[berrygoat]

Hey Gang,
I'm changing out the Master Cylinder on my 69 GTO to the correct double bail one with bleeders instead of the later rectangular one that is on there now. I have never done one of these with the bleeder screws. Do I need to bench bleed it or can I bolt it up and bleed back into the reservoir using the brake pedal from the bleeder screws ? Thanks !!!!

[Verdoro 68]

Do it on the bench. The cylinder needs to be level to get all the air out.

[Txbobcat]

Easier to bench bleed than bleeding the brakes and sometimes you wont need to bleed the brakes.

[berrygoat]

Originally Posted by Verdoro 68

Do it on the bench. The cylinder needs to be level to get all the air out.

Using the bleeder screws or the tubing outlets ?

[Simple Man]

I would use the tubing outlets. Used to be, when you bought a MC, they would give you a couple of plastic fittings, and some plastic tubing, long enough to reach back into the reservoir. It made bench bleeding pretty easy.

They probably don't include those anymore.

[geeteeohguy]

The easiest way to do it is on the bench. I always back flush mine and never need to bleed the brakes. I fill the MC about 1/3 full, and while it is level and in a vise, I take a syringe filled with brake fluid and inject fluid into the outlet ports. You will see bubbles at first, then a solid stream of brake fluid. Do this at each port, and bolt it on the car. Done. Takes less than 5 minutes and works every time. No need for tubes, pumping, etc.

[pressgod1]

ditto...bench bleed first!!

[im4darush]

Or you could buy a vacuum pump / bleeder and do the whole system. Pretty cheap these days. Nothing eats paint like brake fluid.

[69lm69gp]

First time I ever replaced a master cylinder on a car (my 69 GP) I didn't know to bench bleed it. So after a couple of hours pump it/hold it and head scratching I brough the car to a local tire/repair shop and they pressure bleed the brakes. I got a job offer out of it for a full dollar an hour more than I was making at Sears at the time. Started as a tire changer the next week.

Now I always bench bleed. Why add more air into the system then you need to?

[GRX]

Here is how I bench bleed my master cylinders. Hose, clamps, and a couple lengths of hard line. I like to use the catch jar so it's easier to see bubbles and prevent them being pumped back in.

[Keith Seymore]

The last one I did ('2000 Tahoe, aluminum m/c with plastic reservoirs) the manufacturer recommended bench bleeding by gravity bleeding.

Seemed to work well (there was brake fluid running all over the place by the time I was ready to install it).

K

[GPMESQ]

Originally Posted by im4darush

Or you could buy a vacuum pump / bleeder and do the whole system. Pretty cheap these days. Nothing eats paint like brake fluid.

Mighty Vac allows all manner of bleeding without any help...used it on the master while bolted up on the car to the booster too...works like a charm...

[cuz68]

What do you all use as a plunger?

[GPMESQ]

Originally Posted by cuz68

What do you all use as a plunger?

You just attach the hose to bleeder, pump it up and open bleeder...no need for someone to pump pedal; attach it to MC bleeder and do the same...the vac draws fluid into a holding reservoir...just dont let the MC go dry...