M/C bench bleeding

[Chumley]

I just got a new (rebuilt) master cylinder with the two bleed screws on it. Can I "bench bleed" it with it installed on the car? What is the procedure using these screws? ( I don't have a vise or a bench) Thanks, chumley

[Modern Motoring]

best bet is to purchase a m/c bleed kit. It's two plastic tubes and a few fittings. The tubes run back into the top of the master. Protect the entire area around the m/c as brake fluid is harmful to paint and bleeding the brakes tends to make it go everywere!

[ijasond]

just make sure that the new master cylinder is level when you bleed it the first time. use a jack to raise the rear end & put a level on the master cylinder.

[joe_padavano]

Originally Posted by Chumley

I just got a new (rebuilt) master cylinder with the two bleed screws on it. Can I "bench bleed" it with it installed on the car? What is the procedure using these screws? ( I don't have a vise or a bench) Thanks, chumley

If the M/C has bleeder screws, you don't need the bench bleed kit. That's for M/Cs that don't have bleeder screws and thus includes fittings to screw into the M/C ports. In your case, simply connect a piece of vacuum tubing from the bleeder nipple back into the reservoir.

[Chumley]

I got one of those Mity-Vac kits for do it alone brake bleeding. I hooked the pump hose to each bleed screw and pumped out fluid while tightening the screws. Do I still need to run the tube into the reservoir? The instructions with the pump did not address M/C with bleed screws. Car has ben sitting for about 3 weeks since I bled the system. Hope to get to it this weekend to see if I was sucessful. Thanks, Chumley

[ijasond]

the purpose of bench bleeding is to ensure that there are no air pockets trapped in the master cylinder. There's no reason you can't "bench" bleed the system after it's installed in the car, just make sure that the cylinder is level when you do it. If it's not, air could get trapped in the corners of the ports, only to be fed into the system later. Level level level, it's crucial in a new system.

[joe_padavano]

Originally Posted by Chumley

I got one of those Mity-Vac kits for do it alone brake bleeding. I hooked the pump hose to each bleed screw and pumped out fluid while tightening the screws. Do I still need to run the tube into the reservoir?

Nope. You did fine.

[joe_padavano]

Originally Posted by ijasond

the purpose of bench bleeding is to ensure that there are no air pockets trapped in the master cylinder. There's no reason you can't "bench" bleed the system after it's installed in the car, just make sure that the cylinder is level when you do it. If it's not, air could get trapped in the corners of the ports, only to be fed into the system later. Level level level, it's crucial in a new system.

You're absolutely correct. I'm waaay to lazy to bench bleed my M/C, so I usually just crack the flare nuts on the lines into the M/C and let the fluid dribble out of there first (with appropriate rags in place to catch the fluid).

Of course, that was before I got my pneumatically operated vacuum brake bleeder. This is perhaps the BEST tool I've ever purchased. It uses shop air (run through a venturi) to create a vacuum for bleeding the brakes - sort of a MityVac on steroids. Plus, there's no pumping, since that always seemed to allow air back into the system between pumps when the tube doesn't seal completely on the bleeder screw.

Oh, the best part is the brand name of the bleeder - Vacula (I'm not making this up).

http://www.vacula.com/

These things list for over $150, but I found mine at a swap meet for $15.

[Bubba57]

I agree with Joe, Vacula is the way to go when bleeding brakes. I restored a '72 Cutlass a few years back and replaced all brake likes, wheel cylinders and Master Cylinder. It literally took all of about 15 minutes to bleed the complete system. Beats hell out of laying under the car getting soaked with brake fluid...l