1969 E Type Series 2 OTS
Converting from left to right hand drive involved moving the fluid reservoir feeding the brake pedal master cylinder to slightly higher location on the right hand side of the bulkhead and relocating the fluid reservoir feeding the servo tandem master cylinder to a bracket attached to one of the sloping blanking plates on the left hand side. This effectively makes the right hand reservoir approximately 75mm (3 inches) inches higher than the left hand reservoir (they were at equal height when left hand drive). Filling both reservoirs to say three quarters full results in the higher one draining into the lower one to the point that it overflows. This occurs with the car simply standing unused overnight taking typically 12 hours. Looking at the diagram in the workshop manual, the fluid must be leaking past a seal in the single master cylinder and at least two seals in the tandem master cylinder which seems unlikely. The pressure differential created by a few ounces of brake fluid must be minimal but given its low viscosity perhaps it enough.
A temporary ‘fix’ has been to raise the left hand reservoir a couple of inches, then only half filling the right hand reservoir thus allowing the levels to equalise. The brakes do appear to work really well.
Both master cylinders and servo were replaced with new units by the previous Texas owner in 2017.
Any thoughts / advice greatly appreciated.
Bob Exelby
Hi Bob, Well you have certainly stopped the flow of fluid through the MC.However I suggest that you have not really handled the root cause! The bf should not be able to flow past the seals, which will need to be replaced, and maybe the MC barrel needs to be resleeved or the unit replaced .Lets see what the brainstrust has to say!
Bob,
Do you know which supplier the new Master Cylinder came from?
I have just realized I have the same problem, but lessened. It has taken perhaps 6 months for my rear rear reservoir fluid level to rise and front to fall. I did not think it was a problem when I took out some fluid but that I had overfilled it.
I bought a new Master Cylinder in 2017 and in 2018 it was the subject of a recall. There was no apparent problem with it. I put the new one in and now realize there is a problem with it just as you describe.
Today I Emailed my supplier explaining the problem
Looking forward to your reply
Dennis 69 OTS
I just reread the thread (thanks Andrew) and agree my problem is not in the Master cylinder but in the booster.
I rebuilt my booster at the same time I got the new recall replacement master cylinder. There was nothing wrong with the booster but I thought rebuild never hurts!
I now suspect that the seal in the booster that separates the front and rear circuits must have been defective as there was no fluid transfer between circuits before I rebuilt the booster.
Dennis 69 OTS
Both brake pedal master and booster tandem master cylinders came from XK’s Unlimited between October 2016 and May 2017 Dennis.
Same supplier for me
I will report on what they reply to me
They have been pretty good with post sales support.
Dennis 69 OTS
Bob,
I believe that it only requires only one seal on the “shuttle” piston in the slave/servo cylinder to leak (or be installed backwards) for fluid to transfer between the reservoirs when the brakes are released. As you probably know, some of the instructions supplied with slave/servo rebuild kits in the past incorrectly specified the orientation of one of these seals. I’d be surprised if a “new” servo would have this error, but stranger things have happened. Bad rubber seals have been a feature of “new” clutch and brake cylinders over the years…
You have correctly identified that the seal in the middle of the shuttle in the booster is allowing fluid to leak from one circuit to the other.
As you are in the middle of a conversion, you can place the secondary reservoir on the bulkhead wall whewre the old master reservoir was. This will mean both cylinders will be at the same height so the flow between them will be minimised.
You can also try packing each reservoir with red grease and bleeding the brakes with fresh brake fluid. This may extend the working life of the seal in the shuttle for a few more years before you bite the bullet and replace it.
(The only other place where front and rear circuits meet is at the PDWA (see s3 shop manual for details), but you may not have one of these and I can’t see how it’d affect fluid transfer unless the little piston between the circuits were totally corroded.)
If you are bleeding the brakes and see red brake fluid appear in the “wrong” circuit, then you have confirmed the problem exists.
kind regards
Marek
Hi Bob,
I fought the same problem in my "72 Series III. Turned out I had two failures causing the issue. The first one was the PWDA switch that Marek mentioned. The seals in mine were cracked & broken allowing fluid transfer between the two circuits. After fixing that I still had the transfer issue, but at a slower rate. So I sent the servo cylinder to Apple Hydraulics and had them sleeve it. Then, I installed a rebuild kit from one of the usual suppliers. But that did not solve the problem ! So I sent the servo cylinder back to Apple and they diagnosed that the new rebuild kit seals were slightly undersize, causing the leak. They rebuilt it using seals from their source and that finally cured the problem. Lesson learned for me was don’t trust the rebuild kits…have the pros install the kit from their reliable sources.
Richard
Hi Bob,
Who was your supplier for the slightly undersize seals and when did you buy the rebuild kit?
Thanks
Dennis 69 OTS
Dennis,
I bought the kit from XKs Unlimited in Dec 2018.
Richard
Thanks for your assistance gentlemen, greatly appreciated.
Hopefully I’ll get the summer out of it as it is then add the tandem cylinder rebuild to the ever expanding list of winter jobs. Perhaps by then a reliable source of known correct rebuild kits will have been identified.
Bob Exelby
Well, i am reading this blog with some excitement, as i have the same problem with my 1972 XKE after i replaced all the brake flex hoses (completely clocked) and tried to bleed the brakes. When i first discover that brake fluid is sieving from the main brake reservoir into the secondary (took me a while to figure this out …) i checked my repair handbook and came to the same conclusion, that it has to be the middle seal in the shuttle piston (lip outward facing) that is bad. After a bid research i decided to buy a new booster with brake cylinder from Moos Jaguar (they took over the part business from XK Unlimited i believe). I put this sucker in (man-oh-man - can’t be more difficult) and bleed the brakes again with a friend (the old way). The brakes are not 100% (needs a second push) but more concerning is that brake fluid makes it way again from the main reservoir to the secondary one. That really frustrates me, since i have no clue how this can happen with the new booster unless the assembled the seals the wrong way… The one thing i haven’t checked is the PDWA. While i understand that a bad seal in the PDWA would allow brake fluid to move from front to back, it should not get back in the secondary reservoir (if i understand the system correctly). I will pull this out today, but i am still searching for help of what’s going wrong.
Btw, i also don’t really understand how brake fluid really gets into the rear brakes, unless you push it with pressure through the secondary reservoir. However, when i bleed the rear brakes fluid war drawn from the main reservoir, which might point to a bad seal in the PDWA. What’s the best way to bleed the brakes on the XKE??
Andreas
Huntington Beach, CA
Hi Andreas
You resurrecting this thread reminded me that it would be good to follow up on my problem. I replaced the servo rather than go through the rebuild route. This significantly slowed down the sieving between reservoirs but did not entirely stop it. I would estimate that over a month a thimble full would transfer. I’ve now put both reservoirs at the same height on the right so that has to resolve it. Not a proper fix (entailing a long length of pipe from reservoir to servo), but definitely a solution.
To bleed the brakes I pressurise the each reservoir to around 10PSI (NO MORE) then crack each bleed nipple whilst very slowly pumping the pedal. Be aware that air bubbles in the bleed pipe can often enter through the bleed nipple threads which fools you into thinking you still have air in system. A helper is needed to close the bleed nipple on the slow downward stroke of the pedal. This ensures air does not get back in through the threads. All a bit laborious but it seems to work.