Tandem or Single diaphragm booster?

I'm pretty sure the booster on my 86 C-10 is toast as I can't get it to hold any vacuum when I try to pump it with my Mityvac. (Can't even get it off ZERO with vigorous pumping.)

So I called a local salvage yard that sells used parts - figured I'd try there first before rolling the dice on anything from a parts store these days. And they asked if I had a single or tandem diaphragm booster. Well I was immediately stumped as I've never heard of such a thing. My booster looks just like all the other power brake boosters I've seen on 73-87 squares for years. So I didn't know what to tell the guy.

Would the law of averages dictate it's a single or tandem diaphragm?

Far as I know, the single ones tend to be larger diameter and not very thick. And dual diaphragm boosters tend to be a little smaller in diameter and a little thicker.

Got a picture of yours?

You could cheat and look at the pictures on RA.

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ron350 said:

You could cheat and look at the pictures on RA.

Click to expand...

Looking at the RockAuto selection, one of them does say "with 2-3/4" rear brakes on one of them - that one is labeled as a dual-diaphragm unit. So I have to assume that means I have a single diaphragm booster (since I have the standard brakes).

Anyone know if it'd be a bad thing if I got the dual diaphragm booster and put it on my standard brake set up?
I did harvest all the parts from a junkyard C10 with the HD system to install the HD system on my truck. (Although a popular post on here about that upgrade said the booster was not unique, so I left it behind.) So I might add those brakes at some point down the road. It'd be nice to have the booster in place ahead of that - as long as two diaphragms in my booster doesn't wreck havoc on my standard system.

Need to know JB3 (single) vs JB5 (tandem).

For that we have to know your GVW (5600 vs 6100)

K

Yes - 2.75 rear brake would be tandem; 2" rear brake would be single.

K