2004 Tundra rear brakes not bleeding

I've had the Tundra since new and worked on my cars/trucks for years (225000 miles), but haven't run across this prior. I installed a new master cylinder and when I try to bleed the rear brakes nothing comes out. I removed and checked the nipple but didn't see anything that was obstructing it. The brake fluid is getting to the Load sensing proportion valve (LSPV) but not out to either rear brake drum. I've taken the valve apart (last night) and cleaned it up and then re-installed but no change. Does anyone know how to adjust the LSPV? (I not believe I know how to adjust and will do so asap)

I didn't mention that I installed a new master cylinder. I am not sure if the rear brakes were fully working before I installed the master cylinder though. I have read several strings where it fails and there is nothing that tells the driver it isn't functioning properly.

Any ideas would be appreciated.

 

I’ve had the rear portioning valve go bad and not let fluid past it

 

Its either the proportioning valve or the ABS. Something has to be plugging it though, I just did this on my truck not long ago and there was no trouble bleeding the system.

Does the brake pedal build pressure under your foot when trying to bleed it? If the MC is working it has to be pushing something somewhere, even if its just compressing air.

 

I took the LSPV apart last night and the insides were pretty dirty, but it seemed to clean up nicely and the o-rings and seals looked fine after the rebuild but still no brake fluid was able to pass through. I was able to get brake fluid up to the LSPV bleeder, but not out through to the drums.

There isn't a lot to it, much like a master cylinder. Maybe these photos will help someone else in the future.


FYI- I used a plastic mobile phone glass repair kit tool to pull out the various seals so I wouldn't damage them, also there were some pits in the metal so I used some emery cloth to smooth them out as best I could. (see photos in original post)

 

That's too bad. What are you going to try next? Let us know how it shakes out.

 

I'm going to try adjusting it tonight. I'll update this based on success/failure.

 

Check to see if there’s a load sensing valve. I believe it goes from the axle to the frame, kind of looks like a toilet float assembly. The more weight that’s put into the bed of the truck the more it compresses this lever and the more fluid goes to the rear brakes making the rear brakes work harder.

 

Hello AJKkane. I'm not sure if my pictures posted above but the LSPV is what I disassembled last night and cleaned.