I am searching for a rig to tow my GF horses/my Jeep and do double duty around the house as a pick up. I located an 1997 FL60 with the 5.9 cummins and a nice, paint matched, flatbed on it. It is at a Pete dealer and I am prob. going to request a dyno test today. I know that the dyno should show 80% of the rated power. However, I am a bit confused as to whether this is the rated HP of the engine or rated HP at the flywheel? I searched the dyno posts but couldn't find the answer to this exactly. If this engine is rated at 210 the dyno should show at least 168hp? I know that is not a real powerful engine by any means but our loads will not be that heavy so I think it will be sufficient. Also, the truck has 193,XXX miles on it. Is there anything specifically I should look for on the truck problem wise? I think the 5.9 is rated for a rebuild around 350k-400k? It was driven by an owner/operator prior to being traded in.

One other concern I have is the gear ratio. They claim it to be 4.75. That would mean a top speed of around 55 according to the governed speed posted on the cummins site if I am reading it right. anyone have any input on this?



Thanks for your help

it'll be a screamer, My fl70 with 3.90 and 22.5 rubber could use more gear (.78 OD). I would hitch it to a typical load and go run 100 miles and see what you think then.

Those miles on the cummins are not an issue IMHO.

If you are doing local stuff fine, but if you want to do 75+ on long hiway trips it might not be tyhe best option.

thanks for the input. I don't really plan on hauling down the freeway at 75+. I will most likely just tow somewhat locally at a speed more like 60-65mph. Any idea what I would be running rpm wise at that speed with those gears? I have been trying to analyze the info on the cummins site but its always nice to hear some real world experience.

It would be nice not to have to "scream" down the road for both comfort and economy reasons.

Top speed would also be dependent on the tyre size and transmission OD ratio. If it has 19.5 tires and a manual transmission with 0.75-0.80 OD ratio I would be planning on swapping/regearing the third or jumping up to 22.5 tyres/wheels. Swapping to 22.5's on a lo-pro chassis can be problematic depending upon the rear deck wheel openings and suspension ride heights as well.

If it has the Allison MD 3060 auto transmission they have a .75(fifth) and .65(sixth) OD ratios so with a 4.75 gears and a 245/70/19.5 tyre you are looking at 2000RPM for a 60MPH cruise speed and 75MPH when the engine is defueling at 2500RPM.

it has the allison at-540 auto. Any thoughts on this trans?

it has 19.5 rim/tire as well.

thanks for the info

The AT 540 would be a 4 spd auto with no OD so 40MPH@2000RPM and 49MPH@2500RPM which leads me to believe that you have been told the wrong rear end ratio, tranny model or tyre size.

I talked to the rep today and he said it is the at-545 and not the 540.

I swear the salespeople at these places know so much less than the enthusiasts/truck drivers who patronize their dealerships. You would figure if it was their livelihood to sell these trucks they would take more of an interest in the equipment.

thanks jasonmt for the info.

AT 545 is still a 4 spd automatic with a 1:1 fourth gear with a maximum GVW and/or maximum GCW of only 30,000#'s as well. Same comment as my second post, that you have been told the wrong rear end ratio, tranny model or tyre size. Is there a chance that it has a two speed rear end?

If for some reason the truck is setup with a 4.75 single gear rear, AT 545 and 19.5 tyres I would not touch it as I would imagine that it is a one of a kind combination for good reason.