Not third gen but still GM.

The diff in my 91 454SS started howling the other day. Not bad but noticable over the loud exhaust. Tonight after work I finally took a look under the truck (it's lowered and hard to get under) and saw oil everywhere around the pinion. No problem I thought. I got 50,000 kms on that pinion seal. I'll just pick up a new seal and some oil and replace it.

Nope. As soon as I unloaded the driveline I could see the pinion moving up and down. I took off the driveshaft and pinion yoke to see that the front pinion bearing had seized rollers in it. The diff still had lots of oil since it was coming out the front as soon as I popped the seal out but the oil smelled burnt and was metalic.

Looks like I'll have to limp into work tomorrow and get the diff rebuilt. I just hope the ring and pinion are still OK. This is a 9-1/2" diff with 4.10 gears. Maybe this would be a good time to have 3.73's installed. With the 4L80E tranny, that would make a big improvment in fuel mileage however the speedo would need to be recalibrated. I have no idea how the computer would react to the gear ratio change if it wasn't recalibrated.

I guess those dragstrip launches this year finally took their toll on the diff. That's a lot of abuse when you have to get 4600 pounds moving from a dead stop.

 

Sounds like the perfect time to swap in a fab 9 housing and a bullet proof center section then if your at the track and something happens to either truck/car, you have a back up gear just think'n ahead for ya and help'n spend your money's

 

if you have play in the pinion then both ring and pinion are done! buy a new set

 

Did some price checking today and parts for a GM 9-1/2" are expensive and hard to get. I found a complete diff with 4.10 gears for only $400CAD. All the bearings looked new. Open carrier, no brakes. Bad thing is that it was for a one ton and even an axle swap won't make it fit my truck because of how the backing plates are positioned for the large drum brakes on the one ton. It needed new spider gears but the seller provided me with them. I bought the diff anyway. The only place that had 4.10 gears in stock wanted $460 for them. The cheapest I could find a bearing kit was $160 so I feel it was a good deal.

Pulled mine apart after work. Yuck. Not that bad really but the outside pinion bearing had flat rollers and I had to beat on the pinion to get it out of the bearing. The race fell out of the housing so I was a little worried the housing was going to be bad. I took the races out of the new diff and they went in nice and tight into the diff in my truck so that was a relief. My diff is a GovLock and there were a few teeth missing around the ring. As nice as it would be to keep the GovLock, I opted to just install the open carrier in my truck. I can always upgrade to some sort of locker later but right now I need an operational vehicle.

I threw everything together to check clearances. .012 backlash and the wear pattern looked acceptable so I took it all apart again. Nowhere in the shop could a find a crush sleeve for a 9-1/2" diff so I had to call it quits for the night until I can pick one up tomorrow.

The 9-1/2" diff is sort of nice to set up. Not as easy as the 9" though. Setting the pinion depth is still hard since the bearing needs to be pressed on and off but adjusting the backlash was nice. On the driver side of the carrier behind the bearings is a spacer and shims. On the passenger side is an adjuster wheel. Tighten up the adjuster to preload the bearings and check backlash. If not correct, loosen adjuster, add or subtract shims on the other side and try again. A Ford 9" you have adjusters on both sides so you're constantly loosening or tightening to get it right. On all the other GM diffs, you need to add or subtract shims on both sides to get it right.

Anyway, it looks like I'll have it back together tomorrow. Same gearing but an open diff. The govlock drives around like an open diff anyway. It just locks up when you get wheel spin but isn't the same as a posi since you don't really get a real posi with both wheels getting the same power.

It's hard to say exactly what went wrong. Not a lot of oil came out when I pulled the cover off. Did I lose most of it when the bearing failed and took out the seal or was there a leak and the level got low enough that the front bearing didn't get any oil? Personally I'd go with that excuse.

Proper preventive maintanence. Check "all" fluids regularly. Fix all leaks no matter how minor they look. Change "all" fluids as per recommended schedules.

 

4L80E? is that a typo?or does this really exsist? i realize there are new things to learn all the time and this definitly would be new to me!!

 

Yes, it's a real transmission.