12-14-2007, 02:12:10 AM
Now I know its not a camaro question but its been bugging me for awhile and I have some solutions planned for it but want some opinions. I have a 1970 GMC 2500 custom. It has the original rear with the factory gears in it. When I take her out on the freeway she just whines out at around 60 mph. I love the gears it has now, great for towing and hauling but the freeway issue is a pain. I was thinking of going to a 700r4 but not sure if that extra gear would do the trick. I also thought about going to a higher gear ration, it has 2:somethings at the moment. When I got it I thought that the last owner put some ungodly gears in it like 4:88's or something causing it to whine out at 60, because its got great punch for in town driving but I checked it out and its the factory rear in it. I guess my question is: any one deal with this problem before with moderate success?
12-14-2007, 10:32:10 AM
I’m surprised that a 70 truck would have a rear with that tall of a gear ratio. Something that (numerically) low would not be a good towing or hauling ratio. Are you sure you have calculated the ratio properly? Have you had the back cover off? If so, you can count the teeth on the ring and pinion gears to calculate the actual ratio. If not, raise the rear off the ground and count the number of drive shaft revolutions you get for every revolution of the rear wheel. If your truck has a posi, 1 rev of the wheel will work, otherwise you need to use 2 revolutions of the wheel.
I have a 70 C/10 that came with a 3.73 and it would easily go to about 80 mph without problem (factory 6 cyl. And 3 speed). I installed a 383 and 700R4 and things work great. I think you need to determine exactly what rear ratio you have before you make any decisions about swapping the trans. Good luck with your truck as well.
12-14-2007, 12:39:28 PM
A 70 3/4 ton will most likely be a 4.10 rear end. Back in 70, pickups weren't yuppie toys. They were designed to do hard work. Most 70 1/2 ton pickups have 3.73 rear gears, and the 3/4 tons usually got 4.10. Other optional gears could be ordered, but I've never seen any factory 3/4 ton axle with gears higher than 3.73. If you want something faster than that, you need to get aftermarket gears and install them yourself. I know you can buy at least 3.42 aftermarket gears for GM 3/4 ton axles, but you probably won't find gears much faster than that available.
If you need more highway speed, an overdrive tranny would be the easiest way to get there.
12-14-2007, 01:07:57 PM
The 700r4 Trans Has A Lower First Gear,and The Overdrive.so If You Do Have A 2.73 Ratio It Is Going To Help On Both Ends.
12-17-2007, 06:02:46 AM
The truck has been a work truck all its life and still is even though I took pretty good car of her lately... I work out of town at least 2-3 days a week and wanted to be able to cruise the highway a little more comfortably lol I think I'll just go with an overdrive for now see if it makes a difference. and because i can heres some pics of my truck lol that and i know how much you guys like pictures
12-17-2007, 06:16:37 AM
If you tow stuff with your truck you may be better off with a Gear Vendors Over/Underdrive unit. It lets you split gears turning your three speed automatic into a six speed with overdrive.