FMTV High Speed Gears

You could maybe try bumping the timing. That will effect mileage. If for better or worse, I don't know.
Edit: Propane injection would certainly help it.

Terrh; said:

It would be interesting to find one with a bad engine and do a 5.9 swap and see what the MPG does.

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LOL, It is called a SD Brazos. The commercial version of the FMTV. They were fitted with the 5.9.

The CAT 3116 was used in Chevy/GMC Top Kicks / Kodiaks in the early '90s. I don't know what their mileage was, but application and setup dictates their efficiency.
Over the Road trucks are geared to run at hiway speeds and city trucks for stop and go driving. If you put the truck into the other environment, they suck.

The FMTV were designed for hiway, city and cross country WITHOUT a dual range transfer case. The Allison MD auto trans is one of the heaviest ( if not heaviest) trans fitted into a medium duty truck. 1st gear ( which is manually selected) is for cross country. 2nd through 5th are conventional gear ratios and 6th & 7th are both overdrives ( the top gears was programmed out on commercial Ford MD trucks because it was too much of an OD). OTR trucks will use manual trans with a bunch of gears to allow the engine to stay in the "sweet" spot. With the low final ratio of the FMTV's, the OD's in the trans are actually powering the trucks to a faster speed rather than be an economical means of coasting ( not a good choice of words, but hope you understand the meaning)

The tires on the FMTV are wide and heavy (340 lbs each) and increase the drag and are never inflated to there max pressure for economical hiway speeds... then there is the full time all wheel drive that takes fuel mileage away. Next you have a truck that weighs in at 18K lbs +/- empty and a cab that amounts to an air brake.... and when you put in a higher axle ratio, the truck now works a bit harder to get rolling and the faster you go, the frontal mass of the truck works even harder against you. And lastly, I can probably guess that some use the gas pedal at 2 positions... all the way up and against the floor... that won't help with mileage.

If I were to hazard a guess, I might guess that a LMTV would get it's best mileage cruising somewhere between 1900 and 2100 rpm ( and whatever speed it is there). It may be a little lower on the rpm, but I don't remember the particulars of the 3116. I do remember the 12valve 5.9's liked 1700 to 1800. I have a '94 Ford F700 w/ 5.9 230hp/605fpt and MT654 that I ordered at the end of '93 ( Fords didn't get the MD trans until June '94 )

My comments are based on my experiences with medium duty trucks from the late '80s and into the mid '90's with my service trucks that I ordered, and with my M1094.
The FMTV's were made from the same commercially available components of that era.

Thanks for that informative post!

I found these as well, Bronto BR6 http://www.westernsterling.ca/heavy...-BR6+4X4-16a9e80b40463845007ca7f040516533.htm

Looks like they are selling them new even. Wonder what they look like after a few years in an oil field. Probably pretty bad.

DID is the word. Bronto was the Canadian name. When BAE Sealy closed, that was the end of production and only existing inventory is left. The last production trucks were for Canadian mining. Sold without warranty.

According to a BAE engineer I had contact with, the mining companies were getting the best value with the Brontos than other trucks used for the same operations, hence the last Brontos were made this year.

As a personal comment. Over the years I've attempted many contacts with various BAE facilities for information on different MVs I've had/have with poor results at best. The people at Sealy were the friendliest and most helpful. I was truly sadden when I was told of the pending closing of the plant and sale of the facilities last year.

DSD277 said:

As a personal comment. Over the years I've attempted many contacts with various BAE facilities for information on different MVs I've had/have with poor results at best. The people at Sealy were the friendliest and most helpful. I was truly sadden when I was told of the pending closing of the plant and sale of the facilities last year.

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I would have to agree with this sentiment. We have one of those 6x6's from Sealy and those folks were absolutely the best to work with.

I'm now interested in tweaking these issues. What is the final results? I'm sure the speedometer can be corrected ect , but are you getting better mileage now ?

It to bad the mileage is so poor on these trucks. The Steyr version with a real underpowered engine gets upwards of 12 MPG with the big XZL as well. I guess the the manual trans makes a big difference

A manual transmission always provides better mileage, depending on the final output ratio.

scottreb said:

It to bad the mileage is so poor on these trucks. The Steyr version with a real underpowered engine gets upwards of 12 MPG with the big XZL as well. I guess the the manual trans makes a big difference

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Apples and Oranges! Completely different trucks. The only thing in common is the cab's sheetmetal. The empty Steyr 12M18 weighs in at around 13.5k lbs verses the M1078 at 18k.
The Tires on the Steyr are smaller and lighter than the ones on on the FMTVs.
As far as underpowered, European medium and heavy duty trucks have engines to match the payload range they are intended to carry. The big Unimogs (SBU) designations generally are roughly the engine HP of the for the spec'ed payload. Most common to most people are the 1300s ( most military used) which have approx 130 horses +/-. The SBU body/ class designations goes from 1000 to 2450, which are approx 100 to 245 HP for the appropriate payload of each truck.

The 12M18 also has a 9 speed tranny and a 2 speed transfer case for on/off road. The FMTV has a total of 7. 1 for off road and 6 for everything else, and 6th and 7th are overdrives.

I was looking at importing a 12M18 when my M1094 came up in 2012.

I think the bare Steyr may weigh even less. Plenty of them under 7.5 tons with a full loaded camper on it. Your 1094 is pretty cool!

Ordering a set from Premier and having them shipped to NJ, anyone up east interested in a set? I go to Gilbert, and the Sussex NJ show. Picking up my m1078 this week from Ft Drum.

I also had a question on removing the axle half shafts from the rear differential if anyone has done this before other than auction addict. I am picking up a M1078 this week and either am going to get it with a wrecker or a Landoll, wrecker is easier but if I go that route I want to pull the shafts entirely. Do they fully come out and the caps go back in?

As for the MRAP axles, are they identical parts wise? Reason being is I am going to have them shipped from TX to NJ and if the only comparable part is the diff then its not worth the extra cost due to extra weight, I would like to have spare parts which is why id pay for extra shipping.

Thanks I appreciate your help.

aheilmann68 said:

Ordering a set from Premier and having them shipped to NJ, anyone up east interested in a set? I go to Gilbert, and the Sussex NJ show. Picking up my m1078 this week from Ft Drum.

I also had a question on removing the axle half shafts from the rear differential if anyone has done this before other than auction addict. I am picking up a M1078 this week and either am going to get it with a wrecker or a Landoll, wrecker is easier but if I go that route I want to pull the shafts entirely. Do they fully come out and the caps go back in?


As for the MRAP axles, are they identical parts wise? Reason being is I am going to have them shipped from TX to NJ and if the only comparable part is the diff then its not worth the extra cost due to extra weight, I would like to have spare parts which is why id pay for extra shipping.

Thanks I appreciate your help.

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Yes, use a pipe wrench to take the huge plugs out. Be prepared to catch some gear oil. Then the shafts pull out using a long bolt, better bring an assortment of metric and standard bolts about 3" long around 3/8" fine thread. Auctionaddict may remember the exact size.


Almost all parts are the same. The rear housing is not. Some of the fronts they have are equipped with hydraulic brakes. Good luck getting them to pick the right type. Most of us have been buying rears as pulling the front differential involves disassembly of the knuckle, as opposed to the simple pipe plug in the rear. But we are giving up valuable spare parts.

NDT,
Thanks for the confirmation on that. I may end up getting 1 complete axle set and I try to ask for only air brake but i'm mainly concerned with having spare gears and such so at the least then im golden.

Found the TM 9-2320-365-34-2 chapters 9 and 10 for the carrier swap. It claims the chunk weighs 400lbs? Is that right? I cant see how. The ones I have coming buy freight weight in at less then half. Also were did you gentlemen source your inner and outer axle seals at?

10Lugger said:

Found the TM 9-2320-365-34-2 chapters 9 and 10 for the carrier swap. It claims the chunk weighs 400lbs? Is that right? I cant see how. The ones I have coming buy freight weight in at less then half. Also were did you gentlemen source your inner and outer axle seals at?

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That must be to thur shaft one 400 lbs.

Love the gear swap idea.

I am wondering, would the three axle FMTV allow for the gear swap as well? IE would I simply order three sets, and it should go, or does the middle axle with its drive shaft coming in from the top ruin this for me? Would LOVE LOVE LOVE To go 75 mph!

Thanks

I called them last week and they were all out

Try calling Torres Metal Recycling in Sealy TX for more axles, they scrapped lots of Caimans as well.
As far as a MTV 5 ton gear swap, you would need all three axles from a Caiman and you would have the option of just replacing the entire axle assy as they are the same except for the ratio.

NDT said:

Try calling Torres Metal Recycling in Sealy TX for more axles, they scrapped lots of Caimans as well.
As far as a MTV 5 ton gear swap, you would need all three axles from a Caiman and you would have the option of just replacing the entire axle assy as they are the same except for the ratio.

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Torres scrapped all there axles also.. I should have bought more !!!

Premier still has about 300 sets left, I just got off the phone with Mike from there and he was quick to say they were not sold out. He likes the business the SS community is bringing and so far he has been helpful in getting axles ordered. They only do money order and pick the axles when they are semi slow so it is not a fast turnaround.