Bench Bleed Master Cylinder?

[banderso]

I'm almost done getting my '45 MB on the road. I have rebuilt or replaced every part part of the brake system from the master cylinder to the wheel cylinders. Is it necessary to bench bleed the master cylinder? I don't really understand the purpose of bench bleeding. What does it accomplish that can't be done by just bleeding the brakes?

In the past I have always had someone pump the brakes to bleed them. Can I do just as good of a job gravity bleeding them instead? Do those vacuum brake bleeders work?

 

[5-90]

Yes, you do. The only other way to make sure you get all the bubbles out of the M/cyl will be with a pressure bleeder, which I presume you don't have.

Those vacuum bleeders work quite well - I've been using them for years. It's kinda nice not needing someone helping you when you bleed your brakes...

 

[92DripCherokee]

there are two other variations on bleeding, but I went with bench anyway. The bench method lets you tap on the MC to dislodge the tiny bubbles.

With the MC on the jeep, a syringe can be used to inject fluid into the front and rear ports (with a filled resevoir, shot by shot the air will displace out.)

A second method off the jeep, which might not work on a dual circuit, is "immersion bleeding". The entire master is submerged, and pumped under a bath of brake fluid. Very messy, but also the lowest tech method to ensure no air is trapped.

No matter what method, an MC bleed procedure is a must.

 

[banderso]

Alright, I'll do it then. Thanks. That's the answer I was expecting, but not the answer I wanted. I have not idea how I am going to get the master cylinder back on the vehicle and attach the brake lines before all the fluid drips out.

As for the the vacuum bleeders, can I just get a cheap one from the auto parts store? Or will some work better than others?

 

[banderso]

With the MC on the jeep, a syringe can be used to inject fluid into the front and rear ports (with a filled resevoir, shot by shot the air will displace out.)

Can't you explain this method a little further?

 

[four_shot]

get a few rubber pugs from the hardware store...use those in the ports and snap the cap for the resevoir on before installing the m/c and you should be able to keep fluid loss to a minimum.

 

[banderso]

get a few rubber pugs from the hardware store...use those in the ports and snap the cap for the resevoir on before installing the m/c and you should be able to keep fluid loss to a minimum.

Yea, I will. Thanks for the tip. It's just one of those things where it's kind of hard to get the brake lines to start threading in. It takes a couple of tries and a little bit of time. I'll get it to work though.

 

[92DripCherokee]

very little fluid will leak out, just enough to form a small bubble. The MC wont empty quickly, it has internal valving to stop that, it will just dribble slowly.

I cant recommend a pressure or vacuum bleeder, i used bench, gravity and speed bleeders.
Mity vac seems to be a favorite around Naxja.

 

[banderso]

Thanks to everyone for the quick replies. I should be able to get this thing done soon.

 

[Starboard M]

Sounds like you already did this, but heres a write up on how to bench bleed a MC.

http://www.custompistols.com/cars/articles/dw_benchbleed.htm


When I did my WJ booster/MC swap I bench bled them while they were in the Jeep. Seemed a lot simpler to me.

 

[Darky]

Interesting reading, but the tech hurt my eyes in here, the Non-Tech forum...:bawl:


Yeah yeah yeah...shut up, I know.

 

[banderso]

the tech hurt my eyes in here

I know, I know. But it's all non-XJ tech.:dunno: