TR4 brake master cylinder cap leaking

[Icarus60 4]

Colleagues

I have a recently acquired a TR4 project and it has a new "Lucas" aftermarket brake master cylinder fitted and it is leaking fluid from the cap. It's made a right mess and the source of the leak has taken some tracking down.

It looks like the fluid is passing around the non threaded part of the cast cylinder wall at the front and is running down the outside and away. The fuller the reservoir and the the more the car moves about the worse the leak. The cap is pressed aluminium and is a bad fit at best. I have just taken the car for a run with a lowiish fluid level and the lid definitely tightened down onto the face seal and a ring of paper towel around the outside of the reservoir.

After ten miles the paper towel was wet and enough to confirm the leak.

Does anybody know where I can get a properly fitting plastic cap to fit this reservoir which is about 2.5 inch diameter.

Any help appreciated

Thanks and regards

Rog

[ianc 21]

I've acquired more than one plastic cap at auto-jumbles, but I believe that Land Rover fitted a plastic cap on some (older) models, so a visit to a Land Rover agent might be worthwhile. Take the alloy cap with you.

Might experience with the plastic caps is that they fit and they seal.

 

Why did I buy more than one? Because I have fitted a low fluid-level detector in one, so had to bore a hole about 1" in diameter in the cap.

 

Ian Cornish

[stuart 81]

A lot of the problem is also caused by the "Flats" on the front and back of the cylinder body casting, they do all seem to be like it too. Plastic cap may help but I always run with a couple of folds of paper towel under it and change it every time I use the car and lets not get into the whole silicon fluid argument again can we?

Stuart.

[kiwi-jim 1]

Rog

The other thing I found helped control the spill was to run plumbers thread tape around the cylinder thread it stopped seepage straight away for me

cheers

[monty 5]

I was shown some while ago a tip from a Motorsport guy. Put a sports sweatband around the cap, level with the top (it will fit nicely). This will soak up any excess fluid preventing it running down to the paintwork etc. Every so often take it off & wash out or replace with another.

[Lebro 18]

Fit a better rubber gasket in the cap, & then do it up really tight.

I use a small strap wrench to tighten (& untighten).

Bob

[ChrisR-4A 7]

Are you sure the top of the master cylinder is flat with no casting Pitts?

I only found out mine did not seal when trying to use an EziBleed kit which uses air to pressurise the system. Some carefull filing and sanding got it flat so it eventually sealed.

I too would like to find a plastic cap with the exact same thread as the alloy ones tend to get jammed on which can be a pain if you want a quick check when away from home.

Chris

[Icarus60 4]

Many thanks for your help.

I was not aware how widespread this issue is.

The machined top surface of the reservoir is flat and I think, like Stuart, it is mainly down to the poor threads and particularly with the flat at the front, matching the low point of the fluid.

I'm going to look to get a fix for this and I'll get back.

In the mean time it's paper towel and a spanner.

Again many thanks

Regards

Rog

[Mark1965TR4aBRG 1]

I have a St George wrist band over each cylinder and over my expansion bottle cap too as they will steadily leak as described above..

 

These get changed periodically.