M923 Safety Issue?

[bsteinborn]

I've been thinking of buying an M923 from a friend of mine. I already own a deuce. Then I came across this information,

"The safety of the M939 series of trucks has been criticized, especially braking performance and stability when loaded. In 1999 the US Army began refitting anti-lock brake systems to the M939 trucks. Until the trucks were modified, they were limited to a 40 mph (65 km/h) top speed by an Army-wide safety order.

Prior to that improvement, 26% of all Army vehicle accidents and 53% of all Army vehicle accident fatalities were in M939 series trucks. From 1987 to 1998 the series made up 9% of the total US Army vehicle inventory, but accounted for 34% of all fatal accidents. [2]

The problem seemed to be that the torque converter would "lock up" in 2nd gear, and would not unlock easily. When the driver attempted to brake hard, often in a sudden or 'panic' stop, and accidentally locked the brakes (no wheel movement, tires skidding), this would kill the engine; this also killed the power steering, and the driver would suddenly be unable to steer. Too often, the truck would veer sideways and either hit something or roll over."

I don't haul anything is this just an issue when loaded? Any fix been done? Did some searching on SS but couldn't find anything. If any 5 ton owners have any information I'd appreciate it. Just want to be as safe as possible. Thanks!

Bryan

 

[Triple C]

I have a 925A1. When we went to recover it my brother in law, a 23 yr. army vet, who spent most of his time working on or with vehicles, was excited to see the tag saying the truck was converted to ABS. On the trip back he was telling me how dangerous the trucks were before that. It was exactly as you wrote about. Apparently the ABS fixed the panic stop issue but I still have concerns about the stability of super singles with a load on uneven surfaces. Fortunately I don't anticipate hauling anything so it won't be an issue for me.

 

[bsteinborn]

I'll have to check to see if the truck has an a ABS system. The ABS must have been the only fix. 1999 was a few years back so perhaps most of the 900 series have been retrofitted before ending up at GL. The truck I'm looking at already has the super singles too. But again I'm not hauling anything. Thanks for responding!

 

[porkysplace]

There is some related information on safe speeds for 939 series trucks in this thread from a couple weeks ago ; Road Speed 900 Series Truck?


Edit ; acouple more related threads
[h=3]Safe Driving Speed and Tire Size on M939 Series
Blown ABS ECU - how not to do that etc.[/h]
Abs mwo?

 

[BKubu]

Fortunately, most of the trucks coming out these days have the ABS MWO applied.

 

[bsteinborn]

Went and checked out the truck a couple of days ago. It doesn't have the ABS modification. Think I should be concerned? Nobody on this site has mentioned any significant issues with the 923.

 

[GHall]

http://www.steelsoldiers.com/showthread.php?46227-M939-A1-A2-ABS-vs-Non-ABS-Trucks

Here's another thread. Hadn't read it in a while, hope this helps..

 

[quickfarms]

It is an issue for a driver that does not have a lot of experience driving big trucks under adverse conditions. CDL training is a good idea. The army issue was compounded by there young drivers.

Unfortunately antilock brakes are being used as a substitute for driver training and experience.

There are things that happen when driving large trucks that can not be tough and can only be learned by experience. They include sliding in the rain bob tailing and blowing tires, front tires are the most fun.

I would like to see a breakdown on the accidents buy truck type and weather they were off road or not.

 

[Triple C]

Amen brother, that gets exciting in a hurry. As I understand the issue with the non abs though, it related directly to the auto trans killing the motor in a panic stop, causing a loss of steering control since there was no power steering. Almost all class 8 vehicles (particularly the old ones) are manual transmissions so non abs does not kill the motor. I could be wrong, or there could be other issues as well. I agree with your training suggestion. If the OP doesn't have big truck experience I would suggest some emergcency stop exercises at the minimum.

 

[quickfarms]

Amen brother, that gets exciting in a hurry. As I understand the issue with the non abs though, it related directly to the auto trans killing the motor in a panic stop, causing a loss of steering control since there was no power steering. Almost all class 8 vehicles (particularly the old ones) are manual transmissions so non abs does not kill the motor. I could be wrong, or there could be other issues as well. I agree with your training suggestion. If the OP doesn't have big truck experience I would suggest some emergcency stop exercises at the minimum.

If you leave the trans in gear or do not depress the clutch you will kill the engine on a truck with a manual transmission.

A large number of the current class 8 trucks have either auto shifting or automatic transmissions in them.

I have heard reports about a lot of 900 series 5 tons having shifting issues with them that sound like the transmission shift points were not correctly set up.

 

[bsteinborn]

GHall, thanks for the link to other thread. It has plenty of great info.

 

[juanprado]

doghead had listed in the classifieds a complete abs retro kit minus the dryer for a m939

 

[Scarecrow1]

First off I commend you on the fact that you were one of the few to be smart enough to do your home work before you jumped in. There is no way to learn unless you listen and many really don't listen well enough. The study does show a significant increase and is the key factor in adding ABS systems on these trucks so that in it's self is a reason not to buy the one with out it . The article also mentioned the increase of role overs related to the singled out 1400-20s. A member stated one time he didn't see the fuss about driving the 5 tons that his mother could drive one. There is a big difference between steering one and driving one ! If you are in the market for a five ton you are on the right road with your research . Good luck I am sure you will make the right choice , you have your priorities in order..........

 

[Triple C]

If you leave the trans in gear or do not depress the clutch you will kill the engine on a truck with a manual transmission.

A large number of the current class 8 trucks have either auto shifting or automatic transmissions in them.

I have heard reports about a lot of 900 series 5 tons having shifting issues with them that sound like the transmission shift points were not correctly set up.

Yep, that's why they were always called a two foot exercise. At least a driver has the means of keeping the truck running. As to the newer trucks with autos, I didn't know that, I have been out of the business for quite a while. I would assume the commercial trucks have addressed that issue since we have such a litigious society. Think the OP and Mike are spot on, these are big trucks and require a particular skill set to drive safely, I join Mike in applauding the OP for the due diligence. Sounds like a guy that will be safe on the road.

 

[quickfarms]

Learn the smith system.

These are heavy trucks and need to be driven like a truck and not a sports car.

Proper driving technique will allow you to avoid probably 95% of the panic stops.

 

[emr]

Driver error was the problem like most times in life, They are tactical trucks, not highway trucks . If they are driven like they were designed to be driven they do not need ABS. But,ABS works and is an awesome upgrade, its not a deal breaker unless one is inexperienced and heavy footed and is the type to stop at the last minute. The trans talk earlier is a myth, very robust trans and shifts like a tactical truck is supposed to, it does everything it was designed to, anyone who says different is only offering an opinion, They have proven more miles than any other trucks in theater in the first and second gulf war and still going, Understand the truck for what it is and was designed to do , dont change it, If you do you make it unsafe. all the best and good luck, Drive it like a person who has a brain and not a show off and you will be fine . So many guys need to speed around and think it is cool, when in fact most are saying the opposite of them.