What is this? (LSPV Valve)

[Grit dog]

^ Makes sense why it's sort of a jigsaw puzzle....because there are no other orientation marks.
I've gotten mine to work a couple times full power, trial and error, you can feel it "click" inside the valve at some point and before or after that is where it is free flow.
Just haven't been able to get a good mark and keep it there.
It's kinda frustrating, but like I said, mine works and its one less project, once i get it on the road, maybe can hook it back to the linkage and keep it open empty or loaded if I clock it right?

 

[Grit dog]

@Blue Ox , do you have a better pic of the parts of that one you posted disassembled?
Can't see the cam and not certain how that spring doohickey on the plastic piece works
Interested how many degrees of rotation is "free flow" vs the prop valve in closed position.

 

[Craig 85]

I’d toss it in the garbage except my brake lines are perfect and haven’t found or fabricated a fitting to simply swap it out without messing with the factory brake lines.

On my '87 K2500 back in the early 90's I disconnected the lines off the valve and made an adapter line to fit between the two OEM lines.

For my K30 here's how I did it. I don't recall if the K20's are set up the same. Once I removed the valve, I pulled the OEM brake line away from the frame and connected it throught the bracket for the valve.

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[Grit dog]

^ Thanks for sharing.
Yes, it wouldn't be too difficult and the setup looks the same on the 3/4 ton.
It's just one of those, "if it ain't broke" type of things. I still haven't even got my frame as shiny as yours....much less optional projects!

That's the thing, if I could just get it clocked right, I could lock it in place with the OEM bracket which is also all in tact and would take mere minutes and cross it off the sht to do list!

Speaking of Hirsch. That's our sons hockey nickname...you know since all good hockey players have a nickname...Jonesey, Schmitty, etc.
He's Hershey or on the ice it's Hersh. For Hershberger.

 

[Blue Ox]

@Blue Ox , do you have a better pic of the parts of that one you posted disassembled?
Can't see the cam and not certain how that spring doohickey on the plastic piece works
Interested how many degrees of rotation is "free flow" vs the prop valve in closed position.

It's more about setting the cutoff point than degrees of rotation for either event.

Here's a pic of another cam I have laying around. Obviously this one is in rough shape, but hopefully you can see the step in the cam.

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It's the step on the right side at about 2 O'clock that changes it from on to off as it turns counterclockwise. There's nothing you can feel as to where that is, which is why they used the plastic gauge tool.

The valve itself sits vertically on the centerline of the brass shaft, if that helps.

 

[Grit dog]

^ perfect so it’s off for about 120deg.

 

[Blue Ox]

No, it's the opposite. The cutout is the range where the extra proportioning is active. The high part of the cam locks it out.

 

[Grit dog]

10-4.

 

[Craig 85]

I still haven't even got my frame as shiny as yours....much less optional projects!

Speaking of Hirsch. That's our sons hockey nickname...you know since all good hockey players have a nickname...Jonesey, Schmitty, etc.
He's Hershey or on the ice it's Hersh. For Hershberger.

It's spray paint FYI. I had a clean California truck to begin with that was off the road for 10 years before I got it.

My Youngest son's nickname is Hershey, lol.

 

[Rudy Mienert]

Following this, as my 87 C3500 could use better braking power, loaded and pulling a trailer. Im still confused, but I am suspecting the forward proportioning valve might be different for trucks using the LSPV. Has anyone replaced the forward when removing the LSPV?...or installed an adjustable, like a Wiwood?

 

[Craig 85]

Following this, as my 87 C3500 could use better braking power, loaded and pulling a trailer. Im still confused, but I am suspecting the forward proportioning valve might be different for trucks using the LSPV. Has anyone replaced the forward when removing the LSPV?...or installed an adjustable, like a Wiwood?

I removed the rear valve on two trucks and got better braking from both without locking up. Both have 33” tires. I can’t recall if I did it on the ‘87 dually I had.

My guess the front valve is the same as all the years prior to GM using this. I had an ‘80 C20 3+3, basically a 1-ton chassis, it did not have the rear valve and didn’t lock up.

The only time I had a problem with lockup was on my ‘79 K15 short bed I did a 3/4 ton axle swap. During that process I added the 3/4 ton master cylinder. That truck also had 33” tires and a 4” lift. I believe on that truck the lockup was due to the short wheel base as none of my long beds with the same setup did it. I was going to add an adjustable valve for the rear brakes, but sold it before I could.

In your case I would remove the rear valve and see what happens. If the rear locks, then install an adjustable for the rear. You’ll just need to make two marks on it, one for empty, one for loaded.

 

[Blue Ox]

Following this, as my 87 C3500 could use better braking power, loaded and pulling a trailer. Im still confused, but I am suspecting the forward proportioning valve might be different for trucks using the LSPV. Has anyone replaced the forward when removing the LSPV?...or installed an adjustable, like a Wiwood?

@Keith Seymore would be the guy to access the records for your truck and see what valves were used.

 

[Rudy Mienert]

@Keith Seymore would be the guy to access the records for your truck and see what valves were used.

I will do that, especially since my truck was missing the glove box, with the codes sticker, and Im guessing at the installed options..

 

[Keith Seymore]

In your case I would remove the rear valve and see what happens. If the rear locks, then install an adjustable for the rear. You’ll just need to make two marks on it, one for empty, one for loaded.

Sorry - we moved last week and the big book of brake part numbers is buried somewhere. I haven't even found my razor and toothbrush yet.

I would do what Craig (most recently) and the others have suggested.

The rear height sensing valve was added as a FMVSS108 "test beater" before antilock brakes were available. Some configurations were so on the edge that we would ask for a specific technician to drive (ie, "we want Wayne to drive that one") and we would run development tests until we got one that passed and then (retroactively) label that one as our Validation test.

Unless you are running Federal brake tests you should be ok without it.

K

 

[Grit dog]

I will do that, especially since my truck was missing the glove box, with the codes sticker, and Im guessing at the installed options..

I don’t think the spid label would tell you specifically. I have a K20 with the LPSV from factory and it doesn’t have a specific option for it.
It was as Keith put it, to dial back the big rear drums for unloaded driving (or testing certification).
On a C30 I would absolutely remove it. Especially if it’s a dually.
The difference in rear braking is a lot. I haven’t done it simply because it’s another project and the truck is a cruiser that had all new brake components when I bought it so never even an excuse to crack a brake line yet.
If it was being used for any towing or hauling at all, it would have been off like a prom dress years ago.