I was looking into the factory manual transmission options for my 1990 F-250, and I was hoping to get your opinion on which one is the best. I've found that there were three options at the time: the Borg Warner T-18 4-speed, Mazda's M5OD 5-speed, and the ZF S5-42 5-speed. As I understand it, the T-18 is heavy duty and well known for durability, and I would assume the M5OD is lighter duty because it is built by Mazda, but I've been unable to find much on the ZF S5-42, other than that it's a 5 speed. I was wondering:

1. Which is the overall best transmission?
2. Which is best suited for the 7.3 444 IDI Diesel?
3. Which is best suited for the 7.5 460 or 5.8 351 Windsor?

 

The T18 was only an option up to 1987. The NP435 was also available and had a lower first gear. If you ask me, the toughest transmission in the NP435. The best overall is the ZF because you have the option of overdrive. The ZF would be best suited in the 460 so you can use overdrive and break 10MPG. The IDI could really use whatever, but different situations warrant different things. I'd put a NP behind it to utilize the low first gear for towing and pulling. But if you do a whole lot of highway, then the ZF is better. The windsor is a similar beast. I have a NP behind mine for pulling and towing and it suits my needs very well. And with the big tires on my truck, its really easy to get going and highway RPMs are in the powerband. The M5OD is nice for a DD in a half ton that isn't going to pull trailers because it's quiet.

 

T-18s and NP435s are beasts. If you're looking for strong you can't beat them. If you're looking for quiet and easy to drive you can definitely beat them. I've had 'em and I've liked them. If I bought a truck and it already had one I'd probably keep it. But unless I expected to be breaking transmissions I wouldn't put one in a truck.

Also there are wise ratio T-18s (from Ford trucks) and close ratio T-18s (from Jeeps). Not sure what other vehicles might have used which, but stay away from the Jeep close ratio. If you're putting up with that heavy of a tranny you want deeper than 4:1 first gear.

I haven't had the Mazda or ZF-5 speed yet. From what I hear the Mazda is pretty much at it's limit in a half ton. Based on that I don't think I'd swap one into a half ton (or bigger) truck.

The granny gear of a T-18 / NP435 is attractive, but it's non-synchro so it's not the easiest to use. And you can always go with lower axle gears with a 5 speed. Overdrive will make them OK on the highway and you'll get the crawl ratio in first.

Keep in mind too that the 302/351 takes one bell housing, the 460 another, and the 7.3 diesel another. Since the ZF (and Mazda?) has a built in bell housing you need to get a trans that came off the motor you're using. the T-18 and NP435 need a separate bell housing, so about any tranny will work, but you'll need the right bell housing.

 

The Mazda M5OD is a good driving around tranny. Not made for heavy hauling. They break under big loads or behind built up engines...

I have both M5 and ZF. If ever my M5 was to fail (witch I don't think it will) as I never tow with it) and I don't think no one has before me either, truck never had a hitch on it, neither a bumper ball. It's a great tranny just to drive around with. One thing I can say I royally hate about it, is the really tall reverse gear!



ZF5, well that's a modern T18 with OD. Not as bullet proof as the NP435, but great non the less.


The ZF however is a VERY complicated transmission to get into if it needs work, and can be pricey.


My ZF5 has 377k miles behind my '90 F250 7.3 Diesel. Never been touched, heck it's still on the original clutch. Original owner.