It wouldn't be bad on the highway as long as you don't mind 4k rpm's to do 70. This is of course a rough estimate, but I do have 4.11's in my 68 cougar and occassionally drive it on the highway (mainly to the track), and I can't stand to spin it passed 3500 for a long time. So, I putt along in the slow lane doin 60 hopping not to get ran over.
I have 4.11's in the 66 fastback with the original 4-speed manual. It is KILLER on the highway. Not so bad for 10 minute highway passes. But get up around 30 and it will wear you out keeping it at 70(approx 4k)
If I were you, I would to a T-5 conversion. The extra gear (5th) would be prime for that highway driving. This is in my current plans. Basically if I've done my research correctly. you need a T-5 (not 94-95), T-5 bellhousing(don't have to, but you will need to make a modification to ur stock bellhousing), driveshaft slip yoke, and a crossmember to support the transmission(you can make one if ur creative) Hope this helps
You don't get into what you have or what rear is being advertised.
More info is good.
About 4.11s:
They are hard on the highway for anything but short trips. If 'occasional' means getting on the 'loop' around your town to the other side of town, then okay. If it means 6 hrs to visit grandma occaisionally, then no.
4.11s must also be used with an engine that can rpm fast and high, compared to stock of course. I have had great success with this gear behind a mild engine with a 218* cam and no converter. The big thing that helped was a single plane intake, a dual plane cannot wrap up fast enough with a small cam.
If you put these gears behind a stock or near stock engine, you will not rpm fast and you will not get into rpms enough to use each gear in the tranny long enough... the car will drive like a dump truck, shifting all the time and going nowhere fast.
Some things to consider.
If you want to put up more info on your car and the item for sale, I am sure folks will muster alot more comments/opinions.
Dave
It has everything to do with your particular needs and what tranny you're running. If you have an AOD or 5 spd, I'd definitely go for it. If you plan on doing alot of highway driving, I might buy it, but change to 3.55 gears. If its not the correct rearend for your car, forget it, as rearend mods for fitment are costly.
If you run over 2800-3000 rpms on the highway for more than about an hour, you'll go insane.
Cool, well judging from what's been said here I think I'll wait on the thing until I can do it right.
For the record the car is a '66 coupe with stock auto and a falcon 8" posi-rear. That was dropped in years ago due to the breakage of the original and the falcon rear was cheap. I wanted to go back and put the right hardware back on her. Sounds like I'll do the transmission, rear, and probably some engine mods all at the same time, now. Probably the best way...