What's better?

[81GMCSierra1500]

Hey guys...

Recent development on my '81 Sierra Classic. Something went catastrophically wrong in the rear end a bit ago, which caused the pinion shaft seal and diff cover seal to blow, which caused the majority of fluid to leak out... Barely made it home, 2km's or so, thankfully. Oh boy was she growling... Now, the main question. I've bought a decent 10 bolt from an '87 V6 (80,000km's), that needs a wheel seal, and in my attempt to fix it myself, I discovered she's got a broken cross pin retainer bolt, but after all, what frickin' 10 bolt on this earth has one that's not broken... The "hip" that needs surgery is a 12 bolt... Are 10 bolt differentials more reliable than 12's? Especially with this 10 bolt being out of a much newer truck? Also, in recent time before the catastrophic failure, it would make a rather loud and quite noticable "ping" noise when reversed the first five feet in reverse... Bad bearing? Gear teeth contact? It only happened 2-3 times before the seals went... I had hit a pothole while trying to escape a red light left turn, shortly afterwards, put it in park, then reversed, and that's when the growling started. Also, the growling, up until just before I got home, would only happen intermittently, and would start at about 30km/h, and would stop below that... The drivetrain has 260,000km's (161k miles), and the rear end had considerable slack (would shift from park to drive/reverse quite violently if the brake wasn't to the floor). I'm just paranoid, as differentials in good condition are very scarce up here, and I need to know that the 10 bolt is going to be good enough...

Cheers guys!

'81

[motornut]

hows the drive shaft u joints,thats a ping sound I've heard

[esbstuff]

Down here rearend failures on auto trucks with 161K are rare. Manual trucks take more of an abuse and usually they are 200K +/-.

12's are better than 10's any day. But with 80 KM's I would stick in and use as is.

Just check your gear ratio especially if 4x4. They have to match 100% on 4x4 or you will get to buy a transfercase too. 4x2's not a big deal, but your speedo will be off...

[81GMCSierra1500]

No doubt rear end failures are rare... This one came as a complete surprise... I had all fluids changed and a diff flush done not long after purchase, The 12 bolt in old Red failed likely due to a clogged diff case vent hose, which somehow caused all the seals to blow... I thought 12 bolts were better, but for now, this one will do just fine. If she stays with me for a while (I'm hoping to keep it a 2 owner truck for the rest of it's life), I'll find a built up 12 bolt. The truck was new in Saskatchewan in 1981, and used as a run-about/farm truck for her first 10 years, she then moved to Vancouver for another good ten years, then moved to Victoria, until I bought her. She was in pretty sorry shape... She needed a new transmission, she had vacuum leaks everywhere, and more... she just needed help... I'd still say that a $500 purchase has carried me a long way... she just needed some love... But anyways, the brakes on this 10 bolt are pretty not great, so I'll swap the brakes from the 12 to the 10 when the axles are out during the seal change, and just get it inspected, and if it won't last, it's not gonna go in... But soon here, there will be some major bodywork in store for old Red.

[Ziegelsteinfaust]

12 bolts are slightly better then the 8.5 10 bolt. If built up the difference is less.

The 12 bolts ring and pinion is 3/8 of a inch bigger, and that is the biggest difference between the two.

I never have had a 12 bolt because I would not pay the money for one. Yes I have killed a few 8.5 twn bolts, but the 12 would of lasted longer by about 30 foot making 11's.