Stupid 5-Ton Allison Transmission Question

[juanprado]

Most of the non abs will still be wearing ndc tires. I saw many in the GL pictures of Barstow from last year that I think were long storage reserve trucks? Another clue is that they will have an alcohol bottle to the bottom left of the primer pump on the driver's side in the GL engine pics.

One m923 came out of the air force here in Hammond that did not have abs. Not many but a few appear to be out there.

 

[wheelspinner]

A question here. Why would you want to disengage a clutch when trying to stop? You want to use all the friction you can to stop. You down shift in a manual trans to stop a heavy load. Why do you think they put Jake Brakes on a truck, to use the engine as a breaking force. Ride a brake down a mountain and it might get to set a speed record!

Panic stops and riding a brake down a mountain are two different things. In a panic stop or a hard stop on a slippery surface you want all traction points stopping equally. By releasing the drive train you ensure that it does.

 

[Suprman]

The original intention of the thread was to understand why the torque converter does not unlock quick enough when brakes are applied hard during a panic stop and the end result is a stall condition the same as if you locked the brakes on a standard shift vehicle without depressing the clutch pedal.

 

[emr]

IMO everyone whom buys these trucks and dislikes the to work your truck hard then stick w/ OE Oil, if you want a mall cruiser throw DEX3 in it... FWIW...

Artisan THANK YOU!!!!!!!!!!!!!!! Sorry I have to say it, REALLY ! These trucks ARE NOT ONLY ANTIQUES They are ALSO >>> OFF ROAD DUTY >>> AKA..>>> TACTICAL TRUCKS!!! There are NO stupid Trans's, only uninformed nube drivers yeeash this " I want my truck to drive like an over the road new truck " baby stuff gets sooooo old . You are looking for a different truck, To ALL the guys who whine >>> buy over the road trucks, they ride like you want, Sorry but calling one of the toughest longest lasting in mileage on the road in theater trucks stupid is well..." stupid. And YES in the first gulf war the 939 series, NOW NOT the 900 series because that is a HOST of different possible trucks The 939 series has more on road miles than the Red Ball express and did it with more than anyone ever expected of them, The NJ and PA units that drove them have the citations to prove it, I can prove it because I was at 2 of the ceramonys when they were given out. Yes I feel better

 

[Suprman]

Obviously the military thought the issue serious enough to retrofit abs into most of the m939 series trucks.

 

[quickfarms]

One issue the transmission in These trucks has is that it is not set up according to Allison specs, the second issue is running motor oil. The third issue is the wedge brakes.

I wonder if the ABS is connected to the the torque converter lock up switch?

The ABS is there to deal with the issues of wedge brakes locking up and the inexperienced drivers.

When I drove a truck with wedge brakes I downshifted to a stop. You can do this with an automatic providing it has a lockable torque converter.

 

[Suprman]

I thought the torque converter lockup was completely mechanical it locks and unlocks per rpms. Why does the torque converter take so long to unlock even though engine rpms have gone below the lock point? If an "inexperienced driver" were to lock the brakes in a panic stop, when the wheels stop the drive train stops and if the torque converter does not unlock in time it stalls the engine. A stalled engine equals no power steering and possible loss of control of the vehicle. This is where the abs came in. It modulates the braking force to allow some wheel spin while still applying braking force. If the wheels are moving then the drivetrain will still be moving even if its slow and you shouldnt get the stall condition.

 

[ARYankee]

Is there any good material out there that describes the operation of these transmissions? I've been trying to sort out a problem that I am having and have no clue where to start or what to look at. I've looked through the TMs with no luck, but then again I may be overlooking something.

 

[quickfarms]

Allison publishes an operators manual and mechanics tips that are available on line.

The torque converter lockup is adjustable, it is my understanding that you can adjust when it licks and unlocks and a delay to smooth out the shifting.

If you disable the torque converter lock up you engine RPM will increase by about 200 RPM at highway speeds and you will loose compression braking.

The wedge brakes are another issue. They are a pain in the ass to get properly adjusted. On a truck driven daily, for a lot if miles, the wedges will get smoothed out and polished but in a truck that is not driven daily you will never get them polished and there operation will not be smooth, this will further exaggerate there tendency to lock one or two wheels. Add some wet pavement and an unloaded truck and it is easy to spin a truck 180 degrees during a stop, the good thing is you will only do it once. I loved the day we retired the wedge brake trucks.

 

[ARYankee]

Allison publishes an operators manual and mechanics tips that are available on line.

The torque converter lockup is adjustable, it is my understanding that you can adjust when it licks and unlocks and a delay to smooth out the shifting.

If you disable the torque converter lock up you engine RPM will increase by about 200 RPM at highway speeds and you will loose compression braking.

The wedge brakes are another issue. They are a pain in the ass to get properly adjusted. On a truck driven daily, for a lot if miles, the wedges will get smoothed out and polished but in a truck that is not driven daily you will never get them polished and there operation will not be smooth, this will further exaggerate there tendency to lock one or two wheels. Add some wet pavement and an unloaded truck and it is easy to spin a truck 180 degrees during a stop, the good thing is you will only do it once. I loved the day we retired the wedge brake trucks.

You don't happen to have a link to the mechanic's tips?

 

[DJones]

You don't happen to have a link to the mechanic's tips?

 

[quickfarms]

see attachements

 

[railroadmike]

The Tee handle transmission lever is very common, and the one in my 939 is like others I have and it has a lock tab at neutral when you move the handle up WITHOUT pushing the button( prevent going into reverse?), I normally don't touch the button when stopping to sit a while or park as this feature allows me to keep my eyes on the road and not the console.

After learning about the lock up issue I practiced at low speed on dirt, it is possible to get good enough to bump the handle to neutral in a panic, I hope...

For some of you ham fisted types that could bust the tab off in a panic(I know some strong fellas) Ive considered designing a lock out gate that fits over the reverse position at the top of the controller base that has a hinge so it can be lifted out of the way when reverse is desired.

 

[quickfarms]

The Tee handle transmission lever is very common, and the one in my 939 is like others I have and it has a lock tab at neutral when you move the handle up WITHOUT pushing the button( prevent going into reverse?), I normally don't touch the button when stopping to sit a while or park as this feature allows me to keep my eyes on the road and not the console.

After learning about the lock up issue I practiced at low speed on dirt, it is possible to get good enough to bump the handle to neutral in a panic, I hope...

For some of you ham fisted types that could bust the tab off in a panic(I know some strong fellas) Ive considered designing a lock out gate that fits over the reverse position at the top of the controller base that has a hinge so it can be lifted out of the way when reverse is desired.

Shifting the transmission into neutral when the engine rpm is above an idle or the vehicle is moving can cause transmission damage.

Shifting the transmission into neutral while the vehicle is moving is an unsafe driving practice.

 

[railroadmike]

I have a good amount of driving experience with allison equipped units(almost 30 years), the occasional shifting into neutral has caused no problems.

As far as this 939 issue if it came to getting into a Oh S**T!! situation, Id much rather damage the tranny than crash the truck, Ive only once activated the ABS and I can imagine it getting hairy at high speed. I hope none of it happens, to any of us...

 

[Csm Davis]

Shifting the transmission into neutral when the engine rpm is above an idle or the vehicle is moving can cause transmission damage.

Okay not saying that this is wrong but would ask for better explanation.

Shifting the transmission into neutral while the vehicle is moving is an unsafe driving practice.

And this is bad why? Every manual shift truck is in neutral many times while driving.

 

[archmark]

Any definitive knowledge if the M939/A0/A1's were delivered from the factory with ATF or the 10W for "extreme use"? And when changing the fluid and filters, is it necessary to "flush" the tranny with something prior to adding the new fluid, whether replacing the fluid with what was removed or when switching to the other type of ATF/10W?

Thanks...

Mark

 

[VPed]

The data plate says you can shift the transfer case into low when below 20 MPH and you have to shift to neutral before the T-case lever will move so I do not think damage would result. It also infers that a competent driver should be able to do that safely.

Threads about converting tranny fluids talk about two or three changes to get the majority of the transfusion accomplished.

 

[wheelspinner]

Shifting the transmission into neutral when the engine rpm is above an idle or the vehicle is moving can cause transmission damage.

Shifting the transmission into neutral while the vehicle is moving is an unsafe driving practice.

its on the Interweb. It must be true.

 

[Csm Davis]

Any definitive knowledge if the M939/A0/A1's were delivered from the factory with ATF or the 10W for "extreme use"? And when changing the fluid and filters, is it necessary to "flush" the tranny with something prior to adding the new fluid, whether replacing the fluid with what was removed or when switching to the other type of ATF/10W?

Thanks...

Mark

I have checked the transmission fluid in thousands of these 939 series trucks and have only seen one or two that had red color ATF in them and can tell you that not anyone I have heard of has said they found one from the factory that had ATF in it. They were ordered with 10wt and I will bet that all were delivered with 10wt. Now if you want to change it do so knowing that they were built to run 10wt and some who have changed to the ATF have lost thier transmission.