The Stovebolt Site Forums The Shop Area Engine Shop higher ratio for old 1 1/2 ton?

anyone know where i can find taller ratio gears for my 51 1 1/2 ton? has a 2 speed rear with vacuun shift. went to a local parts joint that "specializes" in bigger truck diff's and got a blank stare--then the little rocket scientist counter dweeb says--" man, i wuddent even born in 51". i asked him how that was relevent---another blank stare, so how about it--got any ideas?

Kool, what size tires are you running? I am using 8.25 x 20's which are 37.25" tall. If you have the 7.50 x 20's, you could upgrade to the taller tires to kill off some rpm's. Also, if you go with a SBC or BBC, they don't care about rpm's too much. When I drove my dad's '57 3/4 ton, it had 4.57 gears and 33" tires. The 283 was happy at 65-70 mph, which was probably close to 3000 rpm. It got 15 miles to the gallon too....... . I like my Jimmy six, though. It's been hard to kill, plus I have a relative who will give me a running 270 with less than 5k miles, so I'm not too worried about my 248.

I have a 50 1 1/2 ton and have the same problem. I calculated 3400 rpm at 65 mph in high range which is too much. I am looking for a newer model axle. It would be electric shift which would make parts easier to find.

Ditto on what gmc248 said.
Get the tallest tires ya can, 8.25X20 or 9.00X20.
The 2 speed rear axel was NOT just for low speed hauling power!
It was super for using as an "intermediate" gear between 4th and 3rd downshifting on the big trucks. Works great to keep up rpms on uphill hauls.

When the big ones were going up a hill you could switch from 4th gear High to 4th gear Lo and it would maintain the optimum rpms.
4th gear, with Lo on the 2 speed differential, was NOT as low as the 3rd gear dif. in high!

ex: 4th Hi= 6.13:1 rear axel ratio
4th Low= 8.10 "..."
3rd Hi= 10:48 "..."

So going 4th Low is better at high speed downshift than 3rd high.(same holds for downshifting from 3rd to 2nd, etc)

The big trucks truly purrr optimum cruising at about 45-55mph and will run A-ok at about 57-59mph on a level road.
Not bad for the heavy load hauling ability!

More than 60mph and ya really have to concern yourself with stopping power in the old brake system that was designed by Chevy & GMC to stop better with a load than empty.

It's the RPM's and not the MPH on the old trucks. Gotta love a tach!

In short: get tallest tires and get the 2 speed differential working good and thats about as good as it gets. Beats the heck out of driving most old 1940's, 30's, 20's trucks....its just slower than todays interstate speeds, but heck it's an antique!

Ps: If ya can shop old junk yards for a late 40s' thru 1950's++ Chevy shorter wheel base school buses they most likely have the lower 5.43 or 5.14 rear axel for the bigger trucks as these were rated from 10500GVW to 12500GVW, similar to 1 1/2 tons. Some cab-forwards also had better high speed gears.


john
1952 COE 2ton
1947 Coe tractor

[ 11-11-2001: Message edited by: lil' johnny ]

You guys ever consider installing an auxiliary trans. with an overdrive gear? I've got one with an under and an over gear. Just think of it, with a 4 spd. main box, and 2 spd. rear you'd have 24 forward gears!

Good point, Don. A Brownie or a GearVendors over/underdrive box would be nice but the main problem with that is the $$$... At least in my case.
The newer axle idea is good also. This would give you updated brakes, as well as a lower numerical gear ratio.

truck has 900 x20's. have some sketchy info the ratio may be something like 600 to 1 on the high end

I looked through a Chevy parts manual.There maybe another 2 spd rear with a high gear ratio of 5.43 instead of your 6.07 for mid 50's trucks.The differential center section should be the same.Chevy 1-1/2 ton type trucks used steep gear ratios up until around 68 when the larger V-8 engines allowed the use of ratios in the low 5's.The rear wheel bolt pattern may be different or not. Rear end some later C-30 or 40 duallys may be an option.Clark made overdrive 5spds for GM trucks.I have seen them for sale in commercial truck trader swap sheets .The Clark has model numbers stamped in the case. The OD trans ID# ends in VO, and the 5th gear is usually a .80 Looks like the 264VO series is the one used ,but there are other models also.In theory, the trans should be a bolt in.I have looked at Clark trannys for my 46 1-1/2 ton, but the OD's turned out to be not OD. There was a long post last year on Clarks.

Hey guys, I have a 51 1.5 ton also. Single speed rear end with a 54 235.
Is there any way we can get a separate place on this forum. I would like to share and learn more from people that has what I have in common. (brakes,rims,tires,springs,bed etc. thanks, Greg