Lspv ????

[Owyhee H]

So when I got my 85 4runner, a while back, i was having rear wheel lockup problems. This got solved by replacing the rear brakes, drums(severely warped), and wheel cylinders. I also about the same time had my rear springs re-arched and had an add a leaf put in. So i really didn't completely understand what the uses of the Load sensing proportioning valve (LSPV) in the rear of the rig that could contribute to the wheel lock up by having the sagging springs.

My question is what do others do and should I worry that the LSPV is taking too much pressure from my rear brakes with the mild lift that was gained by the re-arch and add a leaf? What do others do when they lift their vehicles to ensure that their rear brakes are still being used, especially when loaded down. Lots of expedition vehicles have mild lifts and carry large loads, so wouldn't it be unsafe if they were proportioned incorrectly?

Just thinking out loud, any concerns here, i haven't heard anyone ever mention this? Maybe the design is such that it can compensate for these differences.

Idaho85

[seanz0rz]

usually there is a bracket that raises the valve the same as your lift.

so a 2 inch lift from stock would require a 2" lift bracket for the lspv.

the idea being that as you loaded the back of the vehicle, the valve would open up more, and cause more braking pressure to be applied to the rear brakes because they have better traction. and this is a dynamic system so on a hard stop as the rear end comes up, the braking pressure is reduced in the rear, keeping traction.

sadly, drum brakes are so terriable, even properly adjusted, they still only offer about 50% of the force of rear disks.

[Owyhee H]

Thats good to hear that they do provide the brackets. I understand how they work and it makes lots of sense that as the loaded vehicle stops it transfers more pressure to the front, I have all sorts of experience and education with dynamics. I believe that stiffer springs would affect how this system works but the majority of the stopping power is in the front anyway.

Well any more thoughts are appreciated.

[corax]

After changing to a different master cylinder bore and installing T100 calipers I ditched the LSPV in the back and used a manual proportioning valve instead (click me). Bias tuning was done in an empty WalMart parking lot after it rained, the goal was to keep the rears from locking up before the front while braking through a turn (normal loading in vehicle).




Some have also just tied the LSPV rod up to the underside of the bed or body
4crawler's solution

[4Rescue]

You'll be amazed how much fixing/correction or like Corax completely modifying the LSPV system strengthen's your braking after a lift I ran with mine not adjusted for awhile after I put my OME suspension/BJ spacers on... It was not so good for awhile braking wise eh

Cheers

Dave

[java]

i ran the same manual proportioning valve as croax, but i put mine under the bed using the oem lines from the LSPV.

[4Rescue]

I also REALLY ewant to do the same MC/Brake upgrade Corax did., Sure sounds like the best set-up and it's all Toyota parts so it's a quality option to boot. Also want to toss my LSPV with something I can adjust to my own needs and uses like the prop. valve from Summit I've been eyeing.

Cheers

Dave