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Caught at a crossroads.

I've owned a 1999 Classic Condo long nose for the past 10 years known as “Josey Whales" and it was love at first sight, and the best $18,000 I've ever invested . I bought the truck from the original owner who is a retired bull hauler. She has a true 500hp BK family 60 series 12.7 Liter non-EGR pushed by a 13A double over 1650 torque Eaton with a 9 month old EZ 1750 torque clutch with Rockwell 3:58 double lockers on 24.5 LPs 16 ply. I'm usually 78-84,000Lbs running from St. Joseph, MO to the New Jersey across the PA turnpike. I like to run my truck 65-75mph in the 12th hole which has me taccing between 16-1825 rpms and I'm fine with that because I was raised to never let a pre-emissions Detroit lug low under a load. I bought the truck less than 200,000 miles after the bull hauler out of framed it and she now has 712,000 miles and 1.9 million on the chassis. The bull hauler ordered the truck directly from Freightliner and never spent a day on a show room floor. When it was out of framed he added a Teflon coated kit on the rods and mains. In the last year I've gladly added a non-waist gate Borge-Warrner turbo, Duralite CAC, air intake gasket, mercury filled torque damper and balancer, stainless coolant tubes, 180° thermostats, 6 inch straights (with no resinater or restrictions), port and polished exhaust manifold, over head adjustment, and power box all from Pittsburgh Power. Prior to my purchase, the bull hauler also had the ECM flashed to bump the tac up to 2,600 rpms, 78% injection and wide open speed while resetting the torque to both ends of the spectrum. I plan on replacing the transmission with a true 2050 torque Eaton 13 speed double over drive and 2450 LB Lype clutch from Pittsburgh Power as well. I'm adding 1 gallon of Mobile Delvac mineral oil every 5,000 miles while changing my oil and filters and analysis every 20-25,000 miles religiously and fluctuating between 5.4-6.3 MPG this past winter. I'm more concerned with the durability of my truck and trailer than fuel mileage (wow is me) in my current operation. But last week I had to replace my in-put shaft yoke and u-joint, all heavy duty parts, on the front drive axle and a chunk of metal came out of the box when I had box flushed. Hence the crossroads. Would I be better off sticking with Rockwell 3:58s or converting to 3:42s? Reasoning being that at those same speeds I'd drop 300-600 rpms and gain a wider range of selection while pulling. Is my thinking correct or flawed? Any suggestions or experienced opinions would be greatly appreciated. FYI before the upgrades at Pittsburgh Power I Dyno at 389hp after, on setting 3 of potentially 9 settings, she put 584 ponies to the ground with a 3.5 inch blow by. By the way, I'm still waiting to install a John Deere true Pre emissions non-EGR 14 Liter 575 hp 60 series Detroit putting approximately 758 horses to the ground with the same Teflon coated kit on it as the 12.7 has which I bought from the same bull hauler 2 years after he sold me the truck for $8,000. That 12.7 just keeps on ticking as long as I keep oil and antifreeze in her. You've got to love that Pre emissions Motown Muscle, they tend to keep you out of the poor house.

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The 3:58 and the 3:42 gears are to close. There will not be a 300 rpm difference. I don't even think there would be a 100 rpm difference in the same gear. The 3:42 will be geared slightly higher than the 3:58 meaning it will run at a slightly lower rpm than the 3:58 but just slightly, my guess is less than 100rpm maybe more like 50-75rpm. If you have to change the rears the 3:42 might be a better option because of your speed, but will only decrease your rpms slightly. I'm with you on the older detroits, got to love them. I'd like to hear more on that 14L series 60 detroit. Keep us posted.

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What do you think about Rockwell 3:08s instead for this same setup? My cousin, who's also a long nose class 8 enthusiast, seems to think that an Eaton 15 speed with a 2 speed auxiliary may be the answer to my problems. Keep in mind that he's a “Yellow Belly" fan.


I think the 3:08 would be to big of a jump, I don't think they will pull nearly as well, just my opinion. Your getting good fuel mileage for the speed your running at, especially for 12th gear. I'd probably just put the 3:42 rears in and keep doing what you do. I don't know anything about the 15 speed with the 2 speed auxiliary, sorry. I'm the same Rick that talked to you before, The system logged me in as a new member. Not sure what happened, I'll have to ask Aaron about it.


I appreciate the response, and I think I'm leaning towards the 3:58s again. I'm just not too confident about getting into the high 2s when it comes to gearing. As far as that 60 series Detroit 14 Liter non-EGR is concerned, those guys in Oregon who helped Kevin Rutherford put the Signature Truck together have a warehouse full of those blocks. Ask Kevin or Bruce about them. I'll keep you posted.


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Not sure if you ever did anything on this, but here is a great resource for comparing multiple setups:

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