NEED HELP!!! (12 Bolt Posi find)

[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 73-81 truck (as I am told they stop making the 12 bolts after that), but it is under a 84 model GMC. The Parking brakes are not hooked up and a buddy warned me that the park brakes are different between the years. Is there any way to use this 12 bolt under my 84 and have a functional Park Brake system???

[454HO]

Not sure about your parking brake question. But a caution on the 12-bolt posi... I would not be too excited if it is a factory posi. Reason is the factory used what is called a Gov Loc differential and these are know to go kaboom on a whim. Perhaps it has been upgraded to a stronger cluth type limited slip differential. I would suggest that you pull the cover and take a look inside before you purchase.

[rare86]

I just got thru putting a 12 bolt in my 85 K10 out of a 75 K5 Blazer. You"ll need a conversion ujoint pn 3-3130 or 240-0356 depending on manufaturer, and get the u joint straps that hold the ujoint to the yoke on the rearend pn 81000 (usually in the help section) As far as the e brake cables, they are interchangable. One thing I did was swap to the 2.75 wide brakes. My 75 axle had 2 inch wide drums and I couldnt find new ones anywhere so I swapped to the 2.75 brakes. Its a simple swap, and probably can use the parts on your existing axle, if the donor has the smaller drums, I would. All you have to do is pull the axle shafts out, and unbolt the backplate. The 2 nch and 2.75 inch backplates are different, so you'll have to swap them. If I was doing what you are doing, I would pull the drums and axles off of the 10 bolt, and unbolt the backplates. You dont even have to undo the brake hardware or cables, just the 4 bolts and the brake line. Pull the 10 bolt out, put the 12 bolt in, reinstall the backplates, and brake lines, put the axles back in ( Id change the axle seals while I was in there, and the diff could probably use fresh oil after 30 years) install drums, wheels, bleed brakes and enjoy. I learned that if I had just swapped the backplates, it would have been alot easier for me becuase the e brake cables are a pain to take out.

[SilverBack]

Thanks a lot guys. Very useful info.