Ok, so most people complain about how gutless the NHC250 is even with a turbo. Even with 5 speed or Allison they still just have that gap between 3-4 and 4-5 and then there is the top speed in question based on what tires you have. Bigger tires may help you go faster but you do loose that low end grunt. What about being able to keep the 42 to 46inch tall tires and even duals and still run 75mph down the highway and what I believe is still power in reserve.
I believe the basis for what I use the truck to do means I need gears but I still don't need a calf the size of Texas on one leg, plus the non benefit of driving a 9 or 13spd in city traffic when I want to go out and cruise and the one road has 450,453,043,343 stoplights on it.
So I decided to try to modify a CAT 7155 in place of the Allison MT654CR. The Allison is good and has performed well but I just want those extra gears.
Overall Specs of the Allison are 34" long from bellhousing flush to tail end not including the output yoke. It's rear mount is situated at around 26" of its overall length and weighs somewhere around 650lbs dry.
Gear ratios are as follow 1st-4.17, 2nd-2.21, 3rd-1.65, 4th-1.27, 5th-1.00, R-10.76
The specs of the 7155 are 36" long and the rear mounting studs sit at 31.5" from face. and weighs around 1500lbs I believe. I am not for sure. I posted the gearing specs on it below. I have two different spec sheets for them so but I don't know how to tell the transmissions apart.
There are other 7155 threads over in the Engine/Drivetrain section and a good bit of useful information.
First and foremost. I know I am going to have to move the transfer case back. Simple enough. My plan is that I am going to move it back far enough to replace that driveshaft with the same shaft that goes on a 931/932 tractor. About 4ft long I believe. It probably wont be that much of a move back. BUT I would rather make a longer jackshaft and attempt to change out of the mechanics style joints over to a normal tab style spice like the rest of the driveshafts. Then I would only have to lengthen the rear section of the front driveshaft. Being that I have a center shaft bearing on mine I believe it will be fine. However if it presents itself it might end up just moving that whole support bracket up and adding another one in the rear and lengthen the front section. Only time will tell. I don't use 6x6 much so the slight use shouldn't hurt a longer shaft. I have desplined front hubs so the driveshaft never moves.
I will be sliding the bed backwards and removing the cab all together for this mod so it will be easier to work around. I don't think I have any height to the cab issues on the CAT. I am planning on making a adjustable up and down shifter setup. It will sit in the same area as my transfer case handle and driveline brake area. I am planning on a scissor type setup so it can go up and down.
The transmission has to have good clean air. As well as a regulator and mister. I ordered both of Parker and should be here Monday. They are what is pictured below. I also added 2 larger than M939 air tanks just below the drivers door. It may look like I have a lot of room but I am planning on putting an air dryer and the regulator/mister in that same area. I will run a T off the compressor main line to the rest of the system into that giving it it's own system. I am going to put a T in as well on the feed line into the spring brake system. in the even of an emergency or a line break on the primary air side I can reroute air to the spring brake system allowing some brake power or even release.
Air tanks were done today. I believe the 10/12 gallons they are should be enough. If Not I can always add one on top of the mounting bracket on the top tank to the outside. I plan on installing the dryer on a plate between the tank and the steps and the regulator mister near the lower tank. The bottom tank fit right between the steps and bolted to them. It has about a 3inch drop below the step itself.
Mod please move to Mods and Hotrods. I kept getting a proxy server flash when I would try to click on it earlier.
I believe the basis for what I use the truck to do means I need gears but I still don't need a calf the size of Texas on one leg, plus the non benefit of driving a 9 or 13spd in city traffic when I want to go out and cruise and the one road has 450,453,043,343 stoplights on it.
So I decided to try to modify a CAT 7155 in place of the Allison MT654CR. The Allison is good and has performed well but I just want those extra gears.
Overall Specs of the Allison are 34" long from bellhousing flush to tail end not including the output yoke. It's rear mount is situated at around 26" of its overall length and weighs somewhere around 650lbs dry.
Gear ratios are as follow 1st-4.17, 2nd-2.21, 3rd-1.65, 4th-1.27, 5th-1.00, R-10.76
The specs of the 7155 are 36" long and the rear mounting studs sit at 31.5" from face. and weighs around 1500lbs I believe. I am not for sure. I posted the gearing specs on it below. I have two different spec sheets for them so but I don't know how to tell the transmissions apart.
There are other 7155 threads over in the Engine/Drivetrain section and a good bit of useful information.
First and foremost. I know I am going to have to move the transfer case back. Simple enough. My plan is that I am going to move it back far enough to replace that driveshaft with the same shaft that goes on a 931/932 tractor. About 4ft long I believe. It probably wont be that much of a move back. BUT I would rather make a longer jackshaft and attempt to change out of the mechanics style joints over to a normal tab style spice like the rest of the driveshafts. Then I would only have to lengthen the rear section of the front driveshaft. Being that I have a center shaft bearing on mine I believe it will be fine. However if it presents itself it might end up just moving that whole support bracket up and adding another one in the rear and lengthen the front section. Only time will tell. I don't use 6x6 much so the slight use shouldn't hurt a longer shaft. I have desplined front hubs so the driveshaft never moves.
I will be sliding the bed backwards and removing the cab all together for this mod so it will be easier to work around. I don't think I have any height to the cab issues on the CAT. I am planning on making a adjustable up and down shifter setup. It will sit in the same area as my transfer case handle and driveline brake area. I am planning on a scissor type setup so it can go up and down.
The transmission has to have good clean air. As well as a regulator and mister. I ordered both of Parker and should be here Monday. They are what is pictured below. I also added 2 larger than M939 air tanks just below the drivers door. It may look like I have a lot of room but I am planning on putting an air dryer and the regulator/mister in that same area. I will run a T off the compressor main line to the rest of the system into that giving it it's own system. I am going to put a T in as well on the feed line into the spring brake system. in the even of an emergency or a line break on the primary air side I can reroute air to the spring brake system allowing some brake power or even release.
Air tanks were done today. I believe the 10/12 gallons they are should be enough. If Not I can always add one on top of the mounting bracket on the top tank to the outside. I plan on installing the dryer on a plate between the tank and the steps and the regulator mister near the lower tank. The bottom tank fit right between the steps and bolted to them. It has about a 3inch drop below the step itself.
Mod please move to Mods and Hotrods. I kept getting a proxy server flash when I would try to click on it earlier.
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