Some help/input

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MoparMark91

MoparMark91

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So I just recently converted to kelcey hayes sbp disc brakes in front and have 9 inch drums in back. I have prop valve installed and 15/16 aluminum mc. For some reason after the car sits when I'm at work for 12 hours the pedal will go to floor, after driving it and stopping numerous times the pedal does pump and stays firm after. I have already bled the system twice and no air in system. I dont know what is causing this long pedal travel as I have the pushrod measured correctly. I bled the mc as well. I was told that these mc font have residual valves for rear? So could that be a problem or maybe air trapped in multiple locations of the lines that collect when car sits or? I've been trying to diagnose the problem for 2 weeks now. Do I need to get certain rear wheel cylinders that have a residual valve in them or what? Any input or opinion will be appreciated I am pretty stumped by this.
 
Where are you bleeding the system? Just at the bleeders? Air gets trapped in higher places and it’s hard to force it down. Try bleeding the master cylinder itself. Also recommend trying to bleed at other junctions located higher than the bleeders.
 
Through the bleeders but I'm also pressure bleeding it and mc has been bled, could be it be something to do with wheel cylinders in rear? They are a year old
 
Ok this is gonna sound silly but have you mounted the calipers on the correct side with the bleeders up (they will mount on the wrong side) ?
 
MoparMark91 said:
Through the bleeders but I'm also pressure bleeding it and mc has been bled, could be it be something to do with wheel cylinders in rear? They are a year old
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Even using pressure bleeders I have seen some oddball instances where a little bubble gets passed by. My favorite go-to is cracking the lines at the m/c. I may be wrong but it’s a quick thing to try. I don’t suspect the wheel cylinders at all. If you’re not losing fluid it has to be the m/c or air in line.
 
My sons Duster has the same setup with swapped on front disc and the small rear brakes. Its been this way for over a year with no issues while we get the new rear ready. I agree with others that the rear wheel cyls shouldn't be an issue. I cant add anymore to whats been posted, best of luck.
 
leechris81 said:
Even using pressure bleeders I have seen some oddball instances where a little bubble gets passed by. My favorite go-to is cracking the lines at the m/c. I may be wrong but it’s a quick thing to try. I don’t suspect the wheel cylinders at all. If you’re not losing fluid it has to be the m/c or air in line.
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So you just crack the bleeder and see if any air comes out?
 
Yeah I was thinking maybe it's the mc or multiple trapped air bubbles
 
The residual pressure valve check valve should be in the M/C. It could be a simple rubber check valve that holds about 4lbs of line pressure.
 
Well I have the aluminum mc fron dr diff and I dont think those have that from what I have been told
 
MoparMark91 said:
So you just crack the bleeder and see if any air comes out?
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If there is a bleeder on the m/c that is great. Ford has done that on some of their stuff. If there is no actual bleeder, I just crack the line as if it were a bleeder. The fluid/air or any combination of two, will come out between the nut and the steel line.
 
You might want to check the adjustment of the rear shoes, because if they are loosely adjusted they will collapse down while sitting until pumped back out to the drums again.
If that doesn't do it a residual pressure valve in the rear brake line should, and you can get those for about 15 bucks on Summit.
You want the 10lb valve for drums.
 
Typically, RPV's are not included in MC's anymore. You normally can see it through the rear brake pressure port at the MC. It's just under the removable seat.

Pump the brakes up until you get a pedal then very firmly push down and hold it. It should be rock hard and remain there indefinitely. If you feel it gradually recede then you could have a leak. It's either going to be somewhere in the system or you have a bad MC.
 
A good clue on rear shoe adjustment causing this is to set the E brake when parked and then the next morning go out and hit the brakes.
If it's fine, then you have a rear shoe adjustment needed.
The E brake holds the shoes against the drums to they don't collapse the cylinders back down.
 
MoparMark91 said:
I was told that these mc font have residual valves for rear? ?
Click to expand...
MoparMark91 said:
Well I have the aluminum mc fron dr diff and I dont think those have that from what I have been told
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Either it has one or it doesn't. If it came from Dr Diff. Contact him and he'll tell you. If it doesn't, you need one someplace in the line. if it doesn't, the first pump will be to refill the rear wheel cylinders. So yes its a possibility. You can also make a little dipstick and check the fluid level of the front reserviour - unless its the type which allows some sharing. Level will come up as fluid gets forced back.
Chrysler tech explains it here: residual valve in 1970 Hydraulic Brake Service from Master Technicians Service Conference Session 274

MoparMark91 said:
Through the bleeders but I'm also pressure bleeding it and mc has been bled, could be it be something to do with wheel cylinders in rear? ...

So could that be a problem or maybe air trapped in multiple locations of the lines that collect when car sits or? I've been trying to diagnose the problem for 2 weeks now.
Click to expand...
Chrysler's tech tip was to gravity bleed the disks, and/or the old fashioned method or pump and close.
My tech tip is use a bleeder hose the seals well at the bleed valve and the other end goes into a container with brake bluid so no air can back in. If you loop the hose high, the bubbles will collect there and not next to the bleed valve.
 
Yeah I'll try the whole process again and see what happens, but like just now I got in my car and drove to work and brakes were firm and great. But when I head home at 630 in the morning that's when the brakes go almost to floor. So I'll try the process over again and see where it leaves me and also order residual valve
 
TrailBeast said:
A good clue on rear shoe adjustment causing this is to set the E brake when parked and then the next morning go out and hit the brakes.
If it's fine, then you have a rear shoe adjustment needed.
The E brake holds the shoes against the drums to they don't collapse the cylinders back down.
Click to expand...
I tried that trick or clue with having e brake on and it still travels pretty far, I'll pop off rear wheels tonight but I'm starting to think mc or I need to add residual valve
 
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