Hi,
I have an 87 F250 4-speed, 4x4 with a 420 diesel engine. I love my truck but hate only being able to do 55 on the freeway. I use the truck as my daily driver and have to travel 30mins to school via the expressway. I have been trying to figure out how to increase the top speed and am looking at replacing the transmission. I enjoy the creeper gear, by hardly ever use it. I thought about going after a first gen. powerstroke zf5, but was told they are crap trans. I talked to my uncle and he said to try finding a 6-speed chevy trans with wide range gears. Would this work? Also is there a way to make a transmission that has a creeper first gear and wide range gears the rest of the way? Any info is helpful.

 

You can get a ZF for the IDI, not impossible to find.

Do you have some super low gearing? Even when I had my 4 speed I cruised @ 70 with ease.

 

The zf 5-speeds have a low 1st, especially when you don't need to rev the engine to use it... Plus, you've got the 4x4, so if you shift to 4x4 low(without the hubs locked), you essentially get a /really/ low 1st gear -- only useful for pulling something around the farm or something like that.

I'm not sure what's wrong with the 1st gen PSD zf's; I thought they were the same as the IDI ZF's. The ZFs do have a weakpoint in the reverse synchros(and actually, all the synchros are more prone to failure than the rest of the trans), but it's not usually a /fatal/ issue; you just have to learn how to wiggle it into reverse if you have a trans that is like that(Or replace the bad parts, but that's more hassle).

 

I thought the PSD trannies were rated at just a smidgen more torque?

 

Here is some info on the ZF6 swap.
ZF6 same pattern as ZF5

Also I thought the later ZF5 Trans was rated the same. Didn't matter if it was gas or diesel.

Here is some ZF5 ratings.....http://www.dieselhub.com/trans/ZF-5-speed.html

 

Sounds like he was told to use the nv5600, and that sounds like way more work than its worth.

The idis came with the zf5-s42 close ratio, the first gen psd has the zf5-s47 close or medium ratio. The s42 is rated at 420 lb/ft the s47 is rated at 470 lb/ft. The s47 also is supposed to have better synchros as theyre a known issue with the s42, but in my own personal experience more s47s have synchro issues than their slightly less durable brother.
The close ratio transmissions dont have a very low first, 5ish:1, your 4spd is 7ish:1. you can get a zf from a 460 and re-drill the bellhousing and have a wide ratio that iirc is close to 7:1 but not quite. IMHO the close ratio is pretty ghey, too low to use normally, not low enough when you really need it.

 

I feel your pain, I just did a swap like this but from c6 to a 460 ZF, I was at 3000rpm doing 70 after the swap I'm doing about 2200rpm at 70 and it feels like it pulls way better, this is with 3.55 gears in the rear.

The ZF tans isnt a bad trans but they can have issues with the trans mount ears breaking off and the reinforcement webbing around the 4x4 shifter mount point cracking and leading to leaks and reverse can be troublesome but other then that they work great.

Just FYI

ZF S5-42 Diesel
1st 4.14
2nd 2.37
3rd 1.42
4th 1.0
5th 0.77
reverse 3.79

ZF S5-42 Wide ratio
1st 5.72
2nd 2.94
3rd 1.61
4th 1.0
5th 0.76
reverse 5.24

ZF S5-47 Diesel
1st 5.08
2nd 2.61
3rd 1.53
4th 1.0
5th 0.77
reverse 4.66