Ok just bought my truck a 92f150 4x2 straight 6 with 172,000 miles. Runs great! HEres the problem that I discovered this morning. When I first hit the brakes going down my parking lot I noticed that the rear tires where locking up and smoking whenever I hit the brakes unless I hit the pedal very very gently and very slowly slowed down. I was only going maybe 15mph to begin with. I also noticed that my front tires were spinning freely. Pedal pressure felt fine, not soft at all and no leaks. Within 1 minute a driving and trying the brakes they returned to normal. Could both of my front calipers be sticking? Could it be a proportioning valve? Fluid looks ok, not super dirty and the brakes did fine on my 150 mile trip home and a 22 mile trip last week and moving around in the parking lot yesterday. This is the first time I had a problem. Any ideas?

 

It could be something in the abs. In my 89 I only had abs in the rear, and something was wrong with the system and it would lock up if you barely hit the brakes. I dont know what part would be the culprit, as I just disconnected all the abs components and redid the brake line to the rear when I changed out my rear end.

 

Interesting that you mention that. No ABS lights, assuming they aren't burned out, but the seller mentioned something about the abs brakes and getting a sensor gummed up. I suppose I could replace the rear abs sensors but that would just be a guess. I assume there are 2 rear abs sensors?

 

Well I'm pretty sure theres one on the differential if I remember right, and I would guess one on each wheel also. You may be able to clean the sensors, I've heard of people doing that. Not sure how though. But that would be my guess since it sounds a lot like my problem. I can't remember if my abs light came on or not.