Dual Reservoir Master Cylinder

by Randy Merritt

Randy Merritt has documented the details of his installation of a new master brake cylinder on his 1962 CJ-3B. It's an upgrade that has been discussed on the CJ-3B Bulletin Board, but one that initially seems quite challenging.

Jon Paulsen describes the reason for the upgrade: "One drawback of the stock master cylinder used on flatfender Jeeps, compared to modern brake systems, is that it is a single reservoir master cylinder (MC). If you lose fluid to the point of failure, you lose all four brakes. Eeeyoweeeee... hope your hand brake and 2nd gear syncroniser works. Modern systems are a dual reservoir. One reservoir per pair of brakes. So, if you lose fluid in one reservoir, you lose about half your pedal height and two of the four brakes. The only real fix for this is to upgrade to a more modern dual reservoir system. The next best thing is to flush the system at least anually, and keep a close eye on fluid level."

Brian asked for advice: "Since I was looking at my Jeepster manual for PCV stuff I ran across the illustration they have of a dual master brake cylinder setup. Has anyone tried to convert to a Jeepster setup? There is also an illustration of the pedal and mounting bracket. Obviously the bracket would need to be acquired or fabricated, but since the Jeepsters used F4's, is there enough room on the firewall to mount the master cylinder?"

JC Jenkins: "I am running Jeepster pedals in my Hi Hood. The firewall had to be re-inforced, the pedal hangers need to be trimmed a little, and I mounted both pedals to the left side of the steering column, to allow space for the gas pedal. I am using the master cylinder from a 1970 CJ-5, soon to be switching to a 1978 master cyl. for the disc brake setup. I am using a small Ford (round shape) master cyl. for the Landcruiser slave cylinder for the clutch. Another reason for the mounting as far to the outside as I could, was to facilitate a large air cleaner on the Buick V6. It's a tight fit, but it works."

Joel Kamunen: "4-Wheel Parts Wholesalers sells a swinging pedal kit with a dual master cylinder setup. It's an aftermarket thing and I've never seen one, but getting rid of that single reservoir master cylinder would be an improvement. Some other domestic vehicles were produced until 1966 with the single master cylinder. I have been looking into the dual master cylinder for the stock under-the-floor location but have come to the conclusion that the swinging pedal setup would be the way to go."

Jyotin: "You can simply drop in a master cylinder from a '68 to '71 CJ-5 -- you'll have to re-plumb the lines. You'll need two proportioning valves to put in the lines as part of the conversion. I do not know where or how to get the valves unless you can find a '68-'71 Jeep in a boneyard somewhere. These are not parts in high demand, so if you can find the Jeep you ought to be able to find the valves."

Randy's Installation

Before the installThe final mechanical upgrade I have done on my 1962 CJ-3B frame-up rebuild is replacing the original master cylinder with a dual-reservoir master cylinder from a 1969 CJ-5. I have been able to gather a lot of information from various sources including CJ3B.info. Various owners have mentioned using the type I just installed, but there is really not a lot of guidance. So here are a few pictures of what the install looks like on my 3B. The picture on the right shows the frame and engine before I started the install.

The hardest part was locating the required parts. Since this cylinder was only used from I believe '68-'71, it is almost impossible to find one of these Jeeps in a salvage yard, and if you are lucky enough to find one it has already been removed. My search lasted over a year and I found mine just by accident in a box of old Jeep stuff a friend was going to throw away. Really the only parts you need are the master cylinder mount that bolts to the left frame rail, the brake/clutch cross shaft support (2 pieces), and of course the master cylinder. The existing brake/clutch cross shaft from your early flatfender can be used as it is the same as the one the new supports use.

First thing is to remove the old master cylinder and hardware. Then remove the clutch and brake pedal arms. Now remove the cross shaft. The only thing that should be left on the jeep is the brake lines, the master cylinder frame mount which is welded to the frame, and the brake/clutch cross shaft support bearing that is riveted to the under side of the frame rail. First thing is to grind off the heads of the rivets and the small spot welds that hold the brake/clutch cross shaft support bearing to the under side of the frame, With that accomplished using a punch drive the rivets through the frame and the support bearing will fall off.

The next and hardest thing to do is remove the old master cylinder mount from the inside of the frame rail. To do this grind off the welds top and bottom. Now the tricky part. The old mounting plate must be cut at an angle to allow the new master cylinder to attach to the new mount. The dual reservoir master cylinder sits inside the frame rail approximately 1/4-inch. The easiest way to describe how to cut the mount is to cut it to match the frame rail on the opposite side. With this done the top inside edge of the frame rail must be cut/ground back approximately 1/4-inch; this will now allow the master cylinder to mount properly. I was able to accomplish the frame modifications using a cut-off tool and a 4-inch grinder. It worked very well.

Rear viewThe install is really quite easy, being entirely bolt-on. Place the new cross shaft support bearing on the underside of the frame rail, as it uses the same holes as the one that was removed. Place the master cylinder mount inside the frame rail and this too uses the same bolt holes on the bottom side. Attach the new pieces snugly to the frame and now you must mark the top side of the frame rail and drill 3/8-inch holes to attach the mount on the top side. See also a top view of the installed mount (20K JPEG).

New cylinderA 3/8 hole must also be drilled in the side of the frame rail to attach the new support bearing as this one uses an additional hole. With the holes drilled and the new frame mount and support bearing installed you can now insert the brake/cross shaft and pedal arms. Install the dual-reservoir master cylinder, connect all the linkage, run new brake lines and you are essentially finished.

Front viewThe new install allows you to run a line directly to the back brakes as with the front, now making them completely independent of each other. Now if either the front or back was to fail you will still have brakes. The last item is to install a proportioning valve in the system to prevent nose diving and rear wheel lock-up which can produce uncontrollable skidding. This might be necessary to fine tune front-to-rear wheel biasing. If so they can be purchased from either J.C. Whitney, Stainless Steel Brake Systems or Wilwood Mfg.

The only problem I encountered was where to put the brake light switch since it can no longer be attached to the master cylinder. This was quickly resolved by attaching it to the top side of the three way block that the brake lines run to on the forward side of the left frame rail.

This modification was completed in one day using only hand tools, a cut-off tool, and a 4-inch grinder. It really helps to have the tub removed as I did, but it can be accomplished from underneath although taking considerably more time.

I undertook this primarily because I installed 4-wheel disc brakes, but even with drum brakes I feel it makes your old flatfender much safer on the road, considering modern road conditions and speed. If installing disc brakes, remember to remove the residual check valve in the master cylinder.

Last but not least, always remember:

  1. This is a major modification to your braking system. You may need to do some things that are not described in this article due to differences between your vehicle and mine.
  2. Modifying your brakes can be dangerous to your health. If you are not sure if you are qualified to do this, don't! Go spend $300 on a kit with directions and a warranty.

-- Randy Merritt

Herm the Overdrive Guy now offers a Dual Reservoir Master Cylinder Conversion Kit.

Thanks to Randy for the report on his project. -- Derek Redmond

Also on CJ3B.info, see Randy's description of Wrangler Springs for a '62 3B.

Return to the CJ-3B Tech Tips page for more Tech Tips on brakes.

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Last updated 23 October 2012 by Derek Redmond redmond@cj3b.info
All content not credited and previously copyright, is copyright Derek Redmond