2nd Gen Non-Engine/Transmission rpm in 5th

[Ncostello]

Gotta 99 2500 5speed stock size tires. Going 65 mph yeilds 1950 rpm or so in fifth gear. Based upon this information, would anyone know if I have 3:55's or 4:10's. Seems like first gear is very low and basically I dont use it unless creeping or taking off on a steep incline. Havent towed with it yet. Plus I have no idea if its a limited slip or not. It has the camper special springs and sway bars so I bet it does. I want to change the diff fluid but dont want to buy friction mod if I dont have L/S. Maybe I could have DC run a build on the VIN. Will that tell all??

 

[mikel]

There should be a tag on the rear end. It's usually stuck under a bolt and will say what the ratio is.



I'll hazard a guess and say it sounds like 3. 55's to me though. The '99 I used to have would do 70mph at exactly 2k rpm with stock tires and 3. 55's.





Mike

 

[Bob Wagner]

test

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[Ncostello]

So if I block up the rear end, I should be able to spin one wheel forward and the other one turns forward also if it has limited slip. If it does not, they should turn opposite directions, like true differential action without posi... . right??

 

[mikel]

Hmmm



Somehow I missed the part about the limited slip.



Yeah, if you jack up the back end and put the truck in neutral without the parking brake on then both tires should turn the same way if there is a limited slip in there. Then put the truck in gear and turn the tire and it shouldn't turn at all if there is a limited slip.



This might be on the tag too, but I don't remember.





Mike

 

[WKener]

Definitely sounds like you have 3. 54's. Also, open your hood, and on the underside, toward the front, there should be a tag identifying your diff ratio as well as if you have a LSD or not.

Wes

 

[MikeR]

There should be a short build tag sticker either under the hood near the latch or stuck in the glove box. The rear diff cover should also have a metal tag that says the gear and if it has LS

If there's no tags in either spot, I'd say go to the dealer and get a copy of the build sheet with your VIN.



Yes, by your rpm/speed you do have 3. 54 gears... with 4. 10's you be spinning about 2250 at 65. You can always jack up the rear and do the tire spin trick to find out, but getting the build sheet offers way more cool info about your truck.



-Mike

 

[24vcummins]

And, if it is a limited slip and both tires turn, while you have both wheels in the air you can turn a wheel one complete turn and count the revolutions of the drive shaft to see what gear ratio you have. About 3 1/2 turns (3. 55) of the drive shaft or a little over 4 turns (4. 10) of the drive shaft. Am I right guys?