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MG MGB Technical - Brake overhaul

Hi, I'm a recent convert to Classic Car ownership, with a 72 GT.

I am going to overhaul brakes this weekend. Have got a rear service kit including Pads, Cyclinders and S/S hose, and a Front kit consisting of new Discs, Calipers, Pads and S/S hoses. Plus replacement fluid.

Is there a recommended order to do these in? Eg -

Service rears, bleed, service fronts, bleed.

Service fronts, bleed, service rears bleed.

Service rears, service fronts, bleed all


Main objective is to reduce the complexity of bleeding.

Any advice greatfully received.


D K Laidler

There is no point doing any bleeding until the job is completed. So it doesn't matter where you start.
Mike Howlett

Frankly I'd do the rears first and then the fronts for no particular reason and then bleed the whole lot at once. Remember to bleed the farthest away first which will ne the NS rear then the OS rear finally the NS front and the OS front. Good luck
Iain MacKintosh

Thanks for your comments.

Which am I going to find more difficult, front or back?

I always like to start with the most difficult job and work towards the easiest...
D K Laidler

Getting the E-clips back on the rear slaves is a bit of a challenge, but with the fronts the disc to hub bolts can be tricky and if you get the hubs off you probably should check the end-float afterwards (end-float?, do I hear you say?).

As has already been said there is no point in bleeding until you have finished the physical part replacement. With both my cars even using a continuous flow bleeding system like the EeziBleed I find I end up with a long and spongy pedal until I get my beautiful assistant to press down as hard on the pedal as she can while I rapidly open and close each caliper nipple in turn, which always get an extra lump of air out, after that they are fine.
Paul Hunt

Thanks Paul.

You got me, End Float? Is it as it suggests, allowable horizontal movement in the wheel bearing?
Darrel Laidler

If you are doing cylinders and have it all apart at least replace the rubber in the master cylinder. It is relatively simple.
werner haussmann

Have you rebuilt the master cylinder? I'm going through my brake system and bought new wheel cylinders as they're pretty cheap. S/S hoses and replaced springs and parts as necessary. I've rebuilt the master cylinder as well. Brakes should be done soon Also only use Castrol brake fluid. I've heard things about other brands and don't plan on chancing it. Also check the parking brake while you're there as well. Lube, adjust as needed. My parking brake was frozen solid.
S.L. LaPaugh

Darrel - yes, free play in the bearing that allows to hub to move slightly along the line of the stub-axle. .002" to .004", set with shims. You are supposed to use a dial indicator to measure it, but in practice if you juggle combinations of the .003, .005 and .010 shims to move in .001 increments, when you get a a combination with just perceptible free play at one combination but none with .001 less, then use the thinner combination plus one .003".
Paul Hunt

Werner, SL, good idea, but I'm gonna skip the M/C this time round, unless I have problems when refilling the system.

Paul, thanks for the info on the end float. Unfortunately after doing the rears without any problems, and getting the calipers and old hoses off the front, I ran in to problems with the hub to disc bolts spinning. was only able to get 2 off each side, so have to get the hub off but don't have a large enough socket. Any one know the size? I measured it as 1 1/8 across flats, but not 100% sure

Darrel Laidler

I didn't think they were anything like as big as that, but are recessed and/or have low-profile heads which is what makes them tricky to undo i.e. a good head and socket are needed and good alignment to make sure the socket doesn't slip off. According to various info the bolt is BTB198, the nut FNZ506, which has a 3/8" thread. I was hoping to find a conversion from thread size to head size somewhere but have run out of time.
Paul Hunt

This source indicates a 3/8" thread has a 9/16" AF head (thread size X 1.5), which is closer to the size I recall.
Paul Hunt

The discs are mounted inwards of the hubs, so the lot has to be removed to replace the discs anyway. I made the same mistake when I bought my car...

I have my front crossmember in storage so I can't check the nut size, but 1 1/8" sounds familiar and is what I could gather from other sources.
Johan Garmer

34mm worked on my 67 GT.

Thanks all for your assistance.

Wasn't able to get hold of a 1 1/8 at short notice, but did get a 30mm which did the job no problem.

Hubs cam off nice and easy and I was able to get the Hub to disc bolts off no problem once I could get a socket on each end.

So I was able to take her out for an hour yesterday afternoon, and brakes front and back are working fine. Have a couple of old front calipers on the garage floor ready for a clean up and overhaul to be kept as spares.

I'm a happy man.

Thanks again

Darrel Laidler

This thread was discussed between 24/04/2009 and 27/04/2009

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