Started to look through the PS magazines I have and found this, not directly related, but another possible "problem" with the drive train...
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Bjorn
MEP-018A (needs new generator head)
Avatar: XM757 in OK prepared for 1,000 mile trip home. Part of 6,000 mile journey in 2006.
1968 M49A2C modified with 1960 M756A2 truck bed and 1975 HIAB 765A knuckleboom, exhaust brake, VIC-1 and more.
1969 Ford XM757 8x8, 5-ton Pershing 1A truck tractor...the "improved MV".
"Some things can't be made better, just differently......a lot of things actually"
That is old news, Bjorn. Yeah, that is a design flaw for sure. I adhere to that warning. However, when I was a newbie to the trucks, the first time I drove one, I had the truck in low range and put it in reverse with no ill effects. The problem comes in when you apply a reasonable amount of throttle. The t-case will have a tendency to crack!
That is old news, Bjorn. Yeah, that is a design flaw for sure. I adhere to that warning. However, when I was a newbie to the trucks, the first time I drove one, I had the truck in low range and put it in reverse with no ill effects. The problem comes in when you apply a reasonable amount of throttle. The t-case will have a tendency to crack!
At least that design compromise came with a warning...(unlike the panic brake-engine-stall problem)...
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Bjorn
MEP-018A (needs new generator head)
Avatar: XM757 in OK prepared for 1,000 mile trip home. Part of 6,000 mile journey in 2006.
1968 M49A2C modified with 1960 M756A2 truck bed and 1975 HIAB 765A knuckleboom, exhaust brake, VIC-1 and more.
1969 Ford XM757 8x8, 5-ton Pershing 1A truck tractor...the "improved MV".
"Some things can't be made better, just differently......a lot of things actually"
I got my bedsides and tailgate on today. I will repeat the test next weekend and see what happens. I will make sure I do it in a straight stretch so I don't end up in John's field!
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Chris Stansbury, founder of Chris' CUCV Homepage in 1998 and Steel Soldiers in 1999.
1985 AMG M998 HMMWV, under the knife
1992 BMY M925A2 - TRADED!!
1991 BMY M923A2, SOLD
in the abs wet video, the rattling sound is the drivetrain loading and unloading. it's not good for it. But better than crashing.
And the non-ABS wet pavement thing is exactly what the driving instructor at the National Guard said would happen. He did not alow us to try it..
Are those videos public domain or does someone own them? I assume they are military test videos and belong to "we the people" but it is right to ask.
Finally, the ABS kits on the M900 series we were trained on were said to be a very simple trailer-type ABS kit based on commercial items.
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Actually it is NOT a design flaw, the Army, Alison and AM General all did separate studies and all came up with the same answer, driver error, the Army ordered a trans with an 11 to 1 gear ratio in reverse, a cat D 6 has a 9 to one, so it is easy to see how low these trucks are geared, there has never been a trans problem that did not" occur during shifting from D to R with the R's up, Meaning shifting with out letting the revs settle to idle will crack the trans in low gear reverse because of the 11 to 1 ratio in a side sshaft trans...that is a catostrofic failure do to the driver, and a lack of training in the begining, These trucks are robust and so are there trans's, it has been proven thru hundreds of thousands of miles thru the deserts of iraq, I will add from the first units in the first war and the first units of the current conflick, the Nj guard saw more miles on the road then most for sure, and the leaders of these groups are most any way, have crossed paths with me at least and alot are good friends, and from Vietnam Vets in theater to new guys the 939 series of trucks are haled the finest cargo trucks in use from the guys who drove em and from there mouths...even over the 800 series from the guys with experince in theater for what its worth . And no surprise the FM class's too, Now it is important to note that there were absolutly no mass trans failures in threater, and that is du to driver training and the fact these trucks and transes are tough, And i have to say having one for 6 years i will say they are tough, They said impossible to over load, and that is a direct link to trans use in my eyes, they performed and stayed on the road, Now there were alot of 939s here at the Armory i hang and volunteer at, And in my quest for info they ran low in reverse all the time, so i have also for 6 years, and the BIG thing is If I were to shift with the R's up I would split the T case like they say, it is a side shaft Trans and one may call it a design flaw, but really it is still in use and will be in many trans's ...It is a matter of what this truck is and how to drive it, the novice should never drive this truck in low reverse because they will ruin it, the Driver who respects His truck and what it is will never have a problem period...... I will add the problems were reported under severe use also, so in my opinion from all I have read they were not even that easy to split in low. But since I pay for it I will baby it, but man she pulls and We have been pretty stuck and reverse in low works real well, but like said I let her settle before shifting thats the key...
Last edited by emr; 01-18-2010 at 20:55.
The Following 2 Users Say Thank You to emr For This Useful Post:
Actually it is NOT a design flaw, the Army, Alison and AM General all did separate studies and all came up with the same answer, driver error, the Army ordered a trans with an 11 to 1 gear ratio in reverse, ..
To nitpick a little, according to the warning label posted above, the Army didn't get the 11:1 ratio for reverse since the transfer isn't supposed to be in "LOW" when in reverse.
I like to compare features with other vehicles, in particular the m656/xm757 series, which kind of got lost in history. The transfer case for this series is a 1:1 unit, but with a six speed transmission, the reverse is still very low, a 6:1 ratio (first gear is 5.3:1).
Looking forward to results from some further testing Chris... The Army placed a speed limit of 40 mph on these trucks, is there a reason for this particular speed that you can see based on rpm and transmission lock-up conditions? You can drive 40 in fourth or fifth gear, perhaps it doesn't lock up at 40 mph when in 5th?
__________________
Bjorn
MEP-018A (needs new generator head)
Avatar: XM757 in OK prepared for 1,000 mile trip home. Part of 6,000 mile journey in 2006.
1968 M49A2C modified with 1960 M756A2 truck bed and 1975 HIAB 765A knuckleboom, exhaust brake, VIC-1 and more.
1969 Ford XM757 8x8, 5-ton Pershing 1A truck tractor...the "improved MV".
"Some things can't be made better, just differently......a lot of things actually"
Looking forward to results from some further testing Chris... The Army placed a speed limit of 40 mph on these trucks, is there a reason for this particular speed that you can see based on rpm and transmission lock-up conditions? You can drive 40 in fourth or fifth gear, perhaps it doesn't lock up at 40 mph when in 5th?
Well, since we got the bedsides and tailgate mounted on Sunday, I should be able to do some testing soon. I will try it on hard packed dirt/gravel first and then try the pavement.
__________________
Chris Stansbury, founder of Chris' CUCV Homepage in 1998 and Steel Soldiers in 1999.
1985 AMG M998 HMMWV, under the knife
1992 BMY M925A2 - TRADED!!
1991 BMY M923A2, SOLD
Did anyone else notice that in the Wet pavement non-ABS test that the driver actually turned the steering wheel to the right when the the truck started to skid around. Watch his hands and head as the truck starts to skid. You can see him lean to the right and crank the wheel. If he would have turned left, the truck might have stayed straight. I think the skid was enhanced to help sell ABS systems.
Very interesting thread. My M923A1 experience was in 1986/87 as a truck (Support Plt) PL. Brand spanking new. I know we didn't have any of the reverse low range/crack the transfer case or max 40mph w/nondirectional tires or you're gonna wreck. Little NET when we turned in M813 that would have trained operators (11B and a couple 88M) what NOT to do. We did LOTS of driving in rain (Washington State) on pavement including I-5 without killing breaking.
Obviously anything since the GMC 6x6 is junk, but ABS with Stability Control is a HUGE improvement in operator and public safety in heavy trucks. I'm coming from a fire truck standpoint. My personal newest unit is a 2007 M2-112 64000lb. I WISH Frtliner had a stability control system available. IH is leading the industry in safety improvements.
I doubt Sam has discovered stability control yet. Might be "issues" with offroad in any case.
... I will add the problems were reported under severe use also, so in my opinion from all I have read they were not even that easy to split in low. But since I pay for it I will baby it, but man she pulls and We have been pretty stuck and reverse in low works real well, but like said I let her settle before shifting thats the key...
