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- #61
Test drive impressions -
Overall the initial drives went well. The Cummins R2.8 is well suited to smaller rigs like these 2-door models, power and torque feel appropriate for the size/weight of the vehicle. There's a fair bit of turbo noise audible, using a cone filter isn't the best setup to quiet that down but fitting a larger canister style filter box would have been very challenging. The engine pulls really well though and mpg numbers in the mid 20's are icing on the cake.
The first snafu was encountered when we headed to the alignment shop. Up on the Hunter we found that there was -1deg caster on the left and 0deg on the right. That was troublesome because it's obviously not a great setup to have negative caster but the real concern was the difference from side to side. Out on the road the problem was evident in a slight pull despite perfect toe settings. There are no plates or correcting arms for the LJ suspension so we decided to order some offset bearings from @cruiseroutfit and chose 1.8deg and 3deg correctors. By installing the 3deg version on the left and the 1.8 deg on the right we were able to get the two sides to match almost exactly and had at least a little positive caster to help steering feel. After the axle rebuild and an alignment reset everything was much improved - no more pull and improved steering feel. The owner plans to flat tow this truck so getting this right was extra important, we don't want sketchy steering behavior when it's behind his truck at highway speeds.
The other real problem we had was noticed almost immediately - gearing. The LJ came with 4.88 gears stock which is awesome for low speed and off road duty. I'm sure it also helped the 2LT accelerate better given it's fairly lackluster performance. Unfortunately, the problem arises when you want to run 70mph which these little trucks were never really intended to do. While the Cummins has the power to do it you end up in the higher end of the rev range and the revs/boost really start to climb. We were hoping we could get away with it but found that when the engine was turning 2800-3000 rpms at cruise speed it was just too much boost and heat rejection in the cooling pack. The radiator temps would climb to 220F during normal driving above 60mph and if you took it up a grade they were even more quick to jump into the red. We contemplated options with the owner but at the end of the day the he really wanted to make sure the truck was highway capable so we made the hard choice...
Out came the 4.88's and in went 4.11's. We went with 4.11 to make the front axle cheap/easy since we could just insert an 80-series front diff in place of the 4.88's. The rear was torn down and we got a set of minitruck 8" 4.11's to match the front. 3.73's would have been a better choice in terms of keeping cruise rpm's down, but given the difficulty/cost of sourcing a reverse cut 3.73 ring and pinion for the front we chose to go this route.
With the truck back on the road the heat management was much improved. We could cruise at 65mph without much concern though we still did experience some overheating while going up grades with the AC on during our hotter days. Our shop is at 8000' elevation which adds an additional difficulty because the air density is about 75% of sea level so keeping vehicles cool is always tougher up here. We decided to focus on the other systems of the truck and accumulate some more miles.
Overall the initial drives went well. The Cummins R2.8 is well suited to smaller rigs like these 2-door models, power and torque feel appropriate for the size/weight of the vehicle. There's a fair bit of turbo noise audible, using a cone filter isn't the best setup to quiet that down but fitting a larger canister style filter box would have been very challenging. The engine pulls really well though and mpg numbers in the mid 20's are icing on the cake.
The first snafu was encountered when we headed to the alignment shop. Up on the Hunter we found that there was -1deg caster on the left and 0deg on the right. That was troublesome because it's obviously not a great setup to have negative caster but the real concern was the difference from side to side. Out on the road the problem was evident in a slight pull despite perfect toe settings. There are no plates or correcting arms for the LJ suspension so we decided to order some offset bearings from @cruiseroutfit and chose 1.8deg and 3deg correctors. By installing the 3deg version on the left and the 1.8 deg on the right we were able to get the two sides to match almost exactly and had at least a little positive caster to help steering feel. After the axle rebuild and an alignment reset everything was much improved - no more pull and improved steering feel. The owner plans to flat tow this truck so getting this right was extra important, we don't want sketchy steering behavior when it's behind his truck at highway speeds.
The other real problem we had was noticed almost immediately - gearing. The LJ came with 4.88 gears stock which is awesome for low speed and off road duty. I'm sure it also helped the 2LT accelerate better given it's fairly lackluster performance. Unfortunately, the problem arises when you want to run 70mph which these little trucks were never really intended to do. While the Cummins has the power to do it you end up in the higher end of the rev range and the revs/boost really start to climb. We were hoping we could get away with it but found that when the engine was turning 2800-3000 rpms at cruise speed it was just too much boost and heat rejection in the cooling pack. The radiator temps would climb to 220F during normal driving above 60mph and if you took it up a grade they were even more quick to jump into the red. We contemplated options with the owner but at the end of the day the he really wanted to make sure the truck was highway capable so we made the hard choice...
Out came the 4.88's and in went 4.11's. We went with 4.11 to make the front axle cheap/easy since we could just insert an 80-series front diff in place of the 4.88's. The rear was torn down and we got a set of minitruck 8" 4.11's to match the front. 3.73's would have been a better choice in terms of keeping cruise rpm's down, but given the difficulty/cost of sourcing a reverse cut 3.73 ring and pinion for the front we chose to go this route.
With the truck back on the road the heat management was much improved. We could cruise at 65mph without much concern though we still did experience some overheating while going up grades with the AC on during our hotter days. Our shop is at 8000' elevation which adds an additional difficulty because the air density is about 75% of sea level so keeping vehicles cool is always tougher up here. We decided to focus on the other systems of the truck and accumulate some more miles.
