I just completed a full front/back brake job on my 89 2WD 22r pickup: new master cylinder, calipers, rotors, wheel cylinders, drums, shoes, and rear brake hardware.

Bleeding took a few hours, but I'm not getting any bubbles at any of the four wheels or the MC. The pedal will build pressure after a few pumps with the engine off, but as soon as I start it up and build some vacuum, the pedal drops to the floor. Surely there is air in the system somewhere, and the only component with a bleeder that I haven't addressed is the proportioning valve.

The service manual makes no mention of the LSPV in its bleeding procedure, and all it says about servicing the LSPV is to take it to a qualified shop.

I've read that these trucks are very prone to proportioning valve failure, but the most common symptoms do not match mine. Fluid is passing through the valve and creating pressure in the rear brakes, just not enough.

So, should the LSPV be bled during a full brake system flush, or is it better left alone? What else could cause the lack of pressure in my system, even after putting multiple bottles of bubble-free fluid through the lines?

ALSO, just a note for those considering a one-man power bleeder... this thing is absolutely, utterly useless:

Brake Fluid Bleeder

Damn its positive reviews and its surprisingly decent build quality. It does not work. I've never had any success with the smaller hand-held pumps (Mity-Vac, etc), either. I may try one of these next:

Motive Products #1 Selling DIY Brake Bleeder

 

Rear right, rear left, front right, front left, then the lspv. That is the toyota way to bleed the air, the way it was explained to me.

 

I bought the Motive bleeder (Motive Products #1 Selling DIY Brake Bleeder) and it works as advertised. I bled every fitting in the appropriate sequence, including the master cylinder and proportioning valve. Some slightly mucky fluid came out of the LSPV, but no bubbles. No bubbles at any of the four wheels, either. Went through two more bottles of fluid and still no pedal.

I suppose I'll replace the master cylinder AGAIN, but I'm not convinced it is the issue. Honestly, I've never bled a brake system without encountering some kind of mysterious, physics-defying problem. It's like black magic. Voodoo. A simple job that should take 30 minutes ends up lasting days... weeks... months...

 

have you checked out the booster?

 

I finally have a good, firm pedal, but now I have insufficient brake pressure to the rear wheels. Even with the shoes adjusted out far enough to prevent the drums from turning by hand, the wheels will spin with the brakes applied. There is some resistance, but not nearly enough to effectively brake the truck in motion.

I tried tying off the LSPV's adjustment rod in its highest position, but that made no difference. The truck is drivable, but the front discs are providing nearly 100% of the braking force. Not particularly safe and guaranteed to burn up my pads/rotors in short order.

Hard to believe the LSPV has failed considering the truck's condition and relatively low mileage. The rod moves smoothly up and down and there is no visible corrosion anywhere on the truck.

ANYTHING else that could cause lack of pressure to the rear brakes, despite good fluid-flow while bleeding and despite a firm brake pedal? I don't want to replace the LSPV unless I'm certain it's the problem. The fab work associated with installing a manual proportioning valve looks like a pain in the ass.

 

Get rid of that valve and get one off of jegs or summit.

Booster or master could also be the cause

 

bump for updates

 

Hi didn't want to start another thread. I'm having something similar to this happening, no fluid to the rear wheels. I get fluid to the front two wheels and at the lspv. I was thinking the rubber hose to the axle could be clogged, but before I replace that, I was wondering if having the truck up in the air supported by the frame rails cause lack of pressure to rear wheels completely?

 

Just jack the truck up and placed the jack stands under the axle, still no fluid. I'm going to replace the rubber hose and report back.

 

Got it bled and I believe it was the master cylinder. I bypassed the lspv and was still not getting fluid so I figured the only thing I didn't change was the mc. It was a pita figuring out which master cylinder I have. My truck was US built and a Canada jst version Mastercylinder.