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MG TD TF 1500 - break bleeding

I'v read many threads about break bleeding problems and methods. It appears that air bubles may be trapped in the wheel cylinders even after using the bleeders.

A detailed study shows there are several high points in the tubing that may also trap air even after using the wheel cylinder bleeders.
- front flexibles
- tubing between the two front wheel cylinders
- relaxation loop for the rear break plates

I guess that actually, air is not trapped in those points because it is pushed down by the fluid thanks to the quick depress of the pedal during the bleeding process. It might not be expelled if you are not quick enough on the pedal?

But air is trapped in the upper part of the wheel cylinders. Not all cylinders.
The cylinders are all oriented to have the bleeder on the upper side except the rear cylinders of the front wheels. I think that those two are particular culprits for bleeding problems. The best way for bleeding would be to remove the upper shoe and let it gently expell air till liquid overflow.

Another consequence of this break disposition is that the 4 other cylinders are never empty when renewing the fluid for regular maintenance. Chances are that the liquid inside these cylinder is never drained.

The debate is open.

Laurent.


LC Laurent31

I agree Laurent, bleeding is difficult. I agree the wheel cylinders should be hand bled off the car or If on the car, before the Lines are connected.

Some how, either off or on the car, the piston should be compressed, then fluid sucked into the void under pressure causing the piston to expand. (Need to have a way to stop the piston from pooing out.)

The piston, should be compressed again, fluid sucked in, repeat until no air,

Perhaps a short length of old brake line with clear hose attached could facilitate this.

I also feel that the brake line between the front, front and rear pistons should be bled separately, by cracking the rear compression fitting open while an assistant puts pressure on the system.

After spending a lot of time and DOT-5 just getting my system tight, I am reticent to loosen anything, but I am going to try bleeding the front to rear lines, next time I have a "helper"


Jim B.
JA Benjamin

I think you guys are overthinking this. Lots of brake fluid, a clear tube, a big Mason jar and a helper to spot bubbles or lack thereof is all that is required for the initial bleed.

The biggest hassle is filling the master cylinder constantly without getting brake fluid where you don't want it and visualizing the level are my biggest complaint. But getting old and less flexibility has exacerbated that.
Christopher Couper

If you have an old master cylinder cap it can be modified to stop air entry while bleeding,
Remove the internal baffle,tap a connection into the vent hole, fit a plastic tube, fill the M/C to the top and fit the cap. Dip the tube into a full container of fluid and pump away, the fluid will be replaced by vacuum.
This is what I did for 40 years until I fitted a remote reservoir and have always had a solid brake pedal.
Ray TF 2884
Ray Lee

I had real problems bleeding the brakes on my TF. My wife was getting tired of pressing the brake pedal and I hated being drenched in brake fluid - horrible stuff. Eventually I was told, possibly from this forum, to lock up the adjusters on the shoes before bleeding. The job then took five minutes.

Jan T
J Targosz

Chris is right. Two suggestions: if using Dot5, it bubbles when you pour in to the MC. Pour in very slowly to avoid this. With the Dot 5,I do tend to have a bit of spongy feel likely to bubbles trapped as above. If I re-bleed in a day or two, this seems to fix and all is perfect. George
George Butz III

When I am filling a new system, I fill the system from the wheel cylinders by pushing the fluid back under pressure toward the master cylinder. My bleeder has a bladder in it, air on one side and fluid on the other, only takes a pound or two of pressure. As the master cylinder fills up, the fluid has to be sucked out as not to overflow. I have various caps for the MCs to automatically dump the overflow in a container, but none for the MG units. Be easy to make one, just never did. PJ
PJ Jennings

Apart from your many ideas for bleeding, any thought about the pipe high points or the cyclinders that are never drained when flushing the liquid ?

Laurent.

LC Laurent31

the high flow rate in micro bore pipes moves the air to where it can be vented.
If I clamp off all three flexibles I have a rock solid pedal,so no air in system.
Ray TF2884
Ray Lee

This thread was discussed between 24/07/2018 and 27/07/2018

MG TD TF 1500 index

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