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MG TD TF 1500 - Flushing Brake Lines

I am in the process of rebuilding the brakes, all new cylinders, hoses, shoes.

I have flushed the front brakes by connecting a vacuum bleeder to bleed nipples, removing pipe from MC and adding a hose into a can of the flush medium. That all went smoothly after a little air was used to clean out a blockage.

Trying the same on the rear end now, can get air from bleeders to MC pipe, and from MC pipe to bleeders, but when I put the hose at MC end of pipe in the medium and apply vacuum, the vacuum disappears as I open the bleeder but no fluid is being sucked in.

Should I be trying to suck the other way. i.e. at MC end with hose on bleeder immersed in fluid.

I am cleaning out before going to Silicone fluid as the car will be laid up for 6 months per year.

Thoughts?

Thanks.

Peter
P G Gilvarry

I should also flush it with alcohol or acetone (the latter is preferable), then blow through with compressed air, and change the seals.
Dave H
Dave Hill

I am trying, but can't get it to flow. Trying from the other end first, will be using alcohol.

Thanks.

Peter
P G Gilvarry

If the bleeders are old and worn you won't get a vacuum seal because the bleeders leak down the thread. If you replace them with new and apply a little silicone grease, the vacuum will be restored.
Dave H
Dave Hill

It is more efficient to push not pull flushing solvents through your brake lines.A perfect vacuum only develops 14.7psi, not going to produce an effective purging action.
G Evans

Peter- you say "all went well until a little air used to clean out a blockage" Care to elaborate?

Has it occurred to you that your solvent used has created a blockage by swelling the synthetic rubber in the wheel cylinders?
Sam Coleman

That's not going to happen with alcohol.
Dave H
Dave Hill

Peter,
Not sure as I have never used vacuum method, is it possible that the vacuum is collapsing the rubber hose that connects the rear axle to the forward brake system?
I would assume you will be replacing that as well?
Rod.
R D Jones - Ex Pat

It doesn't collapse them and is only a partial vacuum. No need to replace the hoses, just flush them.
Dave H
Dave Hill

You got something stuck in there. Seen this many times with just regular pedal bleeding, when the wheel cylinders need re fitting. Usually is is very old degraded rubber bits inside the system. No damage blowing air instead of a vacuum at bleed nipple.
Duncan M

Or rust from the cast iron master cylinder.
Dave H
Dave Hill

Mystery is resolved. I had first removed shoes etc from front brakes, had drums turned/skimmed and flushed the front lines successfully.

Then I turned my efforts to the rear, no shoes in place at front, just drums and the old cy;linders.

Obviously when clearing a blockage using air I blew one of the front cylinders apart, albeit, it had not moved in 13 years. So when I was vaccuming I was getting air from an open cylinder in front wheel.

I have now completely rebuilt brakes, the pedal and pipes are original, well, they were repaced about 17 years ago. I have replaced master and all wheel cylinders, all shoes and hoses. New copper washers too.

Today I introduced DOT5 fluid into the system and with assistance bled the system, have good pedal, after the 5/8" of free play the pedal goes about 1.5" and all brakes work.

When the car arrived from Australia all the wheels were locked and I had to move it on dolleys, tonight it is on it's own wheels and rolling freely. Only the handbrake to adjust first thing tomorrow, then onto the electrics to see what works.

Very successful 2 days, tomorrow I clean the floor and move along....

P G Gilvarry

Good stuff. When you set the handbrake its a good idea to have both rear wheels off the ground so you can be sure that retardation on both is synchronised.
Dave H
Dave Hill

This thread was discussed between 30/08/2016 and 03/09/2016

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