disk brake upgrade MC question

68 CJ5-I am slowly gathering parts to convert to disk front brakes. I see that most also convert to dual master cylinder, I currently have the single w/ drums up front. I saw a MC for sale with dual chambers for 74-77 CJ5 and other applications. In Steve Lane's write up he used a dual from a 67-71. My question is: Would this 74-77 dual MC work OK? What sizes specs or qualification should a MC meet to work correctly in this application.? No smaller than 1 inch bore, 1 and 1/16 bore etc? I dont understand when you look up MC's, why there are different part #'s listed for manual drum, power disk, manual disk? You look at them or pictures of them and they look pretty much the same. What info am I missing here?

Josh

 

all i know is that drums use a check valve to hold some residual pressure on the drums, and disk brakes use more fluid.

 

So, maybe if you get a MC for manual disk brakes no matter what the original application, they will hold enough fluid and be OK? As long as you use the correct pressure valve?
Josh

 

The residul is for the disc's.
Heres the deal all the different setups need a slightly different MC so you would need to specify what you want. Power, no power. disc no disc. ect to get the right one.
I am gussing you would want the same as me. disc front, drums rear no power.
Ala CJ7.
You also will need a proportioning valve.

there are tons of articals on this try a search here I know this has been writen up on the CJ3B site as well.
I am buying mine from Herm here is the link. just tell him what you need and he will fix you up.
http://www.hermtheoverdriveguy.com/id27.htm

 

Yeah that is what I'm trying to figure out. I want disk front 10 inch drum rear no power. I am looking to buy a particular MC that is for sale( Good deal). I was only told it is for 74-77 CJ5,CJ6, CJ7. I'm trying to figure out if it will work.

 

I would just go to your local parts store and get a no power front disc rear drum for a cj7. 25.00 to 50.00 bucks.
I am not a cj5 expert but I think they mostly came with front drums...

Call Herm at that site I posted he will know exactly want you need.

 

The stock MC on my 71 model is running my 10" rears and my dana 30 front disks just fine. I have residual pressure valves for both the disk and drums as my Mc had the factory style missing on them. The MC on the 72 and later have the lines on the wrong side for an under floor MC and pedal assmembly.

 

You were right! Thanks for the insight. I never would have thought the output ports were on the wrong side but they are. I thought all MC's had them on the same side.

Thanks for sparing me the trouble. Josh

 

I am also prepping to upgrade to disc front and dual res. MC. I mistakenly thought I could buy the MC for the later model as well. You saved me some trouble. But this raises another ?. How do I get the right residual valve for discs in a mc that was only made for drums? I was orig. planning on ordering the kit from Herm, along with the MC, but I found the bracket off of a '68 in a box of parts that I bought. It looks almost identical to the part that Herm fabs, so I don't need the kit, just the MC now.

 

Call Herm he will tell you what you need.
Very helpful nice guy.

I have been talking to him about this but havnt asked which is which, MC.
there can be a problem with the lines coming out wanting to be up against the bellhousing but Herm has been working on a nice fix for this..

 

If you read the write up in the tech section it explains what you need.
Remove the 10# res. valve that is in the M/C. Get an inline 2# res. valve to replace it. I picked one up at a local speed shop for $15.00.
Make sure you flip the brake lines on the M/C, very important. The front brake line goes to the back brakes and the back brake line goes to the front brakes. I just went through this upgrade and received great advice from this site. The last point made all of the difference in the world.

 

for anyone interested, i have a dual reservior master cylinder setup complete with pressure switches, junction blocks, push rod, master cylinder, and both brackets from a '70 cj5. private message me if interested.

 

I put dana 44 front and rear off a wagneer on my jeep (its a 69) front disk and rear drum all I did was to remove the check valve from the front line on the master cyl. the I just keep a eye on the fluid level. I have had it that way for 7 years or so and never had any problem. It is not exactly right but I plan to upgrade to swing peddles some day.R)

 

I just did a 4 wheel disk upgrade and my 69 cj 5 and used a mastercylinder off of a 74 cj 5.
The 74 master cylinder had no residual valves in it and also it was a 1 inch bore. It also had the brake lines coming out to the pass. side just like the oringal. I went to the 74 master because my local napa wanted about 200 bucks for a new master and Krage hasnt been able to get me one. I just had to trim the cover to get it to clear the frame otherwise it bolted in. I also made up an adjustable pushrod to get things to work a little better , but it wasnt really needed. The brakes work GREAT.

 

Why does it matter? I believe it, just didn't know it made a difference. I think I did it the other way on mine (front to front). Stock '70 dual master with dana 30 disk front and stock 10" drum in back. It works ok, however, I sometimes have to pump the pedal one time to get enough braking to stop quick. Thinking I could try switching the lines at the MC.

 

If you read the posts in this thread it will become apparent.
http://www.earlycj5.com/forums/showthread.php?t=14411&highlight=dual+master+cylinder

 

Thanks Mike for reminding me about that thread.

If I get the chance I think I'm going to try changing mine.

I still don't understand the reason that it would be better one way over the other. The MC looks like it would have the same capacity either way. And, from the Factory it was front to front, rear to rear. If it's better I'll take it, even if I don't know why.

 

I agree I have not been able to find someone to explain to me why it makes a difference, but since I just went through this I am a believer. I have checked with a number of friends with otehr vehicles (74 Blazer, 68 Mustang etc...) and these are set up like the thread, front ot rear etc....Prior to changing the brake lines my pedal would go all the way to the floor and finally stop the vehicle. I could tell the front brakes were not grabbing like they should. Now that I switched them around I have almost full pedal and I can actually lock up the front brakes.

 

I am using a stock M/C. Both resevoirs sure look the same. Does it make sense that the resevoir closest to the piston gets more push, therefore more pressure?

 

Digging futher into the FSM does show which port is which. Under master cyl. reconditioning, assembly, it states, "Install the secondary piston assembly first and then the primary piston which is supplied in the repair kit." This would indicate that indeed the front port is for the rear brakes and the port closest to the pushrod is for the front. Of course I went out and looked at mine and it's wrong so I have a project for Saturday.