My 86 4wd F350 is on it's 3rd 4speed. The truck is 460 powered and runs great. I use it to haul mulch and topsoil and the trans is just not up to the task. I have seen info on upgrading to a ZF5 but can't find any details. Thanks for any help!!

 

I wouldn't say the ZF is more stout than the T-18/19 you already have.

Many of us have done it.
Mostly for highway mileage.

All you need is a clutch and to have your flywheel drilled for the ZF style pressure plate.
The taller tunnel hump and you need to relocate the transmission crossmember because of the mount.

Try to find the '96 S47 variant as it is rated for an additional 50 ft lbs.

 

So that's all thats required? Just need to find a S47 from behind a 460 and the flywheel drilling? Does the ZF have a lower first/granny than the current trans?

 

I don't know WHAT is your current gearbox...

My 4x4 460 came with a 6.32:1 T19c.
The ZF is not lower than my old gearbox.

 

Sorry bout the dumb question, wasn't looking specifically for my truck but a general guide as to what was in them. I need to do some digging. First gear is not very low so when hauling or towing, it could be a little lower. I'm going to look into the current box and see what the ratios are. I was hoping the ZF might have a better low gear, something along the lines of what is in yours...thanks!!

 

I find it odd that your first gear doesn't meet your needs; I use my 1981 F350 4x4 with a 400 cid engine and a T-18 (don't remember the ratios) 4-spd to haul a 6x12 trailer full of firewood through the mountains of Colorado down to my house in Denver and it's entirely OK with it.

 

The single window T-18's all had the 6:32 gear, I believe.
Not having synchro's would be a non-starter for me...
I think the earlier New Process gearboxes did too.

Have you ever considered going to a bigger truck?
There's really no reason you should be going through gearboxes given the gvw of a 350.
If you're hauling THAT much weight you should be in a 500/600 with a 370/429 and a Clarke gearbox.

 

Can you take a photo of your current trans?
None of the h/duty 4-speeds should be failing like this or have the fast 1st gear issue, except maybe a close-ratio T19......but that would only be hard on the clutch.

Could someone have installed a 4-speed OD transmission SMOD, SROD etc? That would explain the weakness & the higher 1st gear.