I am planing on putting a np435 in my 71 f250 when the c6 gives up (it has 278,000 on it). so is this a good ideal. what rear gear ratio would match this for good highway driving, mine is 3.73. my truck will need to pull a 6000 pound trailer from time to time

 

the final ratio on both transmissin is the same

 

final on the 435 is 1:1. first is 6.71:1 I have one in my bronco with a 300 L6 with 355 rear end. with that it cruises on the highway pretty good and pulls a car like its nothing. If you want good highway driving maybe a 2.73 rear end I would throw it in with the gears you have, if you dont like it you can swap out later. since you probably have a 9" shouldnt be any trouble.

 

I know what the ratios are in the np435, shift do you know what rpm yours run on the highway. I love 4 speeds and my last was in a 85 fiero, but it did not run good on the highway with 4.10 rear gears. thats why I ask

 

As rbaker posted the final ratio on both the C6 and NP435 is the same. What ever your cruise rpm is with the C6 it will be the same with the 4 speed.

 

i think i was in the 2500-2800range, but as mentioned above that wont change for you, just 1st gear will really be the difference. The torque/hp curves will be totally different with your engine but i always liked the 4speed on the highway because i could be going 70, get into the pedal and the truck would take off. It put the rpm right in the sweet spot for me at that speed

 

1953/85 F250 = Dana 60

Ford never offered anything higher than a 3.23-1 ratio (1980/85 only), and those gears are almost impossible to find.

Most common are: 3.73's or 4.10's / 4.56's were also available, as were > > 3.54's (1968/85) which are almost as hard to find as 3.23's.

Dana 60: 2.75-1 / 3.00-1 / 3.23-1 / 3.54-1 gears are available in the aftermarket sector, but they are not cheap.

 

If you plan on swapping in a 4-speed, you might want to consider a T19 instead. I put one in my '68 and love it.

The T19 came in a close-ratio and a wide-ratio version, I used a close-ratio tranny from an '86 F250 diesel. It has no granny low, and all four forward gears are synchronized. First gear ratio is 4.02:1.

When I used the '68 for towing with the NP435, I really could feel the huge gap between 3rd and 4th, especially when pulling a hill. I'd start to run out of steam in 4th and have to drop to 3rd, then the engine would be screaming. Go back to 4th and it's lugging. With the T19, the spacing between the gears is much more even. It shifts much more smoothly than the NP435 as well. It's nice to drive with it being a true 4-speed with all four gears useable. So far, I've never really needed the granny low and don't miss it a bit.

It's a straight bolt-in swap for the NP435, the only difference being that the driveline yoke is larger so a new u-joint it required which has two different sizes so that it will fit your existing driveshaft on one side and the tranny on the other.

I'm running the stock 3.73 rear end, which is fine for my underpowered 360 but when I get the Cummins in there I'll go to a 3.54, which I already have. Got two of 'em, in fact...

 

I cant Argue with TigerDan's logic on the T19,ive owned a Scout that had the close ratio version,and it was a smooth tranny to drive. In day to day driving,it is better geared than the Np435

 

Or convert it to the Nv4500 5spd o/drive a little more work but maybe something you may like.. my 2 cents..
orich

 

the t19 I might go if I can find one, the Nv4500 cost a little to much for me and are not that easy to find in a junk yard

 

I did this very swap in my '69. (Haven't updated my sig yet.) Only I didn't wait for the C6 to go, I just swapped in the NP.
As mentioned above the final ratio is the same in both transmissions so it doesn't affect highway driving at all. And 3.73s do fine on the highway. In fact mine came with 4.10s and even when I had those cruising at 70+- wasn't a problem.

 

And just my 2 cents here, not to offend anyone so just take it or leave it. But I hate the T19. My '85 has it and it's redundant to have to shift that extra gear to get the same 1 to 1 end result. If it was an overdrive it would make sense, but not as it is.
Again, just my 2 cents.

 

I can understand that to a certain extent, but I like shifting gears so I do indeed like the extra gear...and if you do any towing it really makes a difference with a relatively underpowered truck like mine to have that extra gear.

As for the NV4500 swap, I'd be into that as well but for the above-stated reasons it really wasn't under too much consideration. NV4500: $1k-1500 for a decent used one (unless you get lucky) if you can even find one, and the T19 was free. I also scored a GV O/D unit so I threw that in there as well.

 

If you don't have the the GV adaptor that fits the to getother your looking at $600 the last time I talked to that Co. that's out of So Cal. Plus if the unit has one on it now for a different trans they want it! And will not give to you any credit or discount on the correct one..Plus, I don't like to deal with a Co. like they our..The more I looked in the putting in a GV unit the more, I got turned off. The delayed shift time for one. I'm sure you'll be puting out around $1000 to install it. Cutting the driveline in most place is $200bucks and the list goes on. My 2cents
orich