Skinner, you hit real close to this one when you gave the guy from nasa the instructions to do the diagnostics.

Can Anybody help?

1990 - Ford F250 200k mi.

I am having real sticky brake problems. My rears are intermittently dragging until they smoke. I have been through 3 pairs of brake shoes. I have replaced the driver side e-cable. I have replaced the springs after being overheated. I have had a blowout due to overpressure from overheating. After i just got done with another brake job last weekend, I had passenger side dragging and possibly drivers side too, both wheels were hot, passenger side was smoking. Just before i did the last brake job both were smoking. Before the brake job before that one, it was the drivers smoking mostly. I did have a bad e brake cable that was keeping the e brake slightly compressed and i heard that that will cause stars to adjust too tight. The stars were not too tight however, they dont seem to be adjusting all that well. Pedal is real spongy, you can feel the front brakes hit, then the big sponge until the back brakes hit, by then the pedal is near the floor. I did two brand new wheel cylinders in the back this time and the master cylinder is brand new. I have suspected a bleeding problem for some time, but now i am almost convinced this is not the problem.

Ok for the latest info, down to the nitty-gritty. I checked and found that i do have a RAB-1. the black/orange wire by the headlilght dimmer switch is not connected to anything, where is its counterpart? It appears to be completely missing!!! anyway i grounded it to chassis and diag will not start. so poked a test light into the black/orange and the amber rab light will come on then but no diag flashing. I did a basic test first to ensure that the red and amber lights were functioning properly, they seem to be. Red comes on when key is in start, and amber stays on for a second after starting. Why wont my rab enter diagnostic mode? I read SKINNERs idea to short the RAB Fuse terminal lead-in to chassis ground after pulling fuse after key-on, i will be trying that tomorrow. I did a little hunting around and trying to figure out the manual (haynes) that is lacking a bit of info on the brakes. I managed to find the HCv valve, and noticed that there is brake fluid leading ONLY from the point at which the 4 wires exit the plastic housing on the valve unit. I suspect that this valve is causing the pressure to remain extremely high on the rear brakes. That doesnt explain why when i do get a lockup they stay that way until i let them cool down for about 10 minutes then they are fine.

The one diagnostic code i can give you is the Red Brake Light(in dim mode), and the Amber RAB light come on simutaneously, and stay on for a while, for no reason when i am on the highway(not limited to times when i am using the brakes, happens when i am havent used them for a while). When this happens the brakes get real close to the top of the pedal and it seems as if they actually work better as if the front and rear were both grabbing at the same time where they dont normally due to the nature of the underlying problem. Could this be the RAB bypassing when the lights stay on?

Could it be the HCV Valve, or am i calling the part by the right name? I am talking about the valve that has the rear hydraulic line input, and two outputs that go directly to the rear wheel cylinders, and it has 4 wires for the rab system.

Could the proportiniong valve bad, or need adjusting? I assume it doesnt need adjusting because the red light goes off normally and doesnt stay on all the time(except for then accompanied by the amber intermittently for atleast a few minutes and sometimes as long as the whole duration of the drive).

Could it be the rear speed sensor?

Could it be from the fact that i have recently been running a smaller spare on my rear passenger side causing the differential in the rear end to give false readings?

Could it be faulty/rusty e brake components in the drum?

This is really getting at me, and has been an ongoing problem that has lasted about a year now.

Please help, I wouldnt go to the experienced mechanics unless i really needed the help.

I can and will gladly test for ohmage or voltage on any connecters if anybody has any ideas. There is just too many options in the manual for me to try them all. I will have to wait until i get a diagnostic code or a suggested check.

Thanks.

Wolf

 

an update;

but still hopeful for a much needed reply;

I noticed today, the red and amber lights came on just after a quick stop at a red light, the lights were on when i looked to the dash after accellerating through the green light but were not on before the stop.

Another thing i noticed is that the pedal was still close to the floor, i may have mistated that the pedal was near the top when the lights were on, but it seemed to be prior to the new shoes being put on. I believe the brakes are still trying to adjust tighter, they may still be on the loose end because the stars dont seem to tighten them to proper adjustment position very quickly.

Please help, i have the day off, and have the time today to buy and replace the hcv valve if that is the problem. I will go test the rab again now to see if i can get it into diag mode.

Nope; still can not get it into diag mode. When i pull the fuse the light comes on and stays on as to be expected i guess, but grounding the not-hot side of the fuse terminal does nothing. ugh! I'm not supposed to ground the hot side am I?

Wolf

 

Darn, doesnt anybody have any ideas? 2 days and running here no replies. I had two days off in a row too.

Please help.

 

ok wolfdog lets see if this helps ya,in the hanes manual they say to find the rabs diagnostic port connector ,wich is down under the dash by the parking brake THE CONNECTOR HAS TWO MATING HALVES(ONE OF WICH HAS A BLACK ORANGE WIRE CONNECTED TO IT)DISCONECT THE TWO HALVES-- turn the key to the run position -- ground the black orange wire,this should start the abs lamp to flash then count the flahes.i know you tryed this but try again and when you did this was the key in run position and use your dome light peg in the door jamb for a ground they work good.allsoe get the same size tires on the back that will be one less thing that could be causing the problem,allsoe have you thought about buying a master rebuild kit for the rear drums ?all that heat is bad for those parts and you said the self adjusters were not working, and have you checked the drums for warpage? i think you need to concentrate on getting the codes to come up.try to get that orange black wire hooked back up to the port plug in ,i think the reason your not geting any codes is the pcm for the abs is not reading any when it happens.hope i helped

 

Don't rule out dragging brakes.Eliminate things 1 by 1.
!st get the right tire back on.
next, proccess of elimination
Make sure all mechanical pieces move freely in the rear brakes
Cables release, brake arm pivots freely, Shoes retract all the way, (check the backing plate for ridges where the shoes ride, grind them flat and use a little high temp grease,

Next check all hydraulic lines for pinching, twisting, and crushing.
Check the flex hose at the rear axle. They break down and act as a check valve not letting the pressure release. (My prime suspect)
If you can get the rears to drag Jack the rear up and crack a bleeder. If you can spin the wheels afterward it is a hydraulic problem. (hose).

Next simply pull the RABS fuse and see if the problem disappears.
If so follow the diagnostics in the autozone manual.
They keep it pretty basic and easy to follow. Use the previous and next arrows to navigate or you will miss pages.
Ford Pick-ups and Broncos 1987-1996 Repair Guide

Good luck and let us know whats up.

 

bump