Gears, Diffs, and pops..and tires

[lochenjons]

The previous owner put differnet gears in the rear of my truck, I dont know what they are but I know originally they were 3.73. I want to find out what gears are in the back so if I pop off the diff cover its that easy right? There isnt all kinds of oil or anything thatll come out or do I have to torque down the bolts or anything? I would think there would be the diff fluid or something but I dont really know awhole lot about these things. Its a 12 bolt btw. Also because of the np203 tcase I have, both axles are always powered. And because I have different gears in the front, if I go really really slow it'll pop and jerk a little. Thats why I really want to know what's in the rear so I can put the same up front. And also if I go from 33" tires to 35"s it would rev lower on the highway and I'd get worse mpg cause of the weight? I think thats what I've been told, because at freeway speed and without OD it revs pretty high right now.

 

[MattK]

yeah the best way to tell is to pop the rear cover off. sometimes the ratio (or the tooth count) is stamped on the ring gear. otherwise you'll need to count the teeth on the ring gear and divide it by the teeth on the pinion.

gear oil will come out. have a large pan under the diff as it is the cover that seals the oil in. when you go to put the cover back on you'll need to clean and dry the mating surfaces of both the cover and the diff housing. either buy a new gasket or do what many do and lay a bead of rtv, let it set up and bolt it down. the filler hole i believe is on the passenger side of the diff housing towards the pinion. pour gear oil in there until it starts to dribble out.

i can't remember torque specs but it's not much. you'll be fine tightening them down with a ratchet.

 

[lochenjons]

Is the gasket something I could get at kragens or autozone or something? If getting a gasket is easy enough I'll just do that. And how do I know what gear oil to use?
Thanks

 

[MattK]

Is the gasket something I could get at kragens or autozone or something? If getting a gasket is easy enough I'll just do that. And how do I know what gear oil to use?
Thanks

yeah you can typically get them from those types of places. just be aware that axle is pretty old and you might wanna call around before you drive around.

gear oil is gonna be 80-90w, common and cheap. just buy a gallon of it, you should end up using over half of it.

 

[lochenjons]

Ok I'll do that whenever I get the chance. What about switching to 35"s? Will it rev lower on the highway but get worse mpg?

 

[Hogback Fabrication]

It will rev lower on the highway. Mileage depends on what gears you have. If you do have different gears front and rear I would fix that ASAP and pray that you haven't already fried the spider gears in your t-case.

 

[Confedneck79K30]

yeah, different gears in the front and rear, with a fulltime case can hurt things... fix that first for sure... you dont need a gasket for the diff, you can buy a bottle of rtv or silicone sealer for the gasket

 

[lochenjons]

Changing the gears in the front is going to be a pain isnt it. Whats involved in that and should I even attempt it without knowing what I'm doing really