M108 gets overdrive gear

Bought M35-tom's used overdrive .71 gear set and finally got around to installing it in the M108.

Truck now runs 2500 rpm, 62mph, on stock 9.00-20 tires. When I get the 11.00-20's on, top speed will be 68mph, not that I will drive that fast.

The top speed gain is really nice. It's also nice to shift into 5th gear and feel like you actually have another gear. I've always thought 5th and 4th were too close together. Then the rpm drop for running at 55 is another benefit.

Using the low range to split gears between 3rd and 4th works perfectly now, no more big jump in gears. 5th gear low range now is 32mph, instead of 28, and is perfect for shifting to high range 4th.

Overall, I'd have to say this is how the transmission should have been made from the factory.

As to the install, it ended up being a pain. Mostly due to me. Forgot to lube a gear on the mainshaft and seized 3rd gear to the mainshaft. So had to get another mainshaft. I used the gears out of my gasser transmission to replace the one's that seized to the mainshaft.

Also used the syncros out of the gasser, that turned out to be a mistake. Transmission didn't shift right, so I put the originals back in.

Overall very happy, and Tom was very helpful in answering any questions I had.

Dennis

Good job on the upgrade, that will make driving the M108 to Haspin a little faster!

So your truck has enough "uumph" to push the taller gears in addition to the 108 being heavier than a typical cargo truck?

Did you remove the transmission to do all of this?

What did you forget to lube? Did you install clean dry parts on the top shaft? It seems like a little idle time with the trans spinning would have allowed normal lubrication distribution.

I'm also curious as to the ability to maintain speed with the 20,000# weight of the M108. All this M108 activity has me trying to work the time out so that I can do the cab swap on my truck.

I've been running Tom's gears for about a year now and I love it. My deuce is 14,500 curb weight and I've towed my 7900lb hmmwv behind it and it pulls with ease. I do have my fuel turned up and I have 1100 tires. I can easily maintain 65mph and 70 when needed.

The install is not for the nubie but tom is now offering a trans core swap for those that wish that route.
The install of the gears needs to be done on a bench, meaning R&R of the trans. The time savings are worth it and it's not that hard.
A shop press and a good set of heavy tools and I can do it in about 2 hrs.

doghead said:

Did you remove the transmission to do all of this?

What did you forget to lube? Did you install clean dry parts on the top shaft? It seems like a little idle time with the trans spinning would have allowed normal lubrication distribution.

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Yeah! Thanks for the pics. You certainly dropped the ball on this one, hehe.

I guess I have something else to put on my "want list".

Heck with pics, it was a marathon of work. Transmission has to be out of truck to remove input shaft, that allows you to remove the counter shaft and change gears. On the stock 5th gear, and .71 gear, you can pull the mainshaft out while in the truck. On the .69 gear, 5th gear on the counter shaft is a little to big, so you have to slid the countershaft back to install the mainshaft.

M108 is not going to haspin this year, just M35. But it is going to GA.

I have enough power to get up to speed. Reason is the pump is turned up to 1200 pre turbo. I just installed a K&N filter, that allowed me to crank the pump even more and still keep the temps and smoke down.

Not really sure why the gear seized. But it happened in about 3 miles. Also I was a quart low on oil. Got in a hurry and paid the price for it. Second time around the gears were installed with a mix of gear oil and grease. And transmission was full of sae 50.

Did not have a shop press. Used a gear puller and a little heat to get it apart. When installing I heated the gears in the oven to 300, and used a brass hammer to tap them on.

There, self appointed policeman, I fixed it for you! LOL

Thank you.... If I were not here this place would go to he&* in a hand basket.

I believe tom recommends 40wt oil.

yes, my data plates and oil info plate say 40wt, but 50 is also fine. 50 is just harder to find in many places unless you order it special.

thanks for the positive feedback dennis and john, it really does make the truck feel better!

tom

I'm happy to see another of Tom's kits get installed.... I am anxious to get a kit myself. My deuce is on it's 3rd transmission in 7,000 miles (since 2006) and it has basically failed too. On the Tower Park convoy last month it started making some noise at idle with the clutch released (input shaft bearings?) and now the noise is gone but it is very difficult to shift.

I don't hide the fact that I've grown to hate the Spicer 3053, but I try to believe people when they tell me that the failures I've experienced are because I've been putting in used transmissions of unknown condition. But can my luck really be that bad?

I'm planning to build a transmission from the ground up, using Tom's kit and all new bearings, synchros, etc. and install a new-style pressure plate and clutch at the same time, but I fear a 4th failure.... and it would be an expensive one.

Jon

JDToumanian said:

I don't hide the fact that I've grown to hate the Spicer 3053, but I try to believe people when they tell me that the failures I've experienced are because I've been putting in used transmissions of unknown condition. But can my luck really be that bad?

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Yes-my luck is the same. I've played with old cars (and now trucks) for almost 20 years and I have NEVER gotten lucky trying to save a buck and using takeout/used parts.

I've tried everything that you hear supposed "experts" and old timers alike brag about getting away with-fresh bearings in old engines, knurling valve guides (instead of replacing them), takeout parts, etc and I've gotten burned every single time.

I think I eventually came to the conclusion that a takeout part was a takeout for a reason.

I finally gave up and just do everything the way Dad told me to-the expensive way

one upgrade that I would like to do on the bobber soon. How do you think the truck would do with 46's and toms kit?

i would like to see you do the trans with near stock tires, and then borrow some tires to see if you really want to go that fast. i think that you may find that 14.5R20s are enough.

tom

good point, i may pull them off the A3 for a test run

no one has done a bobber yet, data and input wanted, you could be the first!

tom

Will put it on the "to do" list.