1969 mgbgt brake problem

[poolystan]

Hi, I have a 1969 MGBGT which has developed a brake problem. After a recent 10 mile trip I noticed an awful smell coming from both front brakes. I jacked the car up and tried to turn both front wheels, both were binding and very hot. I decided that since the calipers seem to have been on for ever I would replace them with genuine lockheed replacements. With the new ones fitted and bled I went on a test drive, the problem is still there but now the wheels are sqeeking a lot and still getting hot,I then took off the vacuum pipe from the inlet manifold, blanked off the union and crimped the flexible pipe another test drive and it was still the same. Any ideas as to what could be going on would be much appreciated. I upgraded the brakes a few years ago by installing a servo and it's worked fine. thanks

[suffolkpete]

Sounds as though the flexible hydraulic pipes have collapsed internally and are not allowing the fluid to return after you've applied the brakes. Try replacing them.

[poolystan]

thanks pete I'll give that a try ,I might try a length of hose to test it prior to buying a new one, is that worth a shot ?

[poolystan]

Sorry pete I thought you meant the flexible hose from the manifold. The two flexible hoses have been replaced when I put the new calipers on.

[Luxobarge]

I'd investigate the master cylinder, it sounds as if something is stopping the fluid returning back into the reservoir after the brakes have been released. I'd suspect a broken up seal, or some other sort of blockage, or something that is preventing the pedal from fully returning.

Can you confirm that there is no binding whatsoever on the rear brakes?

All the best with it

[mr rusty]

The master cylinder gets my vote too- the clue is in both fronts being affected. I remember this happening to me on the North Circular in one of my many Allegros many years ago, it was nighttime and the discs were dimly glowing like an F1 car! The rears weren't affected, I still don't know why because it was a series one with no brake balancer. A master cylinder overhaul will sort it.

[arceye]

Yep, if you have already done calipers and flexi's I'd go master cylinder as well, had it on a Viva 1800 years ago, about eight miles and I'd grind to a halt........

[poolystan]

thanks for the replies guys, there was no binding on the rear wheels and I fitted a new after market master cylinder when I restored the car two years ago, less than 1000 miles travelled. Something strange happened though when I was bleeding the brakes with a friend on the pedal, every time I opened the bleed screw and he depressed the pedal he said he had to bring the pedal back up with his foot under the pedal as it was'nt returning on its own ?. With the system bled and a firm pedal I thought I had done a successful job, obviously not though. Daft question time, adjacent to the bleed screw there is another screw, what's that one for? I never touched it but was just wondering, thanks

[JPB]

I'd be looking for a n/o/s master cylinder and fitting a seal kit to that instead. Some of the aftermarket parts are truly appalling but with dry n/o/s, although the rubbers will be past it, you'll have a good surface to run new seals on. Also, you may have found why pressure bleeding or vacuum bleeding at the nipples can be better than pumping away at the pedal, so whatever you do to replace this dodgy cylinder, don't bleed it by pumping the pedal. I'd just fill the reservoir then - keeping the fluid topped up as required - use an empty old battery hydrometer to draw the fluid and any air that's present out at each nipple in your car's correct bleed sequence.

[Luxobarge]

I suspect that the pedal not returning when bleeding is the clue here - if the pedal doesn't fully return, the master cylinder piston will never uncover the feed hole to the reservoir, and the system will behave like a totally sealed system. Then, when the fluid gets a little hot the fluid will expand, which will push the brakes on harder and then they get hotter and so on in a vicious circle as it were.

Or something like that

Not sure if your pedal box is like a Midget one, but on that it has a black cover with 4 screws, remove that and you get a good view of the pedal push rods and the top of the pistons - you can easily see if they are returning properly, or if anything is amiss at the pedal end.