Hard Shift from 2 to 1st gear.

[DemocracyEnaction]

I read a few comments on here saying that it happens to them. It's obviously happening to me. Is it normal? Should I be worried? If I work the brakes right it seems to help. I still have to change all fluids. I just recently got the beast home

 

[Suprman]

Common with alot of mil trucks. Which one do you have?

 

[DemocracyEnaction]

m934a1. 1984

 

[JohnnyBM931A2]

Mine started to downshift a lot smoother after I replaced my military issue trans oil with NAPA hydraulic/transmission fluid. Others have experienced similar results.

 

[Scar59]

Look at the condition and set up of the transmission modulator cable/linkage. It's the pull cable that attaches to the throttle lever at the IP and left side of the trans.
There are several threads discussing the correct rigging and a you tube video that address the issue. A new cable may also fix it , if the rig is correct and the cable is still dragging.
The maintenance manual (TM) also has the procedure for correct rig.

 

[DemocracyEnaction]

Thanks guys I appreciate the input.

 

[profo]

Mine started to downshift a lot smoother after I replaced my military issue trans oil with NAPA hydraulic/transmission fluid. Others have experienced similar results.

What was the napa fluid name? Or weight

 

[JDToumanian]

You certainly don't want a transmission banging into gear hard enough to do damage from shock, but in general, the faster it snaps into gear, the better. Lower temps, longer life. Smoothness=slippage=heat+wear. In the automotive world, that is what "shift kits" do... Take away the slushiness and make the transmission snap into gear faster.

Jon

 

[Andyrv6av8r]

Look at the condition and set up of the transmission modulator cable/linkage. It's the pull cable that attaches to the throttle lever at the IP and left side of the trans.
There are several threads discussing the correct rigging and a you tube video that address the issue. A new cable may also fix it , if the rig is correct and the cable is still dragging.
The maintenance manual (TM) also has the procedure for correct rig.

Link to video or name of video?

 

[mcmullag]

I would keep searching, there was a thread where a fella had pics about how he adjusted the linkage coming from the engine.
My trucks did it too, so did my friend's, seemed like the whole truck shook as you came to a stop and it downshifted 2 to 1st gear.
Seems like that has to hurt the drivetrain and suspension over time.
Here is one thread where many folks have the same thing
http://www.steelsoldiers.com/showthread.php?97945-M923A1-Allison-Hard-downshift-into-1st

 

[ghitch75]

I had a 1985 IH S series 1954 with a 5 speed Allison with Dex3 in it and it down shifted hard when empty........with 10 ton on its back you could hardly tell shifted up or down...

The trans are setup to shift with a load not empty......


My M931A2 down and up shifts hard with no bed or 5th wheel on it.......It has 15w 40 in it.....

As far as fluid goes a buddy of mine is a engineer at Allison's plant in Indy he told me when i had the IH to change it to motor oil from Dex3 because under heavy load the Dex3 could cause slipping of the clutch's with the modifiers in Dex3....It was just used every now and then to haul gravel for the farm....


I never changed as i sold it when i got the M931A2....

The M931A2 it going to get a dump bed put on it and then i'll see with about 12 ton on it's back if it shifts hard or not....

 

[74M35A2]

Lube the modulator cable which goes to the throttle linkage, easy to do on the throttle linkage end. Pull back the boot and drown it in WD-40 with a straw while pulling on the cable core and letting it snap back. Mine shifts smooth as butter, like it should. It should never be rough, it is not normal (common maybe yes, but not as designed). Mine became rough after off-roading once, so I lubed this cable and it returned to gravy smooth. To paint a picture, I can have a full McDonald's Coke with ice on the floor of the cab with the lid off, slow to a stop, and it won't spill.

 

[ghitch75]

Lube the modulator cable which goes to the throttle linkage, easy to do on the throttle linkage end. Pull back the boot and drown it in WD-40 with a straw while pulling on the cable core and letting it snap back. Mine shifts smooth as butter, like it should. It should never be rough, it is not normal (common maybe yes, but not as designed). Mine became rough after off-roading once, so I lubed this cable and it returned to gravy smooth. To paint a picture, I can have a full McDonald's Coke with ice on the floor of the cab with the lid off, slow to a stop, and it won't spill.

I'll give that a try...

 

[therooster2001]

I don't have a major downshift issue, but researched it, as I have more than I expect (no load). The TM readjustment for -23 is 3-365 as most of the threads reference -24.

Readjust per TM (99nouns the last post shows results from a test), lube like heck (74M35A2 mentions in several posts), and replace the modulator cable (brasco) is the consensus. Now I have to check mine!

http://www.steelsoldiers.com/showthread.php?134829-M939-A2-Series-M927-A2-Driving-Question

I'll have to do the Coke test.

 

[DemocracyEnaction]

Right on!

 

[ghitch75]

Adjusted my cable as per the TM......1/16" play at the pump.......Shifts like it is suppose to!!!.......No more trying to throw you threw the windshield when down shifting in auto......

Thanks therooster2001 for the link!!!!!