4WD trans in 2WD truck

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4WD trans in 2WD truck

Postby justin.loehlein » Wed Mar 27, 2019 4:16 pm

I have a '90 D250 with an auto in it right now and am planning on replacing it with a manual trans. I have two transmissions to choose from - a Getrag from my W350 and a 4x4 G56 from a 6.7L truck. I'd like to put the G56 in my W350 since that is my "nice" truck and put the Getrag in the D250. I know it's a pain/not cost-effective to convert the Getrag to 2WD specs, but is there any reason a 29-spline slip yoke or u-joint carrier couldn't be used with the Getrag and just have a proper driveshaft made? Forgive my ignorance - I'm new to 4WD stuff.
1990 D250, 5 speed
1993 W350 waiting to be restored
justin.loehlein
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Re: 4WD trans in 2WD truck

Postby Philip » Thu Mar 28, 2019 6:16 am

The 4x4 trans has no way of securing a drive flange to it. It does not have a threaded end on the shaft.

The G56 into the 2WD is a problem. The stock cross member can't be used. The is not enough room in the tunnel for the G56 and the straight cross member the 2WD uses. You would need a $X$ cross member to us the G56. The $X$ cross member will make you loose 4" of ground clearance.

A 4x4 G56 and a 2wd G56 are the same. The only difference is a bolt on drive flange and rear seal in the trans.
93 W350 Club/cab w/duals, buckets & console, B&W flatbed, G56, 6 spd, 3:07 rears, gages, HX40/16, 4" exhaust, 6X.018 sticks, rear air ride suspension
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Re: 4WD trans in 2WD truck

Postby justin.loehlein » Thu Mar 28, 2019 8:10 am

Thanks for the info, Philip. Any reason a slip yoke can't just be placed on the 4x4 trans output shaft?
1990 D250, 5 speed
1993 W350 waiting to be restored
justin.loehlein
fuel screw!!!!
 
Posts: 33
Joined: Thu Feb 25, 2016 8:15 pm
Location: Richmond, VA
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Re: 4WD trans in 2WD truck

Postby Philip » Fri Mar 29, 2019 6:51 am

justin.loehlein wrote:Thanks for the info, Philip. Any reason a slip yoke can't just be placed on the 4x4 trans output shaft?


It would need to be attached solid to work. If its sliding around it will need to be lubed or it will start to wear splines and no telling what other problems you would have. It would be best to find the correct trans or have yours converted to 2wd configuration.
93 W350 Club/cab w/duals, buckets & console, B&W flatbed, G56, 6 spd, 3:07 rears, gages, HX40/16, 4" exhaust, 6X.018 sticks, rear air ride suspension
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14mm rotor
 
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Re: 4WD trans in 2WD truck

Postby justin.loehlein » Tue Jun 25, 2019 6:48 am

Just to close this out, I ended up making it work. We'll see for how long. Because the driveshaft is 2 pieces and the slip yoke is on the rear half, we figured there shouldn't be a lot of in/out force on the flange at the output shaft of the transmission. That, plus the fact the worse that happens is I destroy a Getrag made me a little more comfortable experimenting.

Mounting the trans was easy. I just used the 4x4 mount and got rid of the 1" riser on it. The resulting driveline angle is the same as the auto trans we removed.

I got the output flange and u-joint carrier from a G56 (part numbers 5142860AB, 5183074AB). In order to attach it, I welded a 16mm stud to the output shaft of the Getrag (I cut down a bolt and "machined" a nub that centered it in the existing hole on the output shaft). I also cut down a spacer that fit inside the flange and would hold it off the weld (so I was bolting to a flat surface). I had to cut the flange shorter so it didn't sit too deep and I welded the washer that comes with it to the surface of the flange so when it was bolted solid, it wouldn't slide towards the transmission.

That all bolted together fine and seems fully reversible. I had the driveshaft shortened and balanced and have been driving around for a few hundred miles. Night and day difference. Overall, I'd say not a really practical solution, but since I had the 4wd Getrag laying around and I found the flange and yoke for ~$200, it made sense.

It would have been less sketchy to take the mainshaft/output shaft out of the transmission and have a machine shop cut or EDM in the threads to accept the bolt that comes with the G56 output shaft, but I didn't want to go through the effort of tearing the transmission apart.
1990 D250, 5 speed
1993 W350 waiting to be restored
justin.loehlein
fuel screw!!!!
 
Posts: 33
Joined: Thu Feb 25, 2016 8:15 pm
Location: Richmond, VA
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