3/4 ton "brake thingy"

[Storm Chaser]

On the rear axle of my 2wd crew cab, the flexible brake hose goes into a contraption mounted on the axle. It has some kind of pivot arm on it and also acts as the distribution to the rear brakes. It looks to me like the lever moves as the pinion rotates. My buddy's truck is a 3/4 ton (86 I think) and it has it also. However, my 76 3/4 ton doesn't have it and the 84 3/4 ton 4x4 I used to have didn't either. What is it and what does it do?

[red caddy]

My '77 crew cab had one , as does my '86 1 ton. It's a load sensative brake bias adjuster. as you load the rear suspension, it allows more braking to be done by the rear brakes (drums) The idea is to not allow the rear drums to lock up if the truck is lightly loaded, but allow full pressure to the rear wheel cylinders, when the truck is fully loaded.

It's just a fancy barrel valve that reads load weight as a function of the changing distance between the frame and rear axel. BTW, disconnect the arm and fully open the valve when bleeding the rear brakes, (I learned this trick from an old GM shop manual) otherwise, you can chase an air bubble for days... RED

[dieseldr4]

my 86 c30 has it too.. when the p.o. lowered the back, they left it alone, hence i got the truck with no rear brakes and the linkage and mount were wasted.. i bypassed it, my truck stops like it should and even with a couple "hold my beer" panic stops ive never had the backs lock up...i know out here these trucks are popular, so finding things like that is hard to do... btw , with a trailer loaded up to go racing with all my tools, equiment, stock car etc, it stops fantastic... hope this helps...

[red caddy]

My '86 1 ton SWB, narrow dually will lift the duals off the ground with a hard stab on the brakes, 'course there is almost no weight on the back right now, only the flatbed frame and the hitch receiver. The brakes are a little touchy on sandy or wet roads, but not scary. I don't drive it unloaded very much anyway. Finishing the bed, adding the genset, tool box and extra tankage will likely improve the braking around town though.

With the car hualer on and load leveler hitch, the old girl stops very well, (proportioner installed and properly adjusted) even in the rain. When I bought the truck, the PO had bypassed the prop and touching the brakes in a turn, on a wet or sandy road, empty, was a gay-ron-teed pucker factor spike... RED

[old Rusty C10]

can you take a pic of it?

[red caddy]

Sorry Rusty, I ain't got near big enough stones to do that again, on purpose. That was not a "hey, hold my beer N' watch this" moment. I was tryin' not to kill a "nearly dead" snowbird in a Kia (with Jersey plates) that pulled a "swoop N' squat" in the fast lane on I-75. The front's didn't lock, but the duals did, and bounced hard, leaving palm sized contact patches 3 or 4 feet apart, for a long ways. Not something I want to do again for a you tube video. RED

[powerdriver 1958]

do you see the part in this pic?

[MylilBowTie]

It should be on the frame.

[GM72K10]

I think this is what he's talking about. All K20s and C or K 30s should have these.

[red caddy]

I'm sorry, Rusty. I missunderstood your question, perhaps this pic will help RED

[Storm Chaser]

Yea, that's what I'm talking about. Is there a year range they were used? I looked at my 76 again and it didn't look like it ever had one.

[78 Chevyrado]

Does that valve take the place of a proportioning valve, or just work with it?

[red caddy]

AFAIK, it was an "add on" with certain suspension packages, towing packages, fleet trucks, chassis cab's and so on. The front cross member mounted proportioner is stock on most all trucks, '60's and up. Every "hydraboost" equipped truck I' ve seen had the extra valve, but I've never seen a "hydraboost" on half tons either. RED