Compatible 12-bolt Rear Diff's

[SUX2BU99]

Can somebody give a quick rundown on which years and diff's interchange as a direct bolt-in? I have an 81 1/2 ton, 5-lug axles and 12 bolt. Looking for the same to directly bolt in. I think I read on here that 10 bolts which were put in 1/2 tons to replace the 12 bolt in 82+ have different yokes on them. That doesn't sound like direct bolt in to me.

I'd like to know what years of trucks, SUV's and vans I can scour the local papers and craigslist for. I found a 3.42 posi (which is what I want) from an 88 Suburban 4x4 but I don't know yet if it's a 12 bolt or how many lugs.  I sure do find a ton of 14 bolts from 3/4 tons though.

[Captkaos]

1973-1981 = 12bolt
1982-1991 = 10bolt.
If you want something that will bolt in, get one from a 4x2 NOT a 4X4 from any 73-81 2WD Pickup, Blazer or Suburban 1/2T.

[Blazin]

88 will be a ten bolt, if its 4x4 it will be 6 lug if its 1/2 ton. No other option.
10 bolts are a direct bolt in. the u joint is wider and the caps are bigger diameter. It still bolts right in with no modifications. You have to replace the u joint with a combo joint. 10 bolt size one way, 12 bolt size the other. Bolt in!
 Anything from a pickup, suburban, blazer will be a direct fit. Vans do not fit.
 As far as using a 4x4 10 or 12 bolt 4x4 / 6 lug, all you have to do is swap your axles, baking plates, brakes, & drums over to make it 5 lug.

[SUX2BU99]

Awesome, thanks for the detailed info!  I wrote the guy and he confirmed back to me that it's a 10 bolt, but the good thing it's a 5 lug. That's cool that a combo u-joint is available. So I got 2 out of 3 things with this 10 bolt: it's a 3.42, it's a Gov-loc, buuuuut it's a 10 bolt. If I had a 10 bolt right now, it wouldn't bug me so much but I got a 12 bolt and I just added more power to my truck. What's your experience been with 10 bolts and them holding up?  The diff has about 85k miles on it.

[Captkaos]

The 10 vs 12 are virtually identical in strength.

[SUX2BU99]

Oh really? Didn't know that. I guess the big differences between the 10 bolt to the 12 is a little smaller ring gear diameter and a few less splines on the axle shaft?  I suppose since I'm not towing anything or dumping a clutch a high RPM on slicks or using a transbrake, I'm probably pretty low risk for busting a 10 bolt eh?

[Captkaos]

We put a wild 454 in an 81 with a TH350C and 10bolt and shot about 150HP nitrous to it.  This was a weekly event as it was street raced when we were younger and was taken to the track OFTEN.  The TH350C couldn't take it and lost all forward gears after about 3 months.

My brothers 2000 Silverado has the same 10bolt with 3.42 and an Eaton and it used to be at the track every weekend on ET drags hitting 1.8 60ft for over 2 years 10 months out of the year.  It is Turbo'd and made 575lb/ft.  The rearend is what came in it from the factory except for the Eaton.  He has been through 4 trannys so far.

10bolt ring diameter is 8.5"  12bolt is 8.875"
10bolt pinion diameter is 1.625" (30 Spline), 12bolt is 1.438" (30 Spline)

[SUX2BU99]

Beauty! Thanks Chris. I won't be discouraged then at all about buying this one. Dude wants $350 but it's about a 3 hr. drive from home. If I can't find something locally, I'm going to take this one.

[Captkaos]

HOLY MOLY!  $350?  Is it completely rebuilt?  Around here a used 10 or 12bolt generally is like $75.

[SUX2BU99]

   Say what??  Wow, no up here it seems that min. price for a diff that isn't blown up is at least $100 for an open 10 bolt with highway gears. A posi 3.xx doesn't suprise me for over $300. 14 bolts are everywhere for $100-200. This one is just pulled off a wrecked Sub with about 85k miles on it. One dude has a car 12 bolt for sale for $1500!!  It's an aftermarket rear end though but still....

[VileZambonie]

Where do you live?

[cracker0169]

for $350 I think that i would find a rear end with my gears and just order an auburn pro series and bypass the junk gov lock! 3.42 gears shouldnt be too awful hard to find! personally, Im a 12 bolt fan. 30 spline axles vs. 28 splines not to mention 8 7/8 ring gear vs. 8.5.

I did buy a 10 bolt one time however for $400 dollars (delivered to me however). Its a front axle with 3.73 and an eaton posi with new in box timken bearings and seals and brand new hub assemblies. I figured $400 delivered was quite a fair deal even though I had to but the hubs together...

[Captkaos]

Axle spline count can be changed via the carrier buy using the 88-up limited slip.  The only negative against the 10bolt then is a ring gear that is 3/8" smaller in diameter.  Everything else is larger.

[SUX2BU99]

I called around to some wrecking yards and found more 10 bolts; no 12 bolts. Prices varied from $400 complete, to $150, to $95 (u-pull). Nobody had ratios available. It's a see-for-yourself kinda thing. The $150 is about 7 min. from my house so I might as well check that out and pull the cover to count teeth. A Gov-lok would be nice, which is what the $350 one has, but I'm not set on one. Less to blow up   lol

[SUX2BU99]

Can anyone who knows give me a number for what a ring/pinion swap would cost for labor? If you don't want to publish prices, how about time in hours? Justmulling over whether it's worth it to drop about $200 on a new ring/pinion and have it put into my 12 bolt, or to buy a 10 bolt with what I want for about $350 and a new u-joint and put it in myself.

I just called probably the biggest place around here that specializes in rear ends and they quoted me $750-850 to swap the r/p with a USED one (allowed $225 for that, I can buy new for that price....), new bearings and $425 for labor. Sheez. They won't install customer-provided parts either. I remember phoning them in 1995 to fix the Trac-lok on my Mustang GT and put in a new r/p. That was around $1000 too as I recall. Ouch.