Unidrive 8 Speed Repair

[MaineDad 85]

I am repairing my neighbor's 8 speed transmission. This past winter while snow blowing, he lost high gear and could only go in low gear. We purchased another 8 speed from craigslist for $100 and he finished the winter. The original 8 speed has been in a crate on my garage floor for months.

So with the service manual in-hand, I split my first 8 speed and removed all of the gears and shifter forks. As you can see in the picture below, the high low shifter fork, which had been previously welded, was broken. The Craftsman magnet pen came in real handy catching the detent balls, pin and springs!

There is a lot of gunk and some rust, but the bearing all look fine. I need to review how to inspect the differential before I go any further. Hopefully with a real good cleaning, a new gasket, a high low shifter fork, and a new detent plug, she'll be good for another couple decades :D

[MaineDad 85]

Anyone have the part numbers for the high low shifter fork, detent plug and gasket?

[TT-(Moderator) 1,127]

Looks like maybe a 103916 or 110995 Uni-Drive from here, so.....

The gasket is #3912

Hi-Lo fork is #7209

I just squirt a "blob" of black Permatex (silicone gasket maker) in the detent ball access hole, but the plug # is 1243 if you absolutely want to put one back in it.

[dgjks6 6]

I am in the process of doing the same thing - so I am follwing this closely. Take a lot of pics for the rebuild if you can.

[stevasaurus 22,230]

Bearings do look good Micah...take lots of pics please. :D

[Duff 206]

Micah, probably want to replace the oil seals, too, while you've got it apart. There's a chart in the thread pinned at the top of this section for the numbers. They're not expensive.

Duff :D

[MaineDad 85]

Thanks Duff - the seals are a given :D

[MaineDad 85]

Update: Cleaned up the old gasket gunk and used the air compressor to remove any debris. The detent balls and springs in the high low shifter fork went in easy once I used a small star screw driver instead of the 3/16 punch. It's tapered just enough and with the handle you can push the detent ball in much easier.

I used the star screw driver for the detent ball, spring, rod and other ball too in the shifter forks. Everything was going well until i had to put the splined pinion gear over the shaft and high low shifter gears. I cannot get the splined pinion gear all the way down through both shifter gears. Any suggestions?

[TT-(Moderator) 1,127]

For starters.......

Make sure that the #7204 gear (the one the hi-lo sliding gear slides on) is "right side up" and fully seated through the hi-lo sliding gear. (bottomed out on the input shaft)

[MaineDad 85]

Here's a picture of what I am talking about. I cannot lineup both sliding gears to get the splined pinion gear through both...

[TT-(Moderator) 1,127]

Well...... I do see that the 1st / reverse gear is upside-down.

The fork grooves on the gears need to face each other:

Input shaft assembly apart & laid out in order:

[MaineDad 85]

Thanks Terry! You are right, the sliding gear was upside down. So...I had the fun of removing the detent ball,spring, rod and other ball again! Once that was done, I correctly installed the sliding gear and the splined Pinion Gear went right in as it should...

I then used some emory cloth to shine up the axles before I put the differential back in...

Well it tested fine, so I put her back together again with a new gasket and Indian Head Gasket compound. Gear oil was poured in and the new axle seals slide in place over the polished axles and the tranny now sits on some wood blocks on the garage floor ready for another 30 plus years

Guys - if anyone has any fear of opening up an 8 speed, take note - it is easier than I thought. With a manual and some help from Terry and hopefully me now, you too can tame the Unidrive!