So. Yeah. I have that issue of not leaving crap alone so here is another quest/challenge. An MK15A1 rear assembly swap into the 923. Let's just call the truck an XM923A5 or something along those lines at this point. Only thing that is basically a 5 ton is the Front axle, cab, hood, bed. So let's go with it.
Basics are that the mk15 unit is RS580 axles on a walking beam with three 5" tapered parabolic springs so the ride should be alot better. Ratios for the axles I have found to be 5.57 ratio with a power divider front and both containing locker valves on the shaft housing. Rear assembly weight rating specs range from a 58k to 68k rating depending on manual. Not too shabby. It currently has the 16R21s on it however standard Hemtt wheels will work as basically the HEMTT 984 wrecker uses the same axles, hubs, brakes, etc with the only difference being the wheel stud and lug nuts. S cam brakes and ABS are all there as well. Differential uses the same 1710 companion flange a 5 ton uses so the driveline won't change.
The whole rear unit may actually move to the rear of the truck by about 2 inches further back than at current. The between axle width is several inches wider as well.
Issues I have to compensate on is the center cross/brace member that has the torque rods going to it. So either cut the stock 923 member out and add that one or modify/add torque rod brackets onto mine. I would rather use the Mk15 cross member as it has the vertical bolt mounts already in place. However some back bracing on the inside of the frame will be needed. The bogie unit is 34.75" wide inside to inside. A 5 ton frame is 34in wide. So not too much difference but I am planning in using some channel for frame reinforcements like the LWB trucks however mine will run from about the rear of the cab all the way thru the rear frame. Splitting the difference on the 3/4" on each wide will be the work. With all the cold rivets in the frame will probably just snipe some holes in the channel with the plasma to go over those.
Pros behind this: Better ride quality with the springs. Increased weight capacity which isn't really needed. but it will get rid of some of the trailer tongue weight with the shift to the rear. No danger from a busted torque rod shifting a whole axle out of place or losing one. 5.57 gears will allow me to run a little higher speed but the cruising speed is much better RPMs compared to the current. Almost a 10mph gain at 2150rpms. and the axle setup was basically a zero cost option to acquire. Plus the sale of the 16R21s and the rear axle assembly should basically be a + side difference. My main problem now with speed and power is that i can go from 40 to the governor in 16th gear in under about 8 seconds so. yeah quick to top out.
Should be a nice weekend but Maybe a week long project if I can get a good weather outlook.
Basics are that the mk15 unit is RS580 axles on a walking beam with three 5" tapered parabolic springs so the ride should be alot better. Ratios for the axles I have found to be 5.57 ratio with a power divider front and both containing locker valves on the shaft housing. Rear assembly weight rating specs range from a 58k to 68k rating depending on manual. Not too shabby. It currently has the 16R21s on it however standard Hemtt wheels will work as basically the HEMTT 984 wrecker uses the same axles, hubs, brakes, etc with the only difference being the wheel stud and lug nuts. S cam brakes and ABS are all there as well. Differential uses the same 1710 companion flange a 5 ton uses so the driveline won't change.
The whole rear unit may actually move to the rear of the truck by about 2 inches further back than at current. The between axle width is several inches wider as well.
Issues I have to compensate on is the center cross/brace member that has the torque rods going to it. So either cut the stock 923 member out and add that one or modify/add torque rod brackets onto mine. I would rather use the Mk15 cross member as it has the vertical bolt mounts already in place. However some back bracing on the inside of the frame will be needed. The bogie unit is 34.75" wide inside to inside. A 5 ton frame is 34in wide. So not too much difference but I am planning in using some channel for frame reinforcements like the LWB trucks however mine will run from about the rear of the cab all the way thru the rear frame. Splitting the difference on the 3/4" on each wide will be the work. With all the cold rivets in the frame will probably just snipe some holes in the channel with the plasma to go over those.
Pros behind this: Better ride quality with the springs. Increased weight capacity which isn't really needed. but it will get rid of some of the trailer tongue weight with the shift to the rear. No danger from a busted torque rod shifting a whole axle out of place or losing one. 5.57 gears will allow me to run a little higher speed but the cruising speed is much better RPMs compared to the current. Almost a 10mph gain at 2150rpms. and the axle setup was basically a zero cost option to acquire. Plus the sale of the 16R21s and the rear axle assembly should basically be a + side difference. My main problem now with speed and power is that i can go from 40 to the governor in 16th gear in under about 8 seconds so. yeah quick to top out.
Should be a nice weekend but Maybe a week long project if I can get a good weather outlook.
