Well, the PO told me that it had 4.10, but he was less than accurate on a few other things as well, such as the mileage he ALWAYS got (21-22) It gets 18.3 day in, day out.

So how can I tell, I don't have a tach, but I am looking to get one, and would need to know this in order to calibrate the tach.

Is it in the VIN or something or stamped on the diff case?

Thanks,

Avery

 

There sould be a sticker under the hood. There will be a tag on the diff itself, too.

 

Take your VIN # to a dealer's Parts Dept. Ask for 'build sheet". Will tell you everything that came on your CTD from the factory... incl. gear ratios.
Should be free!

RJ

 

the tag on the rear is the easiest way if the sticker under the hood is gone.

 

Mine was replaced sometime in its lifetime, PO. The sticker said I had 3.5 but the gears were 4.1. I would think the majority of stickers are accurate, unless there are many miles on it.

A neighbor told me to, there is another way, something about dividing the pinion teeth into the ring gear teeth, if you have the cover off and can see them. Dont know, I havent tried it yet.

 

Ok, the sticker on the inside of the hood says 3.5 axle ratio, but the PO told me that it had 4.1. PO also did an auto-to-manual swap, so I guess he could've changed out the gear ratio then.

calling him now..

ok, he said it has 3.5

Well that's cleared up now.. thanks guys!

So, my motor is only spinning 2700 rpm when I thought it was 3200. Perhaps I don't have the spring.. that will be the next mod after gauges!

avery

 

sounds like a tach would be a good idea fora stick truck :O.

 

I'd think a tach to be more mandatory for an auto. Then you can see what your torque convertor is/isnt doing. Mine will jump from 18-2100rpm when I goose it at 60mph.

If you get a 3200rpm spring, and hop up the pump, the tach will be a necessity.

There should be a tag on the diff cover between two bolts (if you're lucky). If not, you can jack up the rear, and with the tranny in neutral, turn each tire one full rotation, taking note of how many times the pinion yoke turns. If it's roughly 3-1/2turns, you have 3.54s; a hair over 4 turns, 4.10s.

Daniel

 

41 ring gear teeth 10 pinion teeth =4.10
42 ring gear teeth 12 pinion teeth =3.5

 

Elementry, mark the driveshaft and the rear wheels, jack up the back, have someone turn they both one time around, count the number of turns of the driveshaft. 3 1/2 is a 3.55, a little over four is 4.10

 

Make sure both wheels turn one full turn when doing this or your count won't be accurate. Jack one rear wheel up and turn it TWO times while counting drive shaft turns will give you the same information.

 

but if it is limited slip both wheels will turn together, but as you said, both wheels have to turn same direction, one full turn.

 

When you get a tach 60mph=2000rpm (roughly) I personally love my 4:10's!

 

Enless tire size has changed... It will only work with stock tire size

 

Is this only done on the drive wheel, right rear? I tried this on mine (4.10) on the left rear (non limited slip) and my ration would be 2.5. What happened?