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MG MGA - Moss Classic Gold master cylinders

has anyone tried Moss's Classic Gold master cylinder with DOT 5 silicone fluid? did it NOT leak? are there any reproduction M.C. out there that will work with DOT 5?
any info is appreciated
thanks ,Joe
joe williams


I am using a new MC with dot 5. It is made by Caparo AP ( ). I am told that Caparo took over the Lockheed tooling. The result is an MC made to a much higher spec than Lockheed were making of late. I am delighted with it and it is running perfectly. Mind you, it cost me about double the standard price you see on the likes of Ebay.

Not sure who supplies them Stateside. I got mine from Bob West over here:

Steve Gyles

My opinion would be to NOT use Silicone fluid and only use a DOT 3 fluid which is the specified fluid for this ear of vehicle. DOT 4 and above my give you triubles as the seals are not designed to work with these more up to date fluids.

M T Boldry

New cylinders with new seals work perfectly with silicon fluid. If the cylinder is substandard, the thing will leak sooner or later whatever fluid you put in it. Some "resleevers"cause problems between the casting and the sleeve - only to be avoided in my book as the cost of a new cylinder is only marginally more.

If you have brand new cylinders, silicon fluid will work perfectly. If you are replacing the MC, the wheel cylinders are probably marginal too, so think about replacing them (these are cheap) or at least their seals as well. They should be checked in any case.

Anyone still using old seals is asking for leaks to happen, as brake seals should be serviced occasionally too, and using a 50-year old seal is irresponsible. Flushing fluid is often neglected, which is the prime cause of rusty cylinders because of the water absorbed in non-silicon fluid.

Flushing should also be done with DOT5 periodically - even with cylinder bores in great condidtion, it's amazing what cr*p comes out - mainly black particles from (I suspect) gradual seal wear
dominic clancy

No problems with silicon fluid in 22 years. When I got my present driver MGA five years ago I changed the master cylinder (plus all hoses and seals) and switched to silicon and never had a leak.

There will always be a difference of opinion, so use whatever you feel comfortable with. But do not mix silicon with DOT 4!
Neil McGurk


As Dominic and Neil say, silicon is absolutely fine to use in our car's hydraulic system. I have been using it for 14 years without any problem that I can attribute to it. Yes, I have had plenty of issues, but none of them fluid type related.

I think silicon got a bad name, partly because many users did not use it correctly. Silicon must NOT be mixed in any way with other fluids. Just draining older mineral fluids and replacing with silicon is not sufficient. As Dominic states, the system must be fully flushed before filling with silicon. Better still, to avoid contamination totally, it is better to start with a totally new system, including the pipework.

The following is an extract from a 1999 Safety Fast article:

"When I switched over to silicone on the MGB, I first attempted to simply flush of the system by adding silicone and bleeding the brakes. This sounds like it should work since the two don't mix (are immiscible), and was the method suggested by the supplier. I found, however, the following:- the old brake fluid contained a lot of water, which in contact with the silicone, separated into three layers: water, silicone, glycol. Ordinary bleeding procedures, designed to remove air, left water in the bottom of the wheel cylinders. A sure invitation to corrosion and failure in time. However the brakes work fine at first, since any "non-compressible" fluid or mixture will work. (See the Army emergency procedures for loss of coolant or hydraulic fluid under combat conditions, using readily available fluid from every soldier in the unit. Note that a complete overhaul is then necessary to minimise corrosion afterwards).

I have found that the best way to switch over is with a complete system overhaul. The brake lines should be flushed with acetone which dissolves the glycol gummy residues and removes any trapped moisture. The lines should be dried by blowing with air (ethyl alcohol can also be used, it is not as flammable and won't injure paint). All flexible lines and seals should be replaced so that all rubber that has been exposed to the glycol is removed. I think that the problems some have had with silicone may arise from not doing this. It may be that the problems come from the interaction of the different swelling agents in the silicone with those used in the glycol based fluid."

Steve Gyles

The classic gold MC failed on the clutch side for me recently. (less than 5000 miles of operation but purchased probably 5-6 years ago) I use Dot 5 in this all new system. From my earlier post it seems reasonable to suspect inferior rubber seals as the culprit. I will rebuild with new parts and hope the rubber quality that Moss supplies in the kit are of better quality than their manufacturer supplier of the Classic Gold reproduction MC.
David Holmes

I rebuilt the MC today and found the insides to be very dirty and contaminated by black specks of rubber and also some sort of scale. My guess is rust from sitting in the car without brake fluid while I was finishing the restoration. So, this undoubtably contributed to the failure of the clutch side. I flushed the entire system with new fluid and rebled with an easybleed. The only thing I forgot to do was to refill the front tire with air when I was done. All is well with the test drive.
David Holmes

I've been using DOT 5 since I rebuilt entire brake system ( 5 years ago), I had the MC resleeved and have always had a small leaking problem especially over winter storage. just wanted to know if buying a new reproduction MC was going to solve my problem. sounds like it will.
thanks to all
joe williams

The original type of fluid for these cars doesn't even exist anymore. Today's DOT 3 and 4 are basically the same thing as each other, but not the same as what the factory specified. That's a good thing, because modern brake fluids are far superior to what was available back then.
Steve S

This thread was discussed between 15/04/2011 and 21/04/2011

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