Trouble bench bleeding my master cylinder

[95RedCobra]

First of all, do you really have to remove the MC from the car to 'bench bleed' it?

This is in a '66 Mustang.

I have a dual MC for front discs and rear drums with a smallish vacuum booster. I have a simple bench bleed kit hooked up with clear plastic lines running from each output port back into the cooresponding reservoir.

What's happening is that I am seeing bubbles come out of the rear-most port(the one for the front brakes) on every stroke. Then when I release the pedal there are bubbles coming out of a small hole at the rear of that reservoir on the last little bit of pedal movement.

I've pumped the pedal 50-60 times and the same thing is happening everytime.

Anyone have this issue? Why won't the MC bleed properly?

 

[68RCodeConv]

Here's what I do (MC on the car). You will need a helper.

With fluid in the MC AND THE CAP ON have somebody step on the brake pedal and hold pressure. Slowly loosen one of the brake lines just a little. You chould have a big, absorbent rag around the fitting before loosening. The air will bleed out, followed by brake fluid. Tighten it back up snug. DO NOT RELEASE THE BRAKE PEDAL until the fitting is tightened back up. Pump the pedal a couple of times and repeat until nothing but fluid comes out. Do the same thing for the other fitting making sure that the MC does not run out of fluid.

This has always worked for me.

 

[Steve S]

Hi there,

I had plenty of trouble getting mine bench bled in the car, aparently it can be done if you get the MC level by jacking the car. I pulled mine and did it on the bench. It took many pumps, i wonder if you are allowing air back into the system with the setup you are using for bleeding.

I made up my own bleeding set with some old brake lines / fittings and some clear hose method b (See attached distructions).

The other trick is to not pump too fast, this foams the air up, if you bleed it on the bench it must be level.

I got through 1/2 a box of beer while i was doing this, for best results take your time .....



Steve

 

[Rusty67]

I had plenty of trouble getting mine bench bled in the car, aparently it can be done if you get the MC level by jacking the car.

This is correct. If you jack the rear end of the car up high enough to make the MC level then you can bench the MC in the car, I have done this and it does work. Its best to just bench the thing before it finds its way into the car but some times that just doesn't happen.

 

[D.Hearne]

If it's going to be some length of time (like months) before you drive the car, just let the thing sit. I did this (by accident) with my 77 Comet, went from power brakes to manual, changed two lines at the master cylinder and the M/C, it sat for at least 6 months before I drove the car. Never had to bleed it, apparently all the air worked it's way to the M/C and was released to the reservior when I did try the brakes.