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Discussion Starter · #1 ·
The LSPV on my 1980 lifted (~3") longbed pickup with 35" tires was leaking. I tried to find one but they aren't available for an '80 anymore. However I managed to remove the piston, clean up the gunk, reassemble it, and it appears to not be leaking at this point. But I suspect I'm on borrowed time.

My LSPV has 2 lines, doesn't have a bleeder, and has a plug at the top. The pictures of one for a 1983 show a bleeder, show no plug at the top, and has what appears to be an additional port opposite the sliding pin (mine has a blanked off boss). Does anyone know if a LSPV for a '83 pickup will work on a '80 if I plug the additional port?

I realize a lot of people eliminate the LSPV or replace it with a manual proportioning valve but I like having the LSPV.
 

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I would think the newer LSPV could be made to work. Plugging that extra port, like you said, sounds like the only extra work you would need to do if all the fittings are the same size. I am guessing the older LSPV only has one output that is split for both back drums and the newer valve has separate ports for left and right drums.
 

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Discussion Starter · #4 · (Edited)
I thought I'd give this a little bit of a bump. As expected my LSPV started leaking again. I've done a little more research and the 3 port LSPVs are actually a load sensing proportioning and bypass valve (LSP&BV). These feed bypassed fluid to the front brakes (I'm not sure exactly what for).

But my question remains - could I replace my LSPV with a LSP&BV (and plug the bypass port) and expect it to work correctly?

Edit: I found a document that describes the operation of the different proportioning valve systems:

It appears that the LSP&BV is a fail-safe if the front brakes loose pressure. Without pressure from the front brake circuit the LSP&BV will apply unproportioned pressure to the rear brakes (like it wasn't there). It appears I would need to put a Tee in the inlet line and feed this bypass port if I want the load sensing function to operate properly.

Any comments? Has anyone replaced a LSPV with a LSP&BV? Does anyone think just plugging the bypass port would work?
 

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It seems that you would have to plumb it in as designed like in the newer trucks if you really want to keep an LSPV. Try it and see? If it doesn't, plumb it in as designed or get a manual prop valve.

I have the newer style (1988) and I finally got rid of mine and put in a Wilwood manual one near the master cylinder. Cheap, easy and effective.

Looks like a lot of effort to get a set of the lines and fittings or make your own in order to keep your LSPV.

Good luck and post up whatever you decide to do. Dead end threads suck.
 

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Discussion Starter · #6 ·
Yea, it doesn't look like it is worth the effort to keep the LSPV and it may not work correctly after all that.
I'll probably go with a manual valve but if I go through that effort I'll probably go the extra mile and mount it in the cab.
I might try bypassing the LSPV and see how it works but I suspect I won't be happy with the rear end locking up.
I'll report back no matter what I do (eventually).
 

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Discussion Starter · #7 ·
Update #1
I bypassed the LSPV and took a test drive. My rear brakes definitely lock up too early. I don't know how some people can get away without one on a stock Gen 1 brake system.

Off to figurie out how I'm going to mount a manual proportioning valve in the cab.
 

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Discussion Starter · #8 ·
Update #2
I installed a Wilwood knockoff proportioning valve. It looks just like the Wilwood valve but doesn't have the Wilwood name on it. Even with the knob all the way out the rear brakes lock up slightly before the front brakes with an empty bed.
Those of you that installed a genuine Wilwood proportioning valve, can you adjust the valve so the front brakes lockup before the rear brakes?
 

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I had the Wilwood on a 91 pickup and I could adjust it so the rears didn't lock up too soon. The only thing I can offer is that I saw proportioning valves with different specs for the front to rear bias or the percentage of reduction.. I don't have a link unfortunately. Maybe look at what Summit or Jegs has to offer and check the specs. Good luck, I hope you get it dialed in.
 

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Discussion Starter · #10 ·
I decided to live with it for a while to see how it goes. The rear brakes will lock up first at lower speeds (~5-10 MPH). However the front brakes will lock up first at higher speeds. Also, it seems that as the brakes warm up the fronts will lock up sooner.
 
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