New MC ... almost no rear brakes

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David W

David W

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Hi All

Spent a good part of the night reading threw the threads ...

Updated my 70 dart to Disk front and a 8.25 rear from a 74.. worked out all the little things..

Here is whats going on ...
Bled the MC two times ... fronts stop good .. backs still stop like coaster brakes ...

When i look down at the MC as the peddle is being pushed i see the piston move past the intake holes ...
BUT
As the peddle is slowly pushed i get a squirt of fluid up from the front res but not from the back res ..

Thanks for the help
 
Did you look at the combination valve ?I
What master cylinder application ,did you use ?...
And this goes with the second sentence?
Do the rear wheel cylinders ,match what the master cylinder primary bore ,is capable of ?
Did you replace the rear wheel cylinders ,or bolt it in ,as is....?
I am looking at the master cylinder compensation port ,first....

download.jpeg
 
The proportioning valve is very critical to correct brake bias front to rear. I bought all new brakes complete through Dr Diff. so it was a disc brake upgrade with correct master and proportioning valve for a manual disc brake car. I have great brakes.
 
Hi bomber
the MC booster are for a 73... the rear end i put new wheel cyc in for a 73 and the brass is a 71 and up ...
one thing is the rear wheel cyc ...i put the 15/16 bore ones in ... as its a 9.25 rear end
and cant find the info on the MC bore size ..

but i dont get why i have a squirt of fluid coming up in the res but not the rear ..
am i losing my line pressure when this happens

And the squirt of fluid is coming up from the compensation port But only the front res ( rear brake res )
 
How was it before the new M/C?

Are the rears adjusted properly?

A LOT of the pedal height is in the rear adjustment.
If they are not almost touching (probably actually touching is spots) it will take up the pedal travel to get the shoes out to where they can work.

The front is a paper thin gap, and causes almost no pedal travel.
whoops, I shouldn't assume disk front

If front drums, the same applies as paragraph 1.

Are there ridges on the rear drums?
 
Can't answer if the squirt of fluid is normal (suspect not). Try backing up and jamming on the brakes many times. I do that after a brake job. I feel the pedal move less each time as the drum self-adjusters do their job, ending with a stiff pedal (if no air in the system).
 
David W said:
Here is whats going on ...
Bled the MC two times ... fronts stop good .. backs still stop like coaster brakes ...
Click to expand...
How are you testing the front brake operation compared to the rear?
David W said:
When i look down at the MC as the peddle is being pushed i see the piston move past the intake holes ...
BUT
As the peddle is slowly pushed i get a squirt of fluid up from the front res but not from the back res ..
Click to expand...
The fluid coming up is from the compensating port.
1970 Chrysler Imperial Hydraulic Brake Service Guide from the Master Technicians Service Conference Session 274

Rear resevior and piston is for the front brakes.
 
was the M?C put on at the same time as the disk conversion?
 
Just off the top of my head is it a disc drum M/C the rear brakes should have a residual pressure valve , built into the M/C if not you may need to add an external RPV to the brake line
 
where would a disk/disk 4 bolt cowl M/C come from?

I suppose, though....
 
So after a drive down to the brake rebuilder he looks at it and said here a new MC ...
This is what he told me about the squirt of fluid ...
The squirt is cause of compressed fluid passing back over the o-ring and it pushes up threw the balance hole ( the small tapered hole )

New master goes in tomorrow and i let you all know ... thanks for all your replays on this ..
 
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