Drive shaft ?

[cb1965]

Will a 3/4 ton drive shaft fit a 12 bolt 1/2 ton rear end?
Thanks

[chevyrestoguy]

What year did the 12-bolt rear come out of? One thing to keep in mind: the early driveshafts were smaller in diameter but had bigger u-joints (1350). The later driveshafts had a larger diameter but used a smaller u-joint (1330).

You need to measure the yoke on the 12-bolt and see what it measures out at. This will determine if you have a 1330 or 1350 yoke installed. Use this guide for your measurements:
http://www.actionmachineinc.com/ujoi...ringguide.aspx

Any auto parts store can get you the u-joints. You may have a condition where the driveshaft might be a 1350 size, but the rear end yoke is a 1330 size. Not to worry.....the manufacturers make what's called a "combination" u-joint for just that application. It's very common, and it's probably just the ticket to get your driveshaft to work with the 12-bolt.

As far as the length, you should be OK. The second (or aft) driveshaft rides on a slip spline which will give you a little flexibility to compensate for slight length changes. Between the original Eaton 3/4 ton rear end and a 12-bolt rear end, the length difference is nearly the same.

[cb1965]

My '65 is a 3/4 ton and the rear end is also from a '65. Ill try the measurement method. Thanks for the link.

[chevyrestoguy]

I think you're going to be OK. I'm pretty certain that you'll have 1350 u-joints on both the driveshaft and the rear end yoke. The later 12-bolts, such as the ones installed in the '73 and up trucks, have 1330 rear end yokes in the half-ton models. I just went through this a few months ago. My original driveshaft had a 1350, and the '79 12-bolt rear had a 1330. I had to buy a combination 1350/1330 u-joint.

[LostMy65]

My shortbed 65 has the 2 piece drive shaft.
I'll be swapping from the sm420 to a th350.
Does anyone see an issue with shortening the front shaft to accommodate the th350? If so, I also have a one piece shaft from a 79 suburban, but then I'd probably need to get one of these combination u-joints.

[jayoldschool]

The other thing to consider is the center bearing. The 1/2 likely uses the small top hanger, with the heavier truck having the bottom mount heavy duty bearing.

[Captainfab]

Most of the shortbeds I have seen have a one piece driveshaft. You could have the front shaft shortened, but I would think it would be pretty short.

[LostMy65]

Originally Posted by Captainfab

Most of the shortbeds I have seen have a one piece driveshaft. You could have the front shaft shortened, but I would think it would be pretty short.

Yep, that's why I always figured on using the one piece I got from my 79 donor.
But then I started reading threads that the u-joints would be different on the 79.
I might just try and find a one piece shaft off a 72 or older truck.

[jtrichard]

they do make a transition joint that is very common that would most likely work with you rear and the later shaft check with Napa or?? they should have it

[padresag]

they are actually called a "conversion joint"
ron