10 Bolt Axle swap or 12 Bolt retrofit

[Geezer2]

My rear carrier destoyed on my 82 4x4 (2.73 10 bolt) a couple of weeks ago and I have been looking for another diff. Today I was at a major salvage yard and they told me they believe a 1/2 ton diff from 73-87 will work (as long as it is a 2.73 10 bolt) and all I have to do is remove the 1/2 ton 5 lug axles and install my 6 lug axles. I would not have thought the 6 lug would be a replacement for a 5 lug axles but maybe the splines will match, I do not know. This discussion came up becasue I was about to make them a deal on a 12 bolt 2.73 and retrofit it to my truck. They said the spring hardware will never work from the 10 to the 12. Does anyone have a Hollander salvage manual or other sources that would verify some of this info before I undertake allot of of work? I'll be most grateful. Thanks

[rockn30809]

12 bolt will go right in. You will need a conversion u-joint. Can't remember the part# but do a search on here and you can find it.

[Geezer2]

Originally Posted by rockn30809

12 bolt will go right in. You will need a conversion u-joint. Can't remember the part# but do a search on here and you can find it.

OK and thanks, I'll try and run it down

[Geezer2]

I found two posts on 10 to 12 bolt. Nothing mentioned about the spings and hangers. Appears they must of went smooth. The lead on the u-joints helps...thanks
My situation may be more complicated due to my truck being 4 wheel drive. I am not sure how that affects matching the drive shaft to the transfer case. The owner at the salvage yard was sure quick to tell me the spings are an issue. Hopefully someone will chime in with some info

[Driveway Dreams]

I had a stock 10 bolt that I destroyed, and I replaced it with a 12 bolt. Much more confident in that one. You will need to make sure that the gears in the new rear end match up to your front ratio. But I am using a GMB brand U-joint part number 215-0356 to go from my stock driveshaft to the 12 bolt. It looks like it may also be part number 240-0356 (according to gmb.net).

When I got mine, I went in to Checker asking for help to find the right one. Took a couple tries but they got me this one. It fit very well. Good luck.

[rockn30809]

Originally Posted by Geezer2

I found two posts on 10 to 12 bolt. Nothing mentioned about the spings and hangers. Appears they must of went smooth. The lead on the u-joints helps...thanks
My situation may be more complicated due to my truck being 4 wheel drive. I am not sure how that affects matching the drive shaft to the transfer case. The owner at the salvage yard was sure quick to tell me the spings are an issue. Hopefully someone will chime in with some info

Mine is 4wd and with the conversion u-joint everything bolted in with no mods and has been good for 5yrs now.

[Geezer2]

Originally Posted by Driveway Dreams

I had a stock 10 bolt that I destroyed, and I replaced it with a 12 bolt. Much more confident in that one. You will need to make sure that the gears in the new rear end match up to your front ratio. But I am using a GMB brand U-joint part number 215-0356 to go from my stock driveshaft to the 12 bolt. It looks like it may also be part number 240-0356 (according to gmb.net).

When I got mine, I went in to Checker asking for help to find the right one. Took a couple tries but they got me this one. It fit very well. Good luck.

That helps allot. I will check out the part numbers and research. Thank you for the reply.

[Geezer2]

Originally Posted by rockn30809

Mine is 4wd and with the conversion u-joint everything bolted in with no mods and has been good for 5yrs now.

Wondferful. Was the 12 bolt from another 4x4? Did you use your old springs? Can I use my axles from my 10 bolt 4x4 so I can keep my same rims????

I found a couple of 12 bolt non 4 wheel drive but boy was the guy at the salvage yard was sooooo firm that it would not work. Had to do with the connectoin of the springs. I guess I'll have to take some measurements and pics to prove it. Of course I do not owe him an explanation, but no reason to make him mad either. I REALLY appreciate the help rockin30809 and Driveway Dreams.

[rockn30809]

Originally Posted by Geezer2

Wondferful. Was the 12 bolt from another 4x4? Did you use your old springs? Can I use my axles from my 10 bolt 4x4 so I can keep my same rims????

I found a couple of 12 bolt non 4 wheel drive but boy was the guy at the salvage yard was sooooo firm that it would not work. Had to do with the connectoin of the springs. I guess I'll have to take some measurements and pics to prove it. Of course I do not owe him an explanation, but no reason to make him mad either. I REALLY appreciate the help rockin30809 and Driveway Dreams.

Don't know what the 12 bolt was from, a friend had it laying around.
All the 12 bolts I've seen are 6 lug even from 2wd trucks. Not sure if the axle shafts will interchange, I think the 12 bolt axle shafts may be bigger. Maybey find that info on a driveline/axle manufacturer site.
Axle tubes are the same dia on 10 and 12 bolts and the leaf springs are the same width.

[nlped]

My '76 2wd Blazer has a 12 bolt but is 5 lug. The 12 Bolt rearends use a 30 spline axle vs. a 28 spline axle in the 10 bolts ('87 and older). The '88 up rearends use a 30 spline axle, but the spring perches and shock mounts are in different places. But, I can tell you that the rearend out of my '76 and the original rearend out of my old '87 will easily interchange as far as spring width and shock mounts. But I am answering from a 2wd world

Even the 10 bolt 4x4 pre '88 are still 28 spline, so you could just swap your axles into a 2wd rear, but I would be curious as to whether the spring perch is oriented at the same angle as the 4wd.

[Driveway Dreams]

I agree. My 12 is a 5 lug from a late 70s Burb. I am pretty sure that the assembly will swap between 2 and 4 wheel. Just measure and check, unless someone on here will confirm that they will interchange. And like I said before, just make sure your gears are the same front & rear.

[nlped]

Originally Posted by Driveway Dreams

And like I said before, just make sure your gears are the same front & rear.

Amen!!! If they are even slightly different, it will put the transfer case in a horrible bind and cause catastrophic failure of it!

[USSkoval]

1. There were no 2wd 6-lug 12 bolts, 4x4 got 6-lug and 2wd got 5-lug, simple as that.

2. 10 and 12 bolt interchange just fine, just need the conversion u-joint.

3. You can swap a 6-lug to 5-lug and the opposite, but as far as I know, no parts interchange between 10 and 12 bolt.

4. Yes, the 10 bolt got more splines in '88, but remember that axle was still used in 1/2 ton Blazers and Burbs till '91, so those can be used too.

[rockn30809]

Originally Posted by USSkoval

1. There were no 2wd 6-lug 12 bolts, 4x4 got 6-lug and 2wd got 5-lug, simple as that.

2. 10 and 12 bolt interchange just fine, just need the conversion u-joint.

3. You can swap a 6-lug to 5-lug and the opposite, but as far as I know, no parts interchange between 10 and 12 bolt.

4. Yes, the 10 bolt got more splines in '88, but remember that axle was still used in 1/2 ton Blazers and Burbs till '91, so those can be used too.

I thought the 3/4 ton 12 bolts were 6 lug.

[MTCK]

12 bolts came in lots of things besides pickups, blazers and suburbans. It could be from a car, which would make the gentleman at the salvage yard correct. Measure the distance between the spring pads and look at the shock mounts. You should be able to get correct 6 lug axle shafts and drums for cheap and keep your wheels. Just make sure it is a truck 12 bolt.

[LONGHAIR]

Originally Posted by rockn30809

I thought the 3/4 ton 12 bolts were 6 lug.

Only on '88-98 model "light duty" 3/4 ton trucks. They have a semi-floating axles and 14mm lugs.
The heavier GVWR trucks have full-floating 8 lug axles, same as the ones before that time.
In the 73-87 generation the only 6 lug axles were under 1/2 ton 4 wheel drive trucks.

[USSkoval]

Originally Posted by LONGHAIR

Only on '88-98 model "light duty" 3/4 ton trucks. They have a semi-floating axles and 14mm lugs.
The heavier GVWR trucks have full-floating 8 lug axles, same as the ones before that time.
In the 73-87 generation the only 6 lug axles were under 1/2 ton 4 wheel drive trucks.

...And those were 14bolts, not 12

[Geezer2]

Originally Posted by USSkoval

2. 10 and 12 bolt interchange just fine, just need the conversion u-joint.

Absolutely great interchange of information from all. I appreciate the comments by all and now I am armed much better as I deal with the parts.

In the salvage yard there were a couple of 12 bolts and I bet everyone figured they would not work/swap to a 10 bolt. Anyway that is what the owner said.

So, I am off to find and measure.

I remember now, the salvage owner said the spring perches would not match up and of course the u-joints. So now we know both are doable.

Thanks to all again

[LONGHAIR]

Originally Posted by USSkoval

...And those were 14bolts, not 12

Yes, I should have mentioned that...my focus was on "6 lug" and "3/4 ton"

[USSkoval]

Originally Posted by Geezer2

Absolutely great interchange of information from all. I appreciate the comments by all and now I am armed much better as I deal with the parts.

In the salvage yard there were a couple of 12 bolts and I bet everyone figured they would not work/swap to a 10 bolt. Anyway that is what the owner said.

So, I am off to find and measure.

I remember now, the salvage owner said the spring perches would not match up and of course the u-joints. So now we know both are doable.

Thanks to all again

The owner is confused, that's all. It's the 1 ton trucks that have different perch spacing.

[Driveway Dreams]

Be sure to let us know what you find. And, good luck!

[Geezer2]

Originally Posted by USSkoval

The owner is confused, that's all. It's the 1 ton trucks that have different perch spacing.

Yes, I imagine he was confused. There are a tremendous amount of people in and out of this yard, it is right next to a large race track and I know there are a thousand questions shot at him daily. Thanks for your help, will post more later.

[Geezer2]

Originally Posted by Driveway Dreams

Be sure to let us know what you find. And, good luck!

Absolutely, problem is I am transitioning on a move and can't get there the next few days.....but I wil call him today.

However, I did get my rear spring fixed. Three leafs broke (only two could be seen) and they also made me new u bolts for both sides. So I can mount the spring ready for the diff. I suppose I should have taken the other spring off but it has been worked on. I know I should replace both springs at the same time, but this little buggy is short drives only and the budget will not support it while moving. Thanks to all for the help. GREATLY APPRECIATED!!!!!!

[SilverBack]

I have an 84 C10 with a 10 bolt open rear and I was planning to put a 12 bolt posi under it and I found one today at the salvage yard. It is obviously out of a 73-80 truck (as I am told they stop making the 12 bolts after that), but it is under a 84 model GMC. The Emergency brakes are not hooked up and a buddy warned me that the E-brakes are different between the years. Is there any way to use this 12 bolt under my 84 and have a functional E-Brake system???

[rare86]

Yes they swap easily, I replied in your other post. Let me know if I can help in any way.
As far as interchangable parts, the only thing I have found is from the backplates out. If you have the 3 inch brakes, this is a cheap upgrade because the 10 bolts are 2.75 in brakes, and the drums, shoes, and hardware are alot cheaper. 2.75 drums are about half the cost of 2 in drums and easier to find. The spring perches and shock mounts are identical