I have been following the RABS discussions here with interest since I have been living with a yellow RABS light on for some time. I just want to say thanks to all who provided info and links (HardScrabble, thank you). A recent comment about where to find the diag connector on my '91 F350 got me off my behind to go do something about the problem. I found that connector right there by the parking brake. When I grounded it nothing happened at first. I tried it again and wiggled the aligator clip around so as to get a better contact, then when I took off the ground line it started flashing (code 9 = open sensor).

I got under the rear axle and removed the sensor, then checked its' resistance. I found it measured infinite resistance (s/b 1000-2500 ohms). A new sensor was needed ($20.80 + tax at Ford parts). The ford shop manual says to clean the mounting surface on top of the differential, lube the O-ring and insert it till it fully seats. Then torque to 25-30 ft lbs. This is a lot more torque than I would have used but it needs to be fully seated to insure the proper spacing for the magnetic pickup to work. My torque wrench just barely fits under there but I got it on tight and now it is ok (no yellow RABS light). Ford originally used some kind of screw compound on the bolt which made it hard to get out. The manual didn't mention any thing about this so I only put a little lube on the threads when I re-installed it. I hope it won't come loose somewhere down the road.

Unfortunately, while I was under there with 4 tons of truck (almost) sitting on my chest, I noticed the differential housing was leaking. Looks like it is leaking from the front of the housing at the drive shaft (must be a bearing there and a grease seal?). Now that's a more serious problem and is typical of what happens when I start looking around closely for other things that might be wrong. I don't suppose I can just ignore it like I did with that yellow RABS light (a little piece of black electrical tape on the dash put that problem out of mind).

 

There is an oil seal where the pinion enters the differential housing. This is not an easy job for the average wrench turner because that pinion nut is *really* tight.

Assuming you have a DANA 80 rear end, first remove the driveshaft. Then untorque the pinion nut - you will have to rig up a tool to clamp to the u-joint flange to stop it from turning while you remove that nut. Figure that it is torqued to about 500 ft-lbs or so. After the nut is off, use a puller to remove the u-joint flange assembly then remove the seal with a seal puller.

Install the new seal with a standard seal installation tool. Install the u-joint flange and the pinion nut. Torque the nut to spec - be sure to look up the correct torque, but it is in the 450 to 500 ft-lb range.

As a temporary solution, pull the oil level plug and check the rear end lube level. Add gear oil to bring level to the bottom of the plug if required and install the plug. Operate the truck and see just how bad that leak is, or is not.

Lou Braun

 

Is the RABS light next to the left turn signal light?

 

BigBlue,
The yellow RABS light is on the right side of the steering column on my truck. A couple of inches over and down low in a band of black plastic across the dash. It should light up for a second or two when you start the engine.

Lou,
Thanks for the info on changing the bearing/seal. I don't think I'm up to doing that myself but it helps to know what is involved. I will check the lube level and re-fill it. I'm pretty sure it's going to need some, there is diff lube all over the front of the housing, the back end of the fwd gas tank, the stabilizer bar, and even a band of it on the under side of the bed. It must be getting out only when running fast, it doesn't drip down on the ground where I park it.