going to hunt for new ring and pinion gears

[dbenamati]

I talked to a mechanic today and told him of how slow my truck drives and high rpms. It's a 67 3/4 ton, 4 spd. that tops out at 55 mpg. I don't know what gears I have but he suggested that if I search the bone yards for 3.73 ring and pinion, he could change it out and I could have up to 70 mpg's with lower RPM's. Anyone done this and if so, what gears could I use? I just want to move along with traffic, not break the sound barrier

Thanks, Dave

[Mike C]

You need to find out whether you have the Dana or Corporate (referred to as the Eaton) The Corporate could not be had with less than 4.10 gears, but the Dana down to 3.54. Most likely your truck has 4.57, so 4.10 would be an improvement. You can get 3.90 aftermarket for the Eaton, bu they are $350.

['72 Shorty]

If you're getting 55MPG, I wouldn't change a thing

3.73s should ba about right, 4.10s seem a little low for freeway driving.

[Big69C20 Toy]

by the thought that you said 55mpg i think you meant 55mph and in that case you're probably running the ho72 (eaton/corporate) as stated 4.57 and 4.10 were available, i think there were some shorter (numerically higher) gears available. Randy's Ring and Pinion and some other shops carry down to a 3.90 but as stated it's about 350.... for your best bet either grab yourself a new axle setup or possibly dig around for one of those eatons with 4.10 and the locker in it. If you find 2 lockers lemme know as i could use one good luck dude.

[mikep]

+It all depends on the tire size. If its a 3/4 ton your probably running tires that make that 4.56 ( or whatever ) equivalent to a 3.30 in passenger car sizing . You should be doing a lot better than 55 mph even if you had the lowest gears available. At 4000 rpm in final drive gear even with 4.56 gears and 31 inch tires you shoud be going 80 mph . Are you sure your engine isnt just really weak . Check its condition before you go doing expensive rear end work to fix a condition of a problem without adressing the problem first.

[boilrman]

I have an Eaton rearend with 31" tires, 4.56 gears and I am running 55 mph / 3000 rpms on the highway. My inline 6 only has about 8,000 mi on it and the rpms have been this high since I rebuilt and installed it.

I too am planning on getting some higher gears such as 3.73 for the rear and changing them out.

I will keep you in mind dbenamati and as soon as I get them and I willl let you know who from. I think I saw some in the Summitt catalog. I need to actually call and verify they will work as soon as I have the $$ to get them. Hopefully within about 2 weeks I will have this done.

[Jackal2k9]

i have a th350 no o/d with 31.5 inch michelins and 3.73 gears. the motor is turning 2700 rpms at 70 and 3000 at 80. It's hell. at 55mph its fine, damn good actually, but at 70 its roaring(some of this can be contributed to exhaust system). I would trade out for a 12 bolt 3.55 cop rear end or SOMETHING taller any day. Texas HWY speed limit is 70mph so i need it to be able to cruise along at 70 and 2400rpms or so.