Bench bleed master cylinder

[82DMC12]

Hey all, brakes on 11114 are totally apart and I am also replacing the master cylinder. I attempted to bench bleed the master cylinder by placing it horizontally in a vise as it will be installed, filling the reservoir up, then using a screwdriver to push in the piston. I covered the ports with my fingers while letting the piston back out. I succeeded in getting a steady stream out of the rear-most port but never got more than a dribble out the front. Since the ports are wide open was the fluid flowing out the first available port /path of least resistance due to proportioning or is something not right?

Andy

[Cory W]

I did my entire brake system, finishing about two weeks ago, and found the same thing with my new MC. I think it's a different feel due to the 50/50 proportioning for our rear-engined application.

I did what I could to bleed the MC (the same process as you, with the same result), then put it in the car and hooked the lines up. From there I followed the shop manual bleed procedure to the letter. Voila! Solid brakes on all four corners. With my new pads, rebuilt calipers, rotors, stainless braided hoses and new MC, it's better than they've ever felt in my (almost) 4 years of ownership.

I found it funny that the shop manual never specifically mentioned bench bleeding the MC, but being a shop manual I can only assume that it should go without saying.

[82DMC12]

Good to know it's not just me, but I think I read DMCH MC's are now the correct proportion? The ones with the DMC part # stamped are the correct type.

Actually, when I changed my own master cylinder I didn't bench bleed it. Didn't know that was procedure. Everything bled out fine.

Andy

[DMCMW Dave]

Good to know it's not just me, but I think I read DMCH MC's are now the correct proportion? The ones with the DMC part # stamped are the correct type.

Actually, when I changed my own master cylinder I didn't bench bleed it. Didn't know that was procedure. Everything bled out fine.

Andy

I'll probably start a religious argument here but I'm not sure bench bleeding is all that necessary on this car. You'll notice that on much older cars the master is sometime installed at an extreme angle which might tend to trap air inside at one end of the master. This one sits pretty level in the car (just like it would on the bench), so I'm not sure I see the advantage, other than the in-car bleed might go quicker. We pressure-bleed them on the car which gets fluid through the master pretty quickly.

[LEVY]

To me, bench bleeding on this particular vehicle is just a waste of time, as a matter of fact if you don' t know what you are doing it may do more harm than good.

LEVY

[David T]

I have done it both ways and it just seems to be easier if you bench-bleed the master first. I agree it is not much of an angle but it must be enough to trap a bubble in the front section. I use 2 short pieces of tubing and plastic fittings and shoot the brake fluid back into the reservoir. I pump till the bubbles stop. Too many times I mounted the MC and just couldn't get it to pump till I took it off and bench-bled it, so now I just do it before I install it. It doesn't take any more time and is not an "extra" step.
David Teitelbaum




To me, bench bleeding on this particular vehicle is just a waste of time, as a matter of fact if you don' t know what you are doing it may do more harm than good.

LEVY

[LEVY]

It might be easier for you because you already have your setup ready to go. For first timers it just might be easier to door on the vehicle.

I know, you are always right!

LEVY





I have done it both ways and it just seems to be easier if you bench-bleed the master first. I agree it is not much of an angle but it must be enough to trap a bubble in the front section. I use 2 short pieces of tubing and plastic fittings and shoot the brake fluid back into the reservoir. I pump till the bubbles stop. Too many times I mounted the MC and just couldn't get it to pump till I took it off and bench-bled it, so now I just do it before I install it. It doesn't take any more time and is not an "extra" step.
David Teitelbaum

[David T]

I may not always right, but I am never wrong! My advice is ESPECIALLY for the first-timers, I try to give everyone the benefit of my experience. That is what this forum is all about. It is no big set-up. You put the MC in a vise, screw in the two fittings and push the hoses on. Fill the reservoir, stick the hoses in to the reservoir and pump the cylinder till you stop seeing bubbles. A first-timer can get himself into a problem if he can't bleed the brakes and did not bench-bleed the MC. Now he wonders what he is doing wrong or maybe the MC is bad? From many owner's experiences bleeding the MC on the car does not always work for whatever reason. Bench-bleeding always works, that is why I recommend it. It is one less variable to have to consider when someone has a problem. BTW, my MC came with the hoses and fittings from Cardone. You can buy them cheap enough or make them up.
David Teitelbaum





It might be easier for you because you already have your setup ready to go. For first timers it just might be easier to door on the vehicle.

I know, you are always right!

LEVY

[LEVY]

David, that is the reason I believe bench bleeding is not for everyone!

Some one may do a bad bench bleeding then install and have problems, since you said bench bleeding always work, that person will get krazy looking everywhere and not finding the problem.

You may do a good bench bleeding but then do something wrong during the installation and get air back into the pump. Now, tell me that will never happen! That might never happen to you but, it will happen to others.

My best advice is, do a bench bleeding if you feel confident but never think that is a 100% assurance that your pump is airfree!

LEVY


I may not always right, but I am never wrong! My advice is ESPECIALLY for the first-timers, I try to give everyone the benefit of my experience. That is what this forum is all about. It is no big set-up. You put the MC in a vise, screw in the two fittings and push the hoses on. Fill the reservoir, stick the hoses in to the reservoir and pump the cylinder till you stop seeing bubbles. A first-timer can get himself into a problem if he can't bleed the brakes and did not bench-bleed the MC. Now he wonders what he is doing wrong or maybe the MC is bad? From many owner's experiences bleeding the MC on the car does not always work for whatever reason. Bench-bleeding always works, that is why I recommend it. It is one less variable to have to consider when someone has a problem. BTW, my MC came with the hoses and fittings from Cardone. You can buy them cheap enough or make them up.
David Teitelbaum