Allison Trans on the 900 series.. and general 800 vs 900 series preferences..

[tamangel]

Allison Trans on the 939 series.. and general 809 vs 939 series preferences..

curious re: reliability the Allison trans ( MT564CR )..does it hold up well ? Am contemplating either a 814 or a 927 a ways down the road and am trying to go point by point..strengths and weaknesses.. this question just on trans in the 939 series.. although open to general 809 vs 939 series preferences..

Tnx,

Mike W

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[Carlo]

I have a M931A1 and a M923A2 both with the allison auto. I would say its a over kill with this trans and what the truck weighs loaded. I did have to adjust my trans some to loose the hard shifts but now they shift pefrect. I also changed the trans fluid to DEX3. The auto trans lets me concentrate on driving the small roads here in Italy.

 

[tamangel]

I would say its a over kill with this trans and what the truck weighs loaded.

Hey Carlo, are you saying this trans is built too tough for its use on this truck? Seems the more heavy duty, the better on 5 ton MV's..

Mike W

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[Carlo]

Hey Carlo, are you saying this trans is built too tough for its use on this truck? Seems the more heavy duty, the better on 5 ton MV's..

Mike W

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Bottom line its a 5 ton truck. Thats not all that much when you consider todays standard. Allison makes more HD models but the one offered in the 900 series seems to work good. I must be honest I have never pulled anything or big weight but I have drove them thousdands of kilometers and never had a problem or overheat. The only thing I have done is change the oil to DEX 3 and adjust the shift points. I wanted a lower RPM shift and its easy to adjust.


Hope I helped...

 

[MolonLabe2014]

The truck all weigh well over 5 tons, the term 5ton comes from the off road cargo capacity of the many models.

 

[tamangel]

found this manual on Allison Transmissions on a Motor Home (Wanderlodge) site....might be good ref material..

http://www.wanderlodgegurus.com/dat.../Allison AT MT HT Series Operators Manual.pdf

Mike W

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[swbradley1]

I don't think I have ever heard of anyone losing an Allison out of a 939 series truck. 809 series transmission yes, 939 no.

Allison has a reputation for building bullet-resistant transmissions for as long as I can remember. (Bullet-proof would imply you just need a bigger bullet.)

 

[jd 9760]

I just put about 6000# in to bed of my 923 and it drove the same loaded as it did empty. I honestly wouldn't have known it was loaded if I hadn't done it my self. Shifted the same and had the same exceleration and braking under load as it did empty. I was impressed even though I don't think 6000# is a heavy load for this truck it was a good first test. I like my Allison makes so anyone can drive it

 

[quickfarms]

The shift points should be set at between 300 to 500 rpm below governed rpm. Shifting at lower rpm will lug the engine which can cause them to run hot. The big problem with the Allison's is that the shift points are set to low and not optimized for softer shifting.

 

[emr]

This truck and motor and trans have with stood the test of time in severe service, Its a done deal they are tough and robust, there are a few threads on this, i noted in some that the first gulf war the unit here put more miles on in there unit than in history, they have the citations to prove it, they ran mostly 939 series trucks, the old timers i talked with all said they are the best of the m series, The newer guys loved em too, there are NO bulletins on anything about these trucks or there drive trains being a problem ever, the original problem with a low in reverse was proven driver and teaching drivers .... all human error, the problem stopped right after the new training on just how to handle this tough trans kicked in, As for it being to much, no it is not, It actually is exactly what was designed and ordered and used for the specific missions of these trucks, and they work, History has already proved that.

 

[Suprman]

If I was to take my truck to an allison dealer and have them set the shift points what would I tell them for each gear?

 

[jarhead1086]

Bottom line its a 5 ton truck. Thats not all that much when you consider todays standard. Allison makes more HD models but the one offered in the 900 series seems to work good. I must be honest I have never pulled anything or big weight but I have drove them thousdands of kilometers and never had a problem or overheat. The only thing I have done is change the oil to DEX 3 and adjust the shift points. I wanted a lower RPM shift and its easy to adjust.


Hope I helped...

Is it easy enough for a transmission rookie to do it? Is there a manual on the adjustments? Mine seems to shift too early on acceleration and too late on the downshifts going up hill. BTW- I am flying to Florence on Friday and will be in Foligno until May 4.

 

[quickfarms]

Allison covers the adjustment points in there manual

 

[wreckerman893]

Having driven both 800 and 900 series in the Active Army I have to admit that the automatics are nice.
My left knee is shot and not having to work a clutch has convinced me that my M927 is a keeper unless someone comes along with a pile of money.
I'm not a big fan of the Allisons in the M915.....I prefer the CAT tranny in them but not too many were sold with the CAT in them since the Allison was an upgrade that most trucks went through before being discharged from active service.
Since the 900's were newer they are in much better mechanical shape with less wear and tear on them than the 800 series.
They are also quieter and ride better.

 

[jdknech]

The allison is nice, until you are pulling 30K+LB with it (tractor trailer version) then you wish it had more gears... but running empty, it is a dream!

 

[LanceRobson]

It is worth noting that the M915 and M939 trucks were designed during the period when the US had a 55 MPH (90 KMH) national speed limit. Due to the long lifespans of military trailers the there was likely consideration given to the maximum road speed limits of the then current trailers which was generally in the 45-50 MPH range (and still is for many military trailers).

As an additional design consideration, the M939, as a tactical truck, has a much nigher center of gravity than a civilian tuck of the same weight and weight carrying capacity. For that reason one design consideration likely was to limit maximum speed to reduce the chances of rollover accidents on curves and in sudden stops. The higher center of gravity also puts a lot more strain on the drive line and suspension than a civilian truck of similar weight.

I suspect that if the M915A1 had been designed a bit later it would have a seven speed transmission like the later versions. Learning how and why to use the shifter can really make a big difference in performance too.

The big key to climbing at the highest practicable speed is to downshift early into the gear you think you can crest the slope with. The transmission will not downshift until it is safe to do so but will downshift higher in the engine power band than normal enabling you to keep a higher road speed. Similarly, you need to use the shifter to make best use of the engine braking on down slopes.

I will say that I agree with WM. There's a lot to be said for the comfort and convenience of the automatic transmission. I like driving the M915A1 and I'm looking to sell my M813A1 w/w and get an M923 or M925.

tamangle, the AT series transmissions are used in many tens of thousands of medium and heavy duty trucks and in medium duty trucks give 200-300,00 miles of service on a regular basis. They serve in buses, delivery trucks, dump trucks, trash trucks, semi-tractors etc. Some get babied but most get worked hard every day and come back for more. In semi-tractors they are expected to give 500,00 or more miles of service before any major repairs. I don't think you have any longevity issues to worry about.

Lance