1988 Air force deuce brake system rebuild

My deuce was improperly converted to dot 3 and now I have no brakes. When I got the truck I could pump the brakes to get some stopping power, but now there is nothing. It needs a entire rebuild, MC, air packs, and wheel cylinders. It looks like the master cylinder is the hardest part to find. Ideally I would like to find a kit for it if there is one. I have read that parts for the dual brake system are not hard to come by, but I can't even find the part numbers or TM on the MC. Help is appreciated even if it comes in the form of a scolding for not looking in the right place.

Thanks

This may help.

2deuce, go to the Deuce Modification and Hot Rodding section of the forum and look for duel circuit brake engineering. You will find a butt load of information about parts and everything else you did not even know you could know.
good luck.
I would put a link here but my old a$$ iPad can't

Subscribed for later.

I looked at the MC in the manual 9-2320-209-14&P . The part # 5934071 is for the MC, but it looks different than the one on my truck. Mine only has one fill cap. I wonder if there are other differences. My truck is a 1988 M35a2c.Will a part # like that do me any good at Napa or am I limited to a military surplus dealer?

Should look like the one in the manual with a plastic reservoir. Is yours all cast?

I have a 87 dual circuit system and the MC reservoir is plastic and one cap.

That is what I have. Plastic and 1 cap. By having 2 caps tells me that it must have 2 reservoirs in 1 split tank. Mine does not.

my manual TM9-2320-361-24P ...page #0080 00 shows master cylinder part# 12368254. It does not state whether its a dual circuit one. I'll look in the other books as this one does not look like mine. One cap can fill both split reservoirs like on my cars. they just have a internal lower baffle that the fluid runs over to the other side. that way if the back or front brake line blows, there is still fluid for the other as its isolated by the baffle.

2deuce said:

That is what I have. Plastic and 1 cap. By having 2 caps tells me that it must have 2 reservoirs in 1 split tank. Mine does not.

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You have the same master cylinder as my 1988 deuce has. The seals are all readily available from any "O" ring supplier that sells "Viton" and "silicone" seals. "Peashooter" (Aaron) has a great write-up on this on his "brake" information post.
The only seals "not" readily available are the two special "tank" to "body" seals. Their a round funny looking seal. Looks like a spoke wheel. There is a supplier out there that does sell the "special" seals, I just cannot remember who right now. I bought a couple of spares for my system from them.

2deuce said:

That is what I have. Plastic and 1 cap. By having 2 caps tells me that it must have 2 reservoirs in 1 split tank. Mine does not.

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My 88 airforce deuce has the same MC, I think the second cap is back under the bracket but the reservoir is only partially divided to allow fluid to be filled from the front.

MudMarine said:

My 88 airforce deuce has the same MC, I think the second cap is back under the bracket but the reservoir is only partially divided to allow fluid to be filled from the front.

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MudMarine is right. If you have a plastic MC reservoir then it will have the 2 caps, but you can only see one of them through the cab's floor access door. Filling fluid from the one cap will fill both sides of the reservoir. The reservoir has an internal baffle that splits it in 2, but the baffle only goes up 3/4 of the reservoir's height.... so topping it off will ensure it fills both sides.

The only rebuild kit I know of for these master cylinders is the RAYBESTOS MK1624. I'm not sure if they still make it or not however, its getting pretty hard to find (although as of today, there is one on Amazon). This will just include seals and a cir-clip. If you end up needing a new master cylinder, PM me and I can help you find one.

peashooter said:

MudMarine is right. If you have a plastic MC reservoir then it will have the 2 caps, but you can only see one of them through the cab's floor access door. Filling fluid from the one cap will fill both sides of the reservoir. The reservoir has an internal baffle that splits it in 2, but the baffle only goes up 3/4 of the reservoir's height.... so topping it off will ensure it fills both sides.

The only rebuild kit I know of for these master cylinders is the RAYBESTOS MK1624. I'm not sure if they still make it or not however, its getting pretty hard to find (although as of today, there is one on Amazon). This will just include seals and a cir-clip. If you end up needing a new master cylinder, PM me and I can help you find one.

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I knew you would still have your hand on the pulse of these master cylinders Aaron !
For all out there looking for master cylinders, Peashooter is the one to check with. He got me the three I own now.
I don't remember if I ever publically thanked you Aaron, so here it is. Thanks Aaron for all your help with my late model deuce's brakes system ! You were a tremendous help !
God Bless and keep you and your family safe !

Rusty, Do you feel that these master cylinders are a weak point? Is that the reason you have 3? Thanks

2deuce said:

Rusty, Do you feel that these master cylinders are a weak point? Is that the reason you have 3? Thanks

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No, but they are getting extremely hard to find. The vehicles that used them are few and far between, so the supply was limited when they where new. At the transit department we had one "mini" bus that used them. The bus was an extreme failure and all where returned to the manufacturer. It had nothing to do with the brake system though ! It was the whole "body" of the bus was falling apart. That and the stupid "single half leaf" rear suspension. It broke so many times, we had to invest in special fixtures to tow the buses back to the shop.

Here are some photos of a dual brake system. See where the MC hides.












At the moment there is a RAYBESTOS MK1624 seal kit on the popular auction site with the funny seals mentioned by rustystud for under 60 bucks. Perhaps this seal kit is for the dual brake MC I don't know.

It is interesting the auction cross reference list that this kit fits more than 60 applications for this kit. As in Ford hydro boost F700 F800 Chevy B60 C60 C70 + B6P042

frank8003 said:

Here are some photos of a dual brake system. See where the MC hides.
View attachment 759882

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It is interesting the auction cross reference list that this kit fits more than 60 applications for this kit. As in Ford hydro boost F700 F800 Chevy B60 C60 C70 + B6P042

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You would think with that many applications this Master Cylinder would be everywhere, but the truth is those where limited applications. Most Fords or Chevy trucks of those years and that size used "air brakes" . Try and look up the Master Cylinder and you will see what I mean. There are some Master Cylinders that look just like ours out there with larger bore sizes, but I don't know how that would effect our trucks brake system. To much pressure ? Not enough pressure ? You would have to calculate all the variables like brake line size and flow, wheel cylinder size and distance in the system plus lots more. I know in a "sealed" hydraulic system the pressure is suppose to be equal in all parts (excepting where restrictions are used) . But in reality there is differences and the engineers calculate that in. I'm not an engineer so I wouldn't do it on a street legal vehicle. On a "off-road" only vehicle, sure ! I would modify the crap out of it !

On an added "Post Script" . In an identical brake system, the Master Cylinder with the smaller bore size will produce higher pressures but lower flow volumes, while the Master Cylinder with the larger bore will produce lower pressures and higher flow volumes. So going with a larger Master Cylinder bore size can cause you trouble if you don't take that into account.

I just posted about the seal kit.
Raybestos Brake Master Cylinder Kit MK1624 at $58.99 total with 30 day refund buyer pays return shipping.

"At the moment there is a RAYBESTOS MK1624 seal kit on the popular auction site with the funny seals mentioned by rustystud for under 60 bucks. Perhaps this seal kit is for the dual brake MC I don't know."

If I needed a seal kit for an AF dual brake MC I would just buy it to see if it is the correct seals.

frank8003 said:

I just posted about the seal kit.
Raybestos Brake Master Cylinder Kit MK1624 at $58.99 total with 30 day refund buyer pays return shipping.

"At the moment there is a RAYBESTOS MK1624 seal kit on the popular auction site with the funny seals mentioned by rustystud for under 60 bucks. Perhaps this seal kit is for the dual brake MC I don't know."

If I needed a seal kit for an AF dual brake MC I would just buy it to see if it is the correct seals.
View attachment 759981

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That does look like the correct kit.