Allison M916 + Mk48 Cab = 6x6 "FEMTT"

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M920

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Soni, any chance you could measure the "doghouse" area where the radiator sits? I think some repositioning of the 939's radiator will have to happen if I can use it.
Ok....here are the dimmensions for the opening in the back of the Mk48 cab: When installed, the hight above the top of the frame rails is 42". It is 43" wide at the back of the cab for about 3" in, but then starts to taper in at about a 45 degree angle. There are also 2 gussets in each top corner of the opening that measure 7" x 7" with a 45 degree angle.

Let me know if you need more dimmensions.
 

M920

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Dashboard Wiring

I tried to stick with the original gauges in the Mk48 dash since they were brand new, but the tach and speedo have proprietary Oshkosh sensors for the 8V92 Detroit. I could not get them to work properly with the FEMTT's Cummins engine and computer controlled Allison tranny.

So since I needed a programmable speedo and tach, I had to put in an order for a set of my favored VDO "Vision" gauges. Of course the swap was way more involved then anticipated.....WHAT A SURPRISE....!!!!
For starters, all the terminals are different on the VDOs versus the original Dixson and Datcon gauges, and the VDOs all needed an extra ground run to them. This all just being the tip of the iceberg.....and of course having all BLACK wires did not help either....!!!! aua


I decided to use all 12 volt gauges so I could get a broader selection of the gauges that I need / want.
The rest of the truck is going to be 24 volt, so I'm using a CPT 120W dc-dc converter for the power to the gauges. It gets spliced in to the Ign+ wire (number "1076" going to the dash plug), so the whole dash is going to run on 12 volt except for the "hi-beam" light and the two turn signal indicator lights that have their own power wires run to the dash and will remain 24 volt.

I finally got it all ready and will test it in the truck tomorrow. I will let you know how it goes....I think I might be a little nervous.....:roll:
 

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patracy

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I was wondering how you planned on tackling the gauges. I was considering just taking everything out of my cab and extending the harness into the MK48 cab. But I knew the speedo and tach would be an issue due to placement. How exactly do the sending units work on the tach and speedo? I would assume it would be something like this?

http://www.summitracing.com/parts/sum-800600gm/media/images
 

vinceM920

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I'm having cat 7155 issues in my m920. What type allison did you use and how hard was it to change over. Also whats you top highway speed?

Thanks
 

Bighurt

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I'm having cat 7155 issues in my m920. What type allison did you use and how hard was it to change over. Also whats you top highway speed?

Thanks
If you mean in his M916, it came with the Allison. Soni has a special version.

As mentioned his M920 has a completely different drive train, the heart of which is a Cummins ISX 600 if I remember correctly. Soni swapped that himself.
 

wreckerman893

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As mentioned his M920 has a completely different drive train, the heart of which is a Cummins ISX 600 if I remember correctly. Soni swapped that himself.
You will never see another M920 like Soni's. I think he put an 18 speed behind that big arsed Cummins. That sucker will pass everything except a fuel stop.
 

Cycletek

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You are correct in the 7 speed Allison which was an upgrade transmission. Apparently the Caterpillar CD7155 16 speed transmission was one of the originals transmissions. This is the one I was looking at some time back http://www.govliquidation.com/auction/view?auctionId=5659836 don't worry it ended years ago, it says it has an HT740, which is a 4 speed, my mistake........apparently they put a lot of transmissions in these trucks......
 

Castle Bravo

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That makes sense. I have thought about putting a 6 speed Allison in my truck. But in CA trucks only can go 55 legally. And my truck likes 58.

With that trans and its low gear you might run into issues with over torquing the drive train with a transfer case that has low range.
Maybe, yeah. 1st gear is 7.63:1 and with 6.17:1 axles, you would get some pretty low ratios with an even lower transfer case. Putting the truck into 1st gear makes it shudder - You have to do it manually, selecting "D" starts it in 2nd gear normally.

Range406045604070
1st3.51:14.70:17.63:1
2nd1.91:12.21:13.51:1
3rd1.43:11.53:11.91:1
4th1.00:11.00:11.43:1
5th0.74:10.76:11.00:1
6th0.64:10.67:10.74:1
7th0.64:1
Reverse-4.80:1-5.55:1-4.80:1

You are correct in the 7 speed Allison which was an upgrade transmission. Apparently the Caterpillar CD7155 16 speed transmission was one of the originals transmissions. This is the one I was looking at some time back http://www.govliquidation.com/auction/view?auctionId=5659836 don't worry it ended years ago, it says it has an HT740, which is a 4 speed, my mistake........apparently they put a lot of transmissions in these trucks......
I think that GL made a mistake in listing that truck as having a HT740, it probably has a HD4070 or a HD4560. The 740 does not have an electronic pushbutton keypad. The M916A1s and A2s have the HT740 transmission, so maybe assumptions were made. The M915A3 and A4 have the 4560 transmission.

I kinda get the feeling that these Allison M916s with 4070s and air ride addons that myself, Soni, wehring, etc all own are perhaps early modifications vs the 916s that have come out lately with Allison transmissions in them. Our trucks are were modified prior to the April 2008 time period as part of some kind of testing by Northrup Grumman at Ft Irwin as part of the what they called the "Phoenix Team Ops Group." There are at least 7 of these trucks out there. Well, maybe 6 now with this project. :) If anybody remembers those large long wheelbase Mack tractors at Barstow a few months back, these had the same markings and paint as our 916s, so maybe they were part of the same program.

These other M916s with 4070s or 4560s do not have the same air ride addons and have the dual digit Allison pushbutton green displays (WTEC IV) vs the single digit red displays of our 916s. (WTEC III) They also went way up in price since then. Okay, I've revealed enough secrets for one post. :)
 
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