What year and model used the correct master cylinder?

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MOPARoldtimer

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Here's a picture of the master cylinder I am now using in my early A-body. I have Kelsey-Hayes discs on the front and 10" drums at the rear, with a proportioning valve. My complaint is that I have to pump the pedal twice or more before I get a firm pedal. I have been told, and believe, that my present master cyl. isn't moving enough fluid for the K-H front brakes, and I need a master with a larger bore. Of course the parts houses all want to know what application the master cyl. is for, and can't order one without knowing. So would anybody know what year(s) and model(s) used a larger-bore master cylinder suitable for the K-H discs?

Thanks a lot.
 

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Just tell the parts counter guys you want a master cylinder for any of the A Body, disc brake cars from 1967-72.
They were all dual reservoir, master cylinders for those years.
Shouldn't be hard to get.
 
Do you have the bleeders at the top? and are your rear brakes adjusted up? also make sure your master is fully relaxed when pedal is at the top. I have seen this happen when the rod is to long or not properly installed. I have used 73 up Masters on KH and never had a problem. Steve
 
Thanks a lot for the advice!

There seem to be two different master cylinder bore sizes for the front disc/rear drum Valiants and Darts of the early '70s: 15/16" and 1-1/32". The larger bore master cylinder will move 21% more brake fluid than the smaller one. I assume the larger bore master was used with the Kelsey-Hayes fixed-caliper, 4-piston cars and the smaller master was used with the sliding-caliper, single-piston cars. I am hoping my old master (which I haven't removed yet) is the 15/16" version, and that is indeed the problem. I've ordered a 1-1/32"-bore master, which costs only about $22 rebuilt (Dorman).

While installing the new master cylinder, I plan to adjust the pushrod as specified in the FSM to see if that helps. And if it still won't work right, I'm going to throw myself upon the mercy of Master Power Brakes.

I still need more edification, though, so keep those replies coming! Should I try anything else before bowing down to MPB?

For example: as far as I know, I'm still using the same pushrod that came on the car when it had a /6 and a single-circuit master cylinder. Do I need to get a different pushrod?
 
MOPARoldtimer said:
Thanks a lot for the advice!

There seem to be two different master cylinder bore sizes for the front disc/rear drum Valiants and Darts of the early '70s: 15/16" and 1-1/32". The larger bore master cylinder will move 21% more brake fluid than the smaller one. I assume the larger bore master was used with the Kelsey-Hayes fixed-caliper, 4-piston cars and the smaller master was used with the sliding-caliper, single-piston cars. I am hoping my old master (which I haven't removed yet) is the 15/16" version, and that is indeed the problem. I've ordered a 1-1/32"-bore master, which costs only about $22 rebuilt (Dorman).

While installing the new master cylinder, I plan to adjust the pushrod as specified in the FSM to see if that helps. And if it still won't work right, I'm going to throw myself upon the mercy of Master Power Brakes.

I still need more edification, though, so keep those replies coming! Should I try anything else before bowing down to MPB?

For example: as far as I know, I'm still using the same pushrod that came on the car when it had a /6 and a single-circuit master cylinder. Do I need to get a different pushrod?
Click to expand...

It'll move 21% more fluid, but make it where you will have to use 21% more pressure on the pedal to stop also.
Just so you know.

As a poster above mentioned, you may want to make sure your rear brakes are adjusted up where they should be.
Having to pump twice usually means it is taking that much fluid to get the brake shoes out to the drum.

Here's an easy experiment to find out if that's what it is.
Pump the pedal like you normally have to and hold them down.
Set your E brake and then release the pedal.
Give a min and then hit your pedal again.
Is it solid?

If it is, your rear brakes need to be adjusted out farther.
 
Thanks for the tip, TrailBeast! I tried it, and there was not very much difference between having the e-brake applied or not. Plus, I've already had a good mechanic check my rear brake adjustment, and he said he got it as tight as he dared.

I have a feeling the problem may be with the pushrod.
 
MOPARoldtimer said:
Thanks for the tip, TrailBeast! I tried it, and there was not very much difference between having the e-brake applied or not. Plus, I've already had a good mechanic check my rear brake adjustment, and he said he got it as tight as he dared.

I have a feeling the problem may be with the pushrod.
Click to expand...

How far off the floor is your pedal without your foot on it?
 
TrailBeast asked: "How far off the floor is your pedal without your foot on it?"
About 5-1/2" above the carpet, which I think is more or less where it should be.

An experienced Mopar mechanic told me the following:

"If your car was originally equipped with a single pot master cylinder, the original pushrod will be too short by about an inch. The fix is either an adjustable pushrod or cutting and welding a stock one. Drain the master cylinder. Under the dash, fully depress the brake pedal. Make a note of the distance from the firewall that the pushrod retaining bolt is. This will be the end of the travel of the pushrod. Remove the pushrod from the brake pedal lever. Pull the brake pedal up and out of the way. Push the pushrod in as far as it will go, even if it passes the firewall. Whatever difference there is there will be the amount that you need to lengthen the pushrod."

I'd like to get everyone's feedback on this. A pushrod that's too short certainly would seem to account for my brake problems. I'm a pretty good welder, but what material would you use to extend the pushrod? I sure can't figure what I would use. Or should I just pay through the nose for an adjustable pushrod from MP Brakes?
 
I have a plastic reservoir, non-power, master cylinder from a '79 Aspen on my '64 Valiant with '76 A-body discs and 10" drums. it's attached to the firewall with a homemade adapter plate, and it uses the stock pushrod from the non-power Valiant. Everything fits and works perfectly.
 
The smaller the bore, the higher the pressure. With manual brakes ( no booster ) smaller is better.
 
65 /6 Dart.
Small bolt Kelsey Hayes Disc conversion.
1973 Disc M/C
"Stock" pushrod.

The problem has nothing to do with bore size or pushrod.
My money is on,you have a bad master cylinder, brakes aren't fully blead,or brakes are out of adjustment. Put the new master on,and if your not capable,have them professionally blead and adjusted.

PS: If you could have one "New" part on your car,do you know what it should be ?
You guessed it,a Master Cylinder. Stopping is always good.
 
The picture is showing the correct style MC for disk brakes. Apparently it is not working correctly. Do you have the lines attached correctly? The big reservoir should be plumbed to the front brakes.

Also, did you change out the junction box/safety switch, to a dual-circuit one, with proportioning valve?


MOPARoldtimer said:
Here's a picture of the master cylinder I am now using in my early A-body. I have Kelsey-Hayes discs on the front and 10" drums at the rear, with a proportioning valve. My complaint is that I have to pump the pedal twice or more before I get a firm pedal. I have been told, and believe, that my present master cyl. isn't moving enough fluid for the K-H front brakes, and I need a master with a larger bore. Of course the parts houses all want to know what application the master cyl. is for, and can't order one without knowing. So would anybody know what year(s) and model(s) used a larger-bore master cylinder suitable for the K-H discs?

Thanks a lot.
Click to expand...
 
I already had the brakes pressure-bled, and they couldn't get any more air out of the system than I had already removed by manual bleeding.

I really don't think that a '62 Valiant /6 with a single-pot master cylinder used the same master cylinder pushrod as a '73 Duster 340 with K-H discs, did it? Am I wrong?? Am I wrong??

Plus, the "experienced Mopar mechanic" told me he'd had to do this twice when converting early A-bodies to K-H discs, due to the differences in pushrod length between the early and later cars, and that it worked.

More feedback, please. Let's finger this thing out.
 
When the pedal up, is there supposed to be clearance between the pushrod and the m/c piston or, on the other hand, is the m/c piston supposed to be partially depressed when the pedal is up?
 
I am not understanding the "too short pushrod" explanation. If the pushrod is seated fully in the MC piston (should have a rubber bushing in the groove on end of pushrod), and the MC spring pushes the pedal fully back so that your brake light switch is open, the only thing that should determine pedal travel ability is where the MC piston bottoms out. That should happen before the pedal reaches the floor if it is the correct MC.

I don't think brake pedals on early A's were a different length or lever ratio from later cars. Many people have installed later MC's in early A's, so there is no generic problem with the way the pedal swings.
 
MOPARoldtimer said:
I already had the brakes pressure-bled, and they couldn't get any more air out of the system than I had already removed by manual bleeding.

I really don't think that a '62 Valiant /6 with a single-pot master cylinder used the same master cylinder pushrod as a '73 Duster 340 with K-H discs, did it? Am I wrong?? Am I wrong??

Plus, the "experienced Mopar mechanic" told me he'd had to do this twice when converting early A-bodies to K-H discs, due to the differences in pushrod length between the early and later cars, and that it worked.

More feedback, please. Let's finger this thing out.
Click to expand...


All A-body's from 63-76 used the same 6 1/2" overall length pushrod.
Can't be anymore clear than that.

Measure your 62 and see what you got.
 
I discovered that the Cardone master cylinder no. 10-1627 works correctly!

The one I was using before was obviously incorrect.
 
the fixed 4 piston caliper early disc brakes use a 15/16" master which is no longer avail.
a 1" bore should work fine and require about 12% more leg.
What size piston is in the Cardone 10-1627
 
I think it is 1-1/32" (1.031"), but I'm not sure. It might be 1". Pretty sure it is not 15/16".

It is the same master as came stock on the 1976 Aspen and Volare.

10-1627 is the Cardone part number for the remanufactured master; 13-1627 for their new one.

The pedal pressure is somewhat higher than it was before, but it is always going to be high with non-power disc brakes.
 
Dorman M79772 15/16" crosses to NAPA NMC P2067M

Dorman M71258 1" crosses to Cardone 10-13231 1" ; NAPA NMC P1874

Dorman M80266 15/16" crosses to Cardone 10-1571 15/16" ; NAPA NMC P2122, NMC M2122

A/C delco 18M57 15/16"
 
Jkirk said:
Dorman M79772 15/16" crosses to NAPA NMC P2067M

Dorman M71258 1" crosses to Cardone 10-13231 1" ; NAPA NMC P1874

Dorman M80266 15/16" crosses to Cardone 10-1571 15/16" ; NAPA NMC P2122, NMC M2122

A/C delco 18M57 15/16"
Click to expand...


Good info.
 
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