Brake bleeding problem

D

Don W/Norfolk

Senior Member
I have a brake system bleeding problem. I’m out of ideas and need help. (My wife says I need help even why I have ideas, but that is beside the point…)


New system installation in a ’40. Running a Corvette dual master cylinder, residual pressure valves fore and aft, discs up front and drums on the 9" rear. All new lines, calipers, and wheel cylinders. Bench bled the MC before installation.


I intentionally left the right front and right rear lines “cracked”, and after topping off the MC and pumping the brake pedal, I observed fluid at those two corners.



At that point I stopped pumping the pedal and switched to a vacuum bleed system with a Mighty-vac pump. Starting with the bleeder closest to the MC (the lf), I’ve sucked a lot of air and little fluid. Can’t get to a point where it is even 50/50 air/fluid.



I’ve checked all the bleeders closed tight, pumped the pedal and do not observe any leaks (put dry paper down and left overnight – no spots).


All suggestions for a course of action are welcome. dw
 
Why not just bleed conventionally?

I don't know anything about these vac thingies but i suspect they'll do a great job of sucking air in around the bleeder threads and out through the bleeder, which of course might explain what you're experiencing.

I've had good experiences with the air fed pressure bleeders but strangely i always resort to the good old manual method.

Chris
 
I agree with Chris. I have tried several of the "new" ways of bleeding but have settled on the old way with the exception of having a helper. I originally had a "one man brake bleeder fro NAPA that is a plastic bottle with a magnet attached so it can be held above the bleeder valve. Also has a clear tube with several "ends" to push into bleeder valves. Then you simply pump pedal up, go to the bleeder valve and open the valve and the air is released up into the bottle. Once there is no more air bubbles in the tube, that brake is done. I was in Harbor Freight and saw the same thing for cheap so I bought four new ones and put one on each bleeder valve so I don't have to move one around. This works very well for me.
 
If your mc is under floor,try and get the wheels lower by jacking up.
Adjust back brakes.What I do is just crack the bleder little and pump about 10 times when you see if on floor ,let it run by graity and close.Then do others the same way.
I have a Mustang MC with adjustable valve in back.Don,t let MC run dry keep filling,and only push pedal half way down.
 
i found on my 39 when i put all new everything on it, (all stock) it took awhile to get all the air out, just patience, which i dont have alot of. :)
 
I was told to start at the wheel fartherest from the MC. Then work back. Daddy said to do it that way when I did my first brake job as a teenager... a loonngg time ago!
I don't know if that will make any difference.
Keep in mind that the system could have gotten air back into the lines between the time you let off the brake the last time and then got to each wheel to close the bleeder.
If you are working alone, (aren;t we all?) you might want to invest in the new one way bleed valves that are available in most auto parts stores now. I've not used them but understand that they replace the usual bleeder and will only let air and fluid out and not allow air back in. When finished, you tighten them and leave on the car.
I hope this helps.
Keep working,
Al
 
Have virtually the same type system in mine and had some of the same problems bleeding. After installing Speed bleeders the problem went away.
 
Not that it will affect your bleeding problem but I don't think you want residual
pressure valves on the front disc brakes.

Bob
 
The vacuum pump is where you went wrong. Do it manually. Get your wife to help. She can push the pedal when you tell her to. She won't even get dirty.
 
Cracked new fittings are nortories for allowing air to be sucked in. We always ASSUM that every fitting we did is perfect. The other thing you can do is to remove the the bleeder and put a couple wraps of of Teflon tape on. This way, if the threads are leaking air it will seal the threads.
 
51 MERC-CT said:
Read the first post, he said he bench bled it.
Click to expand...

That's funny... I read about leaving lines "cracked" and topping off the master cylinder but, I didn't see about bleeding the master cylinder before it was installed? (By the way, I've never done this myself, so maybe I'm way off base.)
 
sounds just like the setup on my 47 merc.corvette style dual m.c.lid didn't match with the hole in the floorboard,so I got a remote fill,mounted on inner fender,under the hood.No luck bleeding,I think partly because the lines are higher where they split for the front brakes,and the calipers are lower than the lines.I got an $8 walmart pump sprayer,removed the wand,and hooked it to the remote fill hose.I now have about half a pedal as opposed to no pedal.I want to adjust the freeplay,and bleed again with more pressure.I was afraid to blow the hoses apart last time.
 
If you "cracked" the rf and rr bleeders and left them like that to bleed the other side, aren't you sucking air into the system via the "cracked" bleeders when you let up on the brake pedal?
 
Just a follow up post.
Thanks to all who offered suggestion. The final solution was a combination of several.
Replaced a defective copper washer at the left front
Installed "speed bleeders"
Pumped, pumped, and pumped some more
Finally have a pretty firm pedal. Want to go round one more time after letting it sit overnight to make sure I've got it all.
Thanks again for all the help.
dw
 
OK! Great! Now when are you and your lovely wife coming to Smithfield for some ice cream?
I knew you could fix it.
Keep working,

Al
 
Hey Don,
Thanks for the update! Good on you for figureing it out! Today, I am at the same situation that you have evidently solved. Started at the furtherest whl cyl and worked to shortest line. Only thing, so far, is a LOT of air, no pedal and an 'asistant' that quit on me and threatened to do harm to the car,etc. Huh, I told her to do her best, as the guy who put this abomination brake system together....had already done the dirty work!!
Hm, since she quit...those bleeders sound pretty good!
 
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