I had a lingering doubt about the rear axle because I had never driven the truck that it came out of. I doubted that there was a problem in it, but for two reasons I purchased a complete 14FF assembly out of a you pull it yard. The first reason was I wanted to try a complete axle assembly--untouched--and see if anything changed with the vibration and second (more importantly) was I wanted to go with a higher gear ratio--3.73 as the 4.10's are just too much gear for a torque motor. They are fine for a small block, but running them with the Cummins was a chore as the motor wound up too quickly and spun too fast on the highway.
I finally got fed up one day and went shopping. One yard--nothing, second yard had one that could have been something, but the SPID label was gone and I did not feel like pulling a diff cover in a mud puddle, so I passed. The third yard had what ended up being the cat's ass. I found a super-clean '97 G3500 passenger van. I checked the SPID label and found the GT4 code indicating the desired 3.73 ratio. I pulled it out and loaded it onto one of the wagons tha they provide and dragged it about 1/8-1/4 mile to the cashier. I left it outside as it had completely kicked my ass dragging it across the yard on two flat tires and it not being light to begin with. The cashier made me bring it inside. I stated that it is what it looks like and it looks the same out there as it would in here, but she still made me drag it inside (thank you nice lady). I paid my money, loaded it in the truck and headed home and unloaded it.
As a side note, I had looked at the van that this came from and I wondered why a truck this clean was in the wrecking yard. It had no insurance company information on it, but then I found the "c4c" on it. Ahhhh, the wonderful Cash For Clunkers program. Well, I cut the SPID label off of it and when I got home I ran the vin on the state website to see how many miles it had on it when it was last emission tested--and also how bad it was polluting. I found that it had 157,000 on it and it ran so clean it practically made air. Yeah, great truck to take off the road guys.
So, I wanted to put this diff in without touching anything. I only had one problem and that was the parking brake cables were the later design that I had initially wanted, but couldn't find. Now I had them, but I had already set the truck up to use the older bolt-in style. Now, I could redo the truck and use the newer cables, but I did not feel like doing all of that to swap out a diff. I happened to have a set of one ton (13x3.5") backing plates that use the bolt in parking brake cables. I swapped those on with all of the late model brake components that came on the axle. One sweet bonus of this swap is I get
slide-off brake drums!!! Woo-hoo!! I did have to pull the hubs to swap the backing plates though, but when I did I checked out the bearings and they look great. The gear oil smelled good. I got a unit that is in great shape.
I cut the perches off and welded them in the correct place. Before I swapped the new axle in I took my 2.5 deg angle milled Zero Rates and turned them around thus raising the existing pinion five degrees. That made no change at all. I got home and pulled the diff and swapped in the new one. While I was taking it apart one nut on one of the new u-bolts galled. Nobody in town stocks them and spring shops are closed, but a couple phone calls later to some fellow gear heads had a replacement located and the project back in motion.
I got the new diff in and bled the brakes and went for a drive. The first thing I noticed is how nice the truck drives with the higher gears. I can drive around without having to use fifth gear. Prior to the swap, my maximum speed in fourth gear (1:1) was 55mph. I had to be in fifth to merge onto the freeway. Now, my top speed in fourth is about 65mph. It doesn't seem like much, but it make a huge difference in drivability. It spins slower on the freeway such that it quiets the motor down significantly. The motor lays down above 90mph now instead of 82mph. All in all it wa worth every bit of effort to install. I can not convey how much nicer this thing is to drive now that the motor spins slower. The fatigue factor of a roadtrip will be lessened significantly.
It has the cool, ribbed-for-her-pleasure housing:
So, it drives soooo nice now, the vibration...
oh yeah.....
remains alive and well!! No difference whatsoever!!
Argh. I guess I knew it going in, but I
really hoped it would take care of it.