just purchased one and installed it. Works perfect. Another good source for for the higher volume MG parts is http://www.rockauto.com/

Frank Grimaldi

Ralph,

I'm sure I have the chrome originals, but will speak to my MOSS vendor tomorrow to what is available. Not sure I can source Stainless Steel on this side of the pond, but like the idea.

Steve,

Do you have a procedure for flushing with denatured alcohol. I would assume you would pump down the DOT 3 until gone, refill with alcohol and repeat, but how many times, twice?

Frank,

I will check with my local Autozone on availability, sounds like a good way to go. I would most likely do both sides and have a benchmark for next time. Was their a 'core' charge?

Thanks to all,

Larry C.
Larry C '69 Midget

Check the websites for all the local chain autoparts stores. Sometimes the price will be cheaper online and the stores will match the price. Some stores also have coupons available to use in the store.
Kimberly

If hoses are good, then you have some corrosion either on the piston, on the cylinder walls or both causing the sticking piston. The rebuilds on the market are the way to go. $50 or less per side. And if anything goes wrong, you usually get a warranty. A lot easire to just replace the units then rebuild the old ones.

Also, another area to check is if fluid is getting back to the master cylinder. Not sure on the 74, but if my brake light switch gets turned in a couple of turns it is enought to slightly block the return hole.
Bruce-C

Binding can just be due to sticking pistons. If it was the hose to that caliper collapsed and acting as a check valve you wouldn't be able to pry the pistons apart, but if you slackened the bleed nipple you would get a spurt of fluid from it. Just removing the pads and working the pistons in and out, cleaning them with string with some brake fluid on while they are out, may be all that is required, for a while at least. But if there is visible surface corrosion when they are out then they and the seals really need to be replaced. The seals need a special tool, all in all it *is* probably easier to replace the calipers in that case. Make sure you can slacken the 'other' end of the hose before you start, and unless the hoses are new it is a good idea to replacem them at the same time and do a proper job. You need to be able to slacken the hoses as a minimum because the thread start in a replacement caliper is almost certainly going to be in a differnt place, which will mean winding the hose up unless the other end can be slackened and moved to suit.
Paul Hunt

Larry-
Just as you would in bleeding the system, start with the passenger-side rear wheel, then the driver's-side rear wheel, then the passenger-side front wheel, and finish with the driver's-side front wheel. Get a Mighty-Vac and suck all of the old fluid out, then flush the system while keeping the master cylinder full of the denatured alcohol. Keep flushing until it comes out clear. Next, get the denatured alcohol out with your Mighty-Vac and let the car sit overnight so that the denatured alcohol will evaporate out of the system. Next, refill the master cylinder with brake fluid, then suck it through the system with the Mighty-Vac. Finally, bleed the system and then you should be good for another year.
Steve S.

Steve,

Thanks for the update on your proceedure. I had read about using denatured alchohol to flush the system, and assumed it was a compatibility problem between DOT 3/4 and synthetic. Good idea to leave the system open over night to drain, and evaporate. I also plan to evacuate the entire system front, and back as they share a common reservoir.

I have used a mighty-vac during previous hydraulic maintenance, and it does work well. I'll post an update when finished in about a week.

Thanks to all,

Larry C. '74 B/GT & '69 Midget
Larry C '69 Midget

For stainless steel pistons try John Farrell Auto Parts, 57D Alder Street, W. Babylon NY 11704 Phone: 800 454 7977 Fax: 631 694 7217
http://www.fortunecity.com/silverstone/tread/1046/id23.htm
Andy Taylor

Andy,

Thank you for the link, I will add this to my files for future reference. I purchased new stainless steel caliper pistons this week from Jim Knight at British Racing Green here in Newark, DE who is also my local MOSS 'rep' who had them in stock.

I plan to start work on the brakes this weekend, and will let everyone know the results.

Regards,

Larry C. '74 B/GT & '69 Midget
Larry C '69 Midget

Just a small aside here: I was at the auto parts store yesterday, happened to look at the brake fluid on display. Every brand of DOT 3 and 4 had the word "synthetic" on it.
Tom

This thread was discussed between 21/09/2008 and 27/09/2008

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