Bench Bleeding Master Cylinder

[sworxx]

I have to install a new master cylinder in my 68 2000. It is the dual circuit type, and I wat to ensure I've done everything to rid the sytem of air. Anyone know the best way to bench bleed this MC successfully? Photos and diagrams mucho appreciated but not expected. Thanks. Happy Holidays!!

[S Allen]

Straight from the brake section on the main web site.

"Bench bleeding the master cylinder is highly recommended before reinstalling. Bench bleeding will remove the air and replace it with fluid. It is kind of a messy job but well worth the effort. Bench bleeding requires a short length of tubing with the correct fitting on one end (early) and two pieces for the later dual brake M/Cs. Remove the fill cap or caps. Install the tube or tubes routing the tube from the fitting back up into the reseviour as close to the bottom as you can get it. Secure the master in a vice so you have both hands free to begin pushing in on the rod. Put brake fluid in the reseviours being careful not to put too much in. Now begin pumping on the rod. Add fluid if you need to but pump until there are no air bubbles present. You can now install the brake master in the car. "

Good luck!

Steve

[sworxx]

Thank you, Should've looked there first.

[Guest]

Ok now I tried to follow the instructions for bench bleeding and I have a few questions. When you have it out of the car, how do you keep the brake fluid from pouring out the bottom where the lines enter the MC? I have a new MC and it has rubber plugs, but any pressure on the rod and it squirts out the bottom and shoots out the insubstantial plugs!! Any simple solutions to avoiding this?? Also the instructions don't even mention opening the bleeders or if there is a specific order for dual tank MC's. I just opened both bleeders and tried before I had fluid shoot all over the place!!!

He was right, it is kind of a "messy job"

[Minh]

Dunno if this is a solution, but how's about submersing the entire thing in a small bucket of fluid?

[Guest]

The quoted message says you need two pieces of brake line with the proper ends (threaded part that screws into the m/c). You route some rubber lines from that back into the m/c reservoirs so they squirt fluid back inside. Granted, when you put it in the car you'll have a moment when you disconnect that line and plug your real line in that spills some fluid.

Honestly though I've never bench bled and haven't had an m/c fail on me prematurely.

[S Allen]

When you bench bleed all you are doing is running fluid through the resevouirs. That is why you need the short brake lines hooked up to where you will connect them in the car and then route them back up into the resevouirs. You clamp the master in a vice so you can pump the rod to get the fluid moving.

I must admit I have never done this personally either and have never had a problem. I just do the normal bleeding sequence starting from the wheel furthest from the M/C and do the M/C last. A Motive Power bleeder is money well spent though. I just put the info on the site because many people swear by it.

How did you make out any ways?

Steve

[Fergus]

Okay, I've done it. First I tried a m/c rebuild kit, then 3 months later, when I was replacing my m/c, I went down to pick-a-part and found a single brake line from a 520 truck. (remember 510's are metric, not correct fitting). I cut the line in half, so now I had 2. I bent each into a 'C', and pumped until I saw no more bubbles. It is necessary because the bleeder on the m/c is between the lines, so it is only partially effective. Then, bolt it back in the car with the C's still on. Then ya fill the reservoirs to full, and you have to pull the C and install the line before the reservoir goes dry and sucks air. I wrapped the area underneath, making a trash bag into a tube for the drainage to go to the floor.
I am with Steve on this, it was only marginally better than the traditional bleeding of lines, long to short, then repeating, for a total of 3 times around. I honestly believe that using ramps under the back wheels when doing the back helps. Maybe this is because I am rather large, so I get better control on the bleeder screws, maybe it is the 'air bubbles float to the top of the system' theory I was thinking of at the time. Oh, and don't risk doing all this without first buying a really good quality flare nut wrench. The bleeder you strip will be your own.
Fergus O, with the brake fluid marinated forearms.