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MG TD TF 1500 - Soft Brake Question

The last time I had my TD out the brake pedal seemed very soft. The first time I stepped on the pedal it went almost to the floor. After pumping a few times it seemed to recover and I enjoyed the ride but not with full brake pedal.
Prior to that ride it had always been fine.
I checked all lines for signs of leakage and found none.
I checked around all the drums to see if there was any oil seeping out and there was none.
I checked the brake fluid level but it is very close to full. The fluid does not touch the cap but when I remove the cap the fluid is still up to the threads.
If there is air in the system how to get there?
All suggestions most welcome.
Thanks,
Mort
Mort 50 TD

Hi Mort

I changed to silicon on the TD when I renewed the master cylinder and I maybe had to bleed the brakes 4 or 5 times before I got air out of the system, this was over a period of several weeks. Don't know if this has happened after brake work or even if you are using silicon which is notorious for bubbles when filling. I also found on the MGA that the master cylinder was drawing air on return which was only fixed with a new master cylinder. None of this probably helps you just my experience.

Barry
B Bridgens

I have done nothing to the brakes for years except to check the level in the reservoir. The last time I did that was about a year ago.

Mort 50 TD

Mort - The pedal to the floor means there is a leak, if nothing else was done to the system. I doubt there is air, but the fluid is probably leaking past the seal. A good time to pull the master, check the hoses and cylinders, and the pedal shaft bushings (groan).

Sorry.

Tom lange
MGT Repair
t lange

Mort - I ran into a similar situation with out TD, although not when driving. I was adjusting the brakes on the TD and though the front brakes adjusted fine, the rear brakes would not adjust far enough out to make good contact with the drums even though there was good thickness of the linings. It took some time of fussing with the brakes before the penny finally dropped. I had to think about the difference between the front and rear brakes to understand what was happening - The front brakes use two wheel cylinders, one for each brake shoe, while the rear brakes use a single cylinder for both shoes. This results in the wheel cylinder for the rear wheels to extend twice as far to actuate the rear brake shoes than the front cylinders do. This results in the rear cylinders running out reach to press the shoes against the drums. I had to get a set of masks with spacers welded to them in order to push the shoes far enough to contact the drums.

I don't know if this is your situation, but it is something else to check. Cheers - Dave
DW DuBois

Tom,
I thought of a possible leak also but I can find no evidence of fluid anywhere around the drums or any of the fittings or along any of the lines. Also the reservoir seems pretty full. If there was a leak I would suspect the brake fluid would be diminished. I checked all lines both metal and hose.
I replaced the pedal shaft bushing three or four years ago and have kept it lubricated so I doubt that it needs replacement. Even so how would that affect the soft pedal?
If the seal in the master was leaking wouldn't I see evidence of the leak?
Mort
Mort 50 TD

Dave,
I understand and agree with your analysis of the brake geometry.
What is puzzling is that since I got the car six years ago I am replaced virtually every part of the brake system, new drums, new shoes and new cylinders.
They have been working fine ever since.
How would the situation you describe relate to this sudden change in pedal pressure?
Mort
Mort 50 TD

Mort,

If no leaks are evident the piston seal in the master cylinder may be failing. When you stet on the brake you can create several thousand pounds of hydraulic pressure forward of the piston. (Depending on how panicked you are) A leak past the piston seal returns the fluid to the reservoir so no loss is evident.


Jim Haskins 1953 TD
J M Haskins

there is a point where we all say "well it worked yesterday".
All systems fail sometime and without warning.
If there are no leaks then the master cylinder seal has gone. It is happening far too often and is normally bad seal material.
When you rebuild the cyl make sure the piston returns fully. I fully prime the master cyl before fitting by running a pipe from the outlet into the reservoir and pump until there are no bubbles.
Be gentle as the recuperation hole will spit fluid at you!
Ray TF 2884
Ray Lee

Mort - "How would the situation you describe relate to this sudden change in pedal pressure?"
Just something else to check. Cheers - Dave
DW DuBois

Mort
This same scenario happened last month with my TF. And, I had just replaced the TRW master cylinder in January. I was sent a replacement and with that, all is firm. Like others had said, there was an internal leakage in the MC.
Thanks to Abingdon Spares for making the replacement easy and fair.

Tom
'54 TF
T Norby

Thank you all for your timely responses. As several have mentioned I think the MC needs attention.

I will post this question here and in a separate post.

Where can I find some good write-ups on the removal, replacement and rebuilding of the master cylinder for an early TD?

Mort 50 TD

This thread was discussed on 08/10/2016

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.