How come all my manual drum cars have disc master cylinders?

Hey guys:

I am currently working on a 1968 Valiant with 9" manual drum brakes front and rear. I total went through them. 3 new soft lines, 1 hard line, wheel cylinders and all shoes. I initially wasn't going to replace the master cylinder until one of my Youtube viewers pointed out that it had a disc brake master cylinder.

So, I got on Rock Auto and ordered a new Raybestos(now made in China) MC. I actually ordered two, because the guides say that the same MC interchanges on several other pre-71 Mopars, including a 1967 Chrysler 300 with power drum brakes. I have a '66 but it has already been upgraded with a factory dual-circuit system.

My problem is that I cannot get fluid to the rear. Crack the line at the MC and it's dry. The fronts bled, and I got a very hard pedal with about 1 to 1-1/2" of PISTON TRAVEL before I get resistance. The new master has either a 1" or 1-1/32" bore( I already installed it but I took the time and effort to go out and crawl under the dash to measure it.

So, any ideas what's happening here? I think the idea that one master crosses over from a manual drum with 9" brakes to a power drum car with large brakes sounds suspect, but you guys know more about these than I do. I realized way into this job that the brakes changed somewhere around '71 or '72 because everything from my '73 parts car is different...hubs, MC, and hardware.

Pictured is the Raybestos MC36221 MC I received as spec'd for a 1968 Valiant 9 and 9 manual.

Here are two other disc brake master cylinders that were installed on a manual drum car, plus the 300 had one also. The front MC is a 3699263 Mopar MC which is for a later car for sure. Has a 1 or 1-1/32 bore. That's the one that was being used on the '68 The rear MC was installed on my '73 manual drum 9 and 9 parts car, same specs, plus another that is on the 300.

1. Are the manual disc MC's an acceptable interchange for a drum car, the residual valves notwithstanding?
2. What are the spec differences between the early and "late" manual drum MC's? The books call for different part numbers.
It amazes me that 3 different cars had the wrong master installed. Is there REALLY a manual drum pre-'71 or so master or do they truly interchange with the power drum cars? Sorry for the long post but there is a lot of confusion on this. Thanks!

The master cylinder in your first post is the correct unit for an all drum car.


Alan

The master cylinder installed is correct. The correct disc brake master cylinder would look almost identical except for the casing is deeper to hold more fluid. That one is quite rare too so part stores would hand over a later model master cylinder per their interchange books. The one difference in this interchange that some run into is the pedal rod length difference. It's more correctly a difference in the length of master cylinder castings. They would need to readjust their brake lamp switch position. I'm going to guess the current position of your brake lamp switch is preventing full return of master cylinders piston. Could be why no fluid out to rear. Just a guess.

In 68 both Manual Drum and Power Drum used the same master cylinder.
It should look like this (cover design may vary).
If you have a rectangular cover it is this one.



Alan

As long as you keep both chambers full and have removed the residual valve to the discs, ANY M/C will work. The dual chamber size is a nod to lazy people who never check their fluid level.

If you cannot get fluid coming out from the chamber that supplies the rear brakes, which should be the one furthest from the firewall, then either;
1) the mc has not been properly bench bled, or
2)the compensating port is not open, or
3)the dang thing is defective.

#2 could be due to a wrong length pushrod, go look for the fluid fountain after releasing the brakes, which indicates returning fluid. Watch out!!, the fountain can be a geyser if you have air in the system: and with brake-fluid everywhere on the paint, you have a bigger immediate problem.

TylerW said:

1. Are the manual disc MC's an acceptable interchange for a drum car, the residual valves notwithstanding?
2. What are the spec differences between the early and "late" manual drum MC's? The books call for different part numbers.
It amazes me that 3 different cars had the wrong master installed. Is there REALLY a manual drum pre-'71 or so master or do they truly interchange with the power drum cars? Sorry for the long post but there is a lot of confusion on this. Thanks!

Click to expand...

A lot of things vary from year to year, somodel to model depending on brake pedal leverage and the wheel cylinders.
The aftermarket guides are sometimes just wrong in their attempt to reduce the different part numbers they stock.
1968 is a particularly tricky year on the mechanicals (changed to tabbed shoes, but before the change with the self-adjusters)

I beleive this is also correct for '67-'68 MCs
Drum Brake Service Highlights (Session 260) from the Master Technician's Service Conference

In 1970, non A-body disk cars got floating calipers. And the 9" A-body drums go away.
1970 Chrysler Imperial Hydraulic Brake Service Guide from the Master Technicians Service Conference Session 274

Those disk/drum master cylinders are now harder to find. So definately keep if you need, or keep an ear open for people looking.

"Mastershake" on Moparts has written up at least one article on correct master cylinder castings and part numbers. He's made some updates and corrections since it originally came out but still a good starting point especiall for the things you asked about.,
Moparts - Members In Print, Brad Schroeder "Pumping Points", Mopar Action (jpgs)
http://www.moparts.org/Tech/MoparAction/Master_Cylinder.pdf

I started a cheat sheet here for A-body disk master cylinders.
It would be great if people add info to it.
Years___Application_____________p/n_______Bore
1966... Fixed Ft calipers, Manual.....................1"
1966... Fixed Ft calipers, Power......................1"
67-70.. Fixed Ft calipers.............2808600.....1"
71-72.. Fixed Ft calipers.............3461178.....1 1/32
73-74.. Floating caliper, Manual...3580146.....1 1/32
73-74.. Floating caliper, Power.. .3580112........15/16
1976?......................................____4647..........15/16

Good info, thanks

if some moderator can let me edit the links above,
The links pointing to imperalclub.org need to be changed to .com
Below is corrected links.
1969 Drum Brake Service Highlights (Session 260) from the Master Technician's Service Conference

1970 Chrysler Hydraulic Brake Service Guide from the Master Technicians Service Conference Session 274

Minor Update

Years___Application_____________p/n_______Bore
1966... Fixed Ft calipers, Manual.....................1"
1966... Fixed Ft calipers, Power......................1"
67-70.. Fixed Ft calipers..............280 8600.....1"
71-72.. Fixed Ft calipers..............346 1178.....1 1/32
73-74.. Floating caliper, Manual...358 0146.....1 1/32
73-74.. Floating caliper, Power.....358 0112........15/16
1975..Floating caliper, Power......____0357
1976?......................................____4647..........15/16

H22A4 said:

Not sure who is being asked for photos but here‘s a 75 master cylinder and booster.
View attachment 1716147348

View attachment 1716147349

Click to expand...

Photos and discussion of original production A-body Master Cylinders

Example of a '74 358 0112 tag originally posted by @Dragon Slayer on moparts

For what it’s worth, attached is the tag on my 75 master cylinder.