need a master cylinder for a '38 P6

[TodFitch]

I would think you could buy new ones at NAPA. I know they have them for my '35 Plymouth.

No, the 1935 used the same master cylinders as the Plymouth trucks (695696) and while that is available it is not the master cylinder he needs. Your master cylinder does show up on Napa Online as does the one for the later P14 and P15. But, near as I can tell, Napa does not have the 1937-41 master cylinder.

By the way the one on your 1935 will bolt into and work on my 1933. In fact that is what I have in there now. But it looks different than the correct one for my car which I have had recently sleeved and will put back in some day.

[JimCno]

I would think you could buy new ones at NAPA. I know they have them for my '35 Plymouth.

[elmo]

i don,t know the part # for the various cylinders , but do know that i have interchanged the ones i mentioned , i have at the moment four M/C sitting on a shelf in my workshop , they come from a37 ply through to a 39 S6 DeSoto, all of them different part # or not are the same .

[1938P6]

Hello my dad and I have 1938 p6 and we used Andy Bernbaum and Roberts Motor Parts we bought our fist master cylinder some twenty years ago  from Burnbaum we had some trouble with it  we got the second master cylinder from Roberts both cylinders looked like the original with these cars you have the make sure the brake shoes are good are were old and the shoes got ripped off the metal part   the adjustment onthe brake shoes are very touchy that happen last year  we had the car for 30 year so we had experience with this car       

[TodFitch]

Tim ,
? if you still need to source another M/C ,? 37,38 and 39 plym ,dodge and desoto were all interchangable, i,m not to sure about chrysler bur assume they were the same . i think plym 46 has the answer , those two holes must be clear, and as ply36 haqs said you might have to do some adjustments , so that after releasing the pedal , the piston leaves the return hole clear. as for the fluid valve , i cant see how it can be installed the wrong way , but should be replaced when you over haul the M/C as they can stick shut when worn.
Rex .

The 1938 P6 used master cylinder assembly part number 858889. That also shows up in the parts book for P3, P4, P5, P6, P7, P8, P9, P10, P11 & P12. so basically any Plymouth car from 1937-41. The Plymouth commercial (PT series) used a different master cylinder (695696).

I concur with the other opinions about the relief hole. Getting the rod length just right is critical. Any too long and your brakes will lock up. Too short and your pedal travel will be excessive. On my 1933 (different master cylinder) it is possible to see into the relief hole while you adjust the rod length. That made it pretty easy to adjust the rod. For those of you who have the master cylinder under the floor I'm not sure if that is true.

Assuming your brakes are properly bled, your pedal travel can be broken into several parts:
1. Distance pedal travels before rod contacts piston in master cylinder.
2. Distance piston in master cylinder moves before covering bleed hole.
3. Distance wheel cylinder pistons move to contact brake shoes (or rods to brake shoes)
4. Distance brake shoes have to move before they contact the drum.

Seems like on my car the master cylinder rod length and the brake shoe adjustment are the only things you can control. And if they are out of adjustment the pedal can be very low.

[elmo]

Tim ,
  if you still need to source another M/C ,  37,38 and 39 plym ,dodge and desoto were all interchangable, i,m not to sure about chrysler bur assume they were the same . i think plym 46 has the answer , those two holes must be clear, and as ply36 haqs said you might have to do some adjustments , so that after releasing the pedal , the piston leaves the return hole clear. as for the fluid valve , i cant see how it can be installed the wrong way , but should be replaced when you over haul the M/C as they can stick shut when worn.
Rex .

[Tim B]

Hmmm.... I want to insist that it is installed correctly, but it would be a thing to check.  The M/C has had several people look at it to attempt to determiine some fault;  nothing was ever apparent.  We compared it's internal assembly to the illustration in the FSM.

Just to clarify;  are you referring to the piece at the front of the internal spring inside the M/C?

[John Hendricks]

I think I recall a similar post on the old POC board.  There is a one way circular fluid  valve at the end of the pushrod piston.  Is it installed the right way?

[plym_46]

Make sure the fluid return port in the bottom of the fluid reservoir is open and not restricted in any way.  Look into the bottom of the reservoir withe good light you should plainly see two holes.  One feeds fluid to the piston and one allows it to return when you let off the brake.  If it is restricted it will not alloe the brakes to release.  Also make sure your reservoir is not overfilled and that the vents in the cap are open.

[36 Ply]

Tim-

I don't know how much this will help, but I had a similar situation some years ago with a '36 P-2 sedan. When I installed the "new" master cylinder and bled the brakes, I found through trial-and-error, that  approximately 1/16 of a turn (or less) on the pushrod with an open end wrench was the difference between a decent pedal and hardly any pedal at all; the adjustment was really touchy.

Regards, and good luck,
Pat O'Connor

[Tim B]

We've installed a new master cylinder from one of the MOPAR vendors, and at this point I would rather get my hands on a rebuildable used one and have it sleeved.

There's something about this new M/C that simply won't work;? brake shoes are properly adjusted, wheel cylinders and hoses are new.? The car's brakes continue to lock up, and no amount of adjusting the push rod on the brake pedal seems to make any difference.? In order to prevent the brakes from locking up, I have to shorten the pushrod so? much that I have almost no pedal at all.  The brakes were better prior to all our work than they are now.

Any ideas that I may be missing something?   Otherwise I'd be interested in knowing if someone had a surplus original master cylinder that I could buy.