AndyBill402 Posted July 11, 2011 Share Posted July 11, 2011 I didn't know where else to post this question. I've changed out the master cylinder and the two rear brake cylinders. They were leaking. The front calipers are dry. I bench bled the m.c. I bled the brakes with a Phoenix DIY. All the air is gone. Still no pedal, no matter what I do. I thought it might be the booster because I do hear a hiss when I press the brakes with the engine off. Using my Mity Vac I pulled 15" of vacuum on the booster. After nearly 30 minutes it's still holding strong at 15". I presume that means my booster is good. The one-way valve is also good. I can blow air through it in one direction, but not the other. So, what's wrong here? I need some hi powered help. Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted July 11, 2011 Share Posted July 11, 2011 Proportioning valve?? Quote Link to comment Share on other sites More sharing options...
stangeba Posted July 11, 2011 Share Posted July 11, 2011 "No peddle" Do you have any sensation that the peddle will pump up or stop you at all? Is it like the rod fell out from the inside peddle to the MC? If the MC is a rebuilt unit, I would start there. Did you visually compair the two MC's and were they the same? Do you still have the old MC? Put it back on and try that. (I don't trust any rebuilt part done at a commercial re-builder) Bruce Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted July 11, 2011 Share Posted July 11, 2011 loose rear brakes will cause a low pedal too Quote Link to comment Share on other sites More sharing options...
Big Jim Posted July 11, 2011 Share Posted July 11, 2011 You may need to bleed the whole system. I think you have to do something at the proportioning valve to get them bled properly. Quote Link to comment Share on other sites More sharing options...
robs70monte Posted July 11, 2011 Share Posted July 11, 2011 Do the old 2 person bleeding one person holds the pedal while you open the bleeder then close it and then the other person pumps it up and holds it again while do the other side and repeat till you get a pedal Quote Link to comment Share on other sites More sharing options...
AndyBill402 Posted July 11, 2011 Author Share Posted July 11, 2011 There's a little "button" on the front of my proportioning valve. It's a factory valve. Don't I need to push in that button during any brake bleed? Quote Link to comment Share on other sites More sharing options...
MGD72Monte Posted July 11, 2011 Share Posted July 11, 2011 I did not have to touch the proportioning valve after I replaced the master cylinder and neither later as I replaced the entire front brake system. Theoretically after you bleed the mc then all of the individual brakes (in the proper order) you should have a firm pedal and the booster has nothing to do with that because you bleed the brakes with the engine off. Quote Link to comment Share on other sites More sharing options...
MagicDragon42 Posted July 11, 2011 Share Posted July 11, 2011 Yes. The button on the proportioning valve should be depressed when you bleed the brakes. The "tool" to do this looks like a C clamp. When bleeding, start with the wheel closest to the master cylinder (left front) and then the right front, left rear and then right rear. Â Mike Quote Link to comment Share on other sites More sharing options...
DavidTX Posted July 11, 2011 Share Posted July 11, 2011 It is possible that you got the wrong master cylinder. If you have disc front and shoes one the back the correct one is 1 1/8" bore. If you got one for manual brakes then the rod is too short and will not depress the plunger on the master cylinder. Quote Link to comment Share on other sites More sharing options...
FRANKIE T. Posted July 12, 2011 Share Posted July 12, 2011 Just had the same problem.Changed master cyl but still no pedal. Thought it was the booster but then as i was pumping the pedal up my son in law noticed fluid coming out of the rear right line. Put new line in and now have brakes. JUST A THOUGHT. Quote Link to comment Share on other sites More sharing options...
AndyBill402 Posted July 12, 2011 Author Share Posted July 12, 2011 Tomorrow I'll check for any leaks. Good thought. The m.c. looks exactly like the old one right down to the bore, so I assume it's correct. If I have to take it off again, I will double check. I read up on testing the booster. It appears I have a good booster. Now, can someone tell how I know if my proportioning valve is working correctly? The little button on the valve doesn't seem to want to move with the engine off. I haven't tried it with the engine on. What's that little button for, anyway? Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted July 12, 2011 Share Posted July 12, 2011 I had that issue once, ended up cracking a front bleeder and putting a hose on it and letting it drain into a can while I bled the rears. Quote Link to comment Share on other sites More sharing options...
DavidTX Posted July 12, 2011 Share Posted July 12, 2011 I just recently flushed, drained, replaced hoses on my 71 and didn't have to do anything to the proportioning valve. Now is the time to check and replace your hoses. If you do check for new copper gaskets before you leave the store. I was missing one gsaket for the banjo fittings. Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted July 13, 2011 Share Posted July 13, 2011 Way to many variables here. Did you have good flow from the bleaders when bleeding the brakes? How did you bench bleed the master before you put it on? was there any reason to belive the fluid may be contaminated with anything other than brake fluid? better flow in the front than the rear? or no flow? You could get a set of brake hose clamps and install them on the 3 brake hoses and try the pedal to see if its hard if so release them one at a time to see where the problem is. Most likely its not the booster that is just an assist device so you dont have to push so hard on the pedal when brakeing. Good luck but its just a matter of narrowing it down to one problem but getting there may take a while. Quote Link to comment Share on other sites More sharing options...
AndyBill402 Posted July 14, 2011 Author Share Posted July 14, 2011 Cny first gen 71, I bench bled the m.c. per the instructions that came with the m.c. It involved attaching some plastic adapters where the metal lines screw in and then attaching a length of clear vinyl tubing to each adapter. I routed the tubing back into the resevoirs. I filled the resevoir about 2/3's full of new brake fluid and then slowly pushed in the plunger again and again until no more air came out into the tubing. Then, I capped the plastic adapters and took the m.c. over to the car where I stalled it. I then bled the brakes. I'm now going to do it again. I can't find anything wrong. Quote Link to comment Share on other sites More sharing options...
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