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Triumph TR6 - Master Cylinder Leak

Happy Spring to all, I replaced my master cylinder with a new unit last Fall and after my last run Jan. 20th, it leaked all of its fluid out thru the butt end and servo area onto the ground. Since the unit was new when installed I mounted and bled as per all previous threads (brakes worked great) at both ends of the little beast too.
So after losing all the dot 5 I had poured into it (only the large reservoir) I decided that before getting going I would rebuild the master. I had 2 masters 1 on the car and the older 1 off of it I rebuilt the old one for practice and all went well then rebuilt the new one taking care with the rear seal especially. It seems as though it is still leaking at the rear from only the large rear res. The kits I used were LBC Lucas and the rubber seemed very pliable. Is there a different kit I should use? I remember some BBS'er talking about seals from 1 manu. or another being dung maybe Steve P. I am not sure also any tips from the accumulated sages out there would be appreciated. I sealed the master at the servo with pliable gasket compound as well I will have to check the front brake pipe for leaking also.
Best regards 64 degrees here today
Keith '72 TR6
K.B.Dixon

Check and be absolutely sure there is no leak at the resevoir/master cylinder gasket - that can look like a master cylinder leak. Got me one time.
Brent B

Like Brent, I had a similar leak between the reservoir and master cylinder - used two seals instead of one to seal it - turned out the plastic reservoir had a small warp and the extra seal provided enough bulk to close the gap. Never leaked again.
R.C. Blair

Hey Thanks for the replies,
Like both of you I was leary of that area for 2 reasons, 1st my old master had pliable silicone type sealer in those areas, and 2nd the instructions on the Buckeye site suggest using a gasket in a tube in there also. My concern was if others had a problem with the Lucas rebuild kit and their replacement sealing rings. But since my initial post I think I have found the demon. After checking all the connections at the master (I also use plumbers tape in this area) and finding nothing wet I moved on to the bottom still nothing. Continuing on I found my PDWA to be very damp but only on the top portion it seems to have been leaking at the connection on top where the wires attach for the Dash idiot light. It is a Plastic plug type connector so be careful not to over torque it if you have a similar problem. I topped it up and drove about 60 miles today top down in 65 degree weather, hopefully this is the cure of my brake fluid leak. The advice I have either 1st hand received here or found in the archives is always very useful, but as with most experience is the best teacher.
Best Regards,
Keith
K.B.Dixon

Sorry for the late reply, but have been out of pocket. I don't recall saying anything about individual kit suppliers. I did say something about the cylinders having a reputation as not being a particularly successful rebuild candidate. You have age, corrosion and all working against you at this point and I do agree that the level of the kits available are not as good as had been in the past.

From the last post, it does look like you may have a leaking PDWA or way off center PDWA. The seals for the PDWA are outboard of the double tapered area of the shuttle piston. In normal position, the pin on the switch sits in between the two tapers sections of the shuttle piston. This double taper area below the switch should be dry. I cannot say for sure if it is possible to move the shuttle valve a sufficient amount that leakage would occur from an off centered piston. I would suggest that you pull the switch and see if the piston is centered. Take a look at this URL from the Buckeye site. It shows a disassembled PDWA and a couple of different style shuttle pistons, things will make much more sense looking at the pictures.

http://www.buckeyetriumphs.org/technical/Brakes/MCPDWA/MC.htm
SteveP

Keith
If I am not mistaken, the PDWA should have a brass washer on the plastic switch. I agree with Steve, it should not leak at the switch..if it does suspect bad "O" rings inside. They are easily replaced other than the fact the PDWA has to be removed and it is brake bleed time....did not u say it was time to replace the brake fluid anyway:)
Make sure the PDWA is centered as its' design is to shut fluid off to either the front or back brake system. It will more than likely need re-centering after any brake bleed.
Rick C
Rick Crawford

Rick,
You are correct in that the area where the Plastic "switch" screws into the body of the PDWA is "dry". The seals on the shuttle keep the fluid in the brake line "circuits". But the shuttle does not cut off the circuits in any way when the shuttle is activated, or off center, as happens when you have a leak in a brake line. It merely activates the switch to indicate a fault in the system.

Mark
Mark

Thanks for the advice,
The pdwa does indeed seem to be leaking and it is in the center section area. In checking Moss/LBC they are about 125.00 to replace with new can you buy the rings separate and if so where is the best supplier.
I will have to check the archives on this.
Thanks, Keith
K.B.Dixon

Steve, I also found that it was Steve from Toronto who had mentioned that the Lucas repair kit was the better one to use, Thanks for your help,
always check the archives
Keith
K.B.Dixon

I'm not aware of a Brit Car parts supplier that sells a kit for the PDWA. The URL provided for the page on the Buckeye site has information on sources, size and material type for the o-rings. Make sure you get the right type of seals, otherwise you will get to do it again. It's not that bad here since there is a McMaster-Carr local, although I will admit that they can be a pain somewhat removed from the neck to deal with. I probably wouldn't fiddle with them at all, but they have so much stuff that is tough to find anywhere else. It boils down to what is more painful, dealing with them or spending the time trying to source the stuff elsewhere.
SteveP

Mark
It was 2 years + ago I rebuilt my PDWA. At that time I got the distinct impression (from its design) that the piston did actually cut off fluid to the failed side...as well as the light coming on at the dash. If you go to the above mentioned Buckey site the pic of the PDWA piston (lower picture of the 2)is tapered past the O ring and I thought this is a "seat" to shut fluid off from the input side. My piston was the lower pictured one with O rings and not the above one with the "boots".
Could it be that the piston with the boots did not shut off fluid (smaller end piston) and the other one with O rings did ( larger end piston)?...design improvement?

Keith, since u are the one with the PDWA removed, does it appear that the fluid is shut off when the piston slides to either end? If it does not I would say a design flaw.
Rick C
Rick Crawford

Rick C,
I have not removed as of yet, I have ordered some parts to replace in this area. New seals, ring to seal a new switch (my old one is junk)and new pipes to run down to it(old bolts are stripped require vise grips). But I leave for Maui on the 11th so I won't get into the repair until I return week of the 22nd. Life's a real bitch.
Regards,
Keith
K.B.Dixon

Rick,
On the PDWA sealing off the "failed" circuit, the answer still has to be no it does not.
There is only one seal at each end, and it is oriented to seal off the shuttle bore, not the brake circuit itself. There would have to be seals on either side of the shuttle, oriented to the openings of the brake circuit from the MC, and to the caliper or wheel cyl.
Nelson has done a great job of helping a lot of people with his informative documentation. I was able to help him, by doing the rather simple CAD drawing of the "replacement" shuttle that he produced on his lathe.
I also have the later style of shuttle with O-rings, and recently did the "rebuild" on it using a kit from TRF. It had a "Lockheed" label on the box, and contained four o-rings, two smaller, and two larger. I do not know what the larger ones would fit, but I used the smaller, and they were just right. I think the kit was around $6 US.

Mark
Mark

Mark
Thanks for the answer...one learns something every day. It would have been a simple design change to give you "shut off" to the failed side. I was looking at this from a safety standpoint and not having total brake failure (one side remains functional). I guess someone decided it is better to have a split reservoir system for front and back.
Rick C
Rick Crawford

This thread was discussed between 27/03/2003 and 05/04/2003

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