I have a low first gear T-18 in my 66 and it certainly could use another gear. Is there any popular trans swap I could do and still be somewhat stout?

 

Are you sure it's not an NP435 in that F350? It is the F350 your talking about, correct? It should be the 5N4AU case marking. I'm not sure if you've had your warranty plate decoded or not. If so, I neglected to record it so if you want to post a pic of it we can see which trans it was originally and I'll add it to my list.

If it is the F350 you have an FE engine in that, right?

If it were a 1965/66 F100/250 2WD the gasoline NV4500 is a good choice which is plenty stout, 5th gear overdrive, short throw. You just need the adapter from Advanced Adapters

https://www.advanceadapters.com/prod...it/#top-review

I believe with the F350 you'll have the front and rear engine mounting - In this case the bellhousing is part of the rear engine mount. It's a deeper bellhousing than the 2WD bellhousing and the input shaft stickout length is longer than your average transmission. As a result of that you can't swap in the NV4500 like the 2WD trucks can with the shorter bellhousing depth.

For example, the input bearing retainer on a F100/250 2WD truck is listed as 4.57" and for the F350 it is 5.39". The difference in the length is just indicative of the longer input shaft and retainer. There is no NV4500 that has the correct amount of stickout.

One possible solution to still use an NV4500 would be to convert your truck to a side-to-side mount, eliminating the front/rear mounting. Then go to the shallower bellhousing from the 2WD truck and fab your own transmission support. You'd need the adapter above - read the review section. You'd need a new clutch disc I believe, depending on what you have now. Probably need to adjust the clutch and possibly a different adjustment rod.

One option anyway.

 

Depending on what you do with your truck, you could also try re-gearing and see if that gives you enough of a difference when you're topped out. My 66 has the T-18 and 4.56 gears in the back so at some point I'll probably re-gear to help with highway driving.

 

if you're not doing a lot of heavy towing, a Tremec TKO 600 is a cheaper option than the NV4500. The NV4500 is a real truck trans though so it's the one to get if you plan to tow heavy loads.

 

The NV4500 doesn't bolt up with a custom bell housing. There is now a new option from Tremec and it's the TR4050 which will bolt up and decently priced.

 

That looks pretty sweet. Now they just need to mill an alternate input shaft with - instead of the 6 1/2" length - a 7 1/8" length and then by just swapping that out we could probably use that one on the 1965 F100/250 4WD, 1966 F250 4WD and 1965/66 F350 with the stock bellhousing, I suspect.

 

Do you know what they do for a throwout bearing retainer?

 

I put a 4:1 low all-synchro T-19 in my current truck. With the 3.25 rear, first gear is usable, and a bonus is that the ratio spread is a little better than with the double-low four speeds.
I turned the trans crossmember end-for-end and it bolted in. It was replacing a three speed, so I had to scrounge a driveshaft, but your driveshaft just might work.
The T-19 is found behind the earlier diesels and some 460 trucks. Identification can be difficult; there are (I think three) possible low-gear ratios.
Eric

 

F350 with the 352 engine and Dana 70 had three possible rear axles ratios stock. 4.88 (standard), 4.10 and 5.13 optional. 4.10 and down was the carrier break so if it is a 4.10 you can go lower ratio without changing the carrier.

 

What about a Ranger torque splitter unit?

 

Gear Vendor. That's what I did.
https://www.ford-trucks.com/forums/1...=+Gear+Vendor+

 

I couldn't find a price anywhere, but it does appear to just bolt up. I bet it's right at $3K, but that's about the same as a rebuilt NV4500 without a core and an adapter from Advanced Adapters.

If anyone is considering an NV4500, you can use the tailshaft housing from the earlier NP4500 that has a mechanical speedometer drive. Of course you will need to install a speedo drive gear on the back of the output shaft, but they just slide on. The NP4500 uses a different transmission mount, so make sure you get the right one.

 

thanks for some of the options folks. My truck was decoded. However, I can not remember the info. Here is the factory plates.

 

Looks like the Transmission is a code A which is NP435 with the 5N4AU case marking like I suspected.

 

Yes, NP 435. An excellent truck transmission that withstands hard usage, abuse, and more torque than the designers envisaged. It's just the ratios that are not what we want. I mentioned the T-19. There exists as well the NP 445, also known as the close ratio NP435. It is found in Chrysler trucks and is externally almost identical to the 435 but for the fine-spline input. It has a usable low gear. I had one in a '70 Fargo 200 that left my driveway for $400 a few years ago. They are rare.
Eric