M35a2 weird brake system issues

[cbrTodd]

Congrats on confirming that you have the highly desirable dual circuit brakes!

I have never worked on a short air pack but there is a stickied thread that shows how to rebuild one.

New-Style (Short) Airpack Teardown & Repair with Photos

Since the TMs show where these new-style, short Airpacks are located and how to remove them, I'm only going to focus on what the TMs and other printed literature don't cover. I've searched high and low but haven't been able to come up with any kind of drawing, schematic, or instructions for...

steelsoldiers.com

I rebuilt my long style air pack last year and it wasn't too bad. The TM has decent instructions and 'Tactical Repair' on Youtube has a video covering it. I found rebuild kits in multiple places but I got mine from Big Mike's Motor Pool and it worked well.

On a truck you're not familiar with, opening up them both and installing a seal kit seems like relatively cheap insurance. I know the air packs are considered direct replacements for one another in the older trucks so I would think you could mix and match in a dual circuit truck but I haven't verified that personally. Maybe there is something about it in the latest M35A2 or alternatively the M35A3 TM?

 

[ToddJK]

Update

i have one long style and one short style air pack on the truck

I HAVE DUAL CIRCUIT BRAKES!!!!

That's a huge plus!

 

[GASCANS001]

Do you have pictures of the underside of the truck? I don't see an '88 with all the signs of it being an AF truck with split brakes and a plastic reservoir not having the second air pack unless things have been drastically altered.

Update. When I try to bleed with two people when soldier b is pushing In the pedal fluid is returning into the reservoir and spewing out the top of the cap.
Any ideas?

 

[Gypsyman]

Could be as simple as a bad seal in the master but there are guys here that are light years ahead of me on troubleshooting the split brake system.

 

[GASCANS001]

Could be as simple as a bad seal in the master but there are guys here that are light years ahead of me on troubleshooting the split brake system.

I’ll second the bad seal on the m/c

do you know if the typical rebuild kit for the single circuit is the same as the dual circuit

 

[Gypsyman]

Going from memory I believe the rebuild kit for our dual circuit trucks is the Raybestos MK1624. Hopefully someone will jump in here and verify that. @peashooter is one of our resident brake experts.

Edited to correct the member reference.

 

[peashooter]

Going from memory I believe the rebuild kit for our dual circuit trucks is the Raybestos MK1624. Hopefully someone will jump in here and verify that. @peashooter is one of our resident brake experts.

Edited to correct the member reference.

The rebuild kits are pretty hard to find these days as i suspect they quit making them, but in all honesty they really werent much just a couple orings and a c-clip. Id just buy a new master cylinder.
A nearly exact replacement for the 1988 airforce deuce is the Dorman M39477. It will be the same with the only exceptions being the reservoir will be labeled Dot3 (but dot 5 can be used since seals are EPDM), it will have slits in the reservoir cap seals to act as the breather, and it wont have the remote breather fitting installed (both of which you can add or modify on your own, but are only needed if you would be fording water deeper than the height of the master cylinder). These can be found online (such as Summit Racing).

 

[Gypsyman]

I have the following alternate rebuild kits in my notes but I haven't been able to confirm that they are correct. All of these kits include the springs and pistons. Pretty complete kits if you can find them. Again, confirm before searching.

Alternate/OEM Part Number(s):

GM 15513991
GM 2054811
Ford E0HZ2004B

 

[Gypsyman]

More information that may or may not be helpful. If you search Rock Auto for the Dorman M39477 (out of stock) it also brings up the Raybestos MC39477. These are on clearance for $53.84 plus shipping but would require you to swap your reservoir over to the new master cylinder assembly. The one small technical part to the reservoir swap can be found in old posts by peashooter. It just requires compressing the master cylinder pistons before bolting on the reservoir to avoid damaging the small residual pressure valves.

Possibly a viable option that would give you a very cheap brand new master cylinder if the reservoir fits properly.

 

[peashooter]

More information that may or may not be helpful. If you search Rock Auto for the Dorman M39477 (out of stock) it also brings up the Raybestos MC39477. These are on clearance for $53.84 plus shipping but would require you to swap your reservoir over to the new master cylinder assembly. The one small technical part to the reservoir swap can be found in old posts by peashooter. It just requires compressing the master cylinder pistons before bolting on the reservoir to avoid damaging the small residual pressure valves.

Possibly a viable option that would give you a very cheap brand new master cylinder if the reservoir fits properly.

I tried doing what you mentioned by swapping a plastic reservoir onto one of the raybestos m/c years ago and feel like it didnt work, but cant remember the specifics. I dont think the parts were interchangeable.

 

[Gypsyman]

Good to know. Thanks for jumping in.

 

[GASCANS001]

More information that may or may not be helpful. If you search Rock Auto for the Dorman M39477 (out of stock) it also brings up the Raybestos MC39477. These are on clearance for $53.84 plus shipping but would require you to swap your reservoir over to the new master cylinder assembly. The one small technical part to the reservoir swap can be found in old posts by peashooter. It just requires compressing the master cylinder pistons before bolting on the reservoir to avoid damaging the small residual pressure valves.

Possibly a viable option that would give you a very cheap brand new master cylinder if the reservoir fits properly.

What if I got that master cylinder and just did my own remote Reservoir attach it to the far wall or something?

 

[GASCANS001]

The rebuild kits are pretty hard to find these days as i suspect they quit making them, but in all honesty they really werent much just a couple orings and a c-clip. Id just buy a new master cylinder.
A nearly exact replacement for the 1988 airforce deuce is the Dorman M39477. It will be the same with the only exceptions being the reservoir will be labeled Dot3 (but dot 5 can be used since seals are EPDM), it will have slits in the reservoir cap seals to act as the breather, and it wont have the remote breather fitting installed (both of which you can add or modify on your own, but are only needed if you would be fording water deeper than the height of the master cylinder). These can be found online (such as Summit Racing).

I found 2 different master cylinders at my local Napa that “cross-references“ to the Part number you gave me

 

[Gypsyman]

What if I got that master cylinder and just did my own remote Reservoir attach it to the far wall or something?

If what peashooter said is correct and the reservoir won't cross over then the standard remote top plate wouldn't work either.

 

[GASCANS001]

I've done master cylinders and it worked ok.
I was very poor then and I don't recommend the practice.

I found that when I took the oil screw out of the old style pack. Brake fluid came pouring out. I’m going to assume a rebuild?

 

[rustystud]

Here's what I did with my brake master cylinder. In picture one you see the adapter I bought that bolted in place of the plastic bowl. Then I mounted a double reservoir to the firewall and ran stainless steel teflon hose to the master cylinder.

 

[M37M35]

The Raybestos MK1624 is the correct rebuild kit for the MC, but It's not available at RockAuto anymore, which is where I got mine from. You might be able to find it somewhere else.

What if I got that master cylinder and just did my own remote Reservoir attach it to the far wall or something?

That would probably work as long as it didn't leak around the snap-on lid. Maybe glue it on with RTV.

RockAuto also shows Cardone 138005 as a cross reference and it's in stock.

I found that when I took the oil screw out of the old style pack. Brake fluid came pouring out. I’m going to assume a rebuild?

There shouldn't be brake fluid there, so it would be a good idea to rebuild both airpacks while you're at it. That way you know you've got a good brake system.

 

[M37M35]

This thread has some more part numbers and more info on the dual circuit brake system.

DEUCE BRAKE LINE REFERENCE GUIDE (Sizes, lengths, fittings)

POST 1~ SINGLE CIRCUIT BRAKE LINES POST 2~ DUAL CIRCUIT BRAKE LINES POST 3~ BRAKE PARTS REFERENCE GUIDE POST 32~ BRAIDED STAINLESS FLEX LINES/HOSES POST 40~ DUAL CIRCUIT MASTER CYLINDER BRACKET INFO & CAD FILE SINGLE CIRCUIT BRAKE LINE INFO I've been selling Stainless Steel Braided Flex hose...

www.steelsoldiers.com

 

[GopherHill]

Here's what I did with my brake master cylinder. In picture one you see the adapter I bought that bolted in place of the plastic bowl. Then I mounted a double reservoir to the firewall and ran stainless steel teflon hose to the master cylinder.View attachment 875001

That is a very elegant and well done engineering job. Would be they came that way.

 

[rustystud]

That is a very elegant and well done engineering job. Would be they came that way.

Thank you.