Lowering M931a2 5th wheel

Considering lowering the 5th wheel on a M931a2 to a accomidated a civilian semi trailer, the concern is the the angle of the trailer and the height with low bridges. Starting with changing of the tires- at present the original 49in singles are installed but lowering the height of the 5th wheel -I would have to reduce to size of the tires to a G177 or 1100 x 20 wheels and rims- the question is what is the aprox loss of height in ulitizing these tires, and if the civilian 10 bolt rim onto the existing military 10 bolt configuration, and then also the possibility of the use of low profile tires with aggressive tread pattern also could be in consideration as a option.
The trailer is still being used with another civilan tractor so modification
or changing it is out of the question.
Another option with the lowering of the frame with the smaller tire size is changing out the militarys 5th wheel which is a 4 way type
(front to rear and side to side), with a civilian 2 way type (front to back)-
which will also lower the height a few inches, and from my guessing I need about 8 to 10 inches to make this work.
So checking the threads I could not locate any information, so any information or advise would be helpfull.

If you change the fifth wheel to get a lower height, you will need to change the ramps, also if a lower fifth wheel, watch for the the rear frame corners hitting the trailer on rough terrain.

I measured two 931s side by side. The 11-20 truck was 46" at the rear most point of the ramps, the 14-20 truck was 48". So switching to G177s would gain you two inches. Standard civi fifth wheel plate height is 48". You will have a long way to go to legally carry a 13'6" trailer no matter what you do.

I just got my "New" 931-A1 with super singles and am wondering if you found a way to lower it enough to haul a standard 5th wheel trailer?

6x6guy said:

to a accommodate a civilian semi trailer,

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6x6guy said:

The trailer is still being used with another civilan tractor so modification or changing it is out of the question.

Click to expand...

... so you talking about a specific trailer not just anyone that you come across...

Should we also assume that the trailer is a "hi-cube"? - which is pretty much all the modern ones, in that it max's out at 13'6" on a very low fifthwheel.

I don't think that you have many options other than changing 5th wheel and tires if the trailer is already a high one though with a 931 you are a lot closer than I am with a 916A1 and a 5th wheel height up in the 60's. At least the rear end of my trailer is a "low boy" - I need to add 16" to the goose neck to get it to ride level. Looks awful!

I ran into the same issue this week. I had a 13,6 trailer to deliver and it measures 14,7 when hooked to the truck. I also have a donor truck with a civi 5th wheel that I at least considered. I know it was mentioned above that over rough terrain the frame corners would possibly contact, but another issue is the flex of the rear axle. If you've ever gone through an abrupt ditch or backed up a sharp grade you'll notice the axle would contact a trailer if the 5th wheel was any lower.
I think a dolly is about the best worst way to get trailer to proper height.

Yeah agree...
- moving a friends trailer - get a dolly. (Unless there is nothing low on route of move - then I'd probably go for it, risking an unpermitted oversize ticket.)
- your own trailer (for keeps), I'd probably slope the roof line of the trailer to 13'6" pll to road when coupled or make the front end of the trailer, a step deck...

Just remember that with a dolly you will have very little weight transferred to the tractor, so you will have to be very careful braking. You might consider adding ballast to the tractor fifth wheel.

Backing up will be fun.