SporkTek

My brakes failed today on my 86 4Runner. I'm not sure where the problem is at this point. I recently replaced my master cylinder and bled the entire system (including the LSPV) at the same time. I drove it for about two weeks back and forth to work and then this morning on my way in I've got barely any braking power. I have a full resivoir but my pedal goes about 80% to the floor and then catches. I think I've only got one or two wheels actually braking. The 4Runner doesn't pull to one side or the other, but I definately get a lockup and a squeal easier.

I'm willing to entertain the idea of a faulty-from-the-factory brake master cylinder, but I'd like other opinions as well. I bought this cylinder from a local parts store that's run by my uncle-in-law and I'd rather know exactly what the problem is before going in and buying (or possibly returning) a part. I'm a but curious about the LSPV. I've not read much on it's operation or what happens to it when it fails. I know that in some cases it can rust out and start leaking and fail, as is the case for the LSPV on my dad's 86 pickup, but I'm interested to know if the LSPV can somehow fail internaly and turn into a full bypass, allowing all fluid to return to the front rather than just a portion for proportioning.

I'd like to block off the return line temporarily to test weather or not the LSPV is the source of my troubles. My dad suggests unscrewing the fitting and sticking a nail down the tube that has a large enough head to keep from falling in but small enough to allow you to then screw the fitting back into the cylinder. Where would a conveinent place to perform this test be?

leebee

i had a similar problem with my old 86, turned out it was the mc that had gone south. if you recently purchased one, it should have some sort of warranty from the seller or mfgr. take it back for a replacement and start over. kind of a pita but should do the trick for you.

lee

86Original

IIRC, the LSPV doesn't have a return line. I believe that it just throttles the amount of fluid going to the rear brakes. You may want to consider disconnecting the rod and lifting it all the way up so it lets the fluid to the rear, unrestricted. See what your results are. then try it with the rod tied down, fully restricted and see what your results are. That would tell you whether the LSPV is working correctly. Up should make the rears grab sooner, down should keep the rear from grabbing at all, the fronts will slide first.

HTH

SporkTek

I'm certain the LSPV has a return line. I've done a little Googling and I've found some how-tos for removing the LSPV and putting a manual proportioning valve in place that speak of a 'return line' and a 'pressure line'. Most pages are for a tacoma, but most of the stuff looks the same. I could be mistaken, as I haven't been under the back of my 4Runner for a while now, but I'm still thinking there is a return line.

Anyway, I'm going to look into the brake master cylinder further when I get a chance and see if the problem is there or not.

Thanks,
Matt

Superflex84

the lspv does have a return line. it goes directly to a tee at the rf corner and feeds the fronts again.