Polander

I already started a thread about my random break issue, but now I seem to have narrowed it down to the LSPV (I guess) and just want to get some input from you guys. Or see if anyone knows anything more about the LSPV. Didnt find anything in the search beyond how to eliminate the LSPV and not planning on going that route.

So I've put my second MC on in a week and a half. First one may or may not have been bad, but second is definately pushing fluid. (Tested by bleeding at line outs from the MC). Bleeding in proper order, rear wheel cylinders good, booster good, no leaks...

Fronts bleed fine. I CANNOT get fluid from the rear bleeders. Can get fluid out of the bleeder on the LSPV itself, but nothing out of the lines headed to the rears from the LSPV (tried breaking right at the LSPV). Also the "button" on the bottom of the LSPV that is engaged by the rod from the track bar seems to be prone to staying in the UP (or in) position. Button moves freely, but if I understand how this works correctly the button should be in the out position to be engaged by the rod when sensing a load. I believe this is because I am not getting pressure inside the LSPV. Pulled the thing off and cleaned it really good but seemed clean to begin with and changed nothing.

Talked to Toyota in Grand Junction, CO and the parts guy has never sold one single LSPV in the 21 years he has been there ($198 from dealer) and the service manager was familiar with the system but never had to work on it. Not the best news as far as hoping I've narrower the problem to the LSPV.

So my plan is to drive to GJ tomorrow and pull a used one from the junkyard, put it on and have the dealer 'power bleed' (not vacuum bleed) the system for $100. Figure maybe I could have some blockage somewhere and I've gotten no where with the old fashion pumping the pedal or the vacuum bleeder. No one in town has any ideas and I've already burned up $50 trying to get others to diagnose, or get this thing working.

Help if you can! Thanks.

abecedarian

The LSPV gets two 'pressure' lines from the brake master cylinder: one from the front brake circuit and one from the rear circuit. (In spite of what you may have read elsewhere, there is no "return" or "bypass" line from the LSPV.)
If the front circuit fails, the LSPV senses that (due to the pressure line from the front circuit) and applies full brake pressure (regardless of load) to the rear brakes. If the rear brake circuit fails, the LSPV permits the front circuit to operate independently of the rear.

Polander

I'm more than a little foggy on how this POS actually works, or where the "Load Sensing" part actually comes into play, what im wondering is if mine is bad due to the symptoms I'm having.

Since mine is NOT permitting fluid to the rears (at all) does that mean my "rear circuit" has failed, and has it failed at the LSPV, I'm wondering if a malfunctioning LSPV is my issue. I barely have a pedal and no fluid to the rears. Front system seems fine.

abecedarian

www.autoshop101.com/forms/brake08.pdf

4Crawler

iTrader: (3)

Did you raise the sensing rod on the axle when you installed your 2" OME springs? If not that is tricking the LSPV into thinking there is almost no weight on the rear end and it may be shutting off most of the brake pressure from reaching the rear brakes. LS part of the valve is pretty simple minded, if the frame and axle are close together (springs compressed) then the load is assumed to be high and full rear braking is allowed. Frame far away from the axle (springs extended) and load is assumed to be low and thus rear braking pressure is reduced to keep from locking up the rear wheels. Adjusting the sensing rod can help restore proper operation:
- http://www.4crawler.com/4x4/ForSale/...l#LSPV_Bracket

Or another option:
- http://www.4crawler.com/4x4/4R_suspe...ortioningValve

MurphyzRunner

[QUOTE=4Crawler;51079109]Did you raise the sensing rod on the axle when you installed your 2" OME springs? If not that is tricking the LSPV into thinking there is almost no weight on the rear end and it may be shutting off most of the brake pressure from reaching the rear brakes. LS part of the valve is pretty simple minded, if the frame and axle are close together (springs compressed) then the load is assumed to be high and full rear braking is allowed. Frame far away from the axle (springs extended) and load is assumed to be low and thus rear braking pressure is reduced to keep from locking up the rear wheels. Adjusting the sensing rod can help restore proper operation:
On my 85' runner the LSPV was cut and the sensing rod was strapped up...well I put a 93 rear axle with sky's rear disk and I've bleed the brakes a couple of times but still don't feel 100% so do I need to bleed the LSPV or can I just get rid of it all together??? What are the pro's and con's - I mean if mine is strapped up anyway then there's no reason to run it right?

4Crawler

iTrader: (3)

You do need to bleed the LSPV as part of bleeding the brake system. Per the FSM it is the last thing to be bled, although I typically do mine after the passenger rear brake since I am already there and set up.

The LSPV can be removed but you generally need to replace it with some sort of proportioning valve. Most folks use the Wilwood prop. valve with the necessary adapters or get a kit from Front Range:
- http://frontrangeoffroadfab.com/nfos...e53c353abbbcb4

MurphyzRunner

[QUOTE=4Crawler;51082934]You do need to bleed the LSPV as part of bleeding the brake system. Per the FSM it is the last thing to be bled, although I typically do mine after the passenger rear brake since I am already there and set up.

The LSPV can be removed but you generally need to replace it with some sort of proportioning valve. Most folks use the Wilwood prop. valve with the necessary adapters or get a kit from Front Range:

Thanks for the reply 4crawler so if I get rid of the LSPV and go with the proportioning valve do I need to replace my master cylinder with one that's made for disk brakes like a 80's supra?? or will i be o.k with the stock unit.

4Crawler

iTrader: (3)

Stock M/C is fine with stock brakes, all you are changing is the LSPV for a simpler PV.

Junkers88

Small hijack here.

Hey 4C would some of this explain why the brakes on the rear of my 4runner are really thin? With the back end sagged like it is with the stock springs I'm guessing the LSPV thinks there's a huge load in the rear and thus is letting me use more rear brake than I need. The PO said he put new shoes on the rear last year and they are already thin. He and I both couldn't figure out why the front pads seem to last about 3 times as long as the rear shoes on the older 4runners, could this be the reason?

Thank you.

MurphyzRunner

Good to hear....I bet the m/c is a pain to bleed/replace I guess I will be removing my LSPV this weekend. thanks for everything.
Murphyzrunner

4Crawler

iTrader: (3)

Sounds like as good a reason as anything.