Lower Transfer Case Gears

If I am not mistaken Grampa’s Jeep actually has a 56.7 to 1 gear reduction. T90C 3.339 x TL 3.16 x Final Drive Ratio 5.375’s.

Edited by oldtime - 24 Feb. 2022 at 2:30pm

Update: Got the parts from heat treat and had some trouble. First a re-cap

I made 5 sets from the standard 8620 material. The last time I made these, the parts shrank about .003. This time, I had the blanks normalized and tempered before cutting the teeth. It worked. This time the parts barely changed after heat treat. About .001 or less. ....

The 9310 parts are a different story.   According to the cert sheet, the material was already norm & tempered so I just made the blanks, had the teeth cut, and sent them to heat treat. When I got these back, the ID’s on the parts shrank .005 on the small gears and .008 on the big gear.   Strangely, and luckily, the teeth didn’t change very much so the intermediate gear and output gear are still useable but the spline on the input gear is way too small.   I took them to a shop with an EDM. .... long story short, they junked out 4 of 5. The one that is useable is still sloppier than I want but I’m going to use it till I can make a replacement. I’m going to make another batch of input gears of both 8620 and 9310. This time I will have all the gears normalized and tempered. Let’s see what happens. In the mean time,



... I made this fixture which makes it easy to test the parts for backlash fit and sound. The jig has bearings in it so I can run the assembly with a drill.



I throw a little lapping compound on them to take off any sharp edges or blemishes:



I’ve sent out two sets and I plan to have at least two more sent this week. Hopefully, three.

Sorry John, I have to make a new input gear for your set. This is the easiest of the three to make. I’ll have the blank made this week.

Edited by jpet - 05 Mar. 2022 at 7:53pm

Jeff-

Has anyone just tried to use a short stud in the upper right hole?  You would have to start the nut on while assembling but I think there is enough room to make that work, depending on one's welded cover.

When you cut a large hole case and then have to seal / weld a cover on the case , there just is not room for a nut, stud, cap screw... and the cover.  Through bolting it is the only option I can see.  I tried to figure out a different way but there is no room on the large hole case version of this project.

The head does not collide with the gear

I think if I were going to do this, I might wrap some Teflon or something on the bolt so that it doesn’t fall out of the hole so easy. If the bolt ever falls out, you would have issues. This intermediate gear will not come out unless the output shaft is disassembled. The up side is that the output gear is so small that you can put the shaft assembly (w/ pesky snap ring) together outside the case:



Edited by jpet - 11 Mar. 2022 at 2:15pm

That’s cool Ernie, I have mine in too now. Got about 200 miles. cu in Moab!

I just got back from Moab EJS with the X98 gears in my M38. The lower gears were great to have! I had decide to go with the t90a and I really like the gear selection with that combo. The high gear range was nice getting to the trail head and on the trail where the lower gears were not needed and the low range was nice to have on the obstacles. The low 1st was great for crawling and if I didn't need to slow crawl or needed a little bump 2nd low worked good. I'm very Happy with the X98 gears!

For the record, this is a 4.3 Chevy in front of an SM465 truck tranny, not an 4 cyl with three speed. When I ran the numbers, the spur gears are not strong enough to hold up to the torque that BAM BAM is capable of putting out when they are put behind my 17/47 gears. I went with them because Jack O’Brein uses the same original spur gears in his 4.86 set. IDK, maybe the gear was defective, maybe this maybe that. I am encouraged that my gears were not the weak link. My next move is this:



I’m going to try using the 18/33 spur gear set from a 1-1/4” hole case. The picture above shows a 39 tooth slide gear compared to a 33 tooth gear. The 39 tooth gear is 7DP but the 33 tooth gear is actually 6 DP and has a larger base as shown in the pic. In hind site, it sorta makes sense that Willys changed this gear set when they went to 29 tooth input gear and 1-1/4” intermediate shaft for newer Jeeps with V6 and V8.



This will make my X98 Super’s final ratio 5.07 instead of 5.13. I think the added strength is worth it.

.... more.

Edited by jpet - 27 Apr. 2022 at 1:15pm