Front Disk Swap residual pressure

Morning all.
I'm gathering goodies to get my new d30 swapped into my cj and I've got the dis conversion ready to go except for one thing. (note I am using a complete d30 with the 2-bolt calipers)

I know that i will ned to change either master cylinders, proportioning valve, or residual pressure valve for my jeep.

Here's the difficult parts though. I've got through the floor pedals on a custom mount made by the PO to accomadate the 70 body. It is a dual chamber master. I figure he did this one of two ways
1) hacked the mount of a 70-71 cj and used the 70-71 dual chamber master.
2) made the mount from scratch and used a 72-75 dual chamber master.

So my options as I see it are the following
1) replace the master with one from the corresponding 79-86 disk.drum non power cj
2) add a disk drum combination valve behind the current master.
3) Remove the residual pressure valve from my currnet master and plumb a new 2# one in for the disks.

So With these options I have a few questions...
1) how hard would it be to put a later cj master cyl into a under the floor position?
2) If i use a combination valve do I still need to worry about residual pressure valves?
3) How do I remove the Residual pressure valve from my current master and can I remove it only from the front circuit and leave it in the rear?

What do you think is the best option?

 

oh and I searched "disk swap pressure", "disk swap residual", and "disk swap valve" and couldnt find the answer.


Thanks.
-Dante

 

I helped a buddy do his. We pulled the front brake line from the master cylinder, run a sheet metal screw into the hole and pull out the residual pressure valve (spring and rubber plug as I recall) re-install the part you pulled with the screw. Install 2# valve in-line to the front brakes. Wilwood makes a residual valve for disc that you can buy from Summit Racing online. You don't have to do anything for the rear drums.

 

cool. that was the same conclusion I came to. Thanks!

 

Question for you guys. I did the same thing mentioned above, swapped to 2 bolt caliper disk brakes and pulled the residual valve out of my master cylinder, but I didn't put in a 2# in-line cajigger. I have no issues with braking, kinda curious what that does....

 

It acts as a check vavle to keep fluid constantly on the piston so that when you press the pedal, there is no chance of an air bubble developing, especially at angles.

x2 on the Wilwood RPV, solved the problem on mine. I definitely did need one on the front discs, and I definitely did not need one on the rear drums.

 

Clint, you say you did have trouble without the valve? I just installed front and rear disc on my Jeep and I'm wondering if I might need to run some sort of valve to both ends. What do you think?

 

Residual pressure valves are usually only used when the MC is at the same level or lower than the disk brakes. Modern brakes do not use them to my knowledge.

Quoted from Wilwood's sight:

 

That's good info. My MS is on the firewall so I hope to be okay without them. Thanks.

 

I have through the floor pedals, my master is still higher than my brakes, but It might not be the highest point in the system. Also I figure that a little residual pressure might help keep the brake pedal a little firmer.

 

I only had trouble when ever I had the nose toward the sky, but then it was serious trouble! The first time it did it I almost shat my britches! Thought it was a fluke. Then it did it again. Thought it was air. Bled and bled and bled. Did it again. Put in the RPV and all was right with the world again. Whenever it would do it, it was essentially like you were running out of fluid. I could pump and build them up, but that first pedal would go straight to the floor. I had definitely switched out to the discs on the front, but don't remember if I was running the firewall MC or frame MC at that point in time.

 

Clint, your loss of brake pedal is very curious to me. I've had the same thing happen to me a couple of times after my disc brake conversion but only after an extreem off road obstacial. After bouncing up a hill my brake pedal went to the foor. I've got a firewall mounted master cylinder but I'm wondering if a RPV would help in my situation?

 

Yes, that is exactly the symptom they cure.
Posted via Mobile Device

 

Clint, did you run a 2 pound valve to the rear brakes or a 10 pound to the front? And how did you plumb it? Thanks in advance.

 

2lb for the disk and 10lb for the drums per Wilwood. Thats how my setup has been running for 3 years now with no problems.

 

Yup.

I'm going to have to look at the JEEP to jog my memory, but I think I used flared fittings. They are inline down near the caliper. Thinking out loud here, but wondering if you couldn't just put them up higher and effectively have more fluid volume under pressure.

 

Since the fluid doesn't compress, it shouldn't matter.

 

I have a MP Brakes catalog and they indicate to put the residual valve after the proportioning valve. That's easy for the rear brakes because there is one brake line coming out of proportioning valve and going to the rear brakes. The residual valve could be plumbed in that single line.There are two brake lines that come out of the proportioning and go to the front brakes. Would that require a valve per brake line?

 

Are you sure you have a proportioning valve and not a metering block. The catalogs do not show a prop valve for a 1976 cj. I know that the 1975 and older Jeeps did not use a proportioning valve. If you have a metering block the RPV's go before that block. 4 wheel drum brake setups usually didn't have a proportioning valve from the factory.

 

When I did my disc brake conversion I took the calibers and proporting valve off a later model junk yard CJ and installed all of it on my rig. I assumed it was a proporting valve I took off the junk yard jeep since it had factory disc brakes.