[BobHalfa]

Tried to search this but wasn't successful: how do you bench prime a brake master cylinder before installation? Previously, on other vehicles, I would mount the cylinder and connect the lines and have someone push the pedal down as I loosened the lines and repeated that process till no more air came out and would then go to the wheels. Is there a better way?

 

[Andrew]

Put fluid in the gravity reservoir ports and work the piston with a screwdriver, etc. til fluid comes out the pressure ports. Can be done with or without the reservoir. It's not essential, but it helps get the fluid moving quicker once you install the MC. It's not really any different from doing so on the car, other than you're "bleeding" the MC with no lines installed, so (1) you confirm the MC works, and (2) it's a very short route from inlet to outlet.
Andrew

 

[Dragline]

A recent discussion here.

 

[Dragline]

Why is it stated that MC bench bleeding must be performed prior to installation?

Good question. Air trapped in front of the front piston seems to be the trouble.

To me, assuming that the MC is good, it doesn't matter whether the MC is bled on the bench or in the car as long as its front is slightly elevated when doing so. If it's in the car, raise the front when bleeding the MC and then lower the front and raise the back when bleeding the system. If the back end of the car is raised for system bleeding and the MC has not been bled nose up previously, the MC pointed downward is less likely to allow the trapped air in front of the front piston to be release.
$0.02

 

[vf31rhill]

Harbor Freight Tools sells a suction bleeder which you attach to the fartherist away cylinder. It has a small resiouvor (sorry, I can't make my spell check recognize this word for spelling purposes) which captures the fluid you draw through the system. One person can bleed the system without any problems. This rig costs around $40.00 but I bought mine on sale for $25.00. This is the best way to bleed brakes that I have ever seen. For good measure you can keep adding new fluid to the master cylinder resiouvor and make the rounds, bleeding out the whole system and in the process you will be replacing all the old fluid with new.

Robert Hill in Memphis, Tn

 

[60sRacer]

I've had plenty of problems with vacuum bleeders over many years. Got a pressure bleeder and have loved it.

Brake Bleeders and Brake Tools | Simplifying Service | BrakeBleeders.com

Robert

 

[jcslocum]

Bob,

I clamp the ear of the MC in a vise, fill the rez up and pump with a screwdriver in the push rod hole. Phillips fits best since it's round. I put 2 foam ear plugs in the fluid line connections after they have been covered with a little bit of Saran wrap. Place a pan under the MC to catch fluid and push the screwdriver in and out. This will expel the air in the bores. The ear plugs will keep the fluid from running out all over when carrying the MC around the shop. Install and bleed the system

Only use new fluid.

 

[BobHalfa]

Thanks for the advice. I'll tackle it on Sat. afternoon and report my results...Bob

 

[BobHalfa]

I bench primed the master cylinder as described above and that part worked out fine, but I'll never do it again. I had trouble getting the two front brake lines to thread into the master cylinder and lost all of the fluid out of the reservoir before I could get the lines started in by hand. It just created a big mess and I had to resort to my old way of filling the reservoir and bleeding the lines at the MC and then onto the wheels.

 

[papajam]

Here's a little trick.
Install the lines into the M/C by hand BEFORE bolting down the M/C. This allows one to move the M/C around a bit to obtain proper fitting alignment. It also eliminates the risk of stripping a fitting.

 

[Gubi]

For the record, the one time I installed a new MC I just installed it dry. Loosened one fitting at a time at the MC and had someone pump the pedal a bit to purge the air from each, then bled at the wheels normally. Had no trouble getting a firm pedal.

YMMV.

 

[60sRacer]

There are many tricks we've all developed to deal with the difficulties of bleeding the brakes. Then I got a pressure bleeder, and now I wonder why I suffered in the wilderness for so many years.

Robert