Tatra MTVR Prototype M923A1 - Tatra 815 Frankenstein

gearhead

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I wanted to share an interesting vehicle that I acquired out of Barstow/Yermo a few years ago for all you Tatra and M939 fans. From what I’ve researched this truck was put together to evaluate the Tatra system as an option for the MTVR vs Oshkosh. The truck had "test vehicle" stenciled on the door and had heavily modified brackets in the bed and bolted to the frame which I assume were used to apply load or mount test equipment. It also looked to have an early version of CTIS installed as well.


How was this put together?

From what I can tell.....Driveline and suspension are from the Tatra 815. To power this rig a N-14 Cummins mounted to an Allison HD4560P 6 speed trans. It was a tight fit for sure, and the cab and hood have been lifted 3 inches to accommodate the taller motor. Additionally, there is an air starter to get this thing going - not sure why but probably to fix clearance issues with an electric starter. Lots of switches that I’m still figuring out but it appears I can control different sets of axles from the cab. Pictures better tell the story:)

Ignore the generator and air compressor mounted on the new pictures- those are so I can get it started if I lose air pressure and are not original. I will take engine and interior photos and anything other requested and post more later.
 

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fuzzytoaster

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I remember watching that green one sell on GL years ago. It sparked the threads about the "M939A3" program that was scratched to fund the MTVR and FMTV series.

Do share more photos! What's on the data plates?
 

Rusty Loads

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Looks like it's running them kooky 16:00 R21 tires like I'm using (original Tatra wheels) w/tubes. Don't forget the oil in the hubs...It probably has planetary reductions...very spendy to fix.
 

gearhead

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Looks like it's running them kooky 16:00 R21 tires like I'm using (original Tatra wheels) w/tubes. Don't forget the oil in the hubs...It probably has planetary reductions...very spendy to fix.
Yes im not really a fan of the 16R21s but there does not appear to be many other options for the 16R. The rims look to be a custom split rim version without a tube which were relatively easy to mount the tires on. They feel more like a tire for a loader or other piece of equipment. Im using standard gear oil in the hubs is there a different weight Tatra requires?
 

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gearhead

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I remember watching that green one sell on GL years ago. It sparked the threads about the "M939A3" program that was scratched to fund the MTVR and FMTV series.

Do share more photos! What's on the data plates?
Data plate is pretty standard for an m923a1 doesnt look like they changed it, from the frame to the tatra unit it has "MTVR" stamped on them but thats about it
 

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gearhead

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That is one cool truck! I'm sick of shifting gears! I'd love to have an auto in mine. What is it like to drive?
The automatic works well and the N-14 sounds great. Without weight on the suspension it bounces down the road pretty good, but the power to weight ratio and gearing are what I wish all the 939 series trucks originally had.
 

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Rusty Loads

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I have some friends on the Canadian Oil patch running 2 of the 8x8 Tatra. They say nothing will keep up to them in the bush in the winter. It's a suspension many other trucks wish they had. I wish I had a tubeless version of this stock wheel. The whole tube thing was a pain in keester. As a side note I believe most Tatra trucks running the larger diameter tires such as what you and I have (16:00 R21 or R20) have some kind of a body lift on the cab so the tires don't touch. I have a double cab unlifted and have not touched them yet. Obviously cab height not an issue for you as the whole truck is custom built. It looks like you do not have CTIS which makes the bespoke wheel thing a lot easier.
With regards to hub oil my manual for the 815VT lorrie as they call it specifies SAE80W. From memory (hope it's working) I'm running Amsoil Severe gear in the closest viscosity to that. I've done long road trips and no appreciable heat buildup (I always give them a pat when I stop to take a break)
Here is a pic of stock wheel and some notes from manual.IMG_1316.JPG
 

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Rusty Loads

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You probably could switch to 16:00R20 Wheels and tires. I tried some Alu Hutchinsons...they bolt up but the only problem was marrying it to my CTIS. So I chose the path of least resistance and picked up these 21's cheap and kept stock wheels. If you don't have CTIS the switch may be quite easy providing offset is similar.
 

Rusty Loads

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Now that I look at some of my test pics (it was a while ago)...there is another problem with the US style military wheels..there are a few different ways of centering the wheel and the Tatra uses a different style (of course). So you are looking at wheel mods and stud/nut differences. Hope that helps.
 

gearhead

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I have some friends on the Canadian Oil patch running 2 of the 8x8 Tatra. They say nothing will keep up to them in the bush in the winter. It's a suspension many other trucks wish they had. I wish I had a tubeless version of this stock wheel. The whole tube thing was a pain in keester. As a side note I believe most Tatra trucks running the larger diameter tires such as what you and I have (16:00 R21 or R20) have some kind of a body lift on the cab so the tires don't touch. I have a double cab unlifted and have not touched them yet. Obviously cab height not an issue for you as the whole truck is custom built. It looks like you do not have CTIS which makes the bespoke wheel thing a lot easier.
With regards to hub oil my manual for the 815VT lorrie as they call it specifies SAE80W. From memory (hope it's working) I'm running Amsoil Severe gear in the closest viscosity to that. I've done long road trips and no appreciable heat buildup (I always give them a pat when I stop to take a break)
Here is a pic of stock wheel and some notes from manual.View attachment 797677
Great Thanks! Really helpful info 815 info in english seems to be difficult to find
 

Karl kostman

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THIS is one the the coolest things I have seen in a LONG time!! I am a huge Tatra fan and own a 939 series truck melding these two together has got to obviously produce a BIG winner ! Love the truck and cannot wait to hear more!
Karl
 

tooFATtoDRIVE

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London, United Kingdom
I wanted to share an interesting vehicle that I acquired out of Barstow/Yermo a few years ago for all you Tatra and M939 fans. From what I’ve researched this truck was put together to evaluate the Tatra system as an option for the MTVR vs Oshkosh. The truck had "test vehicle" stenciled on the door and had heavily modified brackets in the bed and bolted to the frame which I assume were used to apply load or mount test equipment. It also looked to have an early version of CTIS installed as well.


How was this put together?

From what I can tell.....Driveline and suspension are from the Tatra 815. To power this rig a N-14 Cummins mounted to an Allison HD4560P 6 speed trans. It was a tight fit for sure, and the cab and hood have been lifted 3 inches to accommodate the taller motor. Additionally, there is an air starter to get this thing going - not sure why but probably to fix clearance issues with an electric starter. Lots of switches that I’m still figuring out but it appears I can control different sets of axles from the cab. Pictures better tell the story:)

Ignore the generator and air compressor mounted on the new pictures- those are so I can get it started if I lose air pressure and are not original. I will take engine and interior photos and anything other requested and post more later.
gearhead,

What a cool truck!!! Do you still have? If you do, perhaps you could take more pictures (or share those already taken) of how the drive shaft between the gearbox and the transferbox is connected, on the transferbox side. If I am not mistaken, the usual Tatra setup is that the gearbox is directly connected to the transfers box. Here, absent of the Tatra gearbox, the Allison automatic transmission is bolted to the engine so there must be some sort of transfer box housing to which the driveshaft is bolted. I would be very interested in seeing that.

The reason I asked is that in the future I would hope to acquire one of the crew/double cabin Tatras 815 8x8 and add a more powerful engine (maybe something like this https://www.ebay-kleinanzeigen.de/s...outside-damaged-longblock/1677259270-276-5451) and an older, non or less electronic, Allison automatic transmission.

Let me know. Thanks
 

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gearhead

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20
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Ramona, Ca
gearhead,

What a cool truck!!! Do you still have? If you do, perhaps you could take more pictures (or share those already taken) of how the drive shaft between the gearbox and the transferbox is connected, on the transferbox side. If I am not mistaken, the usual Tatra setup is that the gearbox is directly connected to the transfers box. Here, absent of the Tatra gearbox, the Allison automatic transmission is bolted to the engine so there must be some sort of transfer box housing to which the driveshaft is bolted. I would be very interested in seeing that.

The reason I asked is that in the future I would hope to acquire one of the crew/double cabin Tatras 815 8x8 and add a more powerful engine (maybe something like this https://www.ebay-kleinanzeigen.de/s...outside-damaged-longblock/1677259270-276-5451) and an older, non or less electronic, Allison automatic transmission.

Let me know. Thanks
 

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Geof

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I wanted to share an interesting vehicle that I acquired out of Barstow/Yermo a few years ago for all you Tatra and M939 fans. From what I’ve researched this truck was put together to evaluate the Tatra system as an option for the MTVR vs Oshkosh. The truck had "test vehicle" stenciled on the door and had heavily modified brackets in the bed and bolted to the frame which I assume were used to apply load or mount test equipment. It also looked to have an early version of CTIS installed as well.


How was this put together?

From what I can tell.....Driveline and suspension are from the Tatra 815. To power this rig a N-14 Cummins mounted to an Allison HD4560P 6 speed trans. It was a tight fit for sure, and the cab and hood have been lifted 3 inches to accommodate the taller motor. Additionally, there is an air starter to get this thing going - not sure why but probably to fix clearance issues with an electric starter. Lots of switches that I’m still figuring out but it appears I can control different sets of axles from the cab. Pictures better tell the story:)

Ignore the generator and air compressor mounted on the new pictures- those are so I can get it started if I lose air pressure and are not original. I will take engine and interior photos and anything other requested and post more later.
Yes, very interesting.

I think that this chassis was originally assembled at STEWART STEVENSON. For a short time they worked with TATRA to develop a independent suspension chassis retrofit. It could be an early NATC assembled chassis, but I am not aware that NATC ever assembled a vehicle with an ALLISON transmission. I have two of the STEWART STEVENSON chassis here.

Much of the M939/TATRA development and testing was done at NATC (Nevada Automotive Test Center) near Silver Springs, Nevada for the USMC MTTR (Medium-Tactical-Truck-Replacement) program. This was an effort to retrofit a M939 chassis over a 6X6 TATRA chassis. There were no other independent suspensions available in the US at this time. I have extensive information on this swap if you have an interest. ISLAND CITY ENGINEERING beginning in 2005 made a similar swap placing a FMTV 6X6 upper chassis over a TATRA 6X6 chassis. The Marines eventually built a new vehicle, the MTVR (Medium-Tactical-Truck-Replacement) rather than reset M939's. It is interesting that the MTTR program at NATC is in reality the foundation program for all US independent suspensions that followed including OSHKOSH. It is also the case that the OSHKOSH and other US developed independent suspension performance is all fundamentally based on TATRA truck performance as the performance specification for the 7-ton MTVR is based largely on NATC MTTR TATRA performance testing. To their credit TATRA and NATC set a high bar. NATC assistance led the USMC to early high-mobility vehicle success compared to US Army efforts.

Twin Disc developed an innovative transmission for the MTTR. The TD drop-box transmission is sandwiched in the TATRA frame to become a frame structural component similar to the TATRA transfer case installed in your truck.

The USMC contacted OSHKOSH during the MTTR program to ask what OSHKOSH TRUCK could offer. This was the beginning of the OSHKOSH independent suspension program that evolved entirely within the OSHKOSH T&D Lab. The OSHKOSH dual control arm suspension was originally developed as competition for the USMC TATRA MTTR program.

US ARMY TACOM at the time held that independent suspensions were unnecessary as the Army attempted to justify the struggling FMTV program. FMTV mobility is miserable and OSHKOSH is presently contracted by the Army to retrofit an independent under the FMTV system.

FMTV+ CHASSIS.JPGFMTV+.JPGM923_TATRA_RETRO.jpgM923 TATRA RETRO_1.jpgTATRA's stiff central tube frame makes it excellent for reset programs. All wheel forces are resolved in the tube frame assembly. The cargo frame simply supports the load. This why TATRA can use an entirely welded cargo frame over the central tube. This is not possible with a ladder frame trucks as the frame torsional forces result in rapid weld fatigue and failure.
 
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