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MG TD TF 1500 - brake issue

During my TD restoration, the whole brake system was rebuilt. This included new rubber (or whatever the material currently supplied is) in the master cylinder.

The brakes on this car have always worked great.

I use DOT 5 fluid, have for 30 years. I know it takes a bit more to bleed DOT 5.

My pedal is firm after bleeding, but very shortly after, it will sink to within a few inches of the floor. But it does stop and the brakes work. Two quick pumps of the brake pedal brings the pedal back to firm, but it sinks shortly after that.

The car has been blead at least 4 times. It also sat for 5 months this summer while I was in another part of the States.

Tried it today and the problem is still there. Blead the brakes again. (RR, LR, RF, LF) filling the master after each wheel so not to get air in the system.

I got a few bubbles out of the RR, but not much. No change in the pedal issue.

As the braking system is pretty simple on the TD, I suspect I got something wrong when I rebuilt the master cylinder.

Bruce Cunha

Try clamping all 3 brake hoses and seeing if it makes a difference. If it does release them one at a time till you locate the cylinder with air then bleed this one with full strokes.
Preferably with somebody opening and closing bleed nipple rather than relying on the foot valve in the M/C.
Ray TF 2884
Ray Lee

I would not be surprised to hear it is a MC issue.

Regards, Tom
tm peterson

Almost has to be MC. A few years ago, Bud Krueger and I had a thread about the lousy rebuild kits available- even back then. There have been so many MC variations over the years, very slim chance of getting the correct kit. I would just replace it, and keep your likely original on the shelf. I also had a recent thread about a fairly new wheel cylinder cup stick, tear, and leak with Dot5. George
George Butz III

Bruce:

Try White Post Restorations in VA. They do an excellent job on M/C's and wheel cylinders. They did mine. When I changed to disc brakes recently, I called them about the original rear cylinders. They had collected water and crud over time and were pretty nasty. I mentioned that they had done them some 20 years earlier. They said those are still covered under warranty! I sent them back and just paid the postage. Came back looking new! The original Lockheed M/C they had done previously was just fine, but had it serviced anyway as I was switching the system to DOT 5 at the same time (re-sleeved with Brass and new seals). They also flushed and function tested using DOT 5 per my request, but will do the same for any DOT fluid you advise you'll be using.

Jim

https://whitepost.com/brake-sleeving-rebuilding-services/
Jim Rice

Thanks all. Jim. Great to know. It is an original MC, so a sleeve may be indicated. I know it has some pitting.
Bruce Cunha

Double check the piston is returning fully and you have free play in the pedal as per the manual. The fluid is not moving from the reservoir into the cylinder between the primary & secondary cup.

There may be a partial blockage in the passage, or the washer is too thick behind the circlip and the secondary seal is partially blocking the passage to the reservoir.

You should be able to see through the Dot5 fluid and look down the transfer hole to the cylinder - a mirror and good light may be required. Syringe out the reservoir and check the passage if you can't see through the fluid.

Good Luck

Tony
The Classic Workshop
Black Mountain
Australia

A L SLATTERY

Pump the pedal with the cap off,the fluid will spurt up as the pedal is released if the recuperation hole is clear.
Ray
Ray Lee

I took out the master cylinder today. The rear boot was full of fluid. When I drained the fluid from the actual cylinder, it was very dark.

This was a fully rebuilt system using DOT 5 as the lubricant.

That tells me that the quality of the substance they call rubber was very poor.

It is going off to whitepost tomorrow for a sleeve and a restoration.


Bruce Cunha

This thread was discussed between 14/10/2024 and 21/10/2024

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.