I changed the fan clutch on my 96 4.0 because it was locked up all the time (and under warranty) previous owner had replaced and had receipt! It did quiet it and never gets hot, but...
Being the OCD parts man, I noticed today that the number that was replaced was a NAPA 271656, listed for 99-02 D1 4.0 which is the same physically other than .450" larger OD and listed as "severe duty". The correct number, by my catalogs, NAPA 281673 is listed for 96-99 D1 4.0 and the only number shown comes up as "standard duty".
Is this a known "upgrade", would you change it to the right one? Russ

 

What's larger, the overall front housing, or the shaft diameter?

Personally I would go with the larger one. L/R made a lot of running changes to try to continually make these vehicles better (which most would say they succeeded at). The real reason they most likely superseeded the part was it was too expensive for the mfgr to make/stock/sell a low selling unit for D1's which are getting pretty old now and a lot fewer on the road .....when the DII unit fits fine.

I personally would stick with the new one.

 

The overall housing is larger - which could equate to larger clutch surface, fluid resevoir, i.e. "severe duty" - it wasn't noticeable when I replaced it. I guess more than anything, I was concerned that it wasn't the "right" number listed per NAPA cataloging. Yes, I admit, I am a picky SOB -!
Thanks for your input on this! Russ