Hey guys. So i was wondering what my rear gear is. On another forum im a member of, they have a gear calculator. I have used the calculator with my tranny gears and knowing the rpm at what speed im traveling. The calculator says i have 4.10 gear.

I tried the lift the wheels off the ground and spin the wheels and see how many times the driveshaft rotates. This is the part im confused with. I lifted it up on jack stands, tranny is in nuetral, ebrake is off. I marked a spot on the tire and driveshaft with some primer i had. To match the two spots back to originating position the driveshaft turns 8 times and the wheel turns a little over 4. How do i break that down into the ratio?

Also i have an open dif. Im doing this on the driver side. The passenger side when i turn it wont turn the driveshaft, (well it will but the driveshaft just falls back into resting position, wont make full rotation) but it will spin the driver tire. Drivers tire wont spin pass. Is this normal in an open dif? I started it up in the air and put it in first(granny gear) at idle and i had to engage the park brake about half way before the passenger tire would spin but the driver would stop.

Thanks for the help
Cody

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Old truck: 82 D150 225, 2bbl, dutra duals, 2.5" straight pipe to dual 2.5" tail pipes. Mud tires, 4spd, old forest service truck.
Current truck: 98.5 Ram 2500 ccsb, sport, 24v cummins, 5spd, 4.5" lift, 35's, 5" straight pipe.

Have you checked to see if the tag is still on the rear axle that lists the gear ratio?

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Casually looking for a Clifford hyperpak intake for cheap.

That driveshaft should turn while a raised wheel is being rotated with transmission in neutral. Slantsix Dan’s recipe works nicely for calculating a rear end’s ratio.

Try lifting both rear wheels off the ground, and see if the drive shaft is willing to rotate.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Reed: where would the tag be?

I did raise both wheels. only the driver side wheel will rotate the driveshaft. The passenger side is rather stiff like the brake is slightly applied and the drive shaft moves very little than falls back to a resting position.

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Old truck: 82 D150 225, 2bbl, dutra duals, 2.5" straight pipe to dual 2.5" tail pipes. Mud tires, 4spd, old forest service truck.
Current truck: 98.5 Ram 2500 ccsb, sport, 24v cummins, 5spd, 4.5" lift, 35's, 5" straight pipe.

The tag will be attached to one of the bolts on the cover of the differential. It will e a little rectangular thing probably obscured by decades of grease and dirt. Crawl under there with a wire brush and scrub around the heads of the differential cover bolts until you find it.

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Casually looking for a Clifford hyperpak intake for cheap.

Ok thanks Reed. Ill probably do that tomorrow when the weather clears up.

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Old truck: 82 D150 225, 2bbl, dutra duals, 2.5" straight pipe to dual 2.5" tail pipes. Mud tires, 4spd, old forest service truck.
Current truck: 98.5 Ram 2500 ccsb, sport, 24v cummins, 5spd, 4.5" lift, 35's, 5" straight pipe.

you most likely have 3.55 open diff 8 3/8 same as 8 1/4 in cars....was what they put in most of our trucks

keep on roddin'
indian

Trucks and vans of this era have labels under the hood which show the original axle ratio. Older trucks had a metal tag in the door jamb. My Dakota has the label in the glove box.

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Joshua

Oh yeah! Thanks for reminding me Josh! I forgot about the underhood tag.

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Casually looking for a Clifford hyperpak intake for cheap.

Wouldn't the tire roating a little over 4 times be the indication it's a 4.10 rear gear and on my old open diff only 1 tire would spin as well the driver side other tire would just free wheel.

Kev

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If one tire is stationary then the other tire has to rotate two turns to rotate the differential carrier one turn. I discovered this with a Lego differential around 1986. Stop one tire and the other turns twice as fast.

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Joshua

Hmm I didn't know that. Thanks

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Old truck: 82 D150 225, 2bbl, dutra duals, 2.5" straight pipe to dual 2.5" tail pipes. Mud tires, 4spd, old forest service truck.
Current truck: 98.5 Ram 2500 ccsb, sport, 24v cummins, 5spd, 4.5" lift, 35's, 5" straight pipe.

If the rear axle has never been adulterated or the previous owner was nice enough to put the tags back there may be 2 tags:

1) one that will denote the ratio (3.55, 4.10, etc...)
2) the other will have a 3 or 4 digit number which is the assembly ID tag
('0613', etc...)

If you find it has the assembly tag not the ratio tag don't get freaked out 0613 is not a 6.13:1 ratio....

Good Luck,

-D.Idiot

So today I did slant six dans thing and I counted 14.5 quarter rotations which came out to be like 3.62 so I am totally lost. I think I'll just take off the dang cover and look. It probably could use a new gasket and oil anyways.

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Old truck: 82 D150 225, 2bbl, dutra duals, 2.5" straight pipe to dual 2.5" tail pipes. Mud tires, 4spd, old forest service truck.
Current truck: 98.5 Ram 2500 ccsb, sport, 24v cummins, 5spd, 4.5" lift, 35's, 5" straight pipe.

Ross,

if you remove rear cover...on the ring gear outside edge will be stamped the ratio

keep on roddin'