Master Cylinder question.

-
Coyote Jack

Coyote Jack

Member #55, I'm old
FABO Gold Member
Joined
May 22, 2004
Messages
8,677
Reaction score
3,852
Location
Baxters Corner N.B. Canad
I ordered a manual master today for my disk/drum setup. Got what I think is a good price to. $25 Can. This is a reman. The question I have is. Will the pedal rod from my manual drum/drum setup or my power disk/drum setup work with this new master?

Jack
 
It should work ,I just went through an ordeal trying to find the correct master cylinder for my 68 Cuda w/disc & drum. The main difference you`ll find is the reservoir for the front brake is generally larger than for the rear, since you have sometimes eight pistons moving, versus the drum/drum where you have two wheel cylinders.The drum/drum master cylinder will have equal size reservoirs and the disc/drum will be about 70frt/30rear. You might want to have the master cylinder that has the asymetrical reservoirs for that reason. As far as the pushrod it can be used with either master cylinder unless you`ve gone aftermarket and gotten away from the factory style master cylinder.
 
My rod worked just fine when I switched. I had no problem using a M/C style with a larger front brake resovoir. I always thought the reason for the bigger resovoir for the discs was because when the pads wear the piston don't return. Unlike the rear drums that have auto adjusters and springs that keep the wheel cylinders retracted.

I wish you good luck getting a good rebuild. I went through 3 rebuilds at 2 different auto parts stores (Napa and O'Reileys) and none were any good. They both get theirs from the same place though. A place called "Cardone Remanufacturing". Autozone also gets their parts there so I didn't bother trying them. I finally found out by doing an online search on the Napa website at www.napaonline.com and found they had a brand new one listed for $37 (funny how their guys didn't notice that in their computers) and I ordered one and put it on and it works great.
 
I guess what I meant to tell coyote is, if he can find the m/c with the large reservoir then use that one, not the one with equal size reservoirs. You bring up a good point fishy with the calipers not compensating as the rear brakes do, but if you use the m/c with the small reservoir, watch that the reservoir doesn`t empty when you bleed those brakes.Those calipers can empty it in a heartbeat. I rebuilt my m/c first and it lasted about 6 months, I guess it`s to the point to where it needs a sleeve. Did you find a m/c that had the larger reservoir for the discs?( Do you have a part# and the manufacturer?) I ordered 5 different master cylinders ,which when pictured showed the large reservoir, but when they all arrived they were equal size. I finally called the manufacturer and they said they get very few cores like that in, so they ship a comparable m/c in it`s place.I ended up using the m/c with equal reservoirs, much to my chagrin. Everything new also had equal reservoirs.I kept my old one though in hopes that one day I`ll find a place to resleeve it.
 
I picked mine up today. It has the large res for the disks. Now it's just a matter of getting the rod off of my old drum/drum setup and bench bleeding, then installing and making sure it works properly. I picked it up at my local Shur-fit Auto, Fenco is the manufacturer, thier part number was M1627, (Canadian outfit). It comes with a bleeder kit even. A buddy of mine is the assistant manager there, so if there are any problems, he will make things right.

Jack
 
I ordered one today using the M1627 #and it should be here tomorrow. I can`t wait to see if it`s the right one. Thanks for the #`s.
 
I went to the auto parts store today to see the latest master cylinder part# M1627 and it did have the larger reservoir, but had no place for the piston retainer to bolt to. So once again it`s back to the drawing board!
 
That is really strange Longgone. I assembled the piston rod and master and after that it was just bench bleed it and bolt it to the firewall. One thing I noticed was that it is exactly the same on the outside as the master on my power setup.

Jack
 
Coyote , I think I missed a key word in your original post and that was POWER. Are your disc brakes power assisted because mine are not, and that is where I believe my problem is ,trying to get the proper M/C. You did say you bench bled it and bolted it to the firewall.Did the back of the M/C you installed have two bolt holes for the piston retainer? My original also has a screw in the bottom center to hold the front piston in, which none of the replacements have had. This is # 6 now.
 
Mine is now a manual master disk front/drum rear setup. The new master I put on has 4 bolt holes. I will get a pic for you tonight and post it in the morning. When I was at the parts store I asked for a manual master for a 73 to 75 Dart Sport.

Jack
 
Here are a couple of pics of the master that I have. Sorry but the best pic didn't download properly.

p1144755729730.jpg


p1144755727723.jpg



Jack
 
To be honest you would have much better brakes and a better pedal if you would have switched to the 2-bolt design. I got an aluminum MC from NAPA for a '80 3/4ton Dodge ram. I used the 4 bolt - 2 bolt adaptor and the new MC. My pedal feels just as good if not better than the PB set-up on my Cummins truck. I used to hit the 2nd turn off road and not I can easily hit the 1st turn off road.
 
That looks like the 1627 I received, but behind it where the push rod goes into the piston, my original has a flange that attaches with two bolts that retains the rear piston and holds the front part of the boot.My original also has a bolt in the bottom that retains the front piston. The 1627 didn`t have that. Does yours?
 
Okay ,we`ve got apples and oranges here. One of these days I`ll find the correct m/c. Thanks for your help though, it`s much appreciated.
 
I think the M1627 that doesnt have the piston retainer is made for manual brakes. The brake rod and pedal hold the piston in while the power brake booster setup needs a hard stop for the piston. Im getting one (Fenco, ordering one today) from Autozone, 20 bucks with a 5 core, Im just going to give them my drum/drum symetrical MC as the core unless there is value here on the board...
 
Six years since the last post... got to be some kind of record :D

While we're here though, Autozone and others show the manual m/c has a 1-1/16" bore but the power m/c is 15/16"? Would have thought it'd be the other way round, but that seems to be consistent over several store sites.

So could I use the power (15/16") m/c with a manual pedal and pushrod?
 
You want the bigger piston for manual brakes.

For example if you can create 700 pounds of force with your leg on a piston with 1 square inch you are creating 700 psi in the system. If you had a larger bore master cylinder that was 2 square inches that same 700 lbs would generate 1400 psi.

The power brake booster amplifies your leg force so you don't need as big a master cylinder bore to get the same pressure in the system.
 
Hang on a minute... it's the other way round!

If through the pedal leverage you have 700 lb of force to apply to the m/c piston, if it has 1 sq in there is 700 psi generated. OK so far.

But if you are applying 700 lb to a 2 sq in piston that is only 350 psi generated... pounds PER square inch! Looking the other way, 350 psi pushing against a 2 sq in piston = 700 lb force...

anyway the difference is proportional to the square of the piston diameters... 15/16 vs. 1-1/16 = 17/16: so relatively, (15/17)^2 = 0.78:1
 
OK, got my Fenco M1627 special ordered.. $25.looks nice. The piston is held in by a circlip, no external retainers. Includes bench bleeder hose and fittings and a small hard rubber "clip" for old pushrod. "re-Hecho en Mexico" 100% factory tested with EPDM seals and premium bleeder kit
061212200105.jpg
061212200119.jpg

061212200253.jpg


Now if the OEM had the piston sitting flush with the edge held in by a wing, this one is set in about 1/4 inch. Dont know if the pushrod seat is compensated for this..Most likely yes. Anything beats my old single pot!
 
Interesting that the power MC has a smaller bore than the manual. That is probably because the power booster is on standoff brackets with a lever. The lever ratio reduces the pedal force that gets applied to the MC. The smaller bore makes up for that. Remember, they must design it so you can still stop the car if the booster fails. I wonder if the same MC is used for power and manual brakes in my C body, since the pedal acts direct on the MC there. That assumes they ever sold a C body w/o power brakes.
 
You must log in or register to reply here.
-

Back
Top