379 peterbilt problems

Depending on the size of your rubber I think the 370's would be a nice choice. I had one with the same setup with tall 24.5's on it and that was a good back road setup plus it worked good on the interstate as long as you don't want to run 80mph all the time. Metal sure could have come from the spiders.

 

With the 15 speed I would just stick with the 3.55's but if you do decide to change gearing one step lower won't show allot of difference.

Before you pull the carrier out of the housing, it's best to measure backlash on ring and pinion with dial indicator so you can go back together with same backlash measurement. This keeps the ring and pinion on it's established wear pattern and less noisey. Failure to measure before disassembly and reassembly will leave you with a gear whine/growl when done.

 

3.90's might be a good choice if you don't do long highway runs in a big hurry, I'm just not sure that you'll see a big difference in the field.

 

I would think with the deep reduction in a 15 spd you wouldn't have any trouble taking off. Thats one thing I always liked about them. The reason I suggested 370's is that I always got along good with them, never liked 390's much, just personal preference.

 

Tall rubber and 3.70's would be very similar to short rubber and 3.55's. I would think the tall rubber would be an advantage to get rolling when offroad and could make the difference.

 

The spider gears running loose on the cross can lock up the side gears (axle gears) and in turn cause the wheels to lock up, skid, hop up and down on pavement. Sounds like you found it. A nest kit should take care of that as long as the housing isn't torn up too bad. I would take a close look at the axles, spline and flange areas for twist and cracks.

 

Both sorry and happy, but it sounds like you found your problem. I believe you will be happy with the 3.70 choice, that would be my personal choice with your engine and trans, but everybody is different. Good luck to you, sounds like your on the right tract.