Hey all, have a rear brake issue here. Truck is new to me so don't know any of the rear brake history, but I have no rear brake movement. My first step was to try to bleed the right rear cylinder the old fashion 2 person way, no fluid would come out, tried the drivers side, no fluid, went to the proportioning valve bleeder, all bleeds correct, no more bubbles. Tried a one way valve on both rear wheel cylinder bleeders, nothing. Hooked up a vaccum pump to both sides, no fluid. Now I would normally think a broken line or something but I've got the bed off and can see all lines, nothing looks damaged. All I can think is the portioning valve. I put an extra bleeder I had into the threaded hole to see if I was sucking air there too but no luck. I'm stumped, anyone have any thoughts?

 

I would suspect one of 3 things. First, are the cylinders shot? Second, are the lines to the rear brakes plugged up? Third would be the LSPV itself. The plunger on it that sticks out the bottom will rust pretty badly and gum everything up. If that plunger doesn't move, looks rusted or pitted then it's time to decide wether your going to replace it or install a manual proportioning valve. DO NOT try an after market POS. They suck. Get one from Amayama if you're going to put a replacement LSPV back in. If you go the manual route then there are a lot of write ups on here how to do that. Good luck. I just got done doing this exact thing on my 86.

 

Good call hshsurf. I'll try to pull a few lines off the valve and see if I can isolate the problem to the valve. When you did your valve did you have a return line in the system or just a supply and output. If you did have a return line do you know where it tied back into the system? I'll see if I can find that Amaya system you mentioned if I can prove to myself that valve is bad too.

 

Since you don't have a bed on the truck, there is no weight back there, the whole point of the LSPV is to adjust the fluid flow to rear brakes according to the load. Maybe you should unbolt the arm from the axle, raise the arm all the up as if the truck were loaded down, and see if you get any fluid to the wheel cylinders.

 

Thanks Cory, I'll give that a shot. Thought for sure I found the issue they had the lines into the master cylinder wrong, the rear lines were comming out of the t fitting for the front wheels and one front wheel was in the master rear position... no joy.

 

I missed the part about the bed being off. Definitely start there...

 

I have a return line on mine. It should tie back in under the passenger side wheel well area. Here's a pix of what my old one looks like. Still waiting on the new one.

 

Thanks Cory, I'll give that a shot. Thought for sure I found the issue they had the lines into the master cylinder wrong, the rear lines were comming out of the t fitting for the front wheels and one front wheel was in the master rear position... no joy.

 

This sounds all too familiar to me but it's been almost 20 years ago since I replaced my LSPV. But it seems like I do remember my return line going back to the Tee at the passenger front wheel also.

But shouldn't a functional LSPV supply minimal pressure to the rear cylinders even if the bed is empty? There shouldn't be a time when the LSPV cuts off all flow to the rear brakes even at minimum load position it should still be able to be bled, right?

My LSPV was completely rusted out so I replaced it with a manual from Summit. I've hauled my 600RR many times and never had any issues nor do bother adjusting the MPV.

The best way I found to bleed these brakes after I went with the MPV was gravity bleeding starting at the farthest cylinder, ie, Driver rear.

 

Hey all thanks for the help, figured I'd tie this one up incase anyone else comes across a simmular issue. Sure enough there is a return line to a tee by the front passanger wheel. Found mine went about 5 inches back from the tee, went under the cab and was then crimped off. Apparently P.O. had been driving with no rear brakes. Some stainless steel lines and about an hour of beer and brakes and she works again. Now on to welding nuts into the top of the fuel tank holding brackets.

 

Thanks for the follow up! It's good to hear resolution. I'm still waiting on my new LSPV from Dubai. Hopefully that will be the end of my brake woes... good luck with the fuel system.