M939-A2 Series M927-A2 Driving Question

[brasco]

I pulled a picture from my phone that I took of my old cable (from a M923A2) and made this simple graphic during lunch - sorry if it is too crude... See below.

You should make sure the truck is NOT running.

Using your hand, pull the throttle linkage to Wide Open Throttle (WOT) and hold. Pull to the left in this picture.

While holding throttle at WOT, pull on Modulator Cable (to the left). There should be a little slack in the linkage - about 2 turns on the modulator linkage. I have about 3/16". This is to make sure that the modulator cable is not limiting throttle travel.

If you have a little slack then you are done. If the modulator cable is limiting throttle travel then adjust the end on the modulator cable until some slack is seen at WOT.

 

[99nouns]

Not to send you in a different direction, but some people have mentioned on here that they resolved the hard shifting problem, especially 2 to 1, by switching to ATF. I personally prefer to use what came in my truck and I've read there is risk of damage to the tranny if you do the switch wrong.

In post #4 you say it is overfilled. Did you mean "not" overfilled? Overfilling can cause damage and probably cause hard shifting. I had problems getting a good reading on the trans fluid level until I posted a thread here and got some great advice. Are you checking it correctly, at idle with trans at running temp? Have you added any trans oil since you've owned it? I know my deuce loves sae30 but the Allison calls for sae10.

Mikey

It is little over the top line about half quart or so and thats how it came, and I havent lost much since then. It says on the dip stick to check when hot and idling. So I did that, and I am using a ISO 32 oil, thats the only 10W I can get my hands on currently. But thank you for clarifying, I double check if I double checked to make sure I double checked.

 

[99nouns]

I pulled a picture from my phone that I took of my old cable (from a M923A2) and made this simple graphic during lunch - sorry if it is too crude... See below.

You should make sure the truck is NOT running.

Using your hand, pull the throttle linkage to Wide Open Throttle (WOT) and hold. Pull to the left in this picture.

While holding throttle at WOT, pull on Modulator Cable (to the left). There should be a little slack in the linkage - about 2 turns on the modulator linkage. I have about 3/16". This is to make sure that the modulator cable is not limiting throttle travel.

If you have a little slack then you are done. If the modulator cable is limiting throttle travel then adjust the end on the modulator cable until some slack is seen at WOT.

View attachment 539171

Thank you very much, I am going to do that and report back.

 

[99nouns]

Ok, it took me some tests and few adjustments, but through the guidance of brasco I was able to adjust according to specs, and this is what I ultimately discovered after about 6 test drives.


If cable adjusted according to TM (or brasco's) specs with 1/16 slack the results were following;


Up Shifts;
1st to 2nd 1600rpm at 11mph semi auto 2000rpm at 16mph auto
2nd to 3rd 1800rpm at 22mph semi auto 2000rpm at 26mph auto
3rd to 4th 1800rpm at 31mph semi auto 2000rpm at 36mph auto
4th to 5th 1800rpm at 41mph semi auto 2000rpm at 48mph auto
5th to WOT 2100rpm at 60mph (stopping at every gas station on the way)


Comment: Very smooth shifting, drove like a race car, pretty scary!!! except 1st to 2nd semi auto shifted bumpy, full auto is smooth, but adjustment really did not make any difference in what RPM it up-shifts.


Down Shifts;
5th to 4th 1500rpm at 40mph
4th to 3rd 1500rpm at 30mph
3rd to 2nd 1400rpm at 20mph
2nd to 1st 1200rpm at 10mph


Comment: Smoother downshifts than what it use to be before when I got the truck since I just adjusted.


Now I am gonna be raising the tension here, hold your anger but I put almost 1/2" slack and test drove again and the results were following;


Up Shifts;
1st to 2nd 1600rpm at 10mph semi auto, did not test auto
2nd to 3rd 1700rpm at 21mph semi auto, did not test auto
3rd to 4th 1700rpm at 30mph semi auto, did not test auto
4th to 5th 1700rpm at 40mph semi auto, did not test auto
5th to WOT 2100rpm at 60mph (stopping at every gas station on the way)


Comment: Did not feel a huge difference in semi auto except I did not test the auto, somehow I was able to up-shift slightly lower RPM when I let the gas go completely.


Down Shifts;


5th to 4th 1200rpm at 35mph Hard to feel hop
4th to 3rd 1200rpm at 25mph Hops
3rd to 2nd 1100rpm at 15mph Feel the hop
2nd to 1st 900rpm at 5mph Hard hat required if you have a hard top (I do)


Comment: Now thats what I call a fuel economy, there was great differance in downshifts I was able to keep 38-40 around 1300 rpm on straight road (no hill) versus it would downshift at 1500 rpm at 40mph if adjusted according to TM, somewhat all downshifts were bumpy than before.


*Disclaimer: All above tests were done in flat land with no hills on my truck, does not reflect what your experience may vary to be, I take no responsibility if you brake your truck while conducting above tests.


Pros & Cons am TM adjustment, IMHO.


Pros;
Smooth upshifting at higher RPMs.
Smooth downshifting at higher RPMs.
Way it was designed to be by the engineers who made them.
Probably the longest life for transmission.
Turbo sounds good.


Cons;
Burns a lot of fuel.
Hard to keep higher gears at low RPMs.
Irritates me they way it downshift as soon as I let the pedal go a little to save a drop of gas.
Down shifts as soon as you hit a small hill.
Even hard to keep the same gear since keeps down shifting
Smokes a lot since I have to keep pushing the pedal to the metal.
You dont really hear the turbo.


Please share your opinions.


Thank you,


P.S.


TM Suggest 2100rpm for Operating speed


Also found the following info in TM9-2320-272-23-3 Page 374-15