10 and 12 bolt interchangability?

[87R10]

I have a 12 bolt diff from a 79 that I want to throw in my 87 while I rebuild my 10 bolt posi.

Do these interchange without driveshaft issues?

 

[bucket]

Pretty sure the ujoints are a slightly different size, so you would need a conversion type u-joint.

 

[hirschdalechevy]

If memory serves , I think the 10 bolt is longer from the axle centerline to the yoke than the 12 bolt , so you may have to have a shorter driveshaft ,( but I think its only an inch or so ) and I think the joints are both the 1350 style but not a 100% , I am a full float guy so I dont mess with 1/2 ton stuff much. Someone will chime in with more info.

 

[bucket]

Some of the 70's 1/2 ton trucks got the bigger 1350, but only if they were a manual trans.

 

[bobkyle2]

S44 is the u joint you need. If i remember correctly.

 

[87R10]

Thanks guys. Needing another driveshaft would be a bit disappointing. Wouldn't be worth a temporary swap then...

 

[da_raabi]

Thanks guys. Needing another driveshaft would be a bit disappointing. Wouldn't be worth a temporary swap then...

Check it first. On the Camaros the 10 and 12 bolts were the same, never heard of a driveshaft problem there. Its worth a quick measure right?

 

[bobkyle2]

No need for a new driveshaft, you just need the bastard joint. I think its a S44 part number.

Its pretty common swap.

 

[87R10]

Thanks again guys. In taking a closer look at these diffs, I've found the spring perches are completely opposite of each other. my 87's 10 bolt axle has them on top of the axle tube, where the 12 bolt has them on the bottom. (came from a 79 c10)

Did these trucks use different spring sizes and configs over the years?

 

[foamypirate]

Looks like someone did a flip kit to lower the truck that the 12-bolt came out of. It moves the perches so the axle can ride on top of the spring, effectively lowering the rear of the truck.