3 vs. 4 spd t-case to 4 speed tranny

[oilcruiser]

Sooo, I am new here as well but have a couple questions regarding a 3 spd t-case. I bought my first fj40 a couple of months ago, a 78 . It has the factory 4 spd/T-case. it seemed to howl a lot so I found a 74 3 spd t-case to 4 spd that was supposed to be good (pissed me off, I paid 450 for it). the trans had a lot of rust on the gears so I rebuilt the original 4 spd tranny, but I was after the 3 spd t- case anyhow. After taking the 3 spd case apart I noticed light surface rust on a few of the teeth, they clean up pretty well with scotch brite so I dont think this will cause a problem. what I did notice is that this case has an extra gear for PTO (no spacer between the gear and rear bearing) VS the 4 spd and the drive gear is narrower than the 4 spd drive gear (about 1/4"). The larger 4 spd gear has 32 teeth and the 3 spd has 29. also the output shaft is smaller on the 3 spd. Is the advantages of a 3 spd worth the trouble? It has a narrower drive gear and a smaller output shaft with more torque? Is the high range speed going to be the same? I really don't want to go any slower on the road and with new bearings etc. the 4 spd will be nice. Oh, the linkage is different on the 3 spd as well. one other thing, could I keep the 4 spd case and output shaft and only steal the gears out of the 3 spd?
I will pre-thank everyone who gives me some guidance.
Jim.

 

[Dudleyfj40]

The gears from the 3 speed will fit in the 4 speed case. Most people just do that to get lower gearing for trails.

I would just swap the gears.

Hope this helps

 

[bikersmurf]

High range 1:1 for both.
3 Low range 2.3:1 vs 4 low range 1.99:1.

I'd keep the PTO gear just in case.

 

[bikersmurf]

High range 1:1 for both.
3 Low range 2.3:1 vs 4 low range 1.99:1.

I'd keep the PTO gear just in case.

The 4speed linkages are better & I believe can be swapped onto the 3speed case... Or so I've been told.
I'd modify your shift plate to allow 2L while you're at it (super easy).

 

[Pin_Head]

Unless your 3speed transfer case is already set up to work with a H42 4speed tranny, then it isn't worth the effort to make it work. Save your money for an Orion transfer case. Noisy transfer cases are often the result of a worn idler gear shaft and bearings.

 

[oilcruiser]

Thanks for the imput. The 3 spd t-case is and was mounted to a 4 spd trans so everything will work that way, what my major concerns would be is the smaller output shaft, narrower width on the driven input gear. My major question is can I use the gears out of the 3 spd T-case and mount them into the 4 spd utilizing the larger 4 spd output shaft. Maybe it is not a valad concern as I do have the driveline brake drum/flange and castle nut.
Thanks Again. Jim

 

[Pin_Head]

The 3speed gears can fit in a 4 speed case, but there is no advantage. The output shafts are the same size, but in late 78 they changed to fine spline. You can use the fine spline shaft in the 3sp case.