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Brakes grabbing

Brakes grabbing

Dear List, I was approaching a traffic light the other day and my left front brake locked up when I hit the peddle. The old timer say's he had the brake shoes re lined locally. Could this be the problem? The shoe's look new, and they appear to be on correctly. - E.W. Blake

Curious E.W.- did this happen just once, and if so,could the road surface and weather conditions at that traffic light have played a part in the locking brake before the "autopsy" begins? - John Morgan

Mr. Morgan, The weather was good, If it were not, I would be dead right now. It is a continuos problem. The other day, the right side (opposite side) locked up. I am thinking it may be bad rubber hoses. The shoes visually look good and are 12 years old but they only have 200 miles on them. I just apply them slowly and gently just to get around but I feel like I am driving my own coffin. I have always been a dare devil, but if I ever had to stop suddenly, I will be in the ditch or I'll hit something. 1. Once the brakes lock up they do not unlock until I am stopped it seams. 2. Only one wheel will lock up and it is ether rt front or left front. 3. the pad on the shoe is toward the stationary rest (or) away from the piston end as shown in the manual. - E.W. Blake

Oi, wot's all this then E.W? 'Ave we bin mixin' our silicone brake fluids wiv our regular DOT 3's then? If so, you're caught red-'anded. If not then how about this? Try filing a slight chamfer across the full width of the trailing edge of each brake-shoe friction lining, not too much, just enough to relieve the sharp corner (if there is one) at the end of the friction lining. Next, check out the wheel cylinders for free return under spring tension- you need an assistant for this as you have to do it carefully with the drum off-one at a time please and not too much pedal travel or you'll pop the pistons out of the cylinders. If free return is erratic-suspect a) the front tilt valve -master cylinder or one of the seals on the primary or secondary pistons swelling/leaking b) corrosion starting in the master/ wheel cylinders or adjuster bars which may inhibit free return of the brake shoes c) gremlins Your idea about the hoses may have a bearing on the matter too so spend lots of money on new 'uns and while you've got the brake system gushing brake fluid all over the the floor to change these, that's the time to check all this other neat and messy stuff. Check the way that the brake shoes slide on the back-plates too, make sure rust doesn't cause any problems with the spring return action of the brake shoes. When you've checked all this out and found it O.K. then, if it still locks up as you've described, lock the car away for 10 years, it's too dangerous to drive. - regards, John Morgan

Dear Jack and everyone, I hope you do not mind but I feel like thinking out loud for a moment. I still have some breaking problems and I am looking for solutions. The breaks were grabbing and throwing me in the ditch and after talking to the list, ( THANK YOU EVERYONE !) I found that the brake shoes had no chamfer on the leading edge of the pad. I ground a chamfer on all, and this helped, but I still have a problem when I come in off the freeway and stop. My breaks stay on and will not release for a while. I try backing up a foot or so, to release them, but this has no effect. I was wondering if putting the duel exhaust on as aposed to the single exhaust may have increased the heat near the master cylinder which is only about 6 inches from the one of the two pipes. There is a heat shield in front of the master but it does not look like it would be much help. Maybe there is moister in the lines and it is expanding or something. I can not imagine what it would be like to have good breaking power..and I am a little frustrated. If I take the car to someone else it will cost me (big time) to figure it out. Besides there is know one in my area that knows much about the xk 120 and its personality .. I was at a service station the other day, and the toothless mechanic guy came up to me and say's, " I used to have a M.G. just like this one when I was in college", I was very pleasant did not correct him. Anyway.. I did not ask him for his thoughts on the brake problems. I am using Castrol GT brake fluid which should work if everything else is right. The master was rebuilt and the shoes are new. I think it is heat related.. my thoughts are... 1. completely change the break fluid? some of which is 12 years old I am sure 2. Increase the heat shield? and go from there... - E.W. Blake

How long is a while? 5 seconds?, 30 seconds? 5 minutes? Is ther time to jack up each whee to see if they all bind? Do you think it is related to engine heat, brake drum heat or speed that you stopped from? >I can not imagine what it would be like to have good breaking power..and I >am a little frustrated. If you are complaining that the brakes do not stop the car well enough, I can only repeat the advice my dad gave everyone regarding Jaguar drum brakes, and that is to ONLY fit Ferrodo or Mintex linings, and NEVER EVEN THINK of fitting US spec linings which have a lower friction coefficient. >1. completely change the break fluid? some of which is 12 years old I am >sure Sounds like a VERY good idea. If the fluid that comes out is badly discoloured, I would seriously consider doing all the wheel cyinder seals and resleeving if necessary. >2. Increase the heat shield? and go from there... Cannot hurt, perhaps you could try throwing some water over the master cylinder to see if it helps? - Good luck, Mike Morrin.

YES! you really want to change brakefluid EVERY year!!! it attracts water and that settles in the cylinders and creates little rust pits! If you read the original road tests they didn't have any problems with the 120 and even the Saloon brakes unless they used them streniously such as in racing. I have has no problems with my Mk-VIII and I drive it vigoriously. We in general arn't in situations where we are pounding the brakes repetedly and therefore the brakes are fine. BTW there's nothing unique about Jag brakes except the wierd method of self adjustment. This requires the drums to be round for minimum drag and tight adjustment. - Regards; Michael Rogers

E.W. I,ve had simillar problems for years. Especially the locking up and differential braking. Sometimes only rear brakes ,which is like no brakes.In your case I would replace the brake fluid and thoroughly clean the system. Look at the flex lines on the fronts these have caused problems in unbalanced pressure. What is the condition of the wheel cylinders? I replaced all of mine after years of fixing them. Then there is the master which I believe is where my problem was most acute. After a zillion rebuilds I bit the bullet and bought a new one. I installed the single unit instead of the tandem to reduce complexity and increase reliability. Some where in there I fixed the problem and I now have excellent and reliable brakes. I autocross, rally, and show my car and feel the braking is up to the performance. I have access to a very good 120 mechanic so am passing along his advice to me. You may be better off to trail your car to where ever knowledgeable service can be had. Good brakes are essential. For what its worth Vic Larsen

Mike, the brakes stay on for a minute, which is a long time after the light turns green... I designed, built and installed a heat shield last night and I am headed for the golf course this morning. I will report later. - E.W. Blake

E.W., I would think that if you were having heat related problems, the heat would boil the brake fluid (or moisture) and cause soft brakes or no brakes. Did you change the rubber flex lines? These have been known to collapse and not allow the brakes to release. It would be rather easy, and not too expensive, to change these and replace all the fluid (should be changed every year or two anyway) and go from there. - Regards, Dick White

Ed Blake, we spoke a couple of times about rebuilt tandem master cylinders and the possible mistakes that can happen during assembly of the cylinder. Just to try helping you getting off faster at green traffic light: Did you push in the piston when you installed the tilt valves? - Arno Wahl

Several things could be keeping your brakes on. 1. Bad flex-hoses are one possible problem. (swelled shut-acts as a one way valve) 2. The master cylinder not fully retracting is another. fluid not returning to reservoir 3. Corrosion/rust in the brake cylinders. 4. The auto retractors on the wheel cylinders are put together too tight. Springs not retracting. 1&2 can be checked by opening the bleeder and seeing if the brake fluid is under pressure when the brakes are locked. 3&4 requires more work and requires some disassembly of the brake assembly. Let us know what you find! Good Luck! - Cleo Bay Jr., 52 XK120 OTS, 56 XK140 OTS, 62 E-Type OTS

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