Allison M916 + Mk48 Cab = 6x6 "FEMTT"

[Fredo Corleone]

I hate the snow it slows us down too! Nice project!

 

[Csm Davis]

Okay you have the best trucks first the 920 and now we find out you have had the best big wreckers all along so here's the question DO YOU HAVE ANY OTHER AWESOME TRUCKS OR TOYS? Yes I think that should be caps. Please share

 

[Csm Davis]

Oh yeah did you put that monster in the wrecker count?

 

[M920]

Oh yeah did you put that monster in the wrecker count?

Well....I did not know if it qualified....since I kind of made it in to a "wrecker".....

 

[Danger Ranger]

Personally Id call it a crane, not a wrecker, but either way, it is one of the slickest trucks I have ever seen, and I don't care who owns it or who built it. It is just overall a really nicely done truck. Well done Soni, I bet you never saw that truck taking over this thread, did ya?

Keep us posted on the new build, but in your down time, tell us about the crane. Thanks.

 

[BBoomerBootCamp]

Soni, good to see you posting a build thread again. Sorry that darn remote never worked out. I would think some tool boxes might look nice on the new FEMTT

 

[patracy]

Soni once again never ceases to amaze me with his builds.

 

[M920]

Steering Setup

Well.....The snow finally stopped and, to put the "icing on the cake", I got the box from Fedex that I have been waiting for.......so it's time to tackle the steering setup!

As I mentioned earlier, I am keeping the steering box and all the linkage in it's original location. The M916-M920 trucks steer so nicely, going down the highway, that I don't want to risk messing that up!

The problem I'm facing lays in the fact that the steering shaft from the Mk48, comes in from the front of the steering box, where as the input shaft of the stock steering box is facing aft.
So after doing some research, my solution is a 1:1 ratio, parallel shaft gear box, made by Hub City Gear, the same company that makes the 90 degree, angle gear boxes, already used in the Mk48 cab. This will reverse the motion 180 degrees and will at the same time correct the rotation to feed in to the stock steering box from behind.

Mounting the new gear box on a plate with slotted holes and on the same frame rail as the steering box, eliminates the need for any additional stub and slips.
This will reduce the additional play in the stub shaft setup to only one extra set of gears.

The pics show the new parallel gear box and some of the extra parts needed. Also, I got the front part of the stub shaft mocked up above the steering box, to fabricate the appropriate mount for the pillow bearing.

More tomorrow.....

 

[M1075]

So when you turn the steering wheel to the left, the tires will turn to the right? Just kidding, Soni. That is the kind of mistake I would make!

 

[AZDeuce]

Soni

If it's not a "state secret" what is the paint/code, for the paint you use on the truck in your avatar and, on your M123 crane truck? It looks pretty close to the Israeli sand-grey, that is a cool color.

Lov'n this latest build, wish I had those skills, this thing is going to be awesome when finished, thanks for sharing how you do it.

 

[M920]

Soni

If it's not a "state secret" what is the paint/code, for the paint you use on the truck in your avatar and, on your M123 crane truck? It looks pretty close to the Israeli sand-grey, that is a cool color.

No "state secrets" on the paint..lol I use "Camouflage Sand" from RAPCO #30277

 

[M920]

So the good news is, that the FEMTT has a fuel tank again. No more jerry can on NAPA buckets!
The bad news is, that the U-joints on the M916's factory steering stub shaft that I assumed to be Spicer 1000 series U-joints, turned out to be Rockwell LN6s!
So therefore the Spicer 1000 series U-joints, that I had purchased, did not fit the steering yoke!!!
Turns out they are practically identical to the Rockwell LN6s, the only difference being about 0.030" less in the bearing cup O.D. !!!

I did find a "conversion u-joint" from NEAPCO part # 1-0616
So now I have to wait to put the steering together until I get that u-joint.


I did get the mount made for the pillow block though and got it welded in place....still not to bad for a Valentines Day.....got to keep the lady happy!!!!

 

[patracy]

Any thoughts of using the rear axles from that MK17 under the truck? I honestly don't recall the ratio they had. But that front axle of the 916 looks to match the axles under the MK units. The bonus would be the selectable lockers.

 

[M920]

Any thoughts of using the rear axles from that MK17 under the truck? I honestly don't recall the ratio they had. But that front axle of the 916 looks to match the axles under the MK units. The bonus would be the selectable lockers.

Yes, I thought of that for sure! After doing some research though and finding out that the Eaton axles, used by Oshkosh in the Mk17, were specifically designed for the LVS only, I decided against it for the following reasons:

-The third member with it's air locking differential and the 5.43 : 1 gear ratio is proprietary to Oshkosh and only built for the USMC PLS. In commercial applications, this same axle housing would house a two speed, air shift differential.

-Most of the internal differential parts can only be procured through government surplus or from Oshkosh direct.

-There are no other gear ratios available for this differential.

-The seven speed, double overdrive Allison transmission is geared almost to high with the M916's factory 6.17 : 1 gear ratio, so I need at least 6.17s to even be able use seventh gear, when running the 16.00R 20 Michelins.

-I'm pretty happy with the performance and simplicity of the factory Detroit lockers and the repair parts for the Rockwells (Meritor) are still readily available in the commercial trucking market.

Now, I am planning on eventually using the the semi eliptical, long leaf, single point suspension that Oshkosh used in the Mk17, on the rear of the FEMTT. I feel that it is a superior design over the Hendrickson walking beam and would certainly give the truck better articulation and a better ride.

Any additional thoughts on this subject would of course be appreciated......

 

[wreckerman893]

Soni.....with your fab skills and resources why not put air ride on it? If you have never driven a HEMMT you will find out that a cab forward (not a cab over) will beat your teeth out. And it will take a while to get used to the cab-forward design when turning corners.

 

[patracy]

Yes, I thought of that for sure! After doing some research though and finding out that the Eaton axles, used by Oshkosh in the Mk17, were specifically designed for the LVS only, I decided against it for the following reasons:

-The third member with it's air locking differential and the 5.43 : 1 gear ratio is proprietary to Oshkosh and only built for the USMC PLS. In commercial applications, this same axle housing would house a two speed, air shift differential.

-Most of the internal differential parts can only be procured through government surplus or from Oshkosh direct.

-There are no other gear ratios available for this differential.

-The seven speed, double overdrive Allison transmission is geared almost to high with the M916's factory 6.17 : 1 gear ratio, so I need at least 6.17s to even be able use seventh gear, when running the 16.00R 20 Michelins.

-I'm pretty happy with the performance and simplicity of the factory Detroit lockers and the repair parts for the Rockwells (Meritor) are still readily available in the commercial trucking market.

Now, I am planning on eventually using the the semi eliptical, long leaf, single point suspension that Oshkosh used in the Mk17, on the rear of the FEMTT. I feel that it is a superior design over the Hendrickson walking beam and would certainly give the truck better articulation and a better ride.

Any additional thoughts on this subject would of course be appreciated......

Ahh didn't know what the 916's ratio was. Guess that rules that out.

I know when I was considering my hybrid M55/MK17 I had worked out the numbers on the ratios. I could get away with a 395 in the rear axles and a 16.00 on the front and the T-case work properly. I know Floridistan built a similar setup, but had his front driveshaft disconnected due to mismatch.

Since you've got lockers already in the axles, there's not really a gain.

If gearing is a concern, what about swapped down to a 800 series t-case? I assume the 916 uses the same t-case as the 900 series that has an overdrive in high range?

 

[M920]

Soni.....with your fab skills and resources why not put air ride on it? If you have never driven a HEMMT you will find out that a cab forward (not a cab over) will beat your teeth out. And it will take a while to get used to the cab-forward design when turning corners.

Richard,
Thanks for your input! Air ride is definately a possibillity in the future. I want to get the truck usable as fast as possible though since I use it alot, but front air ride would be really sweet!
So the plan is to "tweak" things after I get to drive it and find out what really needs "tweaking" and what not.

I have driven HEMTTs and I know exactly what you are talking about on the ride and taking corners in it. It is kind of like driving a big tour bus! lol
I feel that the 6x6 FEMTT will ride nicer then a 8x8 HEMTT, since ther is no Hendrickson walking beam suspension on the front and the weight distribution is better. What hurts the HEMTT, especially when empty, is the fact thar all the weight is concentrated on the very front and the very rear of the vehicle, thus the pitching motion.

 

[jrobinson5093]

Im not familier with cab forward will there be any cooling issuses with the radiator being right behind the cab.

 

[M920]

Ahh didn't know what the 916's ratio was. Guess that rules that out.

I know when I was considering my hybrid M55/MK17 I had worked out the numbers on the ratios. I could get away with a 395 in the rear axles and a 16.00 on the front and the T-case work properly. I know Floridistan built a similar setup, but had his front driveshaft disconnected due to mismatch.

Since you've got lockers already in the axles, there's not really a gain.

If gearing is a concern, what about swapped down to a 800 series t-case? I assume the 916 uses the same t-case as the 900 series that has an overdrive in high range?

Thanks for the good suggestions! The M916 actually uses a single speed, 1:1 rato, Rockwell transfercase
I will switch the FEMTT over to a Oshkosh two speed 55000 transfer case as soon as I can locate one. I need it for low range, since the truck lacks low off road speed.

 

[M920]

Im not familier with cab forward will there be any cooling issuses with the radiator being right behind the cab.

The MK48 cab has a big tunnel through the center of it, that should provide adequate air flow for the radiator.
I guess I will find out....lol