FMTV High Speed Gears

[dronsen]

Hello NTD - when you swapped diff gear sets did you also have to swith out the bevel/hub wheel end gears to achieve 6:14 final ratio?

Thank you!

 

[NDT]

Hello NTD - when you swapped diff gear sets did you also have to swith out the bevel/hub wheel end gears to achieve 6:14 final ratio?

Thank you!

No sir, the ratio change is all in the pumpkin.

 

[buffalorunner]

I would like to know as well if there is anyone selling the gears from these axles or the axles themselves. I am in the south now (GA, thanks Army for making me move during the hottest part of the year), but would be willing to travel to get these gears/axles to help finish my expedition camper build.

 

[coachgeo]

I would like to know as well if there is anyone selling the gears from these axles or the axles themselves. I am in the south now (GA, thanks Army for making me move during the hottest part of the year), but would be willing to travel to get these gears/axles to help finish my expedition camper build.

If I understand this right Bryce (contact via facebook as noted earler in this thead) sells the pumpkin guts/Center Section with R&P attached. It's a fully assembled unit. Lot cheaper than shipping whole axle and easier to install.

Side note about 6x6 and High Speed gears. Talked to him last week. He does sells High Speed Gears for Intermediate axle (front axle of 6x6 pair) but this unit is also attached to the Power Divider* that powers via short driveshaft the rear most axle . So you swap the whole Power Divider out. He said by visual inspection the actual R&P looks same as the other High Speed R&P but that he's not disassembled and compared closely to know for sure. So there is a Remote possibility that the right person with axle rebuild knowledge could disassemble things down far enough to swap the R&P's only in any of the axles if it came to it. Right now with the market having whole center sections and Power Dividers available it's just easier to swap that whole section.

*Power Divider- was calling this the Offset Gear Box in previous post.... for not yet knowing it's official name.

 

[steve6x6x6]

If I understand this right Bryce (contact via facebook as noted earler in this thead) sells the pumpkin guts/Center Section with R&P attached. It's a fully assembled unit. Lot cheaper than shipping whole axle and easier to install.

Side note about 6x6 and High Speed gears. Talked to him last week. He does sells High Speed Gears for Intermediate axle (front axle of 6x6 pair) but this unit is also attached to the Power Divider* that powers via short driveshaft the rear most axle . So you swap the whole Power Divider out. He said by visual inspection the actual R&P looks same as the other High Speed R&P but that he's not disassembled and compared closely to know for sure. So there is a Remote possibility that the right person with axle rebuild knowledge could disassemble things down far enough to swap the R&P's only in any of the axles if it came to it. Right now with the market having whole center sections and Power Dividers available it's just easier to swap that whole section.

*Power Divider- was calling this the Offset Gear Box in previous post.... for not yet knowing it's official name.

I call them gear over box. 3.07 gear with 2 to1 hubs makes 6.14 final ratio.

 

[coachgeo]

I call them gear over box. 3.07 gear with 2 to1 hubs makes 6.14 final ratio.

Would you also say the actual Ring and Pinon that is part of this box looks near identical or identical to the R&P that is fitted in Front or Rear most axle? They have different part numbers buttttt?

 

[steve6x6x6]

Would you also say the actual Ring and Pinon that is part of this box looks near identical or identical to the R&P that is fitted in Front or Rear most axle? They have different part numbers buttttt?

I removed the pinion cover to look at it, the R&P is totally different in the gear over box than the front axle and third axle chunk. The end of the pinion has the oil pump mounted on it.

 

[scottmandu]

If I understand this right Bryce (contact via facebook as noted earler in this thead) sells the pumpkin guts/Center Section with R&P attached. It's a fully assembled unit. Lot cheaper than shipping whole axle and easier to install.

Side note about 6x6 and High Speed gears. Talked to him last week. He does sells High Speed Gears for Intermediate axle (front axle of 6x6 pair) but this unit is also attached to the Power Divider* that powers via short driveshaft the rear most axle . So you swap the whole Power Divider out. He said by visual inspection the actual R&P looks same as the other High Speed R&P but that he's not disassembled and compared closely to know for sure. So there is a Remote possibility that the right person with axle rebuild knowledge could disassemble things down far enough to swap the R&P's only in any of the axles if it came to it. Right now with the market having whole center sections and Power Dividers available it's just easier to swap that whole section. *Power Divider- was calling this the Offset Gear Box in previous post.... for not yet knowing it's official name.

The power divider is a common term used in the heavy truck industry. Your typical 3 axle tractor trailer only the rear axle is powered all the time the center axle is only powered when traction is limited. I used to work at a truck repair shop and we replaced 2-3 of the power dividers a week because drivers would leave them engaged on the highway.

Replacing a ring and pinion is possible but a total pain in the ass.

 

[InMemoryofRex]

Yup, Bryce is awesome.
A rolling rock gathers no moss.
This guy drives more in one week than I do all year.
And he knows his stuff.

 

[dronsen]

I'm planning on doing the high speed gear swap soon...THANK YOU ALL for sharing your experiences, part numbers, process, etc. - I love this place. I've researched all input extensively and feel very comfortable about the project. However, I had one reservation...tire speed rating. I've experienced a high speed front tire blow-out in a large truck and almost s*#t my pants...then felt very lucky to be alive...Would like to avoid repeating.

Here's what I found from GoodYear and Michelin regarding 395/85R20 specifications:

GoodYear MVT - Top Speed 81 MPH (G Load Rating) GoodYear MVT - Top Speed 68 MPH (L Load Rating) Michelin XML - Top Speed 55 MPH Michelin XZL - Top Speed 55 MPH Michelin XZL+ - Top Speed 55 MPH Michelin XZL2 - Top Speed 68 MPH

These numbers are directly from manufacturers for 2015/2016. So, only the G-Rated MVT has a speed rating of above 68 MPH, and only then at 95PSI which is of course impossible to achieve if CTIS is enabled. Most of the surplus MVT's that I am finding have the G-rating...I'm curious if the DoD ever ordered the "L" or if they're all "G"...My rig has XML's for the time being so I can't check - any input there is appreciated.

**Of note, prior year's specifications have even lower speed ratings for some models**

I'm not making any suggestions regarding safety, etc., just clearing some misconceptions that have been cast here and other threads regarding high speed ratings.

I put both docs in my online TM file here if anyone wants to access.

Best,

Dave

 

[scottmandu]

All the Goodyear 395/85R20 tires I have are 'G' rated.

 

[Oxyacetylene]

These numbers are directly from manufacturers for 2015/2016. So, only the G-Rated MVT has a speed rating of above 68 MPH, and only then at 95PSI which is of course impossible to achieve if CTIS is enabled.
Dave

As a workaround, you could unhook your CTIS controller and air up the tires manually from the valve stems. I have thought about doing this for highway trips to inflate the tire a little more, try to eek out that last little bit of speed. Then when you get to where you are going to offroad, hook the CTIS back up.

 

[PowerstrokeNC]

You can also change to an MRAP or Wrecker CTIS box in cab which has higher hwy pressure settings, some have also had success (I think) in reprogramming the module to inflate to higher values.
There is a thread on SS about it somewhere.

 

[Rene M]

I'll never understand why a modern turbocharged/intercooled empty 17,000 lb diesel truck gets the same or worse fuel economy as a loaded 80,000 lb class 8 big rig.

Really? Im shocked they get that good of mileage.
Auto trans
transfer case
parasitic loss at bot front and rear diffs
2 to 1 at the hubs
and last but not least massive rotational loss turning those heavy off road tires and two piece wheels..

a class 8 has a trans and one diff " which turns only one set of tires on one side " unless you lock in the power divider" on street high mileage tires. Release the brakes and push one .... you will be shocked how easy they roll even loaded. Stopping becomes more of a problem then.. lol

 

[123cambo]

has anyone thought about a Cummins 8.3 swap and dump the 3116 Cat?

 

[coachgeo]

has anyone thought about a Cummins 8.3 swap and dump the 3116 Cat?

Curious why you feel that power plant is best option? Ask cause keeping this in back of my mind for distant future when my engine gets tired. Granted this would be best as a new topic/thread cause it is another topic... and so not to hijack this one.

 

[123cambo]

Sorry for the hijack,new thread started on the engine swap question. No responses yet....

 

[sjohn116]

anyone have an idea if more high speed pumpkins are available?

 

[Rebuilder]

anyone have an idea if more high speed pumpkins are available?

Contact Mike at http://premiermetalbuyers.com/ He's got them.

 

[fuzzytoaster]

Contact Mike at http://premiermetalbuyers.com/ He's got them.

Ditto. Act quick as I stopped by there 2 weeks ago and just about everything MRAP related is gone. They may have some stuff hidden away or off site...you never know.