Anyone know of a source for the Load Sensing Proportioning Valve (the thing for the rear brakes to compensate for loads) besides the dealer? None of the local auto parts stores seem to be able to get them. I can try and find a used one (and I posted an ad in the wanted section) but used brake parts are not ideal.... Because my '85 Toyota 4x4 pickup sits for 6 months out of the year every year, the LSPV seized up on it. I can unbolt the bracket off the rear axle and manually cycle the rod, but it doesn't do much to free it up inside.

I've seen very similar, if not exact, previous posts from other people about these symptoms and figured I could also share my story. People suggested a sticking master cylinder, cracked pedal bracket assembly, loose sticky pistons in the calipers, rusted pistons, or a bent line. Before I realized it was the LSPV, I replaced the brake booster, master cylinder, front calipers, front pads, rear wheel cylinders, and re-bled enough times to fill a 5 gallon bucket.

The symptom was that the brake pedal stiffens up halfway through to where it used to, but I had maybe half the braking power. If I stepped on the pedal hard, then it would "pop" and travel further to it's normal position (but not to the floor). The brakes only seem to half work when I don't step on the pedal hard, but fully work after the pop and the rear engages. I've confirmed this by hitting the brakes on ice and seeing if the rears engage at all. Nope! The fronts lock up. If I unbolt the bracket off the rear axle and tie the rod up to the underside of the box, it brakes normally. It also dawned on me that my front brake pads were not that old and had suddenly worn out quick, and my front wheels would quickly fill up with brake dust on the outside, again pointing to the fact that my front brakes were working overtime. Unfortunately I had already replaced all the previously mentioned components before I finally discovered the real problem.

Now I just need to find a good used one or an aftermarket source. If I remember right, the LSPV is very expensive from the dealer.

Take it apart and clean it up!!!

If you don't change the rear end weight much, do what Roger Brown did. It works great. I think yoy know his website link by now. If not, do the search....hehe.

1) Boneyard.
2) go with a Summit (SAE) or Front Range Off-Road Fab (Summit, plus metric adapters) manual adjusting proportioning valve and be done with it. Works better anywho, for most of our purposes.

It comes apart easily and is repaired by just cleaning its innards. I'd do that first as it costs nothing.

Thanks--I guess I'll try cleaning it first (unless I've found a good used one by then).

I took apart the LSPV yesterday and sure enough it was siezed up a bit. It also had clumps of what looked like rust colored grease, but I'm guessing that was just rust/brake fluid. I *lightly* greased the piston and put it back in. Bleeding the brakes wasn't as bad as I was expecting. I only had to do it at the rear wheels and LSPV. I also lowered the height of the valve thanks to the factory slider slots. Braking is back!

I have a factory service manual that has a check procedure involving hooking up pressure gauges to the brake lines and stepping on the brakes to measure line pressure. I didn't have have the special service tools, so I did it by feel. We have tons of icey roads right now, and I adjusted the rear brakes so that the fronts would lock up just before the rears. You don't want the rears locking up first because it will send the vehicle into a spin. So, I went from not being able to lock up the rear tires at all, to getting them to lock up just after the fronts locked up. My drive way is glare ice right now so I was able to test it thoroughly.

I think my LSPV failed for a couple reasons. One, this truck is parked for 6 months out of the year, and I've had to replace all the other brake parts after about 10 years of parking it for half a year at a time. Note to self, start up and drive parked vehicles every once and a while.

Second, my crappy NWOR stiff suspension lift doesn't have any flex at all, so the valve likely moves very little even when I do drive. Plus, the bottom spring in the pack on each side broke, so I removed them. The springs have sagged over the past 10 years, so I put lift shackles on the back. Add to that, I have a fiberglass box, and 3 sand bags in the back end. I have no idea how much lift I have! I do still have the little lift bracket on the LSPV rod at the axle, but who knows how close this is anymore.
Some day I hope to be doing alcans.....