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Starting this build thread off here to start getting more advice and information as I get ever closer to the point of no return. I'm too cheap to buy a newer Dodge and I like me some old iron :flipoff2:
Starting with a 1972 J4600 Truck. Currently has a AMC360/TH400/Dana20 in it with a closed knuckle 44 front and non FF 60 rear with 4.10's. This is how it came from the factory. Engine and tranny have roughly 10K on them since a rebuild. The truck will haul anything and move anything, maybe not fast, but it moves it. Truck currently gets 9 mpg or so empty and 7-8 while towing (at 60mph)
.
Plans for the build:
6BT Cummins mated to a RoadRanger RTO-6610 10 speed transmission. Divorced NP205. Ford Super Duty axles (D60 and 10.50). Going this route to mainly increase milage, hoping to double it at least. Second reason is to make towing easier. I hate the TH400 that is in the truck. There is so much power lost during towing it is not even funny. (tranny is fresh, I just hate slush boxes) I am choosing to go with the RTO-6610 because I have read too many stories about the NV's and Getregs having problems with sheared off gears and twisted input shafts etc. I also wanted to be able to split my gears from a standard 5-6 speed tranny. The RTO provides this ability and keeps all the gears in one box. I looked into under/over drive aux boxes and didn't like what I found in relation to holding up to a 6BT.
A big concern was being able to keep up road speed and not blow up the engine over time (and cause another "$7000 mistake" :laughing: ) The RTO has a .8 overdrive gear on the top end. Being able to do at least 70mph on the road with out over revving was a goal. The old drive line combo could do 90 mph, but the engine was nearing red line. I will be going with 3.73's in the axles, 33in tires, combined with the .8 overdrive this puts the rpms @65mph around 1950ish. 2130rpms at 70 mph. I little higher than great, but it is a start. The tires I have now on the truck are 33's, so the next set may be 34's or 35's to get a better top end out of it. (35's @ 65mph = 1860 rpms :smokin: )
Plans are to start by removing the old drive line and swapping the axles first. Then move into stuffing 10lbs of shit into a 5lb hole. I have a 6BT from a 1994 L7000 that I parted out (see my sig for parts :grinpimp with 65K on the clock. Jus broke in. Will be getting the RTO and the 205 shortly, as they are coming from a yard that is building them. Plans are the KDP fix and clean and paint the engine. Mate it to the tranny and get it in the hole. Once in I will be using the "heavy duty truck mounts" that are already on the engine. This is a mid drive line mount on the SAE#2 clutch housing and the front engine mount.
One of many questions I have thus far that I am still trying to figure out:
Brakes to stop this beast. Was looking at going with a master cylinder/hydroboost setup from a super duty. Is the proportioning valve built into this unit or no? I figured this would be the best set up to take care of the disc front and back axles I have and it was all used by Ford anyways... The PS pump/res that I have now will be plenty to handle the extra usage. Will prolly run a cooler for it too.
and for the picture lovers
The Donor..
![]()
There's a Cummins in there somewhere....
![]()
The J4600
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Starting with a 1972 J4600 Truck. Currently has a AMC360/TH400/Dana20 in it with a closed knuckle 44 front and non FF 60 rear with 4.10's. This is how it came from the factory. Engine and tranny have roughly 10K on them since a rebuild. The truck will haul anything and move anything, maybe not fast, but it moves it. Truck currently gets 9 mpg or so empty and 7-8 while towing (at 60mph)
. Plans for the build:
6BT Cummins mated to a RoadRanger RTO-6610 10 speed transmission. Divorced NP205. Ford Super Duty axles (D60 and 10.50). Going this route to mainly increase milage, hoping to double it at least. Second reason is to make towing easier. I hate the TH400 that is in the truck. There is so much power lost during towing it is not even funny. (tranny is fresh, I just hate slush boxes) I am choosing to go with the RTO-6610 because I have read too many stories about the NV's and Getregs having problems with sheared off gears and twisted input shafts etc. I also wanted to be able to split my gears from a standard 5-6 speed tranny. The RTO provides this ability and keeps all the gears in one box. I looked into under/over drive aux boxes and didn't like what I found in relation to holding up to a 6BT.
A big concern was being able to keep up road speed and not blow up the engine over time (and cause another "$7000 mistake" :laughing: ) The RTO has a .8 overdrive gear on the top end. Being able to do at least 70mph on the road with out over revving was a goal. The old drive line combo could do 90 mph, but the engine was nearing red line. I will be going with 3.73's in the axles, 33in tires, combined with the .8 overdrive this puts the rpms @65mph around 1950ish. 2130rpms at 70 mph. I little higher than great, but it is a start. The tires I have now on the truck are 33's, so the next set may be 34's or 35's to get a better top end out of it. (35's @ 65mph = 1860 rpms :smokin: )
Plans are to start by removing the old drive line and swapping the axles first. Then move into stuffing 10lbs of shit into a 5lb hole. I have a 6BT from a 1994 L7000 that I parted out (see my sig for parts :grinpimp
with 65K on the clock. Jus broke in. Will be getting the RTO and the 205 shortly, as they are coming from a yard that is building them. Plans are the KDP fix and clean and paint the engine. Mate it to the tranny and get it in the hole. Once in I will be using the "heavy duty truck mounts" that are already on the engine. This is a mid drive line mount on the SAE#2 clutch housing and the front engine mount. One of many questions I have thus far that I am still trying to figure out:
Brakes to stop this beast. Was looking at going with a master cylinder/hydroboost setup from a super duty. Is the proportioning valve built into this unit or no? I figured this would be the best set up to take care of the disc front and back axles I have and it was all used by Ford anyways... The PS pump/res that I have now will be plenty to handle the extra usage. Will prolly run a cooler for it too.
and for the picture lovers
The Donor..
There's a Cummins in there somewhere....
The J4600
