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MG TD TF 1500 - Brake problem - TD

Hello all,

Over the past few months I've been carrying out some mild restorative work on FRX 942 to try to get her roadworthy. I have however hit an issue with the brakes,(I did check the archives but can't find a similar issue).

The brake work done thus far:

Wheel cylinders (x6) replaced along with flex hoses.

Front shoes re-lined, rear shoes o.k. but cleaned up.

All adjusters done up to bind on the drum and then back
one click.

System bled 3 times and no sign of any air. I've put enough fluid through the system to renew all the fluid in the lines plus probably the contents of the MC.

No pedal adjustment has been made from when the car
was last driven.

The problem:

The pedal nearly hits the floor. If I pump the pedal
once or twice it comes up to the (what I consider)
correct level and is firm. If I maintain pressure on the pedal it remains firm with no sign of sinking or feeling spongy. If I release the pedal and then wait a few moments it will nearly hit the floor on the next application.

I can't seem to solve this issue so if anyone has any ideas or has had a similar issue please let me know otherwise she remains in the garage 'til next year.


M Spencer

My guess is that you still have air in the system. Did you bench bleed the MC before installing it in the car?
David Werblow

I would have to say the same as David, there is still air in the system somewhere. I charge a new system differently than most people, I start at the farthermost bleeder and pump fluid back through it to the master cylinder, then the next shorter line etc, continually watching the MC so it doesn't run over, removing excess fluid until finished. I have had good luck with this procedure over the years. PJ

Paul sr

You don't mention the master cylinder. Did you replace or refurbish?

My guess is that the rubber cup which compresses the fluid is 'tired' and is normally relaxed away from the m/c wall. When pumped the cup hold to the wall whilst there is some pressure in the system, but after a short while it relaxes back and requires a couple of pumps to get it into position again.

So, a rebuild of the m/c is in sight!

Ian Bowers

Hi again,

Thank you for your comments,

The MC has not been removed from the car. The level was correct and the fluid clear when I checked it before any brake bleeding began, mind you it had been
sitting unused for probably 10+ years.

Unfortunately I don't have the facilities to remove
and replace the MC, so, if it is the issue then off to the restorers she'll have to go (probably Edneys place)

M Spencer

You still have air in the system.
How are you bleeding them, by yourself with a pressure kit or with someone else pushing the pedal down while you open and close the bleeder?
Air is in there, either it has not all been bled out or the bleeding method is allowing air to re-enter.

Good luck
D Hanna

Hi D Hanna,

First 2 bleeds were done with an 'off the shelf' simple clear plastic hose with non return valve and a friend (who is fully knowledgeable on how the braking system works)to open/close bleed nipples. The last bleed was done with the same fellow but 'the old fashioned way' with just a clear pipe with him opening /closing bleed nipple and me pushing/releasing the pedal - with MC top ups inbetween.

M Spencer

I would suspect that you need to readjust the shoes, after you have applied pressure to get the seated tightly (which you have done). Perhaps you adjusted them "tight" just after re-installation, and they weren't well reseated?
I had a similar situation recently, found one wheel shoes could be tightened several clicks. Fixed the problem.
keep us posted
54 TF Emma
A W Parker

Hi Mike,
clamp off all 3 hoses and try the pedal,if solid then you have air in the system or not fully adjusted.
If solid then release the rear clamp and try again,if slack then that is where the problem is, if not then release the RH clamp and try again and so on to the LH side.
Ray TF 2884
Ray Lee

Hi Mike. What type of fluid do you use
silicone. The fluid you are draining are full of air, so don't put that back into the MC.
Empty it in a jar whit the lidoff and heat it a little in <dry place.
Thoralf. Norway TD 4490
Thoralf Sorensen (TD4490)

Mike, if you can access the output of the m/c there is an 'easy' way to determine which part of the system is the culprit. Find a piece of brake line that you can sacrifice. Cut an end off, about 3'ish inches long with the nut on the end. Braze shut the open end of the line. You've just made a plug for the m/c output.
Remove the present line from the output of the m/c and insert the plug. Tighten it down. You should be able to pump up the m/c to a very hard condition. If you have no problems in the m/c you should not lose this hard pump condition. If the pedal goes back down then you know that your problem is in the m/c. You should be able to do this with a very minimal loss of brake fluid. One way of preventing loss is to connect the removed line into one of the loose, old, wheel cylinders that probably have lying around. Good luck. Bud
Bud Krueger

Very good suggestion Bud,,,,

Mike a good suggestion I read here was to bleed the lines with the adjustment all the way in. That way it allows you to work all the air out because the pistons have to move their full travel. Once you have bleed the lines then adjust to lock drum and 1 click back. I did this with silicone and only had to bleed once and have a firm hard pedal.
Richard Taylor TD3983

I've just had the same problem after reconditioning the brakes on my TF. Solution was to adjust the shoes so the drums are locked and then bleed. If the pistons have to travel too far there is insufficient stroke in the master cylinder to fully expell fluid/air.

Good luck

Jan T
J Targosz

I would try AW's suggestion first. Air would be just spongy unless you had a huge amount, loose shoe adjustment would require a couple pumps. Really tighten the shoes to lock the drums, press on the pedal as hard as you can a couple times, then check to see if any adjusters have loosened. If that fails, then proceed localizing the problem, etc. as above. George
George Butz

Mike, did you try googling your issue. A lot about air in the system...including issues where system is carefully bled, but a small leak in the system allowing air to return to the system.
not saying this is your fix, but the few times iI had similar symptoms it was air in the system. Good luck. Regards, tom
tom peterson

I vote for the need for adjustment.
The need to pump up after a period of time is the main clue.
RwB Brown

I had the same problem when I replaced the wheel cylinders on my TD. To cut a long story short,(I could go on for hours about the hassle I had),in the end I removed the brake pipes from all wheel cylinders in turn and used a hyperdermic syringe and injected brake fluid directly into the wheel cylinders, replaced the brake pipes and bled them in the normal manner. Problem solved! If I ever had to change one again I would pre-fill the wheel cylinders with brake fluid before fitting them.
R Bowden

Hello again all,

Many thanks for all your responses.

Thoralf - I'm using new DOT 4 fluid and not recycling
anything that is bled out.

It's interesting that winding the adjusters right off works for some people and winding them hard on works for other people. I shall try both as they are the easiest solution first. If that fails I shall try the clamp and syringe solutions and then if I still have my sanity I'll get the MC tested.

It'll be a couple of weeks before I can work on the car again but I'll resurrect this thread when I have some news.

Thanks all once again,

M Spencer

Don't think I can add much here. Couple years ago I changed all the shoes. Bled the system and all was good. Month or so later I had to pump the brakes to get enough peddle to stop. There were no leaks anywhere even at the cylinders. Opened all the cylinders and replaced the neoprene seals. No problem for the last 2 years. Assumption is one of the seals leaked and allowed the piston to slide past the fluid.

Peter Dahlquist

This thread was discussed between 03/10/2013 and 04/10/2013

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