kennner

I have a 90 4runner that does not have any rear brakes. When in 2wd the rears do not work at all(back end in the air foot on brake can spin the tires by hand). I have pulled the abs fuse to see if they would work which ended up not doing anything(except turning light on in the dash). I have disconnected the speed sensor at the rear axle and still nothing(except for dash light). If I put it in 4wd the rears work great(can lock them up no problem).
Yes I know abs is supposed to stop the rear brakes from locking up, but there is no friction at all in 2wd.
Any help would be great

Poul D'eau

Were you lifting from the frame or axle? Because if you are lifting from the frame and letting the axle hang, the load sensing valve would be shut, preventing any action by the rear brakes.

kennner

I was using a jack under the rear diff to pick the whole rear end up to leave the trucks weight on the axle.

CrazyDiamond

Check for the obvious...fluid leaks, rear pad adjustment (<--important), wheel cylinder function with drum off. Then write me back and I'll see if I can help

TacomaTRD

he said they work when he puts them in 4WD

CrazyDiamond

Oops...sorry...missed that detail As far as I've ever seen, there is no connection, even figuratively, between the brake system and the 4wd drivetrain. I'll check with a few friends and see what they come up with.

kennner

The rear antil lock is supposed to be disengaged when the shift lever is put into 4wd from what I understand. The brakes work fine in 4wd but not in 2wd. I have pulled the fuse and unhooked the speed sensor in the diff to give the abs an error to have it stop working and still nothing at the back tires.
Could it be the ecu screwing up?

MonsterMaxx

the reason the rears work in 4wd is because the t-case is locked in and you are feeling front brakes

sounds like either some sort of serious fluid problem or that the self adjusters are frozen/broken (most likely cause) and that they are out of adjustment

mike_d

i was going to say the same thing, but if you think about it, the tcase is irrelevant: if he's jacked up the back by the diff housing, then it doesn't matter if it's in 4wd or not. the diff will allow the rear wheels to spin opposite directions regardless of what's going on in the tcase.

this i agree with. even if the ecu and abs and everything is broken, the basic operation of fluid to the rear brakes should work no matter what.

it really puzzles me why the brakes would work in 4wd and not in 2wd.

mike

mike_d

i know it's bad to replying to your own post, but i just thought of something for the original poster: do both back brakes not work in 2wd or is it just one of them?

if it's one brake, then i can see where if you have it in 4wd you could get the effect of it locking both wheels. but if both back brakes are not working, the i'm still at a loss for ideas.

mike

kennner

Both back do nothing in 2wd. Both work in 4wd. I was on the autozone site and am going to do all the rundown on abs they have for the 4runner. If everything checks out ok, it's going into the shop and get the abs brake actuator and power steering bled. That is about my last resort thinking it could be air in the abs actuator.

mike_d

how about shorting the switch on the tcase that tells the computer that you're in 4wd while leaving the shifter in 2wd. that way everything is the same mechanically as the 2wd test, but the computer thinks you're in 4wd.

mike