1986 Pickup SR5 4x4. Driving on the highway last night my brake pedal suddenly had a lot more travel before meeting resistance. The truck would still stop, but the pedal would get pretty close to the floor. It didn't get any worse for the rest of the drive. I get home and notice the brake fluid is very low. I also noticed that the brakes felt more firm when the truck is NOT running. I couldn't find any leaks in the break lines, so I refilled the reservoir and bled the brakes. No air out of the rears, a few air bubbles out of the front. No change in brake pedal feel, although it still feels more firm not running. I'm thinking bad master, but kinda weird that it failed suddenly? And I would also think the pedal would continue to drop gradually with pressure, but it doesn't. Maybe there's still air in the lines? Idle changes slightly with truck running and brake pedal depressed, but it's barely noticeable. I think that's normal.

 

More firm when the truck isn't running is perfeectly normal. When the truck isn't running, there's no vacuum assist, so the pedal SHOULD be harder to push down. Again, perfectly normal.

It sure sounds like you have air in the lines some place. Did you bleed the LSPV out real well? Air likes to hide in it, and that will make the pedal feel soft and drop lower. Take it's bar off of the rear axle, and move it up and down a few times, all the way it will go, while bleeding the LSpV. Then hook it back up, and see what's what. Remeber to keep the Master cylinder full of fluid. If you let it get too low, it'll suck air in, and then you have to go through the whole bleeding sequence again. No telling which line the air will go down and get trapped. You have to bleed all 5 cylinder out to make sure you get it all. That's the 4 brake cylinders, AND the LSPV. Every time.

Also, make sure the pedal height is adjusted properly, especially if you changed the MC in any way.

ALWAYS use nice fresh, clean, and dry fluid. By dry, I mean that the fluid is hygroscopic. As soon as you open the bottle, it starts absorbing water from the air around it. Enough wateer, and the stuff is useless. The darker, the more water.

Good luck!
Pat☺

 

Any grinding when braking? Did the front pad material fall off the backing plate?

 

Assuming the brake fluid level was ok before this, I'd be wondering where the fluid went.

 

Found a leak at the LSPV. Didn't have good light the first time I bled the brakes and must've missed it. Need to source a replacement, but at least I know where the fluid was going.

 

LSPV still available from Toyota.47910-35191 (new #) online price $188. Parts guy told me a couple of weeks ago Toyota probably will do another 25% off for Black Friday.

There's also a bush and boot kit still available. 04477-60010 online price $80.

https://japan-parts.eu/toyota/us/198...e-tube-clamp/2
click on 5 digit # in diagram will give a pop up with 10 digit part #

 

I got a different part number for a 1986. 47910-35080.
There's not much to them. Might be worth pulling yours off and seeing what's up. I bet it's full of sludge. mine was.

 

Finally got around to fixing this. It took me a while to find the right part (47910-35080), and I ended up ordering it from Amayama (direct from Japan) for cheaper than I found it anywhere in the US. I think the rubber seal at the bottom of the LSPV was bad in mine. I disassembled, and that was really the only potential culprit. I replaced the boot and bushings as well. I bled the brakes and the LSPV last night and did a test with the bed loaded and unloaded, and the brakes worked well in both scenarios. In hindsight, I probably could've rebuilt my LSPV, but don't mind having a new OEM part. Thanks for the help y'all.

 

Ensure the pedal height is adjusted properly, especially if you changed the MC in any way.

 

^^^^^^^