50 Chrysler master cylinder rebuild.

[Brooklyn Beer]

This will be a first for me. Have mostly dealt with 60's cars where you replace for the most part. So questions first. Can I rebuild it with it still in the car or should I remove it for a good going over?  I am working with a car lift so access is easy. Should I run a hone down it or not? Can I clean it with scotchbrite instead if it is needing a good cleaning?  What are some problem area's on removal and installation of new parts I should pay very close attention too?

[auburnseeker]

Easiest to just pull it out and do it on the bench.  It most likely needs honing.  Then a kit.  When you get it all done,  Clean the outside up good.  I plug mine up and blast them,  Then shoot them with a cast gray finish.  When you put it back together,  I would pull all the brakes clean all the wheel cylinders flush the lines, replace the rubber ones and go to silicone.  Then you won't have to do it again.   I did a get it by job on my Dad's truck as I thought i had just one sticky wheel cylinder and ended up rebuilding all 4 before i was done.  Hindsight I would have ordered everything new and went silicone. 

I'm getting ready to pull the wheels on my 51 Dodge and I'll bet I'm in for a full brake job on that.  Though everything was new when they did the resto but I doubt they went silicone.  Probably should have already bought the kit.  Too many other projects to finish around the ranch first and DMV being closed so I can't register it to drive has made me not make it a priority. 

[Brooklyn Beer]

So a simple brake cylinder hone will work?  Gathering parts now to do the job.  Don't want to tie up the lift right now as i have the 39 Chrysler due this week and want to get that in the air first and give a good inspection and lube before starting on the 50 Chrysler.  Don't get me started about projects. Was up at 3 to beat the heat and get the other side of the old barns new roof finished before we hit 96 today!

[The 55er]

Not a hard job. Hone the cylinder first. If any bad scratches, scores or deep rust pits remain in the cylinder it will have to be replaced or resleeved as it won't have a good seal. There is a good description of the rebuild process and a detailed picture of how everything goes back together in your shop manual. After the master cylinder rebuild you will need to bleed the wheel cylinders at all 4 wheels. 

[c49er]

Sleeve it or replace it with a new one.

It most likely will have a rusty pitted area at the bottom of the bore....you will not be able to remove completely by honing.

...and it will probably seep brake fluid.

If you are a pro....do the job with out pulling the floor pan...

if you are a novice 50 Chrysler owner remove the floor pan...take plenty of pictures.

You also might need to use a press to push the clutch and pedal shaft out of the old master cylinder ..then push it into the new or resleeved one.

You should also own a factory shop manual if you really like this car and want to keep it and fix it right.

I have four 1950 Chrysler's.

[Brooklyn Beer]

Well I am a novice to this type of repair for this car and I do have the shop manual.  I have a complete shop here with a lift and a press and would like to avoid removing the front pan. I have a couple other mopars either side of 1950 I can use as reference if I get lost.

[c49er]

Glad you can do the job with confidence and for once someone does have the shop manual!

So the way I do this job..

I remove the m/cylinder's leaving the floor pan and pedals still in the cars...

I......

**Disconnect the M/cyl. push rod..

**Disconnect the clutch fork rod

**Remove both brake lines at the rear of the cylinder

**Remove the two pedal pivot shaft horse shoe clips with the special

Miller clip removal tool....Or use a 13/16" open end wrench...

**Remove the the M/cylinder mounting bolts

**Wiggle,move, twist the cylinder forward/backward and sideways...to enable pedals to slide off pivot shaft.

They will come off this way...have done many for customers over the years.

**Remove master cylinder.

**Press pivot shaft out of master cylinder...it's supposed to be s press fit

Now......

You CAN hone the master cylinder in the car if you decide..

To do this...

**Remove both brake lines from rear master cylinder plug

**Remove the large hex plug being careful as piston spring and check valve will want to pop out

**Remove cylinder push rod and two slotted screws retaining rubber dust boot..

**Remove piston

**Hone cylinder

 

[Bloo]

DONT try to hone to the bottom of any pits. Then it will be oversize and leak. Moderation is the key. You are cleaning up the original surface, that is all. Any rust or crud sticking up from the original surface gets honed off. Pits below the surface get to stay. That's just how it is. If the pits are in a place that the seal does not wipe in normal operation it will be fine.

 

It is truly amazing how bad a cylinder bore can be and still not leak as long as you do not overdo the honing and make the bore too big. Back in the old days you just had to try it, and if it did leak, you wasted a kit. They weren't that expensive. The track record of "kitted" cylinders like this was still much better than the "remanufactured" cylinders from the parts store.

 

Today sleeving is readily available and cheap. I would sleeve it if there is any significant bore damage.

 

 

[Brooklyn Beer]

Will get the car on the lift this evening and start dismantling.  The manual is not real good on the removal process. But before I do this I am going to see about cleaning out the relief port again. I don't think I was in the right hole when I stuck the paper clip in after going over the drawing closer with better glasses. 

[Brooklyn Beer]

So today as I give a break to the continuing brake issue on the 63 Dodge I tossed the 50 Windsor up on the lift and decided to go look at the brake issue here.  So right away I see the leak and fluid. OK, let me try the easy approach first and see what the bore looks like. Remember this is an unrestored car and the surface rust on the master shows it so wasn't hoping for the best case when doing the simple rebuild approach. The bolt through the push rod was stuck and some liberal PB blaster got it moving. Had to modify a 7/16 deep socket a little to get it past the leave out on the bracket and onto the one end bolt to take off the end plate. Draining the fluid it was nice and clean.  Good sign. The manual that came with the car showed that the previous owner was keen on upkeep judging by his hand written notes. Pulling the guts out and investigating I was treated to a shiny bore with no pitting.  Could not feel anything but silky smooth.  I think I might have gotten lucky. So tomorrow I will run a hone down it quick and flush it out. The rebuild kit I have shows the parts match what came out except the piston is aluminum but the same length. The spring is also about 1.5 inches longer but will chalk that up to use. I did find a factory original kit and will wait a couple days to get that and see how that looks. Big thing I saw on the piston I removed was how sloppy the rubber seal was.  But by everything i have read concerning rebuilding from factory service bulletins, I should be able to do it in the car and save some time..

Edited May 6, 2020 by Brooklyn Beer (see edit history)

[Brooklyn Beer]

[keithb7]

Good update.Glad to hear you are moving ahead with the rebuild. This same master cylinder was also my first reseal. It was a success, although I could have probably had it re-sleeved. I honed it a fair bit, it does weep a teeny bit past the piston out to the push rod. I keep an eye on the brake fluid regularly. I do have several projects on the go with both of my old Mopars. They do indeed keep me busy. I'll likely order a new MC in the future. My tear down seen here:

 

 

[Brooklyn Beer]

I just got mine all back together and found some of the new parts were not up to par with some of the old parts. Thankfully the most important parts seem all good to go BUT the piston was a big problem. The rod did not fit very well and in comparison to the old one only about 1/3 of the way in.  So I took the new rubber off the new piston  and put it on the old piston. (which was brass) The rest of the new parts fit fine. Getting the piston back in sucked especially with the new spring but all is back together. Found one issue.  Brakes are not bled yet.  It seem at the very front of the bore is a lip. Enough so that when the peddle is pulled to the full return it has a catch when the rubber cupped end of the piston is all the way out at full pedal height and is up against the boot collar and piston stop. It is easy to feel in the peddle. But ever so slight and so quick to get past. But it gets a little weep from it. I am going to say it is too much to hone out.  Is it time for a new master ? Once it is past this point it seems to be functioning fine.  I held the boot back and worked the pedal and did not see any weep until it hit that very end of travel point. Can I just adjust the pedal to stop a hair lower and shorten the piston return by a hair or will this cause the brakes to drag ?

[Brooklyn Beer]

Looking at the rubber on the piston of yours. One end is solid while the other end has 2 different layers for lack of a better term. That sold end is towards the piston stop correct ?

 

[keithb7]

The rubber seal is designed flare open on one end. As it pushes to toward the valve it can flare open slightly, ensuring a positive seal against the cylinder wall. 
 

 

[c49er]

His piston is slightly different (late 30's MoPar)  than what should be in your 50.

The piston must come all the way back to the rubber boot plate stop.

This because the smaller hole relief  port hole must not be blocked by the piston.

If it is the brakes will not release properly.

Edited May 7, 2020 by c49er (see edit history)

[Brooklyn Beer]

Now i am wondering if the rod was all the way in the piston.  On the new one no way for sure.  But longer looks better as it won't block the hole. I used the old piston with new rubber. bled 3 brakes before giant tornadic thunderstorm chased me in last night. It seems to be working but I have that lip so when the piston returns all the way it has that "catch" exactly the depth of the cup on the piston. The weep stopped.

Edited May 8, 2020 by Brooklyn Beer (see edit history)

[Brooklyn Beer]

OK, after attempt number 1 friday night with a new kit I did not like it at all. maybe because I was afraid to hone out to much or maybe the cups were too hard but it just would not return correctly at all so after bleeding the rears I quit and waited for the NOS kit and glad I did.  So saturday afternoon the NOS parts showed up and I started over.  Honed out the cylinder more even though I could not feel a ridge by how the new kit was acting when installed.  I fitted the new piston a couple times and the seal was great and no feeling of any ridge so after a deep cleaning with alcohol I put things back together. Everything sure felt a lot better for sure and even without the pedal return spring, the piston return spring had the pedal fully up. Finished assembly with a little fine tuning of the bushing  plate with a set tool and no leaks. Filled it up and bled the system Didn't take long to get a good pedal and then went back around again to be sure. Started her up and YIPPIE, good brakes. Drove around the yard a couple times and parked it as I ran out of time.  Big opening for the restaurants in town and I had the 49 Roadmaster to wash and wax for appreciation day    One question. Should the piston stop at the plate or right before it?  I turned rod in a little to get it off the stop plate some. 

[c49er]

The piston must come back all the way to the steel stop plate inside the rubber boot.

[Bloo]

Always lube up the new seals and bore with the little packet of brake lube that comes in the kit, or some Sil-Glyde. Brake fluid alone often isn't slippery enough when the seals are brand new.