When driving my '66 FHC, the brake pedal at first feels fine. About 20 minutes into my drive the pedal becomes stiffer and the brakes do not completely disengage. The car won’t roll freely once it comes to a stop. I cant tell if its front or rear or both that are causing the problem. If it is a hot day the brakes will stay that way well into the afternoon drive home from work even as I only drove the car that morning. Next day all is fine.
Looking at old threads I thought the issue was the reaction valve and replaced that. No improvement.
The master cylinder was replaced 10 or so years ago along with the servo and flex hoses and new calipers.
Suggestions greatly appreciated?
Been a while since I was on this site so sorry if I missed this answer already. Been working on my son’s MGB all summer and finally getting around to servicing my car.
Complete E Type doofus here, but I had the same problem on my 1964 a few
years ago.
The late, great Jerry Mouton advised me to adjust the balance bar. His
post included specific, easy to follow instructions. I recall it took less
than 15 minutes to do, and resolved the problem 100%.
Suggest you look in the archives for his post. If you have trouble, lmk;
pretty sure I printed his instructions and I can look.
The problem is usually due to the small piston in the front end of the master cylinder which presses against the reaction valve. Remove the reaction valve, withdraw that piston, clean it and the bore it sits in in the MC, lube the piston with red rubber grease and reinstall the reaction valve.
Agree with Mark, the ‘small piston’ has an ‘O’ ring and a seal on it that you may wish to replace. I use a 22cal cleaning brush to gently clean out the piston’s ‘seat’ and use either the red rubber grease or silicone grease.
Cheers,
LLynn
How does one withdarw the piston? I have the reaction valve out and can see the end of the little piston inside the MC, but it does not want to come out with gentle attemps to move it
I have a '69 E-Type with the same problem about 18 months ago. Hopefully, the reaction valve solution will work for you. It didn’t help my brake problem. Neither did the first new servo and slave cylinder replacements.
Brakes worked well in cool temperatures but an hour or more of highway driving, the sticky brakes problem started to show up. I can tell you that my condition was gradually getting worse for a while until the rear brakes locked up big time in rush hour on Hwy 10 in Phoenix, Az. I ended up having British Auto Repair in Scottsdale completely restore my brake system and only then did the problem finally resolve itself. I never did find out the source of the problem as I feel there was more than one fault with the brake system. I hadn’t had the Jag that long so I have no idea of what or when the previous owner had the brakes worked on. I can tell you that the brake fluid was in sad shape and even the caliper housings showed signs of rust. Bad vacuum hoses and tubing also were replaced.
I seem to recall it shot out with pedal pressure. Cleaning and polishing the piston and bore helped temporarily, but didn’t get permanent fix until I replaced the little piston. I believe the rubber seal in the end of the original had hardened.
Thanks John. A slight push of the pedal shot it out into a container I had secured in front of the MC. It would have drained the rear brake bottle if I had not clamped the hose running from there to the MC. I cleaned the bore and lubed the piston oring and rubber seal with Sil-Glyde.
Drew, I hope you have good results. In my case I knew the mc was about 20 years old, and had mostly sat with Dot 3-4 in it, only running 3k miles. After replacing the piston and all the hard lines I switched to
Dot 5, so far all is good.