Anti lock brake actuator

[Flintstone]

I have an 86 4 runner that the rear brake actuator (anti loc) has completely froze up. Probably years of rust. This is a mechanical anti loc device. Is there a place that one can be purchased or a way to plumb the brakes to by pass this device.

 

[fourwd1]

They didn't have ABS in 86. Maybe some more info would help.

 

[Flintstone]

Actually they did have ABS in 86. It was done mechanically and was called a load sensing proportioning valve (I just found out the name). As the rear of the truck raised up during hard braking the actuator was activated by a rod from the rear axle. This reduced the hydraulic pressure to the brakes preventing the rear of the truck from over taking the front. This valve has froze and will not allow the rear brakes to work. Is there any place besides a toyota dealer I can get this part. The Haynes manual say it takes special tools and skills to replace. I appreciate any help.

 

[fourwd1]

Actually they did have ABS in 86. It was done mechanically and was called a load sensing proportioning valve (I just found out the name). As the rear of the truck raised up during hard braking the actuator was activated by a rod from the rear axle. This reduced the hydraulic pressure to the brakes preventing the rear of the truck from over taking the front. This valve has froze and will not allow the rear brakes to work. Is there any place besides a toyota dealer I can get this part. The Haynes manual say it takes special tools and skills to replace. I appreciate any help.

I'm aware of what a LSPV is, but it's not part of an ABS system (at least in the conventional sense). But you're right it helps prevent the rear brakes from locking up. It increases braking power in the rear according to load (as the name implies).

As far as replacing it, there are no special tools required. A line wrench (aka flare nut wrench) helps to keep from rounding off frozen line fittings, but vice-grips work too if a regular wrench won't do it. Once replaced you have to bleed the entire brake system in the proper order (it has a bleeder valve).

A lot of people just bypass it, or replace it with a manually adjustable prop valve.

I have mine disconnected at the axle side and tied up to the frame to get max braking always.

 

[Flintstone]

I figured that there was a way to bypass the LSPV. Driving on the road without some type of proportioning valve could lead to rear end swap under hard braking. The fact that there are two brake lines going to the LSPV may make installing a proportioning valve tricky. Anyway thanks for the the response sometimes it helps to kick a problem around.

 

[cometobanks]

I think the most ussual trick is disconect it and zip tie it to your frame.