> Jensen Healey & Jensen GT Tech > Brakes > Master cylinder rebuild

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Tom Bradley

Joined: 07-15-2013
Posts: 173
My brakes have been working fine, but the brake fluid tank on my master cylinder was seriously discolored and cracking, so I decided to try doing a rebuild:

Considering the condition of the condition of the plastic and from what I have read, removing the tank in one piece was surprisingly easy.  The instructions I had said to pry the tank off with a screwdriver.  I put the whole assembly in a vise and used two screwdrivers, one on each side.  Gently levering up and keeping the tank from tilting, it came out smoothly.  Getting the circlip out was another matter.  I had to use a stainless steel dental pick and put a sharp bend at the end to get under the circlip to pry it partway out of the groove.  Then I could lever it out of the cylinder with a jeweler's screwdriver.  This took some serious amount of time and care not to scratch the metal cylinder.

Inside the cylinder are two pistons.  the first one could be pulled out with a pair of needle nose pliers.  According to the instructions, the second one might come out by shaking the cylinder.  Not a chance.  I had to apply compressed air to force it out.  With the fluid tank off this was not too hard.  I could block the outlet to the tank by putting a flat piece of rubber over the opening and putting it in a vice.  I had a small hand pump for children's toys that had a plastic fitting that fit well enough in the outlet to the brakes.  A couple of squeezes and the internal piston popped out easily enough.  If the tank was still on, plugging up the tiny fluid hole inside the tank looks pretty difficult.

I was surprised at how good the rubber still was.  This master cylinder has not been replaced since I have had the car (almost 30 years) and is probably original.  The rubber still looked perfect and was still pretty flexible, though they mostly broke when I pried them off.  The metal pieces and inside of the cylinder all looked perfect, so  I cleaned everything with brake cleaning spray, lubricated it as directed and put it back together.

When I put on the new fluid tank I ended up using the old circlip.  The new one was quite a bit thicker (over 0.001" thicker).  The tank locked into place with the old one well enough and I was afraid that the thicker circlip would make it impossible to remove the tank without breaking it if I had to redo anything.

As it turned out, everything worked OK after being put back together and the brake lines purged (which is another story).  So no repeats were necessary.

Considering all the work and the expense of the new fluid tank (mine cost around $80), I would say that buying an aftermarket TR6 master cylinder would be the better option if the fluid tank on the old master cylinder needs to be replaced and the TR6 replacements continue to be reasonably priced and good quality.

On the other hand, if the tank is OK and you do not mind messing with hardware, trying a rebuild might be worthwhile.  In that case I would remove the old master cylinder and get it apart.  If everything comes apart OK and the internals look good, buying a rebuild kit could save a good amount of money (mine cost about $35 and included the rubber seal between the fluid tank and the master cylinder).  If in doubt, though, the TR6 replacement is probably safer. 

(How about it guys?  Any feedback from those of you who have bought and have been using an aftermarket TR6 master cylinder?)

Bob 13902

Joined: 04-05-2006
Posts: 35
I've been using the TR6 backfit for many years but I think it is starting to give me problems so I'm planning to take a shot at rebuilding my original Lucas. Thanks for posting your experience. However, I am having problems sourcing a rebuild kit. Looking for info on sources, rebuild kit part numbers, and disassembly instructions/pics...can anyone help?


Joined: 09-10-2012
Location: BROOKHAVEN, Georgia USA
Posts: 325
Tom didn't mention anything about inspecting the bore for corrosion/pitting, especially on the bottom.
For year I had a person in Quincy, CA. resleeve them for me using premium brass, but he retired a few years ago. Recently, I had Apple Hydraulics resleeve a few for me and they appear fine. However, the cost is more than one could get a TR6 one (with the reservoir), so that's why you see so many now.
The problem with the TR6 conversion is their's were mounted on a slant whereas the J-H is flat and if the tank is not totally full, there is a chance of air getting into the front hole.
Another problem we discovered in the '90s that for just a "rebuild", a few were getting a "soft" pedal after short driving; what we discovered was that the rear seal(the big one that works the front brakes) would "rub" over a VERY slight pitting on the bottom(no fluid leak mind you) and would gradually introduce air into the system. Hence, now I only would rebuild a brass resleeved one just for that reason.
best wishes for 2020, bruce

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