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MG TD TF 1500 - TF Hydraulic Brake Adjustment

Just had the rear brake adjustment cams built up to allow full adjustment and the front brake cylinders replaced - all linings checked and seem more than adequate. Checked that all cams are just one "click" off locking the drums, but still the brake pedal goes down a long way before the brakes bite, second application goes down a little way only. After standing a while the pedal goes down a long way again. The brakes are definitely NOT spongy and cams seem to be adjusted OK so does not seem to be a need for bleeding. Have I missed something?
Paul Joachim

Paul, I believe you still need to bleed your brakes - starting with the wheel furthest from the master cylinder (where the brake fluid is stored). Add to that, do you know when the brake fluid was replaced?
If there is any doubt as to the age of the fluid, then I would seriously consider replacing the fluid.

Even though you say that the brakes are not 'spongy', the fact that there is abnormal travel when the pedal is depressed, suggests to me that the brake hydraulic system requires bleeding. I would also suggest that you speak to some a mechanic or an expert on brakes.


Cheers,
Phil
Phil

Paul - You still have air in the wheel cylinders (I know, you have probably blead the brakes several times, but you still have air in the cylinders). Take a good look at the bleeder screws and you will see that all they do is bleed the lines, NOT the cylinders. What I do (and it is messy) is fill the cylinders full of fluid before assembling everything. It is the same on the Magnettes. one way to do it is using a hypodermic syringe, remove the fitting going into the cylinder and shooting fluid in untill it starts running out, then reconnect the fitting. The other way is to take the piston and cup out of the cylinder, fill it with fluid and put the cup and piston back in. This second method requires removing the cylinders that have the piston pointing down, fill them, put the cup and piston back in and holding the whole thing together with a big rubber band while reattaching the cylinder and reinstalling the shoes. A lot of fussing around, but it is the only way I have found to get all the air out of them.
David DuBois

Paul -
Given that the pedal is not spongy, it could be that the excessive travel has something to do with the adjustments, or the shoes not quite centred in their positions.

Reset the adjusting cams so that each wheel is locked up, then try the brake pedal again.

If the travel is reduced, then it would seem that adjustment is the problem. If this is the case, reset adjusters so that wheels can only just rotate, drive forward in first gear, say about 5mpg, jamb brakes on, do same in reverse. Do this a few times, then readjust brakes.

If travel is not reduced, problem could be air in the system

IanF
Ian Fraser

I agree with the above comments. Silicone fluid is notorious for trapping bubbles- are you using it? Cylinders seem to last much longer in our humid environment here, but I have had a time getting everything bled. Also, what about the master cylinder?
If really gummed up (or swollen rubber) the return spring will not push the piston back all the way to fill the cylinder.
George Butz

I can't solve your problem, but I can commisurate in a related LBC. When I re-did my 64 Mini van, I replaced every component of the braking system, including the steel brake lines. I also upgraded by adding a vacuum servo booster. (I have subsequently added the same booster on my TD, but that is another story). The Mini has twin leading front shoes, just as in the TD. I replaced the brake fluid several times (non silicone) and bled the system every way I could think of, including jacking up the front, then jacking up the back, all chasing suspected air bubbles. My symptoms are persistent, and the same as yours. I get pedal travel almost to the floor on first pump, and second pump is short and firm. If I adjust to the point that each wheel drags, pedal travel is reduced for the first pump, but nothing eliminates the dramatic difference between the first and second. Responses to my numerous postings in the Mini world always come back to the suspicion of air in the system. I had not considered the possibility of air in the cylinders themselves, and may try that as another solution.

Andy Moyce
52 TD
64 Mini
Andy Moyce

Hi Paul, I would assume that there is some air left in the system. I have never had any problems with bleeding T Type brakes. Do you use a piece of clear plastic pipe attached to the bleeder nipples ? This is a pretty good way of judging whether any air remains in the system. The wheel cylinders are designed to bleed automatically as the bleeder nipples are on top and should not need to be individually filled. The only point that I can add is to check that you did assemble the wheel cylinders the correct way. I think from memory that it may be possible to bolt one or more upside down. This may make it impossible to exclude all the air. I f this is not the case, I would look at the master cylinder. Good Luck, Paul.
Paul van Gool

Paul:

Another possiblity: There's a small rubber cup inside a steel cup at the very front of the master cylinder.
It's supposed to keep some pressure in lines and also keep all of the fluid from returning to the reservoir from the wheel cylinders. There's also a small O ring that the steel cup sits against at the very front of fthe master cylinder's bore. If they're not functioning correctly the system will pump up as you describe.
Blake

Paul, It is very possible that your master cylinder is "passing" Sometimes a small pinch or cut in the seals causes the problem. You can pump up the petal but if you apply pressure, not necessarily hard but constant,the petal will continue to the floor. If that happens the master cylinder could be your culprit.
Dan H.
Dan Hanson

This thread was discussed between 10/01/2000 and 31/01/2000

MG TD TF 1500 index

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