serious discussion of 5-ton speed increase via gearing (transmission, differential)

[skull bone]

i've got a dumb question? Is there any easy way to make my speedometer read right. i went to 1600 x20 and its way off. runs pulls and stops good tho i have an Cummings 250. and i bobbed it.

 

[jwaller]

i've got a dumb question? Is there any easy way to make my speedometer read right. i went to 1600 x20 and its way off. runs pulls and stops good tho i have an Cummings 250. and i bobbed it.

yup, hemtt speedo adapter.

 

[papabear]

i've got a dumb question? Is there any easy way to make my speedometer read right. i went to 1600 x20 and its way off. runs pulls and stops good tho i have an Cummings 250. and i bobbed it.

YOU BOBBED A 5TON

 

[54reo]

YOU BOBBED A 5TON

it's kinda scary...you and I are seeing things the same way lately...

 

[OPCOM]

If you can't find the right speedo adapter, most speedometer shops can help to retrofit the existing one with the correct gears. At least it's an even number to do mentally.


I think I am going to look closely at the M939 transfer case idea. haha please tell me it's a bolt-up!

Anyone got pictures of one in or out of a truck?
Pics of how it mounts?
A tech manual for one?
dimensions?
Anyone got one lying around?

 

[OPCOM]

Hey Brian.. That whole thing was fun. You mean you would, or wouldn't bob a 5T?

I don't see an advantage over a deuce for a bobber since the cargo space is rendered so small, but.. maybe there is.

 

[73m819]

I believe the output drives are on the opposite side then that of a 800 or a 54 series, I think Jones said this when he was building the baby hemtt

 

[Coldfusion21]

Ya, I remember reading the outputs are flipped. Don't they also have a tendency to break? I would be curious to see what three new sets of gears would run. A lot I'm sure, but how much? 500 a set? 1k a set?

 

[OPCOM]

I sent Jones a PM to ask about this and have been reading the Baby HEMTT topics.

I dug these views out of the TMs, and found a pic. of a 939 xfer, but it's not a good one. The pics in the TMs might be misleading so I am glad you brought this up..

The Baby HEMTT has "...Deuce frame and shortened bed turned into a dropside, HEMTT cab and material handling crane, M-900 series 5 ton axles and transfer case, Cummins 5.9 diesel w/ factory air compressor and high-mount turbo, Allison AT545N transmission..."

 

[98hd]

I should talk to him.

I dug these views out of the TMs, and found a pic. of a 939 xfer, but it's not a good one. The pics in the TMs might be misleading so I am glad you brought this up..

If you compare the TM pic to the actual, you can see cover #14 at the top of the 2nd pic and Plug 32 at the bottom. Based on that the outputs look fine to me.

Also, you hear of people wanting to put 939 axles into their 809 trucks for air brakes. If the outputs were flipped that wouldn't work. I believe you could also flip the axle housing around, swap knuckles side to side and the diff would be on the other side of the truck.

and here is a pic you can see where the diff is.
http://www.airfieldmodels.com/infor...s/m939_5_ton_truck/images/wallpaper/15316.jpg

 

[OPCOM]

The search function - what a wealth of data. The M35 driveshafts are on the passenger side. M818 5T's shafts are on the driver side.

Here is a pic of what it looks like when the tranfer and axle are not like-sided.

from http://www.steelsoldiers.com/deuce-modification-hot-rodding/25041-5-tons-under-deuce-3.html

 

[jwaller]

900 outputs are on the same side as the 800. the front driveshaft only has a carrier bearing in it to clear the larger auto tranny.

 

[OPCOM]

What is the frame width on the M939?

If the frame width on the 900 series is the same as the 800 series (34"), then this seems like a fairly easy swap, aside from the weight of the case. I'm still reading up on the several controls the 939 case has, looks like it's electical as well as mechanical and air.

The M35 and M818 are both 34" wide. M818 is 9" tall. I know this from measuring it wheh we went scrounging for lift gates.

from another thread - some of the other frame dimensions:
Deuce frame U-channel:
Legs O.D. ("flanges") = 3"
Web Width (height) O.D. = 8"
Thickness = 5/16"

5-ton frame U-channel: (Courtesy of Chief1900)
Legs: 3"
Web: 9" (bridge truck has 12" section due to extra material riveted on?)
Thickness: 5/16"

 

[Westech]

yes same frame. Different cab.

 

[kastein]

The search function - what a wealth of data. The M35 driveshafts are on the passenger side. M818 5T's shafts are on the driver side.

Here is a pic of what it looks like when the tranfer and axle are not like-sided.

from http://www.steelsoldiers.com/deuce-modification-hot-rodding/25041-5-tons-under-deuce-3.html

I see that ending badly if the suspension is ever used!

I like the "flip the axle around and switch the knuckles" idea, but wouldn't it require shimming the axle housing excessively to fix the resulting inverted caster? I don't know Rockwells all that well but my suspicion is that the caster is set via the inner C / knuckle mounting bracket being welded into place on the axle tubes at the factory. Also, will the front wheels run backwards if this is done? I haven't quite thought that one through.

Another idea would be to remove the third member and flip it around 180 degrees, but I'm not sure if this will make the axle run backwards and the bolt holes / axle shafts may or may not line up. Like I said, I'm still a rockwell tard.

 

[OPCOM]

That picture was of a temporary setup, the OP took the pic because it looked weird. The thread is very interesting about 5T running gear under a bobbed deuce frame.

 

[OPCOM]

check my wanted ad. I found a shop that will help me (big tools..)

 

[doghead]

I dug this up from an old thread, when I drove my M819 home from Ohio to NY.

On my trip home with the M819, spare motor, trailer with pickup truck on it(est 46000lbs), I managed to get 4.59 mpg. (99 gals/455 miles) 53 mph average over 8.5 hours. 61mph max speed. one fuel stop.

and, 12.00-20 NDT tires are NOT readily available , or inexpensive. I called STA and they have none in stock(hadn't made any in years) and they wanted a minimum order of 14(iirc), and the price was very high(I think I recall $350ish/ tire).

 

[73m819]

Joel(BFR) turned me on to my 1200s off ebay, mine are o4 new, I paid 2000 for 14 tires GREAT price, I looked for about 3 years before I found my 1200s, I was about to go to 1400Rs singles (deal already worked out, but called off) because of the lack of 1200s you can get 1200s in a commercial tire, I have seen this tire on some drilling rigs but I bet the cost is like gold

 

[OPCOM]

Doghead, that is not bad mileage consideing the weight being hauled. I got a bit more coming back from that build, 5.6 on the 16.00's, doing 55-60. In contrast the deuce got 7.2 going there.

I saw a couple of aux transmissions today in a shop. I didn't realize how big these things were till I saw them. The 8013 is huge, as big as an M35 transmission or bigger, looks like way overkill. There was a 60 series, more reasonable size. However I don't want to go that route due to the already short rear driveline in an 818 and having to move the existing T-case and greatly lengthen the front propellor shaft. It's not a good option due to wanting to keep the front drive. Just saying I did see them. It was not clear which ratios they had.