Reversing with the transfer case in low range

[kendelrio]

Hello all!
I was reading the -10 TM and was reading/learning about the transfer case, how to use it etc and one thing I noticed was in the "speed" section for each gear in each range, Reverse was blanked out in "Low" and it unequivocally stated "DO NOT DRIVE IN REVERSE IN LOW" (or something to the effect).

I've also seen in threads here where people mention to not drive in reverse.

With all that said, I **will not** be driving in reverse in low range, but the technical/troubleshooter side of me wants to know "Why?".

Anyone have a good story etc as to why we don't do that?

 

[kendelrio]

Also, I've read the thread(s) where people say they've thrashed or seen thrashed transfer cases.

The answer I'm looking for is the technical reason we can't. I get torque is an issue, but why?

 

[frank8003]

Too much torque for the box so it breaks, very expensive to fix.

see posts 14 +15 in here

Another "Don't Use Low-Reverse on 939 Series" Thread? Yes, But Fact Finding...

Another "Don't Use Low-Reverse on 939 Series" Thread? Yes, But Fact Finding... The "Don't use low-reverse" on M939 series seems to really have a mixed bag of emotions and outcomes. What I'm trying to decipher is, are there any cases of the T-case breaking from low-reverse usage with the front...

www.steelsoldiers.com

Perhaps the following is correct?
1st - 4.17
2nd - 2.21
3rd - 1.66
4th - 1.27
5th - 1.00
Rev - 10.76

 

[simp5782]

Transmission gearing plus torque converter multiplication plus low range transfer gearing = lots of torque. The center bull gear flexes under this and stresses the case and causes them to crack.

 

[Tow4]

It's only a problem if the front drive is engaged. Remove the washer from the transfer case shift rod or turn the rod around so the washer doesn't activate the front drive air switch when the transfer case is put in low. You can engage the front drive with the switch on the dash when you need it.

 

[kendelrio]

Thanks all! Super enlightening!

 

[tobyS]

The center shaft in the box is at an extremely low angle and with torque on the shaft, climbs between the input gear and output, pushing them apart with extreme force, breaking the cast housing. Government in their infinite wisdom put a warning on the dash instead of fixing the problem in the TC (redesign). The closest thing to a fix is stopping the front drive from engaging automatically.

 

[Crf450x]

There was a guy on Facebook the other day that blew his transfer case apart in reverse, high, not in 6x6. He said it was wheel hopping but they don’t necessarily have to be in low 6x6.

 

[Desertshark]

So as dumb as this may sound... is it OK to go in reverse with the air switch on but case still in high and not in low?

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[kendelrio]

So as dumb as this may sound... is it OK to go in reverse with the air switch on but case still in high and not in low?

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According to what I've read, yes.... it's low range that thrashes t-cases

 

[Desertshark]

According to what I've read, yes.... it's low range that thrashes t-cases

Ok thats kinda what I thought. That and when it's in low (handle all the way up) is when you can make the case explode.

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[kendelrio]

Ok thats kinda what I thought. That and when it's in low (handle all the way up) is when you can make the case explode.

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Yes. There were some folks at smarter than me doing math and from what I gathered (any mistake in the comprehension is totally my fault) is that there is a 10:1 torque ratio multiplication happening, and the cases weren't designed for that.