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MG TD TF 1500 - Brake problem

Working on the brake system of an mgtf 1250. I have carefully replaced all wheel end components including pads, cylinders, and everything is adjusted so one more click and you can't turn the wheel by hand. I did not replace the flexible hoses because they look relatively new and they show no signs of expanding with brake pressure. I disassembled the master cylinder, honed the cylinder and installed replacement rubber components correctly (checked more than once). I bled the entire system at all wheel cylinders (more than once). If I press the brake pedal it goes nearly to the floor if I release and press again it goes halfway to the floor and never gets better than that. When I drive it the brakes are functioning after a pump but are weak. I did not bench bleed the master cylinder! I am not sure it is necessary but I will try that next. The pedal does not creep lower with pressure. It seems like there is still air in the system but I am not getting any out at the wheel cylinder bleeders now. The last time I did this with my other TF the same procedure was successful. Has anyone had this problem or have ideas as to what to try. I think it is air so I am reluctant to buy a new master cylinder or flexible lines.
BEW Brett Wright

I had a similar problem on my 51 TD when I replaced the wheel cylinders. I couldn't get rid of the air in the system. I solved it after much head scratching by removing the brake pipe from each wheel cylinder in turn and injected brake fluid into the wheel cylinders with a hypodermic syringe, replaced the brake pipes, and bled the system as normal.
It worked for me, give it a go!
R Bowden

Try slacking off the adjusters one at a time. I think the air compresses in the cylinder and forces out the fluid. I use a pedal pumper (her indoors) and release the bleed screw with pressure in the system. The movement of the piston seems to clear any air from the cylinder. I always have a solid pedal this way.
Ray TF 2884
Ray Lee

Bleed the system one more time. Start at the wheel farthest from the master cylinder and then work the to the ones closest to it. The fronts will be the most difficult due to the design of the cylinders.

Just my two cents.
MG LaVerne

Thanks for the ideas so far. Keep them coming! I did bleed furthest first to closest last. I like Ray Lee's suggestion. I will try that next. Has anyone ever had any trouble with the Master cylinder or know that it requires bench bleeding. The manual sure doesn't call it out as necessary.
BEW Brett Wright

Ray Lee is absolutely correct. I had the same problem and found that I had to fill the front brake cylinders manually to correct it. In particular, the cylinder that does not have the flex hose directly to it will often get an air in it if it is installed completely empty. Cheers - Dave
D W DuBois

Since you mentioned the brakes feel weak, once you get pressure, make sure your front wheel cylinders are also right side up, so you have four leading brake shoes. It is possible to assemble them with four trailing brake shoes.
Dave Braun

Good call on reversing front shoes but I know I have that right(checked it over and over). I think the weak brakes are from compressing air somewhere in the system.
BEW Brett Wright

There's a simple technique to eliminate questions about the master cylinder. Create a brake line plug by cutting off a short piece of brake line and brazing the tube closed. Remove the short piece of brake line from the adapter at the output of the master cylinder. Insert the plug. You should now have an absolutely solid brake pedal once the initial mechanical slack is taken up. If it's not hard as a rock you have something wrong inside of the master cylinder. Fix it. Bud
Bud Krueger

Will a Mighty Vac device work to draw a vacuum on the wheel cylinder bleed screws and in so doing draw fluid down from the lines? Some Mighty Vac sets come with a small container to accept the fluid as part of the kit.
John Quilter (TD8986)

NO. The system design doesn't allow that. Bud
Bud Krueger

But you can use a pressure system. I made mine out of an old weed sprayer fitted with a pressure gauge. The exit pipe is attached to a pipe soldered into a spare master cylinder cap. Pressurize the pump and crack each bleed nipple in turn. Works a charm.
Lew Palmer

I had the same problem after renewing everything including the master cylinder. Solution was same as Ray Lee describes above. However, I also found that if the car is not level (mine was jacked up quite high at the front) I could not get all air out of the system - something to do with the design of the master cylinder return flow release hole I think. Once car was level, all air expunged and pedal hard after only an inch of travel.
N D Wallace

I've just replaced all the wheel cylinders and brake shoes on my TD prior to a trip to Italy and the Stelvio Pass! I used a gunson Pressure Bleeder and drilled and tapped a hole for the adapter in an old master cylinder cap. Using the pressure from the spare wheel, bleeding the brakes was simple, one handed, and quick. Certainly the way to go in my opinion.
Mike Christie

I have made good progress with the cumulative suggestions. I was able to get most of the air out by the suggestion of backing the adjusters off and bleeding. The problem is definitely in the wheel cylinders and is up front. I will arrange for the pressure bleeding to get the rest. At least I can stop the car now. I might drive it a bit and re-bleed. Thanks again for all the great comments!!!
BEW Brett Wright

This thread was discussed between 25/08/2014 and 26/08/2014

MG TD TF 1500 index

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