Bench Bleeding a new Brake Master Cylinder
 

Does anyone know how to do this? My ASE Certified Brother-in-Law (Who Hates Me) said that I have to "Bench bleed" my new brake master cylinder before I install it into my '80 RX-7. He says that if I don't, installation is a royal pain in the ass... Anyone have a clue as to how to do this?

Thanks in advance!

I fill the cylinder, hold it over a bucket and take long screwdriver and pump the hell out of it - about a hundred times.

Sometimes instructions come with the new master cylinder. Its pretty easy, put it in a vise, fill with brake fluid, and pump the piston with something like a screwdriver until fluid comes out the brake line holes, than cap them.

To the best of my knowledge, the theory of doing this is to basically avoid bleeding the rest of the system.

I've always done the same thing - first make sure you can get all the bleeders open on the car. Bench bleed the master until fluid comes out. Mount the master in the car and connect the brake lines. Bleed the whole system in this order - RR, LR, RF, LF.

This way you wind up all new brake fluid. Since brake fluid should actually be replaced about every 2 years, replacing the fluid completely is a very good thing. Just make darn sure you can get all the bleeders open before you start. You should need about 2 bottles of fluid, or slightly more.

I did NOT bench bleed my MC when I rebuilt it. Normal bleeding after installation was fine. I do not quite understand the need for that procedure. I doubt they do it at the factory.

Perhaps like Whanrow said, it may eliminate the need to bleed the rest of the system. But if you are changing a MC on an older automobile, bleeding the rest of the system and getting new fluid in and the old out seems to be the proper thing to do.

On an 80 you really don't need to because the MC has a bleed screw on the side of it that you can used to get the air out of the MC. In fact bleed the MC first, then proceed in the order that Whanrow suggested. Sometimes the brake bias valve gets stuck and you won't get pressure to the rears, you have to get it freed up first by pumping the brakes a bit. The FSM describes this I think.

the FSM does not state anything about bench bleeding. i would think it would be a good idea, but not completely necessary.

here's the page in the FSM:
https://img221.imageshack.us/img221/...sc047010nk.jpg

I just did this last week. I did not bench bleed the MC I just installed the MC filled it with fluid then opened the rear brake bleeder ( see this thread for bleeding details https://www.rx7club.com/1st-gen-archive-71/brakes-tip-bleeding-brakes-526213/ ) Note I have rear drum brakes and the bleeder valve was on the passenger side of the car. I did read that you should NOT press down on the pedal all the way when pumping the brakes to bleeding the system. The MC bleed valve on my MC was on the bottom of the unit making it useless thus I never opened it. After bleeding the rear I did the fronts in the order listed. I agree with the other the bench bleeding is a trick done to allow you to not have to bleed the entire system but the brake fluid should be replaced anyway so I would not take the time to bench bleed the MC. Also there are some good threads on the subject if you search for master and brakes.

Good luck

I bench bleed rather the manual says to or not. I hate air bubbles with a passion. And now that I think about it I should convert the 7 to air disk brakes.

I’ve done brakes for 25+ years, although I’ve never changed an FB MC. Bench bleeding a MC takes me less than 5 minutes and it’s done to limit the amount of air brought into a system. I have bench bled an MC and installed it without bleeding the rest of the system, but that is not the proper way to install one. To bench bleed an MC you want to fill the reservoir with fluid, cover output ports on the MC with your fingers, and pump the MC. Covering the output ports will draw the fluid into the MC cylinder much faster than if they are left open. Make sure the output ports on the MC do not point in the direction of your car while bench bleeding. You’d be surprised how far the fluid will travel, and if given the opportunity, it will shoot across the garage and into your paint job.

My setup while benchbleeding a new MS. Pic about 2/3 down the page on the right:
http://www.negative-camber.org/crispyrx7/929.htm
HTH,
Crispy

Bench bleeding makes regular bleeding easier and shorter, especially for the clutch MC, which can take a lot of time if you don't bench bleed.

I just install the MC, but do not connect the lines. Fill with fluid, and wait. After a few minutes, fluid will start to drip from the holes where the lines attach. At that point, I attach the lines, and bleed the system.
I do this for 2 reasons. 1. The MC has no fluid dripping from it when I am mounting it, or as I am moving it over the paint. 2. I can easily place a rag under the MC to catch the drips as I am attaching the lines.