wmayota

Not quite a football field, but you get the point. I just bought a 88 SAS'ed rig off a cousin to fix up for my trail rig. I just replaced the passenger side caliper and both rear wheel cylinders, bled the brakes multiple times, and there is still no pedal. Driving around the yard to test the brakes, they grab evenly and do not pull, but the pedal went nearly to the floor. I took it a quarter mile up the road, got up to 30-35, and mashed the brakes. The pedal again goes to the floor, the brakes grab evenly, but not enough to safely stop the truck.

This was my cousin's trail rig, so he had taken out the LSPV and blocked off the return line to the front with nothing but a bent piece of brake line. I replaced the T that went back to the LSPV with a 90 degree elbow with the faint hope this would solve my problems, but it didn't. I also readjusted the rear shoes. I tightened the slack adjusters until I just barely heard the shoes grab on each drum thinking my brakes were out of adjustment, but this did nothing.

Now I'm down to either the absence of the LSPV or a bad master as the cause of my problems. Pumping the brakes does not help significantly enough for me to beleive it is the brake master going, but since their is no LSPV I really can't tell.

I'm leaning towards the LSPV, so I was going to put one back on and since the truck is lifted, make a braket similar to this one that Anthony1 made to keep the LSPV at stock ride height:


THAT is my opinion, but I'm looking for other's .02 before I blindly dive wallet first into either cause. Much appreciated.

ToyotaViejo

Hm. If there's no pedal at all, I'd actually think it could be a master over the Load Sensing Proportioning Valve (spelled it out for the search engine).

I have no technical reason for this except my LSPV is rusted just about solid and I stop fine. Well, as fine as 5600lbs of steel stops.

It was not in a Toy, but I had a GMC that the BMC went bad in, and no amount of pumping would re-establish pressure AND the thing barely, barely leaked.

Anecdotal, I know.

highonpottery

iTrader: (1)

iirc, the LSPV is going to affect your rear braking pressure only, and shouldn't affect the front braking at all - so you should still be getting some front-brake grab. if you're not getting any pressure in the system (which is what it sounds like), I would start at the master cylinder.

RRogers

Might want to check your brake lines too. If any of the rubber ones are old they may be swelling under system pressure and thus reducing pressure getting to your brakes.

xxxtreme22r

if anything that LSPV as it sits is putting full pressure on the rear drums. I'm not sure but doesn't the LSPV take away front line pressure and "add" it to the rear not just vary the rear pressure? If it does then that may be one reason why brake effectiveness is lower as drums don't stop as well as disks.

Does the pedal get hard when the engine is off and the pedal is press a few times? And does it stay hard? If not, it's most likely the master.

wmayota

xxxtreme22r-There is NO LSPV on the truck. The P.O. removed it because it is lifted and was used as a trail rig and the lift threw it out of adjustment. Only reason I was thinking it was because my '89 behaved similarly with a broken LSPV. I thought the LSPV adds more pressure to the front as the weight on the rear axle ws increased. You's think it would make sense- driving in slippery conditions with a heavy load, why would you want more rear brake pressure? I also thought drum brakes took less pressure to be applied than disc, so the LSPV would add pressure to the front to prevent the rear from locking up. With the engine off, the pedal will not go hard and will not stay hard. You can start to feel the pressure build as you pump the pedal, but as soon as you stop pumping, it goes to the floor.
highonpottery- The front brakes will grab and lock up at low speed.
RRogers-Haven't ruled out brake lines yet, either.

I did a few searches, and from what I gathered it did sound like the master, but from previous expirience I though LSPV. As I said, when I bought my 89 DD with the broken LSPV the brakes did the same thing- you could not pump up a pedal, but they grabbed alright.

Gradually leaning towards the master. When I replaced everything, at times the resevoir drained completely. I have bled almost a quart of fluid through it, so I assume most of the air is out, but you never know...
Thanks for the help.

xxxtreme22r

really? I see the LSPV there, just not the actuating rod in which is rigged up which puts full pressure in the rear lines. And your thinking backwards on the lspv. It's actually there to lower the rear braking without load in the rear so you don't lock them up on wet or icy pavement. With more load in the rear you can get away will more rear braking without locking up the tires.

What he did there is actually pretty common. Along with people extending the lower bracket on the axle which is what I did since mine is still driven on th street and sees snow.

wmayota

That's a pic I borrowed from another thread. I was just showing what I had planned if I decided to go ahead and put in another LSPV for if I ever register the truck. I can throw up a few pics of my lack of an LSPV if you want, but from what I've gathered in my searches and what you and others have said, I'm probably going to replace the master and try that.

And since I'm going to be doing more bleeding, it may not hurt to replace the old rubber lines as RRogers pointed out.

And here is a link to that thread I was talking about:
https://www.yotatech.com/forums/f116...sv-mod-234280/
If it isn't a link, you can always copy and paste the URL.

xxxtreme22r

ah sorry bout that, maybe I should read all the way to the bottom. lol.

briholt

Update?

wmayota

Brake master was bad. The pedal is still a little soft for my liking, but for wheeling it stops. probably a little air in the system somewhere, but I'm off at school so its gonna have to wait until summer

anthony1

iTrader: (1)

The vacuum "box" can go out too. There's a test for it somewhere on FSM.

wmayota

Are you talking about the booster? There are idling problems with the truck, but I think that's because the engine may have come out of a truck at one point the had auto hubs. In 2WD, anytime you mash the breaks, the truck's idle drops from about 800 rpm down to 200 and fluctuates back and forth. One day while I was sitting before going onto the trail, I had the brakes on and shifted into 4WD and the fluctuation stopped. The truck returned to 800 rpm and stayed there. In 4WD while crawling, the idle will sometimes stay around 1500 rpm, mostly during times while I was using low gear to hold the truck back like when going down a hill. I'll get to the bottom of the hill and the rpms will remain at 1500, even if I let the truck sit and idle. Revving the engine will make the idle go down to normal. At times if I'm crawling and holding the gas steady, mostly bwtween 1000 and 1500 rpm, the rpms fluctuate a little and you can feel the truck stutter. The power stops and goes, stops and goes.

Anyways, I read this about auto hubs on 4x4 wire:
"Toyota introduced the Automatic Differential Disconnect (ADD) 4-wheel drive system on its trucks in 1989, and on the 4Runner with the 1990 redesign. This system is composed of a vacuum-activated shift fork in the front differential driver's side axle tube: when the transfer case lever is moved to the 4Hi position, vacuum is applied to the fork which in turn moves a sleeve to lock the inner stub axle shaft from the carrier to another shaft in the tube. This axle assembly powers the driver's side wheel, while the passenger side is a single shaft from the carrier to the inner CV joint. While in 2WD, the driver's side axle is disconnected within the tube. The ADD trucks also have hub flanges at the wheels instead of conventional hubs; a series of vacuum switching valves (VSV's) in the engine bay to control the actuator; and a transfer case position indictor switch, which controls the dash light."

I'm guessing that the vacuum for this must come from the motor, meaning there would be a line for it somewhere? In 2WD, there would be no pressure on this line. If it leaks, that would affect the idle. I'd think it would be worse in 4WD since there would be pressure on the line? The motor in the truck is tired and warn out. I'm repleacing it this summer, so I'm not too worried about digging into the idle unless it is the booster. It is a curious bug in the truck that would be nice to figure out though.

anthony1

iTrader: (1)

You may have a leak in the brake booster if the idle goes down and stay there. Check the FSM to rest the booster.
Just a thought, did you raise your rear end of the truck before you noticed the brake problem? If yes, then the problem is the proportioning valve.You need to raise the arm to compensate for the lift.

blake.nemitz

heres an easy fix. properly adjust your rear shoes then you wont have to pump the pedal to get them to grab. my .02

subi_stout

brake booster? i had the same problem. pick and pull sepcial... 15 bux

c0ugar69

what type of calipers are they?? if the newer ifs you may have gotten the v6 calipers which will make the pedal go down farther. that happened to me when i put new calipers the ones they gave me were the v6 and the pedal was going to the floor. the fix was to get the master&booster from a 90-95 v6 as it has a larger 1" bore master. my breaks work way better now. hope this helps!!

wmayota

Anthony1: When I mash the brake pedal, the idle doesn't go down and stay. I hold the pedal in and it fluctuates. If it was the booster, it would continuously draw vacuum and cause the truck to stall out, correct? Also, the truck has no proportioning vavle. My cousin that I bought the truck took it off because of the problems you said. The absence of the valve or some air in the system (I realized my resevoir on the master was not completely tight, but I never let it empty) is causing the mushy pedal, but the truck stops.

cOugar69: First of all, I hope your name refers to the car, lmfao. Yeah, it had the later style calipers on it when I bought it. It never occurred to me that the calipers were different and when the right front caliper was froze I ordered an 85-88 caliper. The truck pulls a little left, but stops. Again, I do not drive this on the road and I have sufficeint stopping power, or as good as you can have with 36s.