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Ive got a 77 F 150 4x4 with a 400 and 4 speed, the problem I;m having is the rpm;s going down the road at 60 mph are screaming(I don't have a tach.). There is no tag on the rear end to check gear ratio so I spun the driveshaft and counted tire rotations, the gearing seems to be 411. My question is what can I do to get the rpms down, is there a 5 speed or overdrive that would bolt up or am I going to need to change the diff. gears. I;m going with 35 inch tires and the truck is just a toy not an every day driver..Thanks...
If you have that kind of gearing not much you can do about it other than swap out the gears. There are various over drive setups but I doubt you can find one for that truck. There might be a transmission that's a direct swap that has an over drive but I'm not sure. The problem is also you can't just swap the rear gears but you have to do the front also.
Yea, I know I have to do front and rear, I was hoping someone here might have an easier fix. Is it hard to do the front diff. or about the same as rear??
Do you have the 35s in yet or what size currently? Bigger tires will lower the rpm a little. My jep is running 4.88 on 33s, rpms at 65 mph AR about 2800. It's a toy also so I haven't bothered to change gears or tires. Gearing will take some time and special tools. That's why install prices are so high, you don't just swap out the ring and pinion in one shot.
No, don't have the 35s on, tires on it now measure 28 inchs tall, I know the taller tires will make a difference, I just don't think it will make the difference I'm looking for.
I know for classic cars they make 4 speeds where 4th gear is an overdrive and better yet 5 speeds where 5th gear is an over drive. Most of these are meant for cars but maybe they have one that would bolt up to your truck?
No, don't have the 35s on, tires on it now measure 28 inchs tall, I know the taller tires will make a difference, I just don't think it will make the difference I'm looking for.
going from 28’s to 35’s will make quite a bit of difference. Assuming you have 4.11 now the 35’s will make it feel like you have 3.31. I’d do the tires and then see if it needs anything after that.
28" to 35" will make a noticeable difference. I don't feal like doing the work for you, so figure out what tranny you have, plug the info in currently then compare to 35s. Math never lies http://www.grimmjeeper.com/gears.html
edit:I lied and got curiouse. Np435 close ratio, no tcase since I read they don't have low range, 4.11 gears. 28\" 35\"
Last edited by Brokemillwright; 10-23-2018 at 10:27 PM.
10-22-2018, 05:30 PM
New guy question on a 77 F 150
