Bench Bleeding Master Cylinder Question

[DevilDog Aggie]

I know the procedure for bench bleeding the MC. I had a thought over the weekend and wondered if anyone had tried it before. My thought rather than having to release and cover the ports when pushing/releasing the piston, would it not be easier to put the MC into a "bath" of brake fluid that covers the ports and do it that way? Then you don't have to worry about air being sucked back in. The bubbles would float out on the push and clean fluid would be pulled back in on the release. Just keep repeating until no air bubbles are coming out?

I know the MC will be covered in fluid when done, but clean up is easy and brake fluid is cheap.

Pros/cons???

[LEEVON]

That might work, but I have a kit with a couple of plastic fittings and 2 lengths of clear hose and a clip for the reservoir to hold the hoses in the fluid. Done in 10 minutes with the m/c level on the truck last week. I just have somebody slowly press the pedal while I monitor the air. If your hood is off you and you can see the hose it's a one person job though. Same concept but easy and cleaner.

[LEEVON]

This:

[DevilDog Aggie]

Originally Posted by LEEVON

That might work, but I have a kit with a couple of plastic fittings and 2 lengths of clear hose and a clip for the reservoir to hold the hoses in the fluid. Done in 10 minutes with the m/c level on the truck last week. I just have somebody slowly press the pedal while I monitor the air. If your hood is off you and you can see the hose it's a one person job though. Same concept but easy and cleaner.

Cool! Where did you get the kit? My new booster/MC/prop valve arrive today and would like to work on it tonight.

[GRX]

$15 ... two flare fittings, two short lengths of pre-flared hard line, two hoses .... you get the picture

[DevilDog Aggie]

Originally Posted by GRX

That's a simple setup! Hadn't thought about that. Was thinking it was going to be more of a pain in the rear. But between yours and Leevon's set ups, that is much better than my plan in my head! Thanks guys!! Knew I could count on y'all!

[mr48chev]

That's a slick setup GRX and one I never thought of. I've got a batch of the plastic tubes and adapters that come with some of the master cylinders but that looks like it would be a lot simpler to deal with.

[LEEVON]

Actually I think it came with a power brake conversion my Dad got from CPP for his Nova. Before that I made one like GRX, except I just bent the hard lines over to the reservoir. I couldn't see the bubbles in the lines, but you can see them in the fluid.

[67swb72klb]

i havent bought a new master cyl in a couple years but they came with the plastic bleed kit last time i got one

[RichardJ]

This bench bleading, in most cases is over emphasized and has mythical status of its necessity and usefulness in helping to bleed the brake system.

Prior to the '80s almost all MC's were mounted horizontally. When they started to mount the MC at radical angles it became difficult to bleed the brake system after the MC was mounted.
Mounted horizontally the air will rise out of the bore as soon as the fluid is poured into the reservour. Mounted at an angle, a large pocket of air can be trapped and make it difficult to bleed.

I'm not telling you not to bench bleed a MC that is mounted horizontally if that's what you want to do. I'm just saying you don't need to make a big production out of it.
It is important to get the air out of the ports where the brake lines connect and no amount of bench bleading can help you there.

[GRX]

Everyone has their favorite technique. That set up is something I came up with on the fly about 25 yrs back when doing a complete brake overhaul on my '70 ram air GTO. Been using that technique ever since. You can bend the lines back over the reservoir instead but I find the bubbles easier to manage in the jar. Keep everything clean and dry & the fluid can be re-used.

Great post Richard. True about the air at the connection point. Which is why I always run enough fluid through the system to run any bubbles out. One should always flush the old fluid out anyway. Especially if the system is old. Those replacement one way "speed bleeders" make the job easy.

>> 67-72chevytrucks.com/vboard/showthread.php?t=502531

[DevilDog Aggie]

Thanks for all the great feed back everyone!!!

[bollybib]

Originally Posted by GRX

$15 ... two flare fittings, two short lengths of pre-flared hard line, two hoses .... you get the picture...

Good method. Next time I'll try doing it that way instead of dumping the lines back into the MC reservoirs.

[mahanian]

I bled mine installed on the truck with a kit similar to LEEVON"s. I put a bubble level across the MC and jacked up the front of the truck till it was level then slowly pumped the brake pedal till all the bubbles were out. Worked great!