Binding Brakes

We are enjoying a spell of very spring-like weather here in Belgium, so I took my 140 DHC out for a 100km drive to test my just finished Getrag 5-speed gearbox conversion and it was a revelation. The car is completely transformed with a smooth and silent gearchange, while still retaining the feel of the old Moss box. Inside the car the change cannot be noticed, and I have retained the old gear knob as the rear speed is in the same location as before. The fifth gear is a real overdrive and I recorded about 2800 rpm at 120 km/u. (75 mph) I did notice a problem with my brakes however (4 XK150 discs): they seemed to bind after applying pressure to the pedal. Is there a way to adjust the free play of the pedal to cure this : there is nothing mentioned in the drivers' handbook but I suppose the threaded rod and 2 locknuts connecting the master cylinder to the brake pedal do have a function. Any suggestions ?? - Marc Bertels

Marc: Perhaps Arno Wahl can be persuaded to tell the tale of his Getrag conversion many years ago in his lovely 120OTS. I know he did all the engineering himself and it might be an inspiration for those of us brave enough to consider it. Heads up on the brakes. Adjust to ensure free play, i.e. the piston returns all the way to the stop (circlip). Consider this. I have come across this situation many times in putting cars back on the road that have been stored for some time. The flexible brake hose sometime perishes internally and will allow fluid to enter the brake cylinder but will not allow the fluid to return due to the inner lining of the hose pulling away a blocking the return patch.The brakes then grab, or in some case, even lock. I have been able to get it back to the barn by opening the bleed fitting to relieve the pressure. If your brakes are binding after application, open the bleed valve. If the fluid squirts out under pressure with no pedal applied, this could be your problem. This was not an isolated incident but happened on several cars of mine. I now just replace the hoses as a rule of thumb and have not regretted it. All the best - Bruce Baysinger

Also check the automatic adjusters. I had a problem with them on my XK140. If the nuts on the free movement areas are too tight or the slip plates are rusty/dirty, they may not allow the brake shoe to return. Also check movement of the wheel cylinder itself. They could have gummed up over time. Especially if the car has not been driven for awhile. - Cleo Bay Jr., 52 XK120 OTS, 56 XK140 OTS

I am Glad you mentioned this problem. I have been screwing with my master cylinder for a long time trying to fix this problem to no avail. I will just replace the hoses and see what happens. I can not find anything wrong with the master and there are no crimped lines. - Edgar Blake

I too have binding brakes on the 120 OTS. It is with the workshop at the moment and we initially suspected the master cylinder, but a maladjusted operating rod is the first candidate (and I have told Gavin next to check for a collapsed flex hose - he said he has encountered this before). - Regards, John Elmgreen

John: This problem has turned up more times (for me) than I would have imagined. When I cut open these hoses that looked good (i.e. not leaking) they were nearly swollen shut. The high pressure from the master would push the fluid through, but as it took little pressure comparatively to hold the piston out against the return springs, instant brake drag. Pull a hose and try to blow through it. No blow, no go. Reminds me of a joke....Regards - Bruce Baysinger

Here is another factor on the 140 binding brakes: I had changed the hoses, checked the auto adjusters, made sure I had adequate free play between the operating rod and the piston itself. It seemed that when the wheels got hot the problem occurred. I stared for one heck of a long time at the diagrams of the system. I knew that the brake lights also remained on. Therefore there was pressure in the system. Though the wiring in my car is totally different, the brake light switch is standard. I do operate the lights through a relay so the contacts in the switch itself only carry the coil current. Anyhow, after moving from New York to Arizona, the air temperature was much higher and the brake binding became far more serious that back east. Inside the master cylinder there is a tiny hole at the rear of the resevoir that allows the excess pressure and fluid to back up into the space above. Evidently, the rebuild kit has rubber or neoprene parts and they seem to be ever so slightly longer than the original. Therefore, when the piston is fully back against the stop washer, the rubber seal still covers the tiny hole. I took out the washer, put a block to hold the piston in position so the fluid wouldn't leak. Surface ground the washer slightly. Now the piston could travel far enough back to have the seal clear that hole. It is now a full year and I haven't had any brake binding. Hope this is of some help to others with this problem....I was able to do the whole repair in a rented garage with nothing but small hand tools and didn't even drip brake fluid. Dirtying the floor of the rental would have left me liable for damages. Needless to say, the car was parked over a covering of cartons to protect the floor from the normal drips. - Barry Goldman

Bruce, Have had the brake hoses on my XK140FHC block the way you described several times through the years. The car has often been stored for several years. Have also considered the use of Teflon lined hoses for replacement, but have not as yet tried them. - Gene Burda

To all with binding brakes. It happens very often, that the tandem master cylinder is taken apart and being put back in the most logical manner. That is where the fault happens: Everything is being stuck again into the body, with patience and proper attention in the correct order. Finally the clip goes over the stop of the piston and then? Attention please: Every fool can turn in the return stop valves, even with proper care, but thats where the general mistake happens, the stop valve pin is bent and tends to blocke the return flow of the fluid after braking. I am that stupid, that it happened twice to me over a stretch of many years. The answer is pretty easy and is even mentioned in the manual: When you turn down the two valve you have to push back the piston inside the body of the master cylinder with the help of something like a screw driver, to give room for the little pins of the return valves. When you release the piston it slides back and the two collars of the piston strike the tilt valves, in order to open them. Give it a try and take out the tilt valves. If the little tilt valves look not straight, i.e. they are bent you found the reason for binding brakes. If they are o.k. keep on searching. - Arno Wahl

I think there were similar posts a while back, but the problem was a swollen cup due to wrong fluid, rather than a too long cup....or was that the Humber Super Snipe list? - Jim Warren XK 140 leggo kit

Dear Jim, The swollen cup may be the reason but I use Straight Silicone fluid and it is not supposed to affect the seals. Don't know if thae swelling is valid...I did think of that but re-read the can of fluid! Thanks for the suggestion, I hope it is NOT correct. I do not want swelling seals! - Barry Goldman

Are we talking about the single system or the tandem system? Arno's excellent description applies only to the tandem system in that the single system doesn't have tilt valves. Barry's also excellent description is I believe speaking to the single system, am I on track? Or is it about the 150? I don't have a picture of the 150 master cylinder. My episode of stuck brakes I mentioned to this list a year ago was exactly as Barry said, but occurred even with cold brakes. I blame it on silicone brake fluid swelling the seal. The tiny hole is pictured on page L29 Plate L16 of the 120 manual and labelled "X". I don't believe this particular problem occurs on the tandem system, only the single system, and I don't know if it can occur on the XK150. - Rob Reilly - XK120 FHC 679187

Rob, To clear things up : my car (the 140 with the binding brakes) has the standard 140 master cylinder but with 4 disc brakes from the 150. - Marc Bertels

Hi Barry, I have an xk140 with the same problem as yours and I've had silicone brake fluid in it for over 10 years. My car sat forabout the last 7 and when i got it started and began driving it the brakes started sticking. Itook apart the master cylinder 3 times (without removing it from the car) but nothing worked. Finally frustrated I put this out to the xklovers and I got alot of responses and helpful hints. I found out there is a little pin hole that equalizes the pressure (see your manual) I could not find it on mine, but then after probing through the top access nut i found this tiny pin hole full of crud and plugged. What a lousy design. All the crud from the reservoir falls right into this pinhole. Try to clean this up first and see if it works, it did on mine, works great. Even though my master cylinder had some pitted scars and there was evidence of rusty fluid after 7 years no use, I saved from having to spend a bundle on new parts. And it brakes just fine. Good Luck and enjoy your car - Andy Ottolia

to all, I do not know about synthetic brake fluid, but in the old days, we could not use American Brake fluid because it had alcohol in it which melts the natural rubber piston cups and boots found in older British cars. We always had to use Castrol Crimson or Castrol LMA to preserve natural rubber before we switched to neoprene. I have not seen Crimson since I was a young lad. I know most of you old timers know this but some of us may be new to the problem. - Edgar Blake

Marc - Is this system fitted with a vacuum servo assist unit? - Bob Oates

Bob, Please tell me more about binding brakes and servos on XKs. By the way my non-return valve is in line the right way round. Roger Learmonth

The problem with my 120 re binding brakes turned out to be simply an adjustment of the pushrod for the master cylinder. Regards, John Elmgreen

John: Conrats on the easy fix. It did open up an interesting dialogue that may have helped others. Best wishes - Bruce Baysinger

Bob, I have been on holiday so here is my late reply: Yes I do have the vacuum servo as well. - Marc Bertels

Bob, I believe I have solved the problem after adjusting the rod between the master cylinder and the pedal shaft. Due to the very stormy wheater I could only test it in my garage but the pedal feels much more progressive without the previous binding after the first use of the brake. If only every problem was that easy to sort... For the record, my XK 140 DHC has the standard 140 master cylinder (= 120 single) with 4 XK150 discs + servo. - Marc Bertels

Marc, Very interesting that your problem had exactly the same, simple solution as on my standard 120! Regards, John Elmgreen

If you have any questions or comments send e-mail to: ted@jag-lovers.org
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