12bolt swap questions

[team39763]

My 10bolt gave up the ghost, so I'm swapping in a 12bolt from my friend's truck. I've been searching for posi units and some say they won't work for truck rears and some don't say anything about what they fit.     

1. Is there a difference between the truck and car 12bolts?  What specs do I need to know in order to get a posi unit that fits?
2. Will all 12bolt gear sets fit both cars/trucks?
3. The 12bolt I'm using is coming from a 1978 1/2ton with 5X5 bolt pattern.  What will I need to make it work....new yoke, new spring perches, shock mounts,driveshaft length?

Or should I just buy a good posi unit for my 10bolt?

Any help or advice would be greatly appreciated.  Thanks.

[Captkaos]

1)Yes, passenger car 12bolts have a larger pinion shaft.  You need to tell them it is a 12bolt truck diff.
2)No, Passenger car and Pickup 12bolts are different, they won't interchange.
3)You will need a hybrid U-joint to make it work.  Everything else will bolt in if you are replacing a complete rearend.

If the 10bolt only blew the rear diff, I would just get a good limited slip and replace it.  Now would be a good time to get the gears you want also.

If you call www.randysringandpinion.com and tell them what you have they will send you the correct parts.  I personally would get an Eaton Clutch Limited slip.

[team39763]

Are you sure I shouldn't go with the 12bolt?  I'm getting it in return for my 10bolt.  Either way, I'll have to buy a LSD and maybe some new gears.  I'm up in the air about the gears since my truck seems to drive perfect for me(around town and at the track).

[Captkaos]

I am sure.  My brothers 2000 is running the stock 10bolt with an Eaton LSD and he is putting down over 600lb/ft to the ground on street tires.  He has grenaded 3 4L60E's and the diff is fine.  It is also running ET slicks at the drag strip for over 3 years...

What gears are in it now?  I wouldn't go over 3.42's if you are using a TH350...

[team39763]

I still have the 4.56's in there.
Ok, you convinced me.  I'm gonna go with an eaton posi when I can afford it.  I had one in my 2000, but I didn't know how to pull the differential, so I had to let the insurance take it when they came to collect the truck.

[Fordeatinz71]

yea man, the 12-bolt isn't nearly "bulletproof" enough to really warrant changing it out over a 10-bolt.  you can find plenty of aftermarket goodies to make the 10-bolt plenty stout for your application...

[Captkaos]

WEW, 4.56, that HURTS.
A 2000 didn't have an Eaton LSD in it from the factory, it had a Eaton Gov-Loc... or Grenade Loc as it has been called...

[ccz145a]

Grenade Loc

Does that mean they explode?

[Captkaos]

Yeah, it is usually because of the driver though not the diff.  Offroaders who hammer down on the the throttle.
The work great when used as intended.

[team39763]

I bought a real Eaton and had it installed shortly after I had the 6.0 installed.  All that power was useless without a LSD, actually even with the LSD it was useless.  I ran 16.2 with 5.3 boltons and open rear, then ran 16.2 with boltons 6.0 and LSD. Is it possible to keep a G80 alive if I don't abuse it?  I don't do donuts and my burnouts are only a couple seconds long(I have 10.5" slicks).  I only plan on going to the track 3 times a year at the most.

[Captkaos]

If you are going to be dragging it, I wouldn't rely on it to stay together long.  Does it have a gov-loc in it now?  If you use it like it was supposed to be used (not drag racing) it will be fine.

[team39763]

Yeah, I'm gonna be drag racing.  I'm not sure if it was the gov-loc.  I think I remember looking and it was the spring loaded kind and not the one with the weights that swing out.  Is it possible that I put the wrong fluid in there and it's too slippery to lock up?  I'm going to eventually get an Eaton, but I need something to hold for about 6 more runs down the strip.  Is the spring/clutch type the same as the one with the swinging weights?

[Captkaos]

The ones with the swinging weights is a gov-loc.  The one with a spring/clutch is a LSD.

[VileZambonie]

Eaton and Auburn IMO make the two best streetable units. Auburns seem to work smoother but if you cook one it's trashed since it will wear out the carrier. Eaton uses the multiple disc clutch pack design which can be rebuilt if it fails which is nice but are more prone to chatter than the cone type even with the best of friction modifiers and that can get annoying however in some vehicles you may never even feel it. Nevertheless I would recommend either of the two over a locker or Gov-lock POS anyday.

[team39763]

I'm considering just throwing in some strange axles and a spool.  This truck won't be street driven anymore.  I'm throwing it in the backyard and driving a beater to work.  My wife bought herself a ford truck, so we don't need my truck for transportation.  I took the truck to the track a few days ago and I ran a 12.8 even with the open diff and without any tuning at all.  I'm hoping I can hit high 11's with traction, tuning, and a little weight loss.