GM 10 Bolt to GM 12 Bolt Swap Q's? 89 Chevy k1500

Llmacgregor · Sep 29, 2011

Im looking to swap the rear end of my truck for something a little tougher. I found a good deal on a 12 bolt out of a 1/2 ton with the same current gear ratio (3.73) and lug pattern as my 10 bolt.

Ad:
"This is a rearend out of a Chevy 1/2ton truck. It has 3.72 gear ratio,is 62" from face of axle to face of axle.It's also 6 lug flanges. There are no backing plates for it."

http://bellingham.craigslist.org/pts/2623506011.html

What I am wondering is if anyone has done this, and also if there is anything I may have to change, other then the U-joint. Also what would you say about this swap good or bad.

340SHORTY · Sep 30, 2011

a 12 bolt is always better than a 10 bolt..
are the years compatable ?
GM trucks had coils and leaf springs.
more than likely your backing plates and break stuff will fit the 12 bolt..
you may need to shorten your driveline..

leadfoot067 · Sep 30, 2011

well i think the spring pad width will be different,you didnt say what year the 12 bolt was out of,gm used them from 66 up to 86ish ..2wd and 4wd are different widths and spring pad widths..a bolt in upgrade for you would be the 9.5 semi float 14 bolt with 6 lug axles,they came in the 88-90something chevy trucks it would be a bolt in..

CHOP SHOP · Sep 30, 2011

A 12 bolt is surprisingly strong.
It is from the dana/spicer era and will most likely have a 1310 joint on it.

The 10 bolt in your truck is of the saginaw years and will have a shitty saginaw ujoint.

The 12 bolt will have a longer pinion snout than the 10 bolt. If the truck was lifted and the old rear shaft was a bit shorter than stock then you will probably just need a conversion joint

puke

to go from spicer to saginaw.

If the shaft in it now is the perfect length then you might need to have it shortened. As long as its getting cut then put the correct end on it.

If having it shortened I would have a spicer end on it so it will take the same joint as the axle and eliminate the need for a conversion joint.

And yes the spring pad widths will be different too.

zukkev · Sep 30, 2011

leadfoot067 said:
well i think the spring pad width will be different,you didnt say what year the 12 bolt was out of,gm used them from 66 up to 86ish ..2wd and 4wd are different widths and spring pad widths..a bolt in upgrade for you would be the 9.5 semi float 14 bolt with 6 lug axles,they came in the 88-90something chevy trucks it would be a bolt in..

12bolts were used up til about 81 at the latest---GM started using the 10bolt in late late 78, the 12bolt was pretty much phased out by late 80/81 in favor of the 10bolt... I am not sure about spring width differences, but I do know that rigs that were originally solid axle up front the widths are the same 10bolt to 12bolt...the 88/later trucks I believe are different perch widths as stated earlier... I agree with the statement of finding a semi-float 6lug 14bolt---direct bolt in...:awesomework:

zukkev · Sep 30, 2011

CHOP SHOP said:
A 12 bolt is surprisingly strong.
It is from the dana/spicer era and will most likely have a 1310 joint on it.

The 10 bolt in your truck is of the saginaw years and will have a shitty saginaw ujoint.

The 12 bolt will have a longer pinion snout than the 10 bolt. If the truck was lifted and the old rear shaft was a bit shorter than stock then you will probably just need a conversion joint puke to go from spicer to saginaw.

If the shaft in it now is the perfect length then you might need to have it shortened. As long as its getting cut then put the correct end on it.

If having it shortened I would have a spicer end on it so it will take the same joint as the axle and eliminate the need for a conversion joint.

And yes the spring pad widths will be different too.

Surprisingly, the 10bolts pinion bearings are larger than the 12bolts....it's just that everything else is **** on the 10's...:redneck:

Corey Y · Oct 1, 2011

x3 on the 6 lug 14 bolt. Billy Bobs Offroad has a couple for sale.

t1h5ta3 · Oct 1, 2011

zukkev said:
Surprisingly, the 10bolts pinion bearings are larger than the 12bolts....it's just that everything else is **** on the 10's...:redneck:

yep pinion on the 12b is weaker.

for the $ you'd have into it all said and done ( to do things right) you could upgrade the 10 bolt to hardened 30spl shafts with a better aftermarket posi

(chances are the 12 bolt has an opendiff in it... )