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Thread: Transmission swap question

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    Default Transmission swap question

    I was thinking about swapping out my transmission in my XM818 to a Fuller 10 speed. Was wondering if it would mate up to the NHC 250 Cummins, or if there would be any clearance issues or anything like that? Would the stock clutch pedal work, would there even be enough room between the trans and the transfer case....would the front driveshaft have enough clearance? Any input would be appreciated or suggestions for other trannys that would fit..... Liked the idea of the 10 speed but it's not set in stone yet.
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    The Fuller 10 speed is a great transmission, but it is a wide transmission. It can bolt to the back of the engine if you find the correct bell housing. If you search, the part number should be on a couple of threads here. There would definitely be clearance issues with the air pack. The drive shaft to the front axle might have to have an offset carrier bearing to clearance the transmission. You also wouldn't have any room on your passenger side for a pto. I have looked into the swap for my M818. Have you thought about an Eaton FSO-8406A 6 speed. They will fit for sure. Check this out for other Eaton transmissions https://www.eaton.com/EN/rr/Products...ons/PCT_486870
    Last edited by Brutacus; 08-11-2019 at 16:27.

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    Quote Originally Posted by Brutacus View Post
    The Fuller 10 speed is a great transmission, but it is a wide transmission. It can bolt to the back of the engine if you find the correct bell housing. If you search, the part number should be on a couple of threads here. There would definitely be clearance issues with the air pack. The drive shaft to the front axle might have to have an offset carrier bearing to clearance the transmission. You also wouldn't have any room on your passenger side for a pto. I have looked into the swap for my M818. Have you thought about an Eaton FSO-8406A 6 speed. They will fit for sure. Check this out for other Eaton transmissions https://www.eaton.com/EN/rr/Products...ons/PCT_486870
    Thanks for the response and the info. Hadn't actually thought about that do you know if the shift points between 4 and 5 are better than on the stock transmission? Basically just want a reliable more user friendly transmission but still want to retain the 6 wheel drive without having to do any crazy modding. Also thought I don't have a pto right now would like to keep that option available.

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    Quote Originally Posted by Olly View Post
    Thanks for the response and the info. Hadn't actually thought about that do you know if the shift points between 4 and 5 are better than on the stock transmission? Basically just want a reliable more user friendly transmission but still want to retain the 6 wheel drive without having to do any crazy modding. Also thought I don't have a pto right now would like to keep that option available.

    The shift points for the 6 speeds and the 10 speeds are much better. On the spicer 5 speed transmission, there is a 78% jump between 3rd and 4th gear which is a WIDE gap. It really needs another gear in there to fill up that hole. The gap between 4th and 5th gear in the spicer 5 speed is about 28% which is pretty good. In the 6 speed eatons, the gap between 4th and 5th gear ranges from 59% - 37% depending on which model you have which is good, and the 10 speeds it's about 35% to 38%, which is even better. Everyone who has an M809 series truck has noticed the missing gear in between 3rd and 4th.
    Last edited by Brutacus; 08-12-2019 at 04:23.

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    Quote Originally Posted by Brutacus View Post
    The shift points for the 6 speeds and the 10 speeds are much better. On the spicer 5 speed transmission, there is a 78% jump between 3rd and 4th gear which is a WIDE gap. It really needs another gear in there to fill up that hole. The gap between 4th and 5th gear in the spicer 5 speed is about 28% which is pretty good. In the 6 speed eatons, the gap between 4th and 5th gear ranges from 59% - 37% depending on which model you have which is good, and the 10 speeds it's about 35% to 38%, which is even better. Everyone who has an M809 series truck has noticed the missing gear in between 3rd and 4th.
    Thanks for that info as well.... probably will be going with the six speed so I don't have to modify the truck. It's good to know that it'll get rid of the gap between third and fourth.

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    Quote Originally Posted by Olly View Post
    Thanks for that info as well.... probably will be going with the six speed so I don't have to modify the truck. It's good to know that it'll get rid of the gap between third and fourth.
    A town highway dept near here put a 13-speed in a M813 they had a commercial dump box on. I inspected their work. It's quite an involved project if you want to retain 6x6 capability as they did. Booster pack was relocated due to tranny width, transfer case remounted further back to accomodate tranny length, and the front, stub, and rear-forward driveshafts each had to be custom built to fit. Some mounts also had to be custom built. There was also another issue with having things line up but I don't remember what it was. Maybe it was about the location of the shifter. Whatever it was, the engine had to be moved forward, which required the removal of the stock fan. They had to install electric fans in front of the radiator, the only room that was left.

    If you don't need an active front axle, the conversion to a fuller 9sp, or 10 or 13 or 18 would be less involved as you would permanently remove the transfer case, stub shaft, and front driveshaft. The rear-forward driveshaft would need to be extended, the booster pack relocated, and there is still the possibility your shifter will not come up thru the floor in the right place.

    I've not seen any 6-speed conversions, thus I cannot comment on those.

    This is the converted truck :tyr6x6 project posting.jpg
    Last edited by msgjd; 10-09-2019 at 20:28. Reason: add pic
    M38A1, "XM38A5", M100, "M100" spen w/hoops, M416, M880, M890, M49C, M49A2C, M108, M109A3, 2-M35A2's (sold), M51, 2-M51A2's, M52, IHC M62 w/A2 "upgrade," M813, M817, XM818, 2-M818's, M750 expandable, M116A2 w/1-mep003, 2-mep003 stationaries, ex-army IHC L-172 + multitudes of non-mil heavy trucks & equip. Looking to trade FLD120 w/new DD60 475hp & 10sp fuller for M915A3. Bad knee, want automatic tranny version. MTOC-Engr FLW, MO 1970's and others incl armor to jan91. VSG 2000's

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    Quote Originally Posted by Brutacus View Post
    The Fuller 10 speed is a great transmission, but it is a wide transmission. It can bolt to the back of the engine if you find the correct bell housing. If you search, the part number should be on a couple of threads here. There would definitely be clearance issues with the air pack. The drive shaft to the front axle might have to have an offset carrier bearing to clearance the transmission. You also wouldn't have any room on your passenger side for a pto. I have looked into the swap for my M818. Have you thought about an Eaton FSO-8406A 6 speed. They will fit for sure. Check this out for other Eaton transmissions https://www.eaton.com/EN/rr/Products...ons/PCT_486870
    This intrigues me as I really dislike that lag between 3 and 4, but it raises several questions...

    1) What output companion flange do you use as the mainshaft splines are different?
    2) Does the PTO and associated linkages bolt up to the right side without modification?
    3) How would one modify the poppet valve actuation for shifting the sprag cylinder?
    Brian McMahon, SPC, USA (Ret.)
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    '77 AMGeneral M818 5 Ton Tractor, "Hannibal 8"
    -20K Winch added
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    -Converted to full dual circuit Air Brakes
    Only in my memory, always in my heart:
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    M998 HMMWV 1 1/4 ton
    ELA: 0162-0209


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    Common flanges are available for the eaton six speeds. I've seen them on the trucks at work, I don't know what the part number is though. If one can't be located, I suppose a drive shaft shop would be able to fab something together. I'm sure the PTO linkages would have to be modified, as well as the length of the drive shaft for the winch. Probably would have to make the linkage rods a little longer/a little shorter because the location would be off a little from the stock position. As for the poppet valves for the sprag, I'm looking into getting new gears cut so I can eliminate the sprag/poppet valve setup. I suppose you could switch transfer cases over to the T-1138 also. I'd be a little wary of that because some of those six speeds have 9 to 1 ratio first/reverse gear. Anyways the 6speeds vary in length from 20 inches to 28 inches long and can handle up to 820 lbs-ft. of torque. I don't know how tall these are compared to the spicers. They don't look like these would require much modification to the floor of the M809 cabs, just relocation of the hole for the gear shifter. More modifications needed if the transmission is taller.

    s-l1000.jpg
    Last edited by Brutacus; 09-28-2019 at 15:37.

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    Quote Originally Posted by Brutacus View Post
    Common flanges are available for the eaton six speeds. I've seen them on the trucks at work, I don't know what the part number is though. If one can't be located, I suppose a drive shaft shop would be able to fab something together. I'm sure the PTO linkages would have to be modified, as well as the length of the drive shaft for the winch. Probably would have to make the linkage rods a little longer/a little shorter because the location would be off a little from the stock position. As for the poppet valves for the sprag, I'm looking into getting new gears cut so I can eliminate the sprag/poppet valve setup. I suppose you could switch transfer cases over to the T-1138 also. I'd be a little wary of that because some of those six speeds have 9 to 1 ratio first/reverse gear. Anyways the 6speeds vary in length from 20 inches to 28 inches long and can handle up to 820 lbs-ft. of torque. I don't know how tall these are compared to the spicers. They don't look like these would require much modification to the floor of the M809 cabs, just relocation of the hole for the gear shifter. More modifications needed if the transmission is taller.

    s-l1000.jpg
    All those issues I guess are doable.

    -The sprag can be shifted electro-mechanically through the reverse light switch with a 4-way valve.
    -PTO linkage and drive shaft could be "cut-and-pasted". Question though...would the OEM PTO be compatible with a Fuller Eaton transmission?
    -Some crafty sheet metal work on the cab tunnel would be in order, as the shift lever would sit farther back.

    After some studying, it appears one would have to replace everything from the flywheel back including the whole clutch assembly, release bearing, bell housing so on and so forth. Am I right in this observation?



    Brian McMahon, SPC, USA (Ret.)
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    MVPA Member #33433


    '77 AMGeneral M818 5 Ton Tractor, "Hannibal 8"
    -20K Winch added
    -M923 Dropside Bed Installed
    -Converted to full dual circuit Air Brakes
    Only in my memory, always in my heart:
    XM-1, M-1, IPM-1, M1A1 Main Battle Tanks
    M998 HMMWV 1 1/4 ton
    ELA: 0162-0209


    I bear my allegiance to those...
    Whom willingly swear to the Oath...
    Then pick up a weapon...
    And bravely stand a post.


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    Quote Originally Posted by MyothersanM1 View Post
    All those issues I guess are doable.



    After some studying, it appears one would have to replace everything from the flywheel back including the whole clutch assembly, release bearing, bell housing so on and so forth. Am I right in this observation?



    Yes, you are correct in these observations. I know a different bell housing would be required as the spicer bell housing will not bolt up to the eaton transmission.
    I don't know if a different clutch disc, spring plate, throw-out bearing, and linkage would be needed. If a bell housing with the same dimensions as the spicers, with the same depth, SEA 2 pattern, and the clutch linkage in the same location is available, one might be able to re-use some of the stock equipment. The input shaft on the six speeds are 1.75", but can be changed over to 2" and 1.5" in varying legnths which would also be helpful in using the stock clutch equipment. My observations would be, if the input shaft, and bell housing were the same dimensions as the spicers, then it could be possible to re-use the stock clutch components with 6speed trans. If it's cheaper, or at least more common parts (easier to obtain) then new clutch disc, spring plate, etc. might be better anyways. My preference would be to use a bell housing that keeps the dimensions as close to stock as possible. After that is found, then get clutch components that fit it.

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