Desperately need advice on rear ends.

[Schurkey]

I wouldn't waste the cost of gear lube on an 8.5" ring-gear axle. They're wonderful for what they were intended for--compact and intermediate cars. GM didn't use 'em on full-size cars until full-sized cars were downsized to intermediate size and weight. GM should never have put them under full-size trucks.

Make the switch to a 9.5" ring gear axle. Twice as strong, and the G80 isn't a hand-grenade. And on the pickups, the brakes are better, too. You'll need a conversion U-joint, and new U-bolts.

Downside for the C1500s is that most 9.5s will have six- or eight-lug axles. Six-lug axles would be preferred. You'd either need custom 5-lug axle shafts and new brake drums, or you need new (rear) six-lug wheels; or six-lug wheels all around plus front rotors. I've never done the 9.5" axle conversion on a 2WD, but they're beyond easy with 4WD.

Seems to me that the switch from 28 to 30 spline on the 8.5" axle was in '88 or '89.

 

[Tommy1234]

No problem! I moved this thread over there for you.

Thank you very much

 

[Tommy1234]

I wouldn't waste the cost of gear lube on an 8.5" ring-gear axle. They're wonderful for what they were intended for--compact and intermediate cars. GM didn't use 'em on full-size cars until full-sized cars were downsized to intermediate size and weight. GM should never have put them under full-size trucks.

Make the switch to a 9.5" ring gear axle. Twice as strong, and the G80 isn't a hand-grenade. And on the pickups, the brakes are better, too. You'll need a conversion U-joint, and new U-bolts.

Downside for the C1500s is that most 9.5s will have six- or eight-lug axles. Six-lug axles would be preferred. You'd either need custom 5-lug axle shafts and new brake drums, or you need new (rear) six-lug wheels; or six-lug wheels all around plus front rotors. I've never done the 9.5" axle conversion on a 2WD, but they're beyond easy with 4WD.

Seems to me that the switch from 28 to 30 spline on the 8.5" axle was in '88 or '89.

Totally agree with the bit of the 8 and a 1/2 gear

 

[stutaeng]

I wouldn't waste the cost of gear lube on an 8.5" ring-gear axle. They're wonderful for what they were intended for--compact and intermediate cars. GM didn't use 'em on full-size cars until full-sized cars were downsized to intermediate size and weight. GM should never have put them under full-size trucks.

Make the switch to a 9.5" ring gear axle. Twice as strong, and the G80 isn't a hand-grenade. And on the pickups, the brakes are better, too. You'll need a conversion U-joint, and new U-bolts.

Downside for the C1500s is that most 9.5s will have six- or eight-lug axles. Six-lug axles would be preferred. You'd either need custom 5-lug axle shafts and new brake drums, or you need new (rear) six-lug wheels; or six-lug wheels all around plus front rotors. I've never done the 9.5" axle conversion on a 2WD, but they're beyond easy with 4WD.

Seems to me that the switch from 28 to 30 spline on the 8.5" axle was in '88 or '89.

Yeah, the 5 lug swap is a bit more challenging than a 6 lug 14 bolt 9.5"...

I helped my brother swap a 14 bolt 9.5" 6 lug rear axle into his 90 C1500 RCSB. He bought the axle and front spindles from a guy that was parting out a 97 C2500 LD 6 lug. I think for $400 and the guy gave him some roller wheels/tires. I only helped him swap the rear axle. Just new U bolt for the leaf springs, conversion U joint for the driveshaft, and brake bleeding and that was it. He did the front spindles on his own. His 14 bolt axle was a G80/3.73 over his 10 bolt 3.08 open diff. His truck looks kinda unique/cool being a 2wd with 6 lug wheels, now that I think about it, LOL. He also commented on better braking after the swap. And he sold his 10 bolt for like $200 or something like that after the swap.

The only downside is the newer wheels have something different with backspacing, so I think he had to use some spacers on his front? I don't know anything about backspacing or how that works...

 

[PlayingWithTBI]

Seems to me that the switch from 28 to 30 spline on the 8.5" axle was in '88 or '89.

Yes, FWIU 88 was the 1st year with 30 spline, at least mine is.

 

[kennythewelder]

Here's the thing. What are you going to do with the truck. My 8.5 10 bolt, 342 open diff, lasted me to about 250,000 miles. I did have a 17 foot bass boat that I pulled with the truck, but I only had it 3 years, before I sold it. So I never pull anything heavy. My rear end broke the bearing mount on the carrier. For years, I wanted to put a limited slip carrier, or a lunch box locker. I rebuilt my OE rear end with an Eaton trutrac, 373 gears, all new bearings, races, seals, and a crush sleeve eliminator kit. I spent $1100 and did all of the work myself. This was 1 year ago. I love it. From a dead stop, I can now leave 2 black marks on the pavement. The truck drives a lot better on wet roads too. It is exactly what I was looking for. For me, it is perfect, but this may not be what you are looking for. My truck never sees mud, snow, ice, ECT. Just a lot of rain where I live. I never take it off road ether. My truck is a street, Dailey driver, truck, that jumps to attention when you nail the gas peddle. HP wise, I'm at about 325. I have always been able to put run a OE, 5.3L in my truck, and it became much easier when I rebuilt my diff. The 373 do decent on the HWY also. Around 3000 RPMs at 85 with 275/60/15 tires. Tires also play a huge roll on performance, when it comes to gear ratio.

 

[azmikep]

I wouldn't waste the cost of gear lube on an 8.5" ring-gear axle. They're wonderful for what they were intended for--compact and intermediate cars. GM didn't use 'em on full-size cars until full-sized cars were downsized to intermediate size and weight. GM should never have put them under full-size trucks.

Make the switch to a 9.5" ring gear axle. Twice as strong, and the G80 isn't a hand-grenade. And on the pickups, the brakes are better, too. You'll need a conversion U-joint, and new U-bolts.

Downside for the C1500s is that most 9.5s will have six- or eight-lug axles. Six-lug axles would be preferred. You'd either need custom 5-lug axle shafts and new brake drums, or you need new (rear) six-lug wheels; or six-lug wheels all around plus front rotors. I've never done the 9.5" axle conversion on a 2WD, but they're beyond easy with 4WD.

Seems to me that the switch from 28 to 30 spline on the 8.5" axle was in '88 or '89.

I just installed a Lockrite lunchbox style drop
In locker in my 1990. I had 28splines in my axle. I counted vrs websites so it does matter 28 or 30 spline.
Thru all the research and advice I got here I can say that unless you have to unbolt the ring gear from the carrier; everything is straightforward. My bearings were months old. If your not scared off by gear mesh and bearings I bet you could do it yourself.
Hope this helps and good luck.

 

[Supercharged111]

Yes, FWIU 88 was the 1st year with 30 spline, at least mine is.

Could have been? But my 88 was not 30 spline when I got it. I swapped it when I put new guts in the factory open carrier.

 

[badco]

I had a 12 bolt in my 90. Was a easy swap and the limited slip actually worked. If you got the money the strange differentials are 10x more reliable than any factory units, I have a S60 and its lighter and faster than the 9" i had.