Transmission Upgrade/change

[Jeff Miller]

Adapting an MD-3060 to the 3208 will be an expensive conversion after
the electronics etc.

Although the MT643 is not a high-tech transmission, there are other
(read: cheaper) ways to skin that cat. If the MT-643 is still
servicable, you might start with a good checkup including fluid and
filter change, might improve your shifting, might need work on the
modulator?

As far as the addition of an overdrive and lower diff gears, it
sounds like you'd be spending a lot of $$ and expecting more than
you'll get. You would be saving money to add an overdrive.

I've changed gearing, run the 3208/FC from 210hp (Na) to 300hp
(ATAAC) with 5.29:1 gears to 4.11:1 gears, MT-643 and HP-500 w/ .83:1
overdrive. The simple things I've learned are that 1) gearing doesn't
add power, 2) even with 4:11 diff gears you don't run out of low-end,
3) there is a sweet-spot, depending on many factors such as intended
cruise speed / intended load / expected terrain, and 4) Experimenting
is very expensive.

As far as your goal of a reliable transmission (1 below), a reman MT-
643 with a warranty will cost you less than the electronics for the
MD-3060 (probably).

Goal 2, faster top-end, an overdrive will help but so would 4.44:1
gears which should cost less than $2k. If the gearing spreadsheet is
no longer in the files, I can try to submit it again, or I could
email it to you.

Goal 3, pulling better on hills. This is a matter of gearing, you
have lower gears in the transmission. If you run below 1st gear, then
you're in trouble, I didn't have that problem pulling 14% at 10,000ft
with my 210/Na so I doubt you will with a turbo. I found that taller
diff gearing can actually help somewhat on hills, I was able to
downshift into 3rd at a higher speed and hold a higher speed.
Climbing is largely a product of your power to weight ratio, and
gearing doesn't help that (unless you can't stay in the high end of
the power curve, which on the 3208 is at max. RPM).

I don't mean to discourage your project, I'd rather have a MD-3060
than an MT-643, but unless you can do it really cheap I just don't
see the return on investment either in coach value or performance.

- Jeff Miller
http://www.wanderlodge.net


--- In WanderlodgeForum@yahoogroups.com, "hsaddock"
wrote:
> Folks:
> I am giving serious thought to changing the transmission in my
> 83FC35 from the Allison MT641 to an Allison MD3000. The reasons
> are: 1) current transmission with 112K miles on it shifts a little
> slowly from 1st to 2nd at full throttle - it shifts just fine if I
> back off the throttle slightly and in all other gears. (perhaps
this
> is the beginning of a bigger future problem?) 2) I want to travel a
> little faster at top-end, and the MD3000's 5/6 speeds gives the
> overdrive(s). 3) I want to pull a little better going up steep
> hills so if I lower the differential ratio while doing this
> conversion, I can pull better in the lower gears and still tool
down
> the road faster on the flats with the overdrives.
>
> Has anyone tried this conversion? Comments on anticipated issues?
> The MD3000 appears to be an inch shorter in length than the MT641
> and a similar bolt up pattern so I don't expect to see any major
> issues with mounting. The MD3000 is computer controlled - can it
be
> fooled into working with an older 3208?
>
> Harry Saddock
> 83FC35
> South Windsor, CT