Rear Axle on Work Truck

[sgtsandman]

Limited slip will work if you plan on driving mostly on roads and has less of a tendency to kick the rear out on you than a locker. I would recommend getting a worm gear style over one that uses clutch plates. 1) They don't require additive to operate properly 2) There are no clutch plates to wear out and require replacement down the road. There are to makers out there that make these, Torsen and either Detroit or Eaton.

An LSD will work ok on trails as well as long as you keep it light. Tougher stuff will need a locking differential.

 

[don4331]

Any suggestions what to look for? mileage, physical characteristics of an axle to have a good chance of swapping to something better?

As noted - '03-07 FX II have 8.8 with Torsen differential, next on list you are looking for axle with 4L10 tag (closest to your existing with LSD). Ideally, you pull the brake drums and look for leaks. If you are really ambitious - pull the rear cover; 99% of time, the yard won't have drained the oil, if none comes out, I'd pass, if craigslist and no oil, 100% I pass. Look at wear pattern, and for chipped/missing teeth. Remove the cross pin, the bolt securing; it requires high quality 5/16" closed end wrench and LHF. If the whole bolt doesn't come out, walk away (bolt is locktite in, so a pain to remove, if the whole bolt doesn't come out, it means one axle was loaded real hard in relation to the other to break the pin).

Remove the c-clips and slide axles out to look at seal/bearing surfaces. If the hard layer is worn through at seal surface, you will have leaks later. (You can get kits for seal surface should you choose). If bearing surface is pitted/flaked, you need replacement axles. If it was 28 spline axle, you might be able to use your existing axles (comes with price being right).

I would want to install new bearings and seals at axles ends, fresh oil and new cover gasket. But I wouldn't want to have to do it all over again in couple months.

 

[backporch]

came across somebody selling a R7 rear end for $200. He couldn't tell me much about the truck other than a 2000 with 120K miles. It was picked up as a parts vehicle. Any reasonable assumptions I can make about that rear end condition/durability at that mileage? My gut is to walk away from something that might be no better than what I have.

Might be able to crack it open and do an inspection like you mentioned. Great advice. Just a general question about durability of these units at the age and mileage. Thanks

 

[RonD]

I have an R6, 3.73 L/S, in my 1994, never had any problems, and I don't service anything until it starts to make a noise, lol

Fords 8.8" seem to last pretty well

 

[backporch]

I finally put the truck on jackstands and tried to get it to make the noise I hear on the highway by having it in 5th gear and applying gas and some brake to load up the drivetrain. I didn't hear the same noise...

I did go under the rear end while the truck was in gear and put my ear to the diff... it was clanking and bumping every now and then. looking at the driveshaft from the side, it looked like the driveshaft connection to the diff was moving forward and back slightly. i also noticed after I shut down that the axles/wheels could be pushed in slightly and pulled back out.. there was definite play there on both sides.

 

[adsm08]

The noise when running in the air may be normal. If both wheels aren't spinning in the same direction at the same speed the spider gears can make a good bit of noise, totally normal.

The in and out play at the wheel ends is also normal. On Ford diffs (and a lot of Chevy ones too) the axle shafts are retained by C-clips that go around the end of the shaft and sit into a cut out in the side gear, and the axle shaft is pulled outward until they seat. The cross pin is then installed and it keeps the shafts from going in far enough to let the clips fall off (along with doing other things). Remove the pin, push the axle in, remove the C-clip, axle comes out. The result of that type of setup is about 1/16 to 1/8 inch of play being normal when everything is assembled.

The pinion moving in and out could be a sign of bad pinion bearings. I'd unbolt the driveshaft and see if you can get any play out of the flange by hand.

 

[backporch]

This is a picture of the axle that I found for sale. Ranger totaled due to frame rust. Does anyone know if the axle tubes can rot out on these? It looks worse than mine, but not sure of the thickness of the axle tube.

 

[sgtsandman]

They can rust out just like anything else. One hears much less on axle rusting out issues than sheet metal and frames but it does happen.

 

[franklin2]

I finally put the truck on jackstands and tried to get it to make the noise I hear on the highway by having it in 5th gear and applying gas and some brake to load up the drivetrain. I didn't hear the same noise...

I did go under the rear end while the truck was in gear and put my ear to the diff... it was clanking and bumping every now and then. looking at the driveshaft from the side, it looked like the driveshaft connection to the diff was moving forward and back slightly. i also noticed after I shut down that the axles/wheels could be pushed in slightly and pulled back out.. there was definite play there on both sides.

I was fighting a noise issue when I first put my Bronco on the road. I thought it was the rearend, changed it out. And improvement, but the main culprit was still there. Had a little play in the double cardan joint, had to buy a new H-yoke and replaced the joints. Vibration went away, but still had this dump truck rumble and vibration. I then jacked up the front wheels and spun them by hand. The driver's side was noticeable smoother than the pass side. Pulled the passenger side wheel bearings out, they had little dark rough spots in the rollers. Two new wheel bearings on that side and it is very smooth and quiet now. It sure did not sound like the main problem was in the front right, but it was.

 

[sgtsandman]

It weird how sound travels through the vehicle and fools you. It makes troubleshooting bad ball joints fun.