M35a2 conversion to M35a3 dual circuit brake system

[CBR Metalworks]

I recently bought a 1968 M36a2, the truck had no brakes when I got it, so I went ahead and pulled the master cylinder and air pack off to try and figure out the problem. The front boot on the master poured brake fluid out so I assume that was the problem, but instead of fixing the single circuit system I decided to go ahead and convert to dual circuit brakes off an A3. I bought both air packs, brake pedal/master cylinder assembly, and the associated lines for about $500. I just figured it would be much easier to upgrade now than wish I had later...

The MAIN problem I have found is the pedal mount is completely different on the A2 and A3. The A2 obviously has a clutch, the shaft goes through the frame for the clutch pedal, the A3 pedal mount has that shaft in a slightly different spot which means the hole in the frame has to be drilled in a different spot. I chose to cut the hole in the frame with a torch because I didn't want to fight a 1/2" drill with a 1" drill bit, the hole doesn't need to be pretty. The A3 brake pedal is slightly shorter in length, so I think it will fit perfect, the A2 clutch pedal will likely either need to be shortened, or the hole in the floor will need to be cut larger.


With the A3 brake assembly, if you do not have a drill bit long enough to go through the existing hole (from the other side, not pictured), then you will have to grind or mill off the pictured casting, then drill it out to 1" from the backside. Luckily there is already a 1/2" hole that is there for centering. Even after I drilled to 1" I had to smooth it out some to fit the A2 shaft through it. Sorry for the bad pictures, I had more but they didn't upload right.

 

[CBR Metalworks]

I also took apart the master cylinder to rebuild it because it had a lot of rust at the front of the plunger. I smoothed the bore with scotch brite on a drill, ended up reusing all the O-rings because I could not find O-rings locally that were EPDM, and the existing ones looked fine. This was my first master cylinder rebuild and I must say it was not bad at all, even without instructions. Just be sure to take the top plate and the 3 'pins' out before removing the plunger. The biggest advantage to the A3 master cylinder is that it can rebuilt with cheap O-rings, and does not require any sort of 'kit'. (although finding those O-rings may be hard on a weekend as I found)

 

[clinto]

I saw that auction and I thought it was very misleading/disreputable for the seller to have put M35A2 in the title, knowing the pedal assy. was different.

Glad you were able to make it work.

 

[glcaines]

You can get virtually any size of EPDM O-ring from McMaster-Carr. I'm in a very rural part of North Georgia and when I order from McMaster I normally receive the shipment the next day via UPS.

 

[CBR Metalworks]

He probably did it to make it easier to find. It still stated it was for an A3 though.

Best I can tell so far this should not be too hard of a swap, the advantages of a dual circuit system should make it well worth the effort.

 

[welldigger]

Very nice thread. This will indeed be a nice upgrade.

 

[CBR Metalworks]

The master cylinder bracket bolts up just fine, since it had to be drilled through all the way the top hole closest to the pin is not useable, but the other 4 holes line up with existing holes in the frame. Note I did have to cut another hole in the frame for the pin the clutch pedal attaches to since it is slightly higher and farther forward.
**The clutch pedal linkage had to be shortened about 1", it had plenty of threads showing, no welding was needed. The clutch pedal ARM will need to be shortened about 1", it will have to be cut and welded back together.**


The front airpack bolts up to the existing brackets, I decided to mount the rear airpack just behind it to make it easier to run air/brake lines to the rear. I replaced the hardlines going to the front and the rear axles because they looked pretty rough. It would be ideal to mount the airpacks up under the frame somewhere that would look better, but this will get me by for now.


Below you see where I mounted the fluid reservoir and an installed picture of the master cylinder.


I have one air line to install and a small section of tubing for the rear brakes, other than that it is ready to bleed the brakes and go for a test drive.

 

[glcaines]

The MAIN problem I have found is the pedal mount is completely different on the A2 and A3.

What about the late model A2s that were sold to the Air Force. They had dual circuit brakes. How did they handle the problem that you found?

 

[CBR Metalworks]

What about the late model A2s that were sold to the Air Force. They had dual circuit brakes. How did they handle the problem that you found?

I do not know, I have not seen one. I do know there would be no way to make the A3 master cylinder work with the A2 mount (it would hit the frame crossmember).

 

[clinto]

What about the late model A2s that were sold to the Air Force. They had dual circuit brakes. How did they handle the problem that you found?

There are 3 pedal mounting assemblies:

M44/M44A1 & M44A2 w/ single circuit brakes (i.e. 1986 and older)

1987-1989 M44A2 USAF contract: This allows for the clutch pedal (and winch PTO shift lever mounting)

M44A3. The M44A3 mount does not have provisions for the clutch pedal (which CBR cleverly found a way around) or the shifter mount for the PTO.

 

[clinto]

I do not know, I have not seen one. I do know there would be no way to make the A3 master cylinder work with the A2 mount (it would hit the frame crossmember).

1987-1989 dual circuit A2 pics here: http://www.steelsoldiers.com/showth...ering-Thread&p=1091181&viewfull=1#post1091181

 

[CBR Metalworks]

I got the clutch pedal on, works great. I also finished all the lines to the airpacks. Rigged up a garden sprayer to pressurize the brake fluid reservoir, bled the airpack for the front brakes, and the front brakes. Took it for a quick test drive around the neighborhood (and to the gas station for some diesel), the brakes definitely work, seemed to work best if I pumped it a couple times though. It may still have a bit of air in it though. I need to replace a rear wheel cylinder or two before I fool with bleeding the rear brakes.

Going to pick up a 91' 5-ton tomorrow, it's funny how I go from none of something to multiples in such a short time (never had a military vehicle until about a month ago).

 

[TedCat]

Are the A2 dual circuit masters the same as the A3?

 

[Jeepsinker]

No they are not. They are in no way compatible.

 

[502NDMP]

I have an 1987 M35A2C and I bought it in large part for the dual circuit brake system.

 

[Richard D]

Any updates?

 

[w3azel]

I bought the truck drove it home. It sat for about 18months and then I sold it to my neighbor about a year ago before I moved. I couldn't tell you how much better the brakes are because I never bled them properly but if you pumped them they worked great. More work needs to be done on fit and finish, the pedal was rubbing bad on something and it would stick.

 

[jacklegjim]

Not to hijack this thread but, I just completed putting a A3
system on my 83 A2. I is fully working with rebuilt wheel cylinders using Napa kits.
New hoses and Rebuilt the master cylinder with a Bindex kit.
I used DOT air brake line for the air lines and added a check valve for the output
to trailer brakes. The truck stops good just like it should.
I don't see where this upgrade would make it stop any better
than the single circuit system it just adds a back up if part of the system fails.
It took me about a year to complete working on it a little here and there and collecting parts.
I still need to swap in A3 air tank or add another tank to split the air system.
I have not road tested it yet because I am not finished with the truck
and right now I have the engine torn apart to replace a piston and liner.

 

[rustystud]

Not to hijack this thread but, I just completed putting a A3
system on my 83 A2. I is fully working with rebuilt wheel cylinders using Napa kits.
New hoses and Rebuilt the master cylinder with a Bindex kit.
I used DOT air brake line for the air lines and added a check valve for the output
to trailer brakes. The truck stops good just like it should.
I don't see where this upgrade would make it stop any better
than the single circuit system it just adds a back up if part of the system fails.
It took me about a year to complete working on it a little here and there and collecting parts.
I still need to swap in A3 air tank or add another tank to split the air system.
I have not road tested it yet because I am not finished with the truck
and right now I have the engine torn apart to replace a piston and liner.

If you went with the larger bore wheel cylinders you would notice a big difference in stopping power. Since the larger bore wheel cylinders use more fluid the single air-pack system is not big enough. The A3 deuce has larger front wheel cylinders. Look at "Peashooters" brake post. He has all the numbers to convert to the larger bore cylinders.

 

[Jonboy0666]

So what all parts do I need and where can I get them