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MG MGA - Dragging front brakes are fixed! Thanks MGA guru!

So thanks to Barney Gaylord, I tried drilling a 1/32" hole in the metal cap at the end of the spring in the master cylinder and it worked! No more dragging brakes and the knock offs were just a little warm to the touch after a long drive.
So I think it's fixed.
A big thanks to MGA guru! I would've been shopping for another master otherwise.
Heads up. This was a TRW/Lucas master that was giving me the problems.
R emgeeaa

Is that operation described on MGAguru Tech pages or was it private correspondence? It is not exactly clear to me on what you have done and why it worked.
Mike Ellsmore

Barney's article is at:

M F Anderson

It sort of confirms my thoughts on some new master cylinders. It makes you wonder, for instance, if the spring is too strong, preventing the gradual leakage of pressure Barney describes when the brake pedal is released.

Steve Gyles

I have had this same problem with the re-sleeved MC on my Magnette. I read Barney's advice but found it difficult to get my head around the description of exactly where to drill the hole. A larger diagram would have been a big help.

In the end I copped out and fitted a new rubber end cup from a NOS Lockheed kit which was much softer rubber than the first one and easier to install (The first one had been a real struggle to fit) This seems to have solved the problem.

Andrew Dear

I think the spring fitted is too strong on these repro masters. It was taking over 12 lbs of air pressure to get the piston to return. Drilling that extra hole dropped it to about 11 lbs and air started bubbling up through the release hole much sooner. It's not optimum yet, but I'm not prepared to shell out a bunch more money yet to find a properly built unit. I will drive the car now for a while and see how it does.
R emgeeaa

Andrew, -- See here:
Click on the illustration to get an image twice the size and easier to see. As noted, "The hole needs to be located within the ID of the Valve Washer, and downstream from the edge of the Valve Cup".

Barney Gaylord

Thanks for that explanation Barney. I didn't realise the diagram would expand like that. I see now exactly where it should be drilled. However, as I said, the softer rubber seems to have solved the issue for the moment.

Andrew Dear

Thanks Mick - Barney tricked me as I was looking in the Brakes - Hydraulic section!
Mike Ellsmore

Hi there

I too have recently fitted a Lucas/TRW master cylinder and have problem with dragging brakes. But my installation coincided with the fitment of a servo which I assumed was the problem (reaction piston) and have been very interested to read this thread.

I am tempted to try the spring out of my old MC given the comments above. Would this make any difference or am I barking up the wrong tree?

On other threads I have seen the suggestion to put in an extra gasket at the cover plate end I think due to over expansion of the piston cups. Might this cure my problem?

Curiously I thought that the piston was not returning quickly enough so I fitted an additional return spring to the pedal. This does actually seem to have made the problem worse pointing to a softer spring inside the MC being a possible cure.

I would be grateful for your thoughts before I have to bleed the system AGAIN!!!

Many thanks

ejf horne

Ed, -- If you open two units to change the springs, could you measure the two springs for wire diameter, number of coils, free length. Also if you can, measure the compression height with a known load. You might do this by loading it with a known weight, or by pressing it down on a letter scale to a fixed force, and measuring the height under known load. Still wanting to figure out why the residual pressure is different.
Barney Gaylord

Just put the phone down from Bob West. He totally slated the Lucas/TRW master cylinder. He said that about 10 years ago when he was getting a lot of customer problems with dragging brakes he bought one new Lucas/TRW MC to investigate. He dismantled it and did not like what he measured and saw. He then bought a Caparo version and did the same investigation. It was superb and the closest to the OEM MC that you will find.

Since that time 10 years ago, he has only ever fitted Caparo MCs to his rebuilds and always uses silicon fluid. He has never had one issue with dragging brakes nor any other issues that many misguided people blame on silicon fluid.

I can vouch for the Caparo MC and silicon fluid. I had the same dragging brake issues outlined above. I bit the bullet and fitted the Caparo MC and all problems vanished in an instant.

There is always a 'but' in these stories. Expect to pay about twice the Moss/Ebay/etc price for a Caparo. However, in my opinion it is worth every $/.

And no, this is not an advert for Bob West; just passing on the experience of an expert and one very satisfied Caparo customer.

Steve Gyles

Steve, who sells the Caparo MC's in UK?
Gary Lock


I know Bob West does. Not sure who else.

Steve Gyles

I am not sure why you chaps are buying new (after market?) master cylinders, here (at least in South Australia) we have them sleeved in practically indestructable stainless steel.
Barry Bahnisch

This thread was discussed between 06/08/2011 and 12/08/2011

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