620 4x4 transfer case options?

[Plumbob]

I am looking into either converting my 79 short box or finding a frame that has already been converted and swapping my cab and box onto it, I have seen a few well done conversions and a few hack jobs. Thoughts? I was in northern Idaho while on a camping trip and sitting in the camp site right next to me was a converted 620 with a divorced case from a early 80's 720, it looked like the t case was a direct bolt in (frames are almost identical) and the front axle looked like a modified dana 30. has anyone done this type of conversion or close?

[datzenmike]

The T-100 from a 720 won't 'drop in' a 2wd frame, 720 or 620. The 720 frame is different and allows the trans case output clearance for the rear drive shaft. Here's what happens if you mount one into a 2wd frame.

 

 

There is a cross member in the way. I solved this by welding in a piece of 12" water pipe to keep structurally sound. The 620 you saw probably had a 720 4x4 frame or it was a previously modified 620 frame without the cross frame..

 

.

[Plumbob]

Is this the set up you are running in your truck? Do you like it? It seems like a pretty easy modification to the cross member. Which front axle are you running?

[datzenmike]

Never finished it. There is a clearance problem with the front driveshaft that could just use an eyebrow cut and weld it up to fix. The front axle is from a 'Yoda, the torsion bars are long gone. The plan was a double cardan joint front and Nissan rear to mate it up. The truck started to get heavy, the rear end went bad and all I had was a 4.11 and with 33s highway driving up hills or into the wind is a problem so I put a Z24 in it. Better, but the stock 4.375 would be best.

[mr68gts]

Mine has a transfer case from a cj5 jeep. most of the conversions used this case. axles varied depending on who did the conversion. mine has a dana 30. one of these days i'm going to put dana 44s under it so the gearing match.

[]2eDeYe]

Why doesn't the gearing match? Did you change the axle gear ratios?

[mr68gts]

The factory rear end is 4.375 and the front jeep axle is something else. (dad told me 4.56 when i got the truck from him)

paul

[datzenmike]

Get the rear end from a '74 automatic620 or an '80 720 Cab chassis and you would have a 4.625 H-190 differential. This would be way less work, just have to find one.

[mr68gts]

Still considering 4.88s since they made them for both axles and with 33" tires would be better for me anyway.

I would have to go 5 spd this way though.

[makya]

Plumbob, the transfer case you saw was probably a dana 18 or 20. they were the only ones I know of that were used in the 4x conversions.

[Jester]

Here you go.