The time has come! Monday AM I take the beast over to Tidwell and we start the job of swapping the T-case!
Tom, I had looked at a 6000 spicer with the 0.66. This was also discussed with Mr. Tidwell over at Tidwell transmissions. (they do custom mods and such to 18-wheeler tractors so nothing like this is wierd to them - and they got all the big tools and fixtures)
.66 would make the 2100RPM redline at 62MPH instead of 52MPH. While it's not a bad idea, the T-case is already bought, and will make the redline 71MPH. To me, this gives me a lot of safety margin running 60MPH with the occasional sag to 50 and surge to 62, depending on hills, and the like.
Since there will be no towed or hauled load (M109 body), the maximum weight is a mere 23000. My goal is to stay off the stock redline and run 60-62MPH. If I hit a hill and need a lower gear, I can always go to 4th and just slow down, or even 3rd. I'm used to slowing down for hills, just turn on the flashers when I see the speed dropping to 45.
Stock 5-speed 2100RPM redline speeds for the M818:
7
12
23
40
52
- same redlines with that scary 939 transfer:
9.6
16.4
31
54
71
I think it will be OK. I won't be pulling stumps or pulling down houses, so a very low 1st is not that necessary.
There might be a combination of transmision and gears gears that could get closer to something like comfy 1900RPM@60 (instead of 1900@47MPH stock), but I have not found any, and Tidwell spent a lot of time with me going through transmission and gear manuals, they have been in the big truck transmission biz doing special mods and custom work for a few decades. So in addition to all the discussion here including your knowledge and others, my research, and going over the many choices based on gear sets and boxes in greays old transmission manuals, we have not seen anything that would place the 2100RPM redline at perhaps 65-66, the closest best choices seem to be 62 or 71. Since I really want to cruise at 60 and the goal is to stay off the redline for hours at a time, I thought the best choice was to go for the 71MPH redline and then turn the engine a little slower.
These are the speeds with the upcoming transfer case swap, notice my favorite highway speed range in yellow:
1478RPM=50MPH
1621RPM=55MPH
1768RPM=60MPH
1827RPM=62MPH
1916RPM=65MPH
2063RPM=70MPH
Anyway, wish me luck as the M8109 project takes one step further. I'll try to get pics as we go. I think it will take us about 30 hours total, so maybe a week to get it done. The biggest concern so far from their side is the air lines and servos, I'll have to help there as to where the lines went, will go, and what they do.
One thing I will need to get a holt of is an under-dash switch and valve for the front axle engagement, like in the M35. That was an automatic function in the M939.
The 818's t-case is sprag and requires air signals from the transmission, but the 939 is geared so that part of it seems simple.
For some reason, "Millenium 5-Ton" does not have the same ring to it as "Millenium Deuce".