What is the brak lever assembly attached to the rear diff?

[5akman]

What is the brake lever assembly attached to the rear diff?

I just put a Rough Country 4" spring/block kit on my K20 and it comes with some brackets to re mount the brake lever on top of the differential. Well, it doesn't seem to want to work so does anyone have a picture of the RC brackets in this position? What is the lever assembly anyway? I consider myself pretty mechanically inclined but I'm at a loss here!

 

[crazy4offroad]

Got a pic of it? It sounds like something I've seen on 80s Toyota trucks. It's designed so that when you're hauling a load it increases your rear braking power. But a pic would be 1000x more helpful.

 

[74 Shortbed]

That's what it is, increases brake power with a load so you don't lock up the brakes all the time when you're empty, had them on my duallys..

 

[skysurfer]

@chengny posted a GM tsb that was issued for mechanics instructing them on how to bypass the LSPV (load sensing proportioning valve) so it's not absolutely necessary to retain it. I kept mine but had to add a length of 1/8" thick flat stock mounted vertically to account for the 4" lift.

http://www.gmsquarebody.com/forum/showthread.php?t=5984&highlight=lspv see post #5 for the tsb

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Below is a copy/paste of an earlier post on the adjustment of the lspv.

You can't see it in this picture, but the bottom of the longer arm is attached to an arm bolted to the differential. As the suspension sags under load it rotates the short arm that's bolted to the round valve counter-clockwise, increasing brake pressure to the rear.

I removed the nut and short arm, then rotated the stem clockwise (to reduce pressure) a few degrees before reassembly. Took it for a drive and did a few panic stops. Had to do this several times until I got the brakes where I wanted them.

 

[87scotty]

Is this why i have no rear brakes whatsoever? Mine has not been attached since i bought the truck

 

[skysurfer]

Do your brake lines still go to the lspv or has it been bypassed per the tsb?

 

[5akman]

@chengny posted a GM tsb that was issued for mechanics instructing them on how to bypass the LSPV (load sensing proportioning valve) so it's not absolutely necessary to retain it. I kept mine but had to add a length of 1/8" thick flat stock mounted vertically to account for the 4" lift.

http://www.gmsquarebody.com/forum/showthread.php?t=5984&highlight=lspv see post #5 for the tsb

You must be registered for see images attach

Below is a copy/paste of an earlier post on the adjustment of the lspv.

You can't see it in this picture, but the bottom of the longer arm is attached to an arm bolted to the differential. As the suspension sags under load it rotates the short arm that's bolted to the round valve counter-clockwise, increasing brake pressure to the rear.

I removed the nut and short arm, then rotated the stem clockwise (to reduce pressure) a few degrees before reassembly. Took it for a drive and did a few panic stops. Had to do this several times until I got the brakes where I wanted them.

Yep, that is the assembly that I was referring to. Does it really do what it was designed to do? I guess not if GM got rid of the design a few years later. Thanks for the info and link.

 

[5akman]

Yes, that is the assembly I was referring to. I'll check into either using it with an adapter bracket or by passing it as shown in the link, Thanks!

 

[skysurfer]

It does work, when I was trying to figure it out I turned the adjustment the wrong way and nearly hit the steering wheel when I touched the brakes. If you decide to disconnect it you bypass it hydraulically and remove the valve and linkage as described in chengny's post linked above.

 

[5akman]

It does work, when I was trying to figure it out I turned the adjustment the wrong way and nearly hit the steering wheel when I touched the brakes. If you decide to disconnect it you bypass it hydraulically and remove the valve and linkage as described in chengny's post linked above.

This truck will spend the rest of its life hauling up to 4000lbs of salmon per trip off an Alaskan beach so I guess I better plan on keeping it in place as it sounds like my application is exactly what it was designed for.

 

[74 Shortbed]

There's a tool for proper adjustment, very simple and quick to do..

http://www.autozone.com/repairguides/GM-Full-Size-Trucks-1988-1998-Repair-Information/BRAKE-OPERATING-SYSTEM/Height-Sensing-Proportioning-Valve/_/P-0996b43f80c90e95

 

[Craig 85]

Long ago when I was young and dumb, I did a 4" lift on my k20. The shop that lifted the truck raised the braket off the rear axle, but not enough, so I accually lost rear brake pressure. I was towing a trailer and almost went through an intersection as I did not have enough brakes. I ended up bypassing the valve. I never had an issue of rear lock up in bad weather.

I will eventually be lifting the K30 I just purchased and will probably remove the valve again.

 

[Rusty Nail]

Brak lever!

 

[Wes P]

Posting in all LSPV-related threads for reference:

LSPV delete on '85 C20 increased braking performance.

Basic procedure:
- Remove valve, post-LSPV hard line, hose, axle bracket
- Measure, measure again, cut, drill, tap, weld stop nut on bracket (or add a screw)
- Release axle hard line from clips
- Install bracket, brake hose (180 flip), zip ties
- Bleed brakes

Parts: 2 zip ties.
Materials: brake fluid
Time: 4 hours, leisurely, without experience, being careful.
Note: Be gentle with hard lines. Plug the hard line after disconnecting. Don't empty the master cylinder.

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[Keith Seymore]

It was a cheat to help pass FMVSS brake testing in the days before RWAL or AWAL.

Removing it completely allows "full pressure" to the rear brakes ("full pressure" meaning the full amount after being regulated by the traditional front prop valve/combo valve).

K