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MG TD TF 1500 - Brake Master Cylinder

As my old MC was leaking I purchased a "new" MC off Ebay a few months ago with the idea I would change it prior to driving again. The time finally came to service all of the brake system and the first thing was pulling all drums and checking the brake shoes, wheel cylinders etc and renewing anything that wasn't in good shape. Finally got to the MC and when I pulled it out of the system it was leaking from everywhere.

I unscrewed the large fitting at the rear of the old MC (where brake line screws in) and went to install it in the new MC but the threads in the new MC are a much larger size. It appears that this unit will require a new fitting to be made if it is to be used....anyone ever seen anything like this before?

I have cleaned and rebuilt the old MC as the inside appeared unmarked and I had a spare rebuild kit. Only problem now is that it is back in the car (1950 MGTD) and I can't get it to pump up any pressure. Any hints or do I have to remove it and bench bleed it?

Brian Smith (1950 TD3376)

Brian - Did you get the check valve assembled correctly? Also, is the relief hole being covered by a seal that is a bit too long or not being positioned properly? These are two things that could cause the MC to not build any pressure, along with seals or cups that are not sealing properly. Cheers - Dave
David DuBois

Thanks Dave

I assembled the parts in the same order they were in the MC previously and the same as the WSM. The parts appeared to be the same as I took out size wise but I didn't check the small relief bleed hole. I am on my way out to the shop now so will double check everything.

I filled the MC with brake fluid prior to fitting back in the car but was wondering about "bench bleeding", this wasn't done.

Brian Smith (1950 TD3376)

Bench bleeding is always a good idea, as it removes any bubbles that could be trapped, and demonstrates that the pumping action of the MC is functioning correctly.

Tom Lange
MGT Repair
t lange

Tom, I think that I may have it now. I wasn't sure what bench bleeding was but now that it is in the car I wasn't keen on pulling it back out. Spent time in the shop this morning and pumped it allowing bubbles to bleed back up the two relief holes and it looks like I have pressure now. I will let it sit a while and then check it again to see if the pedal still has some pressure ( like a properly adjusted pedal should have)

The second part of my question was with regards to the size of the threaded hole to the rear of the MC. The hole is larger than the small extension that screws in but in every other way the new MC is identical to the old one. Could probably have one machined but wondered if this was normal, perhaps from a later TD or another car?
Brian Smith (1950 TD3376)

There are a number of repro master cylinders out there now, many internals of which are NOT interchangeable with the original master cylinder type.

Tom Lange
MGT Repair
t lange

Brakes are now working the way they should! I agree that there are many repo MC's but this is an original lockheed and the bore size is the same as the old original, it is only the threaded hole at the back that is larger than the old original. This is the area where the brake pipe attaches but first goes into a fitting that screws into the end of the MC. The WSM shows it as "adaptor - master cylinder". I am guessing that this MC was made for another application so if I could figure it out then maybe I could get an adaptor to fit.

Now if the weather would just cooperate I am ready to drive!

Brian Smith (1950 TD3376)

Brian, try Googling Lockheed Master Cylinders. Bud
Bud Krueger

Brian, compare the casting number on your old master cylinder with the casting number on the new one. Use that as a search parameter on Google. Bud
Bud Krueger

Brian, not sure if you are doing it this way, but when removing the MC it is ok to leave the bellows and the fork attached to the brake pedal and withdraw the MC after removing the rear pipe and the two mounting screws.

There is probably a fitting missing from the MC with the larger threaded rear hole. The fitting would reduce the larger threads down to the size and flared end of the pipe connection. I believe the earlier MCs were that way from the factory.

hope this helps,
Dave Braun

Thanks Dave, you are right on. I have been searching Google trying to find the Master Cylinder model I have but so far no luck. The MC appears to measure out exactly in all respects with the original but the numbers are different and that hole for the fitting between the MC and the brake fitting is definately larger. Rather than continue the search I think I will just get a machinist to make one up and then I have a spare. The old one that I rebuilt yesterday appears to be working well with good pressure and no leaks so this "new" one will go back into my spares.

Brian Smith (1950 TD3376)

There is a seller on ebay right now with seven Lockheed MC's at a reasonable buy it now price. Looks like the real deal. Can return in 7 days. I've bought other things from him, good seller.

'54 TF
Tom Norby

It was common for replacement cylinders to have different threads, so there were different adapters for the line fitting, used to drive us nuts; SOMETIMES the adapter came with the cylinder, and sometimes not. Measure the threads to see what you have; usually it is a change from BS to UN threads; if recent manufacture, it could even have metric threads, god save us.

FR Millmore

This thread was discussed between 28/03/2012 and 29/03/2012

MG TD TF 1500 index

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