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MG MGB GT V8 Factory Originals Technical - Brake dilemma

I have been having a brake problem with my 302 V8 conversion and am wondering if any have had similar problems.
The car is in its third summer and had put about 20,000 miles on it with no brake problemns until this year.A new mster cylinder was installed last season but there was a slight hissing from the servo so at beginning of this season a rebuilt servo was installed.The only other modification that may have affected the problem is the headers were ceramic coated.
The problem is when sitting for a short period with engine running or a short stop of a few minutes --the brakes start to grab on.After a few minutes of driving and it seems the cooling air flow, they release.
I have tried many solutions --changing calipers thinking maybe ceased--the rod on the servo was checked for correct adjustment --its fine,the pedal adjustment is also correct.
It seems like the fluid is heating up and pushing the caliper pistons out.
I was using V8 pads with no problem before but am now using the Ferrado regular pads.
Anybody have any ideas ?
Gil Price

Headers through the fenders? Maybe a heat shield to keep the brake lines cool. Or a brake fluid with a higher temp rating.

That was my thought - the brake pipes are heating up from the exhaust somewhere and the heat is transmitting up/down the line.

Normally ceramic coating would ratiate less heat, allowing the the engine compartment and thus the brake lines, servo and master cylinder to run cooler. There is a lot of exposed brake line in the engine compartment to collect excess heat.
Are you running the same or same style headers as before? Has the rest of the exhaust system (that beyond the headers) been changed or relocated? If you have dual exhaust, perhaps the right hand pipe is closer to the main brake line going to the rear wheels than in the past.
Phil O

Thanks for replies . My thoughts were also that the fluid is getting too hot . The quandry in my mind is that this had not happened before and although the headers are new and ceramic coated--with the previous ones not coated I did not have this problem.THe headers do run through the fenders and the holes are rather large.I also have added large louvers in the hood over the headers and a high volume cooling fan on rad 2800 cfm.It is a pusher in front of rad --no room to install behind rad.
I am going to try to fabricate a heat shield to deflect heat away from the braided steel lines going to the calipers. I have had insulation around the lines going down the back side of the engine compartmentand have not changed that.
Has anybody used the high temp brake fluid --670 F--does it bother the Lockheed components ?
Its a very frustrating problem as it had not occured previously.
Phil--the exhaust system after the new headers is in same location and is a single pipe to the back --the rear brakes are not affected only the front.
The new headers may not be exactly the same configuration and are 1-3/4 inch instead of 1-5/8
Gil Price

Have you seen the flexible heat-reflecting fabric tubing? I think Thermotec or Coolit makes it in various sizes. Slipping that over your lines might help. Joe
Joe Ullman

Just because you ceramic coated the headers doesn't mean the heat disappears. It gets moved down the line and radiates at the most convenient spot. If there is no ceramic coating at an area where an exhaust pipe passes near a brake line, (like where the brake pipes wrap around the frame rails and go back up towards the calipers)it may give you trouble.

The rubber seals in the MG brake components are sensitive to the type of brake fluid used. Caveat Emptor

Can we assume that the trouble really started when you changed the booster? Or did you change the headers (and the problem started) and later changed the booster? What's the sequence of events?

Wayne Pearson

The booster and headers were done at the same time-so hard to say if one or other had effect.
Could well be that it lies in where the heat is released --but the ceramic coating does go way under the car and the collector is about under the pedals and connection to pipe is about a foot behind that , all this is coated.
I do have some insulation on pipes in engine compartment but none on the flex pipe to calipers. I believe I am using what Joe suggested.
Thanks for all the feedback .
Gil Price

Check the clearance between the booster and the rod.
This is a common problem when boosters are changed.
Bill Guzman

I had a brake problem last year that sounds similar to what you're describing. It might be the same issue. The real short story is: After fitting a new master cylinder the brakes (front) would lock up after I drove awhile (10 miles). If I let the car sit(cool) for a few hours the brakes worked again and then repeated locking up upon driving. I discovered that I could crack the brake line at the master cylinder, particularly for the front brakes, and the calipers would release. Eventually I traced the problem to the master cylinder/booster rod contact. Apparently there was enough contact (push) between the booster rod and the plunger in the MS that the relief hole(fluid return hole) was blocked. When the brake fluid expanded due to engine heat the calpers were pushed out. I solved the problem by putting a small ~0.03" aluminum spacer between the booster and MS. I could have machined the rod but I wanted to be sure of the solution.I dont think I'll bother now. Hope this is helpful



Woops, I see that Bill Guzman already adressed this issue. His statement is so clear. :)


Rick and Bill --
I did check the rod length per the shop manual and it is correct --but your description of the problem Rick is about what Im experiencing. I am going to go back and try your solution and see what happens.Thanks
Gil Price

Just confirming what your shop book should indicate as the rod dimension length measured from the housing of 0.400".
Also check your brake pedal freeplay -your problem does sound like your M/C plunger is not fully returning.
BTW - missed seeing the blue oval conversion with you and Tita at the helm in Terre Haute - hope that you plan for the 2006 meet in the Volunteer State......
Graham Creswick

Rick - Bill and Graham
Problem seems to be rectified.
I did check the spec on servo push rod (0.400 in ) and mine was approx 0.365 so I figured it was ok .
I desperation I went to Rick's solution and put a 0.030 aluminum spacer between the M/C and servo . I have since driven some 200 mile into city traffic and on the highways --no brake drag at all.
The strange part to me is that with the push rod being shorter than spec that a thin spacer would make the difference. I guess it was just that extra bit that allowed the return of fluid to the reservoir and not push out the caliper pistons
Many thanks to you all!!
Graham--I was sorry to miss IN V8 meet --just too much on the go. I do plan to get to the TN one in 06, Not planing Watkins Glen this year either.
I have painted my car --brighter yellow and done a few other improvements.
I am anxious to see your Ford installation --am sure its well done.
All the best from Tita and I --Gil
Gil Price

This thread was discussed between 10/07/2005 and 13/07/2005

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