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MG MGA - TRW Master cylinder

I have very recently fitted a TRW master cylinder I bought back in 2010 that has been sitting in the garage all this time. I haven't yet had time to put in the fluid in and bleed it.
But now I have read all the negative press about the TRW unit, about how brakes can drag, and Barney's fix by drilling a hole (but I would prefer not to do that).

So am thinking, I have a few choices
1. Put in the fluid and see if it is ok. Has anyone been happy with TRW? I assume if the brakes dont drag, then it should all be fine
2. Whilst it is still dry, take it out and buy the AP Caparo unit.
3. Or, while it is still dry, buy a rebuild kit, and change the rubber seals, etc. Assuming the Moss replacement seals come from a different supplier?

Any views?

Brakes is not something worth cutting corners with

Thanks, Graham

Graham V

I installed a new TRW master cylinder in my MGA 1500 a year ago, and no problem. I believe the excess residual pressure is only a problem with disc brake cars (MGA 1600), but is okay with drum brake cars (MGA 1500). Apparently the return springs on drum brakes are strong enough to overcome the residual pressure and return the brake shoes so they won't drag. This appears to be a problem only with disc brakes.
barneymg

Thanks Barney. I have a Mk 2 so have discs on the front. I guess I may as well give it a go and see what happens. I will report back.

Graham
Graham V

Just bled the brakes. When I apply the foot brake, then get out of the car and try and spin one of the front wheels (off the ground on axle stands) there is a lot of resistance to the wheel turning. The back wheels turn very much more easily.
So I assume that means I have been hit by the dreaded TRW bug!

Whilst it's so frustrating, I am really appreciative of the MGA community as without you guys, I would be scratching my head and completely out of my depth.

Graham

Graham V

Hi Graham,
I had this problem on both my 1500 and 1600 drum and disc braked cars . On the 1500 car I had 30th machined of the piston to allow it to return properly. on the 1600 disc braked car I put two gasket behind the plate where the push rods come out of the master cylinder one gasket measures 30th
Regards

David
D M SPEAK

Hi David

Thanks for your post. I am not that clever when it comes to the detail, and so have no confidence in myself to mess about with the unit, especially as it's the braking system involved.
Its £135 for an AP Lockheed unit, and whilst I have already laid out for the TRW, the funeral costs would be very much more!

Graham
Graham V

Hello Graham

I converted my 1600 to silicone fluid in early 2012, replacing all brake and clutch hoses, clutch slave internals, flushing out the piping with alcohol and then silicone fluid, and replacing the rear cylinders and master cylinder with items supplied by Bob West. Not at home this week so cant check master cylinder maker but it was what Bob West was using at that time. I immediately had the locked-discs problem. (This was about three days before my wife and I were to drive to Italy.)

After removing and replacing the master cylinder a few times to check components, fluid holes, etc., and finding all correct, but with no resolution of the problem, I called Bob West and spoke with James Horner who recommended Barneys relief-hole-in-valve solution to the problem of residual pressure, and also re-assured me about altering the valve. I recall I used a slightly smaller drill diameter than suggested on Barneys web page.

Carrying out this minor task immediately solved the problem and the car has performed perfectly since (including that Italy trip in 2012 and its two Alpine crossings, 19 French Alps passes on the Route des Grandes Alpes 2015, and a further England-Italy trip in 2016).

I have total confidence in the logic for, and the effectiveness and safety of, the solution applied.

If you wish to consider this solution to the locking discs problem, before spending more money, do not be deterred.

Regards
Mike
M D Card

I have a new TRW m/c sitting on my workbench and I am considering modifying the valves in it.

I wasn't sure from reading up on the procedure if I have to drill holes in the back of both of the valves

Has anyone got any pictures of this?

Cheers
Colyn
Colyn Firth

See here: http://mgaguru.com/mgtech/brakes/bt101a.htm

The little hole goes where the small "2" is pointing in the diagram, outboard of the small rubber cup, but inboard of the thick rubber washer.
barneymg

Hi Mike
Thanks for your words of encouragement. I have already ordered a new master cylinder from Bob West. Hopefully that will do the job for me.

Colyn
No doubt someone will respond with the definitive answer, but I seem to remember reading somewhere that only the brake valve needs modifying. But afraid cant be 100% certain

Graham

Graham V

The brake side only has the non-return valve in the bottom of the bore behind the spring. This is the piece that needs the tiny hole, brake side only.
See here: http://mgaguru.com/mgtech/brakes/bt101a.htm
barneymg

Thought I should report back. Bought a new master cylinder from Bob West and the locked discs have gone away! Thanks Bob.

I do find there is a little bit of drag on one of the front discs, after braking. Not so much that I can't turn it by hand, and not noticeably hot after a 10 minute test run. It does ease a little when I open the bleed valve. Is that likely to be the hose, or the calliper - I guess it's either or both. It's not the MC as the other disc spins freely straight after braking.

Graham
Graham V

This thread was discussed between 18/06/2017 and 27/06/2017

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