4 speed swap driveshaft length

[heffalump]

So I undertaking a 4 speed swap on my burb.. my question is What drive shafts do I need? The original trans is a 400 auto new one is a sm465 with the iron t-case. There is about a 10 inch difference between the two, the 4 speed being the shorter of the 2.. HELP!

 

[bucket]

You will just have to get the shafts cut down and/or re-tubed. If you had went with an SM465/NP208 combo, it would have bolted in with the stock shafts.

 

[heffalump]

So I can use the factory to the suburban transfer case with the new trans and use my stock driveshaft..? Damn why didn't I think of that..

 

[bucket]

So I can use the factory to the suburban transfer case with the new trans and use my stock driveshaft..? Damn why didn't I think of that..

Not if your new setup has the "figure 8" mounting pattern with a 10 spline coupler. That was the most common SM465/NP205 combo that I'm assuming you have now.

 

[heffalump]

Not sure which case came in the burb. I do know it's aluminum and it has the long tail shaft. Just looking at the 2 cases they seem to have the same bolt pattern...

 

[bucket]

So your new t-case (it IS an NP205, right?) has the round, 6-bolt mounting pattern? I'm not so familiar with the later version like that, but if the input/output lengths match up then yes, you can bolt on your original t-case.

However, as far as brute strength goes, the 205 is a good upgrade over the 208/241 case.

 

[heffalump]

Nope the bolt patterns aren't the same... so I am going to need both front and rear driveshafts. I know the front one out of the donor truck will work but I'm not sure about the rear. It's a 78 3/4 ton long bed with a two piece shaft. Suburban could have had this setup from the factory so there should be a factory shaft I can use. . Right???

 

[bucket]

OK, so it is a 10 spline, figure 8 pattern after all.

The correct shaft is out there somewhere, but it would be a needle in a hay stack. There are two good options, both involve grabbing more parts from the donor truck.

1. Grab the rear shaft with the center carrier and mount, install it in your truck after having the rear tube shortened about 2 inches (Burb has a shorter wheelbase).

2. Grab the rear shaft and tell the driveline shop to cannibalize it to lower the cost of the new shaft they will build you. You will need to tell them the distance between your t-case output yoke and your rear axle yoke, at ride height. Measure from the u-joint center to the u-joint center.

 

[heffalump]

Yep got the 2 piece shaft from the donor and it is ideal too long getting it cut down tomorrow. Have to build a new exhaust tonight. The old cross-over had to come our and there just isn't any room to put it back.. sooo true duals with generic Flowmaster it is. Thanks for all the info. Plan on posting a full write-up when it's done. General progress and other stuff here
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