What the heck is this contraption going to the top of my 14boltl axle

[MuddiGGEr25]

I am in the process of pulling the 6.2L and TH400 for the guy buying it tomorrow afternoon and i guess i wasnt really paying much attention the last time i was under there, i thought this was just an exhuast bracket when i glanced under, but its got 2 "brake lines" of some sort going all the way to the front, and a lever system and it ends on the top of the 14 bolt axle, and the RPO code says G80, but i didnt think there was external linkage for that, i thought it was all internal.. also there is a junction under the radiator area that has 4 lines connected to it, i think this connects to that, not sure if its connected to the hydro boost pump or what, ill figure that out when i get the engine out tomorrow

[SkinnyG]

Looks like a load-sensing proportioning valve.

They are good things to have.

[gunrac]

also there is a junction under the radiator area that has 4 lines connected to it, i think this connects to that, not sure if its connected to the hydro boost pump or what, ill figure that out when i get the engine out tomorrow

That is the combination valve you are refering too..

[VileZambonie]

Look at post #3

http://forum.73-87chevytrucks.com/smforum/index.php?topic=16967.0

[MuddiGGEr25]

Ok i read that zambonie, and now i have a question, if the stock springs were so worn that the were near "flat" so i added a set of 1500lb 3" wide helpers springs, and intend to put 2" blocks above the axles will that affect the valve or will i need to readjust the geometry?

[SkinnyG]

Yes.

I had a load sensing proportioning valve on a Nissan Hardbody.  I lowered it 3", and the valve thought I had a house in the back of the truck, and the back brakes locked at every stop.

Pops has a load sensing proportioning valve on a Toyota Tundra, carries a 2000lb camper, and pumps up air bags to make it level.  The back brakes think the box is empty, and he goes through FULL front brakes every year.  The backs don't wear at all.

[MuddiGGEr25]

so I guess my goal should be to get it back close to stock height, but try not to affect the spring rate too much so that it will still "squat" some with the trailer attached so it can "sense" it

[Irish_Alley]

GM put out a TSB about the valve. they stated if a customer comes in with any complaint about the brakes number one step is to bypass the valve. theyre know to be an issue and arnt worth anything

GMC NUMBER: 88-T-151 (this one is about height issues)

http://www.truckforum.org/attachments/gmc-number-pdf.3545/

[MuddiGGEr25]

GM put out a TSB about the valve. they stated if a customer comes in with any complaint about the brakes number one step is to bypass the valve. theyre know to be an issue and arnt worth anything

GMC NUMBER: 88-T-151 (this one is about height issues)

http://www.truckforum.org/attachments/gmc-number-pdf.3545/

Mine defnitely appears to still be functional, as when i have to stomp on my brakes (due to deer, or idiot drivers, etc) my fronts never lock up, and i feel a shift in the braking, because at first the front end goes down and rear up (even more so when a trailer is attached) and then i feel something change within a few moments and the rear goes back down and the front levels out again, usually all within 2-5 seconds depending on how hard i stomp on them,   also seems to help out on loose gravel too when my other burb would lock the fronts on a sudden stop on loose gravel or dirt, this one does not.

Regardless im gonna print this off and keep it with me so if i run into issues i have the part #'s to bypass it if needed