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MG TD TF 1500 - No Brakes!!

Hi everyone,

I have virtually finished the restoration of my TF now moving from the restoration to maintenance phase.

I was out on a run last Sunday about 15 miles from home when my brakes failed to operate. I was putting my foot right to floorboards with minimal braking. I didn't know whether it was hydraulic or mechanical.

I drove slowly home and next morning I inspected underneath the car for any clues as to the cause of problem.

No sign of any leak. Also master cylinder was full of brake fluid. I put the hand brake on just to see if there was any significant increase in play with the hand brake which might suggest a mechanical problem with the rear brakes. The handbrake operated as normal. So I got my better half into the garage to operate the foot pedal while I was underneath the car. Again no leaks but my wife commented that the brake pedal seemed fine. I tried it and yes it was back to normal. Took it for a quick drive, brakes OK. I can't fathom it out. I don't know whether operating the handbrake moved something that was out of line in the rear brake drums or something else has rectified the problem. I am obviously a bit nervous in case it happens again, not nice driving without brakes.

Has anyone had a similar experience and knows what could have caused this temporary failure of the brakes?

Any advice would be very much appreciated.

Best wishes

Dave
D Williams

Dave,
need a bit more info,,
How many miles on the brakes before this happened??
Did the brakes operate satisfacturally before this porblem??
You said >>I was putting my foot right to floorboards with minimal braking<< The peddle actually went all the way down??
Did you try to adjust the brakes after operating the hand brake??
Steve Wincze

If you see no leaks , then I would re-bleed the lines.
Maybe it was air in the line.
G D

Hi Steve,

Many thanks for your reply

To answer your queries:

Brakes shoes, slave cylinders, master cylinder etc all new. Approx 600 miles on the clock.
The brakes worked great before this last run and they work great now.
Yes I the brakes pedal went all the way down.
No I didn't adjust the brakes after operating the handbrake. The brakes just came back and are now working OK

Best wishes

Dave
D Williams

Dave,
From what you have said "No Leaks" "Pedal went to the floor" I would take the Master cylinder out and check everything is in order. Check the bore. Even if it is new, and the assembly of the piston and valves inside. Also check the rubber seals for deformation or nicks. lump of dirt maybe

Fluid would have to have got past all of that for the pedal to go to the floor and not lose any fluid.
Just a thought.
Rod.



Rod Jones

Dave,
Any leaks or air in the line would give a spongie feeling, which you don't have,,,,
I doubt that just operating the hand brake would "correct" anythng that might have been wrong,,,,
Therefor, I'm thinkin' that the problem might be in the master ,,maybe one of the seals allowed some fluid to be temporarily bypassed some how????

I would definately go through a brake adjustment just as a start and rule out that causing any problems,

Steve
Steve Wincze

I see Rod was typing at the same time I was,,,,

Steve
Steve Wincze

Did you smell any hot or burning smell? Or feel the drums to see if hot? If brakes were dragging they could really overheat and/or boil the brake fluid if any moisture in it. More likely to be the MC I think. George
George Butz

Definitely check the master cylinder. Pull the boot back from the housing. If all is new that boot can have a good seal and trap a lot of fluid. first check the level in the master cylinder and see if there is a drop in the level, if yes, pull the boot back. At any rate I would re-bleed the system starting at the furthest point from the master cylinder, ie. opposite rear corner, then near rear, then opposite front and lastly near front, also reset the shoe adjustment since your linings if they were not profiled to the drum on installation may be wearing down the high spots on the shoes, though this would not explain the peddle to the floor. When bleeding the brakes pump the peddle several times and hold pressure then release the bleeder until peddle hits the floor. and retighten before allowing the peddle to return. I'm not a big fan of speedy bleeders as I have known them to not work correctly, yes even new ones. Ideally vacuum bleeding would be the way to go if you have the equipment.

Since you say all is fine now and if there is no drop in fluid level, what likely happened was the cup inside the master cylinder may have stuck on the down stroke in the previous application before the peddle drop and the internal spring didn't push the cup back with the piston after the application. Over time the spring finally had a chance to push it back into place beyond the outlet orifice so the peddle could acquire a fresh stroke. IMHO

Cheers

Bill Chasser Jr
TD4834
W. A. Chasser Jr

Years ago, we had an Audi that had a similar problem, although not recently rebuilt. I had to hit the brakes once and the pedal dropped to the floor. It happened out of the blue and my reaction was to raise my foot and slam it down again, standing the car on it's nose. I wasn't eve sure that it had happened except that my wife was with me and from her reaction, I had to believe that it had. After that incident, the brakes were fine for several weeks, then it happened again. I pulled the master cylinder and found a very small crack in the main seal. Rebuilt the cylinder and never had that happen again. Cheers - Dave
D W DuBois

Hi George and everyone,

I didn't smell any hot or burning smell but I didn't feel the break drums until next morning.

Thanks to everyone, seems that the master cylinder is the prime target for further investigation.

Thanks again

Best wishes

Dave

D Williams

Just finished working with Dave on his master cyl. We stripped it down and the bore is perfect and recouperation holes clear. We found that the secondary cup was tight in the bore (not the skirt but the main body where it fits over the raised section).Fitted all new seals and we had the proper fit.
Primed the cyl out of the car and refitted, bled through and have a solid pedal
I can't see how this would have given the symptoms Dave had, so we will see what happens.
This was a new cylinder from 'you know who' which had been bought some years ago but not fitted, so no comeback.
Ray TF 2884
Ray Lee

This thread was discussed between 22/10/2014 and 31/10/2014

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