• Steel Soldiers now has a few new forums, read more about it at: New Munitions Forums!

  • Microsoft MSN, Live, Hotmail, Outlook email users may not be receiving emails. We are working to resolve this issue. Please add support@steelsoldiers.com to your trusted contacts.

 

FMTV High Speed Gears

coachgeo

Well-known member
4,929
3,314
113
Location
North of Cincy OH
What benefit are people seeking with 2.87:1 gears? Are you trying to go 80MPH?
I have 3.07:1 gears, and the >20% drop in torque (to gain the >20% speed) is noticeable. If I had the option, I would be choosing something between 3.9 and 3.07... whatever was just enough to get me a reasonable 65MPH top speed but keep as much torque from lower gearing as possible. Perhaps 3.4:1?
With 3.07:1, I don't shift into 7th until about 60-62MPH. With 2.87:1, that's going to bump up to 64-66MPH.
Logical question(s). Appears you have a 3116... is that correct? I ask cause in my 3116 with same gears as you and I can't even reach 64mph.... 59 MAX is it with tires at 85ish PSI and 225hp

are you tuned up to 290hp or still have the 225hp?
 

simp5782

Feo, Fuerte y Formal
Supporting Vendor
12,088
9,248
113
Location
Mason, TN
Can always turn the governor up to 2900rpms and get some more speed with the stock ratio.
 

bardicg

New member
9
0
1
Location
Portland OR
What benefit are people seeking with 2.87:1 gears? Are you trying to go 80MPH?

I have 3.07:1 gears, and the >20% drop in torque (to gain the >20% speed) is noticeable. If I had the option, I would be choosing something between 3.9 and 3.07... whatever was just enough to get me a reasonable 65MPH top speed but keep as much torque from lower gearing as possible. Perhaps 3.4:1?

With 3.07:1, I don't shift into 7th until about 60-62MPH. With 2.87:1, that's going to bump up to 64-66MPH.
I would like lower engine speeds around 65-MPH. The CAT 3116 hits peak torque around 1,560-RPM(same with the DT466 I plan to replace it with when it finally goes). No reason to push it beyond its mechanical comfort zone. I plan to be running Goodyear MV/T tires at specified 90 PSI on aluminum wheels with rebuilt axles. Not trying to do anything crazy here. If a tapped out motor bouncing off the governor at 65 MPH works for you that's great. Not my cup of tea though.
 

tennmogger

Well-known member
Steel Soldiers Supporter
1,574
524
113
Location
Greenback, TN
....With 3.07:1, I don't shift into 7th until about 60-62MPH. With 2.87:1, that's going to bump up to 64-66MPH.
i have 3.07 ratio and my truck shifts to 7th at just over 45 mph (GPS verified). That's with "Normal" 395 Goodyear tires. There's a huge difference somewhere and I, too, would like to know what it is. Top speed is untested. Cruise at 55 is comfortable. At that speed the engine is at low enough speed that the fan turning on does not wake the dead. Tires are too out-of-round for higher speeds.

My engines stay at factory hp and with 225 hp I would not want faster gears. YMMV.
 

Awesomeness

Well-known member
Steel Soldiers Supporter
1,811
1,508
113
Location
Orlando, FL
Logical question(s). Appears you have a 3116... is that correct? I ask cause in my 3116 with same gears as you and I can't even reach 64mph.... 59 MAX is it with tires at 85ish PSI and 225hp

are you tuned up to 290hp or still have the 225hp?
I have a 290HP 3116 out of an M1083 in my M1078A0. I changed the engine before the gears, so I don't know what it would do with a stock 225HP engine. I can hit about 72MPH on level ground. I keep it at 65MPH (which is just after the shift into 7th gear at 60-62MPH [GPS verified] for me), mostly because the tires aren't rated for that much speed. At 55PSI (HWY mode on my CTIS) the Load Range G - Goodyear MV/T's are only rated for 40MPH, when fully loaded! I'm not sure how that number changes when at about 1/2 rated load.
Goodyear MV-T 395-85R20 Info.jpg
The top speed boost is nice here in Colorado where our highways all have 75MPH speed limit... you're quite an obstacle to traffic at 58MPH. But I do notice how much less gearing the truck has now, and miss how it was, so I would be shooting for something between 3.90:1 and 3.07:1 if I could choose, so that it would get me just to 65MPH max, but keep gearing as low as possible. Offroad the lower gearing helped. I'm not sure if I would put 3.07:1 gears in again, but it's not quite bad enough to be worth taking them out either.

I would like lower engine speeds around 65-MPH. The CAT 3116 hits peak torque around 1,560-RPM(same with the DT466 I plan to replace it with when it finally goes). No reason to push it beyond its mechanical comfort zone. I plan to be running Goodyear MV/T tires at specified 90 PSI on aluminum wheels with rebuilt axles. Not trying to do anything crazy here. If a tapped out motor bouncing off the governor at 65 MPH works for you that's great. Not my cup of tea though.
With the 2.87:1, 65MPH may be with the engine screaming at the top of 6th, not low in 7th. And you're dropping your torque a further 5%. You gain a little bit of fuel economy, because you're running at a lower RPM where the engine is presumably more efficient, but you're also going faster and air resistance goes up squared (exponentially). Running at 65MPH, low in 7th gear with my 3.07:1, I gained about 0.5MPG over my previous mileage when running maxed out in 7th at 58MPH with 3.90:1.

I guess I'm just saying that if you haven't really figured out what you need, 2.87:1 isn't better just because it's higher gearing.

i have 3.07 ratio and my truck shifts to 7th at just over 45 mph (GPS verified). That's with "Normal" 395 Goodyear tires. There's a huge difference somewhere and I, too, would like to know what it is. Top speed is untested. Cruise at 55 is comfortable. At that speed the engine is at low enough speed that the fan turning on does not wake the dead. Tires are too out-of-round for higher speeds.

My engines stay at factory hp and with 225 hp I would not want faster gears. YMMV.
That's interesting. Mine would barely be in 6th gear at 45MPH (with 3.07:1 gears). Mine has always been that way (original 225HP engine, new 290HP engine, 3:90:1 gears, 3.07:1 gears, even after relearning the shift points in between each of those changes). Mine has WTEC-II, not III.

Anybody else know where theirs shifts?
 

Attachments

1951M1078

Well-known member
1,018
184
63
Location
Glendale,AZ
Funny ? Mine will shift to 7th at about 44 mph.?
And I need a big middle finger photo for people that don't like my 50 to 55 mph. (stock gears)
But I like seeing thing that I never saw at 75 mph.
 

Awesomeness

Well-known member
Steel Soldiers Supporter
1,811
1,508
113
Location
Orlando, FL
Mine will shift to 7th at about 44 mph.? ... (stock gears)
If you shift into 7th at 44MPH with stock gears, you would be shifting at ~56MPH with 3.07:1 gears.

(3.90/3.07) = 1.27
44MPH * 1.27 = 55.9MPH

I'm trying to check the math on Tenmogger's shift from 6th to 7th at 44MPH...

  1. Tire: 395/85R20 diameter is 46.437", and multiply by pi to get 145.886" circumference
  2. One Mile: 5280' * 12" = 63360"
  3. 44 Miles: 63360" * 44 = 2787840" (per hour)
  4. Tire RPM: 2787840" / 145.886" = 19109.694 RPH ... 19109.694 RPH / 60 = 318.495 RPM
  5. RPM of shaft inside hub: 318.495 RPM * 2:1 = 636.990 RPM
  6. RPM of driveshaft: 636.990 RPM * 3.07:1 = 1955.56 RPM
  7. Engine speed: 1955.56 RPM * 0.90:1 (6th gear) = 1760.00 RPM

So he's shifting into 7th at 1760 RPM.

Now my shift at 62MPH...


  1. Tire: 395/85R20 diameter is 46.437", and multiply by pi to get 145.886" circumference
  2. One Mile: 5280' * 12" = 63360"
  3. 44 Miles: 63360" * 62 = 3928320" (per hour)
  4. Tire RPM: 3928320" / 145.886" = 26927.297 RPH ... 26927.297 RPH / 60 = 448.788 RPM
  5. RPM of shaft inside hub: 448.788 RPM * 2:1 = 897.577 RPM
  6. RPM of driveshaft: 897.577 RPM * 3.07:1 = 2755.56 RPM
  7. Engine speed: 2755.56 RPM * 0.90:1 (6th gear) = 2480.00 RPM

So I'm shifting into 7th at 2480 RPM.
 

engem002

New member
5
0
1
Location
Nierstein/Germany
Hi all,
first of all, I would like to introduce myself. My name is Martin, I live in Germany and since 2016 I am the owner of a M1078 from IP/GP. Since 2018 I am reading this forum. The forum have helped me a lot already but now I have a question where I need your support.
In the current configuration of my Stu the number of revolutions by 52 mph is clearly too high. Now I have the standard axles from Rockwell and would like to change to the 3.07 ratio axles. I attach the pictures of the serial numbers.
StuHinterachse.jpgStuVorderachse.jpg


And now my question: Does anyone have an idea, where I can get the suitable high speed gears in germany? Does anyone know someone who sends them and what does the weight of the set (front and rear) is?



One more question: Does anyone have an idea what the C2 / C7 mean?

Thanks again and greetings from Nierstein / Rhein,

Martin
 
Last edited:

Awesomeness

Well-known member
Steel Soldiers Supporter
1,811
1,508
113
Location
Orlando, FL

m-35tom

Well-known member
Supporting Vendor
3,020
220
63
Location
eldersburg maryland
Ok, I was not fully aware of all that, so what are the chances of diffs from a meritor axle of say 2006 fitting a rockwell axle of 1998? I would think that since it is for the Mil they would all have to be the same?
 

engem002

New member
5
0
1
Location
Nierstein/Germany
Hi*,
as written by scottmandu in Post #457, the axes of the two Meritor and Rockwell are the same, so the 3.07 HSG should fit to the older Rockwell axles.
But where can I get them in Germany, or who will deliver them to Germany. Does anyone have any idea how heavy the driving differentials (2) are?

As far as I know, I need the following 3.07 driving differential (right?):
NSN #: 3010-01-570-6834 3010-01-584-7563
Part #: A6 3200W1869 307, A4 3200Y1871 307

Which are supposed to be the same for the front and rear axle, right?

Thanks to all and greetings,
Martin
 

m-35tom

Well-known member
Supporting Vendor
3,020
220
63
Location
eldersburg maryland
2 plus shipping crate is 359 lbs, about 160 lbs each. to Germany would be VERY expensive, UPS is $1200 to $1600 so would have to be ocean freight.
 

Berend

Active member
Steel Soldiers Supporter
135
73
28
Location
Netherlands
Does anybody know how to re calibrate the speedometer for an A1 ? We installed the high speed gears but off course the speedo is way of now. In the front we took off the whole hub. Took us about 1 hour to get both front hubs of. Installing both diffs took us about 5 hours in total with 2 persons. It's an easy job with the right tools.

8C003DE1-3E65-4614-B65B-6FE6E83B292F.jpgIMG_3291.jpg
 

wheelspinner

Well-known member
Steel Soldiers Supporter
3,743
1,504
113
Location
North Carolina - FINALLY !
Does anybody know how to re calibrate the speedometer for an A1 ? We installed the high speed gears but off course the speedo is way of now. In the front we took off the whole hub. Took us about 1 hour to get both front hubs of. Installing both diffs took us about 5 hours in total with 2 persons. It's an easy job with the right tools.

View attachment 782222View attachment 782223
somewhere in here is the dip switch settings that need to be changed.
 

ramdough

Well-known member
1,554
1,727
113
Location
Austin, Texas
Does anybody know how to re calibrate the speedometer for an A1 ? We installed the high speed gears but off course the speedo is way of now. In the front we took off the whole hub. Took us about 1 hour to get both front hubs of. Installing both diffs took us about 5 hours in total with 2 persons. It's an easy job with the right tools.

View attachment 782222View attachment 782223
Do you have a write up on how you did it exactly or could you write up what you did?

What special tools besides a forklift do you need?


Sent from my iPhone using Tapatalk
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks