I have a factory 65 F100 with the large opening fenders. It's got 3:55 or so gears but still doesn't like hwy speeds. My tires are factory height but with the fenders I'm sure I could go as large as 35" if I wanted but I'm thinking 33" at most. Just wondering what others are running. With the gears I don't want to go to high but it will be street driven most of the time with the occasional car trailer tow.

 

https://www.flickr.com/photos/597784...7650625862711/ hi
Hi 4x4alaska, that's a nice looking truck! I'm running 9.00x16 on mine,no issues with clearance but I'm sure it would ride better on radials, I like the tall skinny look.

 

Are you sure you have 3.55 gears? If yes, you should be running 70mph at 2600 RPM - not bad at all for highway.

 

Yea I was thinking about that as well. I need to add a tach and see what it's running at. It has some exhaust leaks but I sure hear a loud gear whine going down the road. Haven't taken it much over 45 yet.

 

That's got the Dana 24 transfer case in it I would assume. Make sure that thing is in 2WD High range.

There are four shifting positions: 4L-N-2H-4H and an undocumented and position between 4L and N which will give you 2wd low.

If you've got it in the undocumented 5th position then you will have a greatly reduced top speed in every gear.

You might also check that your front hubs are unlocked. If not then you are dragging the spinning front end around rather than it free-wheeling. Puts a good bit of drag on the system and can wear things out quicker. Of course, if you transition frequently from 2 to 4wd and back then I can see leaving the hubs locked.

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I dropped it into low range in the street out front just to be sure. I'll hook a tach up and see if I'm just over reacting to a loud exhaust.

 

It's got headers on it going into a single muffler and turning out in front of the passenger tire. It's just clamped together so i can drive it. It had the headers and a completely rusted out dual system when I dragged it home. But I still feel like that dana 24 was making a lot of gear noise. It's fluid was replaced and it's topped up too.

 

I'll let you be the judge of how bad it is, but defective transfer case bearings are a common source of drive-train vibrations. It is well worth the time and effort to have the transfer case rebuilt if you have a lot of noise coming from it internally.

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33's on my 63 f250 with wide opening fenders & stepside/flareside bed. Fit great no rubbing etc. I'd guess 35's might rub a bit.
4:56 gears and it doesn't like the highway prefers the slow lane, 45mph is about perfect.

 

My 1965 is not a 4 wheel drive. But. This is what was on it when I bought it.

 

33's with a 3" lift kit. No problem driving freeway speeds.

 

I have 33's with about 3" of lift as well. Just remember, bigger tires = lower fwy RPMs. (And lower MPG...and less accel/brakes, higher replacement cost, etc.)