What is this? (LSPV Valve)

[Jerry87v20]

Any idea what this is on my 87 v20??

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[bedwards]

Brake load/height sensing valve?

 

[Jerry87v20]

Is that stock?? Or did someone put that on?? It has a 4in suspension lift..

 

[Frankenchevy]

It doesn’t appear to be connected anymore. They probably bypassed it when it was lifted. Unless I’m not seeing it, usually there is a linkage that goes down to your rear axle from the valve.

 

[Jerry87v20]

I think the brake lines are still hooked up...I need to look at it tomorrow... going to put all new brake lines on... and getting rid of that value...just didn't know what it was..

 

[skysurfer]

There WAS a lspv there at one time but the hard lines look like the only thing left besides that angular bracket coming off the top of the differential which can also be removed. Yours looks like someone swapped in some type of valve with a thumbwheel adjuster.

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[HotRodPC]

Interesting though, I wasn't aware that 4x4's ever got that. I know it was only a limited # of years and was done away with, then a GM Service Bulletin came out to bypass it so it obviously wasn't a good thing.

BTW, It's LSPV is Load Sensing Proportioning Valve.

 

[Frankenchevy]

Interesting though, I wasn't aware that 4x4's ever got that. I know it was only a limited # of years and was done away with, then a GM Service Bulletin came out to bypass it so it obviously wasn't a good thing.

The cucv pickups have them. I pulled and saved mine.

 

[HotRodPC]

I actually think what's it's main purpose was for, where most think it's so your brakes work better when you're loaded heavy, it's actually the opposite of that. It's so your rear brakes don't work near as good when you're empty. I believe it's actually purpose was the first attempt at Anti Lock Rear Brakes. If you're weren't loaded, the rear brakes didn't get near the pressure to avoid locking up.

 

[Craig 85]

You have an adjustable proportioning valve for the rear brakes that someone install probably after the lift kit. I was going to install one of those on my K15 I did the 3/4 ton axle swap because the new 13" brakes were locking up too soon. I sold the truck before that though.

@HotRodPC my '85 K30 had one I just remove and an '87 K20 I had also had it.

 

[WFO]

Interesting though, I wasn't aware that 4x4's ever got that. I know it was only a limited # of years and was done away with, then a GM Service Bulletin came out to bypass it so it obviously wasn't a good thing.

BTW, It's LSPV is Load Sensing Proportioning Valve.

My 86 K20 has that proportioning valve. It has the the C6P HD option though.

 

[HotRodPC]

IIRC, it was just 84 to 87 20 and 30 series trucks that got it. I learned today that 4x4's got it too. I thought it was only 2wd trucks that got it.

 

[Rusty Nail]

Good thread.
+1

 

[Blue Ox]

I actually think what's it's main purpose was for, where most think it's so your brakes work better when you're loaded heavy, it's actually the opposite of that. It's so your rear brakes don't work near as good when you're empty. I believe it's actually purpose was the first attempt at Anti Lock Rear Brakes. If you're weren't loaded, the rear brakes didn't get near the pressure to avoid locking up.

I can't imagine you could just eliminate that valve. When I did the C6P conversion on the Suburban the rears would lock violently until I added that valve. It was not safe to drive without it. Absent that I would think some kind of proportioning valve would be needed.

But yes, Ks definitely had them although I think it was only the C6P 20s that got them.

 

[Frankenchevy]

I looked up c6p and kept getting results for gmt400 burbs... what is that option? I have jb8 on a k30 and a load sensing valve..

I’m not potting my load sensor back on for now. Although I did put caddy discs in the rear and a disc-disc prop valve up front. I think others have eliminated the rear pv with no ill result. Just proves you need to be careful with any brake mods for a while; until they’re proven. I’ll definitely be taking it easy for a while.