I've been wandering for a while what this was on the rear diff of my 91 PU 4wd. I thumbed through the Haynes manual and found nothing about it. Here's a pic...



The long bar that runs from the left side of the diff to the frame on the other side of the truck. It appears to be linked to this device...



I've worked on many truck, but have never seen such a thing. My only assumption is that being hooked in line with the rear brake lines, it somehow adjusts the rear brake pressure according to the height of the truck (maybe depending on the load; more weight makes it sit lower, therefore making it brake harder; less weight it would sit higher, therefor needing less brake pressure). If so, is this why I seem to have less rear brakes after putting a little taller shackles on my truck? Everything form the wheel cylinders to the brake drums has been replaced (cylinders, springs, auto adjusters, drums, and shoes (twice, because a leaky cylinder that I didn't replace the first time I did the brake job ruined one side). I did it all around the same I did the shackles, and now the rear doesn't seem to grab as hard as the front (on a dirt road I can lock up the fronts, and the backs wont), and I'm think'n maybe this thing is related if it does in fact do what I think it does. If I'm correct, could rebending the bar make up for the height change; or even better yet, can this be bypassed all together?

Thanks in advance guys.

 

yes it is exactly that. i dont no about bypassing it but u can make a lil bracket that extends where it bolts to the rear end. i bent mine and it worked fine,

 

Yes, your assumption is correct. That is the LSPV. To bring it back to stock simply make a little bracket to raise the mounting point on the axle up x amount of inches you lifted your rear end.

 

I welded a bracket for mine at the 3/4 of the way up position and cut off the bar going to the axle. I never haul anything and the idea of little rear braking power whenever the left rear droops while crawling made me take it out.

 

hmmm, well the shackles didn't raise it all that much; perhaps I could try just rebending it to make the thing work right. Now that I grasp the concept of what it does and how it works, I should be able to get the angle of it right. Thanx for the speeding responses guys!

 

its lspv (load sensing proportioning valve)...not lpsv, etc

 

Yep lift looks like "less load" to the LSPV.

Some options to adjust it:

Bend or modify rod as you suggest.

Bolt-on bracket:
http://www.4crawler.com/4x4/ForSale/...l#LSPV_Bracket

Convert it to a simple proportioning valve:
http://www.4crawler.com/4x4/4R_suspe...ortioningValve

Or swap it for a manual prob. valve like Wilwood.

 

Ok, so I put a bit of an arch in it which made the angle higher, and now the back brakes work perfect! No more lunging forward like it use to, lol. Also tightened up my parking brake cable while I was under it and now my parking brake works! YAY 4 ME!

 

Which way did you bend it?

I have a 4" lift and since my rear brakes barely work. I have the same thing never noticed it before. Wanna give it a try.

 

um... think about that for a second! wich way did it go when you lifted your truck? bend it up.

 

amagin you dropped your axle (lifting the suspension) the LSPV would go down. Bend it up to "fix" that.

 

I noticed something today under my truck... the shocks have TOYOTA stamped on them... I wander if their the original from 91! If so, they've hung in their for 284k miles! That would be nuts, lol. I've been planning on putting new ones on; maybe sooner now than I planned... the front has been bobbing a little after big bumps like rail-road tracks and entering parking lots and such.