I just changed gears in my rear end from 3.31 to 3.73. If Im looking to maintain the closest ratio to what my 4r70w and gear setup has what can I expect from the zf5? Im seeing that there are two different ratio zf5,s that were made? Is this accurate? My old I6 with the mazda had first maxing at around 25, second at 55 ish.. Just curious what I can expect if anyone can shed some light... thanks

 

Diesels got what was called a close ratio gearset.
4.13 in first rather than the gas engine's 5.72.
They have the torque to pull it.
The bellhousing is integral and unique. Small block, big block and diesel have different bolt patterns.
Both have about the same overdrive. .76 & .77 IIRC
The diesel and big block gearboxes have an external slave cylinder.
Windsor pattern has an internal concentric slave.

Early gearboxes were xxx-42 (420 ft lbs) later ones were -47

 

Are you concerned about your cruising RPMs? The ZF5 and 4r70w overdrive ratios are pretty close so you shouldn't see much more then a 100 RPM jump at freeway speeds.

If your concerned with how the ZF5s shift points compare to the Mazda's, they will be drastically different. The only practical time to use first gear on the street with the ZF5 is when you have a load. You will be using it as a three speed with overdrive when unloaded, which means the RPMs will drop a lot more between gears.