M939 Frames...

[71DeuceAK]

So, as I understand it, the early M939s (at least the M923/M925) were built on old M813 frames (M809 series). I assume this held true for the other variants as well.

Question- When did this stop? When were new, purpose-built frames used instead?

 

[NDT]

Where did this info come from? It is typically twice the work to disassemble an old truck, blast and paint the frame, as it is to just form new rails from shiny new steel.

 

[simp5782]

https://www.militaryfactory.com/armor/detail.asp?armor_id=837

https://www.steelsoldiers.com/showthread.php?t=28620

Sent from my SM-G965U using Tapatalk

 

[NDT]

By "stocks", that article is referring to baskets full of crossmembers, air tanks, tail lamps, etc, that are shared between the trucks. The frame is not the same.

 

[Csm Davis]

By "stocks", that article is referring to baskets full of crossmembers, air tanks, tail lamps, etc, that are shared between the trucks. The frame is not the same.

Not saying that you are wrong but how are the frame rails different from the 809 to the 939 series?

Sent from my SM-G930V using Tapatalk

 

[74M35A2]

Same as I was wondering, besides the holes drilled into them..... Isn't it just straight C channel set apart a standard width?

 

[NDT]

The holes drilled is what makes them non-interchangeable without of course drilling more holes. During frame rail manufacture, these holes are easily placed with punches (old) or plasma cutters (new). Adding holes later with mag drills is a pain in a manufacturing environment. With certainty, the holes that receive the front winch frame extensions are different between the two generations.

 

[USAFSS-ColdWarrior]

Are the cross-members, and hence the holes for their attachment any different?
How about brake line and electric wiring routing/mounting points?

 

[162tcat]

Just out of curiosity, why does it even matter? The frame is the same basic design on all 3 series so I don't see how it would matter at all other than the additional work to mod it for the next generation.

Sent from my LG-M210 using Tapatalk

 

[Csm Davis]

Okay so here's the thing going from the M39 series to M809 there was a frame length change up front because of the longer engine the 855 is longer than anything else used in the 5 tons I believe. Going from M809 series to M939 series the engine stayed put but the cab was raised and rear transmission mount added. The front hood mount and radiator mount are different, so all of these crossmembers are different and may be located slightly different from the M809 series.
To answer the OP's question I would think that once they figured out tearing down a complete truck cutting off the old crossmembers and drilling in a dozen or so holes to move things was costing more money than just new production was when they quit. They would have had a contract for doing a few to check fit and cost, probably 10 or less. In 2010 this would have cost around $150,000 or more so even in 1980's dollars it didn't make sense.

Sent from my SM-G930V using Tapatalk