Easiest transmission to swap for the t98

[Dreadwater]

Well, while i prefer to keep things stock i do do upgrades as they wear out and need replaced. That being said, ive decided to change my clutch out, and drop the transmission and over haul it. But while im tracking down parts and such i got to thinking about how many times i wish i had an overdrive or a fifth gear to reduce engine rpms while cruising. What options are there? I plan on keeping the 230 and going to a 205 transfer case and keeping the axles stock. Im not building a racecar or anything and im not looking to go faster persay, just keep the speeds i have now at less stressful levels.

[Barrman]

The old rubber overdrive might be your best bet. Bigger tires. Stock is 34 inches. True 38 inch tall tires 11 inches wide will make 2500 rpm go from 48 mph to 52 mph. If you do the center output conversion on the NP200 2500 rpm is your cruising red line without the screaming.

48-52 mph really is the aerodynamic breaking point of the M715 as well. They will loaf along at those speeds. But, just trying to run 60 will have your foot way more into the throttle, the wind noise will be excessive and any steering issues you have will be apparent.

It is your truck to do with as you wish. I did the big block/NV4500 swap and loved the sound track. Along with the power. But on long trips 48-52 was where the truck was happy. Also remember the highest point of a 6,000 pound M715 is the top of your head.

Now I chug along with a 6.2 diesel at 48-52.

I guess my point is that trying to get a M715 to be happy above 48-52 mph can be done. But it won’t be happy above that and near as fun to drive.

[brute4c]

Absolutely ditto...well said Barrman...perfectly succinct!

I will add that there is no transmission with an OD that is easy to put behind the 230. There is no adapter for the 230 to any OD transmission I have ever heard of.

[Dreadwater]

Hmmm thats what i was afraid of hearing. Thanks.

[Dreadwater]

Bigger tires Will make that much of a difference? Im not trying to go hiway speeds or anything, i just want it to be less strainfull at normal speeds. I am looking into the bigger tire options.

[Barrman]

Yes the tires do make that much of a difference. However there are cost. Normally, they will be heavier. That wears the steering parts faster. The taller tires reduce the mechanical advantage the stock gear ratio gives. Besides a little less power on hills. The bigger tires make the truck less “Playful” in shallow mud.

My stock truck on stock tires used to be so much fun to drive onto a field of dirt after a heavy rain. About the same as doing donuts after a good snow. With the bigger tires the stock engine didn’t have the mph to get them spinning.

When looking for tires please remember that say 35 x 12.5 tires are actually maybe 34 inches tall. Military tires usually are true to their markings. 9.00-16 tires have 9 inch tread width, the .00 means the sidewall is 100% the size of the tread width. So, 9 inch side wall, 16 inch wheel and another 9 inch sidewall. Add them up and 34 inches is what you get. 11.00-16 equals 38 inches.

[Kaiserjeeps]

What about a gear ratio change? Kind of spendy, but so are tires. In the long run it might be worth it. I am running 4:56 gears now. The dana 60 up front came with them, I changed the rear to match. My 37's really measure 35.5 tall. I hope to make at least 60. Should be interesting.

[Twobit]

I've been researching crazy on this same OD dilemma, I drive 2hrs normally for camping and want to be able to do 65mph without running the out of it. I bought my truck already 350 swapped with a SM420 4speed behind it, with stock axles/gears/tires.

Best option I've found was a NV4500. the 2wd version can have a stubby output making it still work with the divorced transfer case. Doubt you will find a bellhousing adapter for the 230.
You could get an under/overdrive "browie box" but it would take alot of fab work, and probably only work in 2wd because it would have to go post transfer case.

I recently went to a 37" tire and that dropped my RPM's by almost 400. Now i'm able to cruse at 65 without killing the old 350 pretty nicely.
I didn't notice any steering or suspension issues at higher speeds. I can put her up to 80 for short stretches with no issues besides RPM's being crazy.
NV4500 swap should give me a crusing speed at 65-70 i think with no issues. Slow upgrades...

[Kaiserjeeps]

Twobit, have you measured your tire height sitting on the ground? Or are you actually close to 37 high? I know most tires are not as tall as stated. Curious as I hope to get some speed out of it also.

So I just moved to wenatchee. Where are you and where is good camping? I am very familiar with WA state. I was born in Seattle. But left there in 1989. I am going to be looking for a place with trees and hopefully a river or lake. East of me there is hardly a tree in sight till you hit Spokane. I need a camping trip. Or three...

[Dreadwater]

Thanks ill keep that in mind