I currently own a 1995 2 dr 4wd geo tracker auto tranny, the rearend is messed up in it (was wrecked previously before i got it, axle bent, not sure if the housing is messed up also) I recently acquired a (unknown year) 2 dr 2wd geo tracker, manuel tranny. im wondering if i can just change out the whole rearend assy, or just get the "guts" out of the 2wd housing and put them in my 4wd housing, are the ratio's the same, does it matter? Im new to this just trying to learn all i can...Thanks for any help/ advise you can spare, It would be GREATLY appreciated!-Nicole

Well I'm fairly new to this too but I can answer one or two questions for you. 

It certainly matters if it is the same gear ratio!! if you have different front/rear gear ratios you will probably break something the first time you put it itn 4x4. 

Check the VIN# to determine the year of the donor vehicle.  It's probably safe to assume that if the engine size is the same and one is manual while the other is auto then they would probably be different ratios but you never know. Check the Tech Specs link at the top of the page for info on gear ratios.  Also, if your truck has oversized tires and lacks power you may want to consider a gear reduction at this time since you already need a rearend...you could just bite the bullet now and get a front and rear from a donor vehicle with the ratio you want..there are calculators available online to help determine what ratio you want given the tire size, or search the model specific forum im sure the different gear reductions have been discussed on ce or twice lol.

If the housing is bent then you should replace the entire thing, which is simpler anyways.  More "simple" but not necessarily "easier" but for us newbies simple is good.

Hopefully someone else chimes in thats all I know. Keep searching the site though...it's all been discussed!

just found out the NEW tracker is a 1991!

The 95 should have a 1.6 16V engine and a 3 speed auto tranny.  If so, then it should have 4.30 axle gears.
The 91 should have a 1.6 8V engine and with it having a 5 speed tranny it will have 5.12 axle gears.

Got it (sorry for posting twice)
So i took the rear end apart and all the teeth on the ring and pinion are fine. The "carrier" on the other hand (has 12 bolt holes, has teeth on it, has something to do with the speedometer) Is more or less, worn out, in the center. Turns out they dont even sell or make this part because its supposed to be a "never worn" part, supposed to never go bad...holy crap...now what?! Anyone ever had this problem?

I think you need to find a new "advisor" - who ever is looking at the stuff seems to have very little more than a basic knowledge of what they're doing - and sooner or later you are going to be led seriously astray.

Nothing in the rear axle is related to the speedometer - the speedometer is driven by two gears in the tailshaft housing of the transfer case - those gears do need to be matched to the final drive ratio in the axle.

The "teeth" on the carrier are most likely part of an ABS (anti-lock braking system) speed sensor - and it would be extremely unusual for them to wear since nothing is supposed to come in to contact with them - nevertheless - carriers do wear and are replaceable.

If that 95 Tracker had been a 95 Sidekick I would have been only too happy to provide you with the part numbers, and a dealer who would probably have them in stock.

Got it (sorry for posting twice)
So i took the rear end apart and all the teeth on the ring and pinion are fine. The "carrier" on the other hand (has 12 bolt holes, has teeth on it, has something to do with the speedometer) Is more or less, worn out, in the center. Turns out they dont even sell or make this part because its supposed to be a "never worn" part, supposed to never go bad...holy crap...now what?! Anyone ever had this problem?

What exactly is worn?

If that 95 Tracker had been a 95 Sidekick I would have been only too happy to provide you with the part numbers, and a dealer who would probably have them in stock.

The parts should be the same between a tracker and sidekick.  So sidekick part numbers should help.

I currently own a 1995 2 dr 4wd geo tracker auto tranny, the rearend is messed up in it (was wrecked previously before i got it, axle bent, not sure if the housing is messed up also) I recently acquired a (unknown year) 2 dr 2wd geo tracker, manuel tranny. im wondering if i can just change out the whole rearend assy, or just get the "guts" out of the 2wd housing and put them in my 4wd housing, are the ratio's the same, does it matter? Im new to this just trying to learn all i can...Thanks for any help/ advise you can spare, It would be GREATLY appreciated!-Nicole

I think fordem is right in that you are being advised by someone who may know less than you.
 
Take some photo's of what you have you think is bad (much better than a description). 
If you have a bent axle from an accident, probability is that the housing is also tweaked (they are light weight as axle housings go) and I would replace the housing.
There may nothing wrong with your third member (differential piece with the ring gear in it). 
As brush buster said, if you have larger tires (or plan on them) now would be the time to make the switch.

Welcome to ZW,   photo's help for clarification.

As for 12 bolt vs 10, the switched in 95 or 96.  If you switch make sure you write it down, you will need to know if you ever order an ARB. 

As for 12 bolt vs 10, the switched in 95 or 96.  If you switch make sure you write it down, you will need to know if you ever order an ARB. 

They switched to 12 bolt rear rings much earlier.  I want to say 91ish.
You may be thinking of when they switched to 26 spline front axles....which was 96.

They switched to 12 bolt rear rings much earlier.  I want to say 91ish.
You may be thinking of when they switched to 26 spline front axles....which was 96.

Ah, I know that one as it is a pain to find 26 spline front end parts.     

The 12bolt vs 8 bolt It may be one of those things where it depends on the market, as my brothers 93 has the 10 bolt rear end.  If it matters, I say pull and check to be sure.

I think you need to find a new "advisor" - who ever is looking at the stuff seems to have very little more than a basic knowledge of what they're doing - and sooner or later you are going to be led seriously astray.

Nothing in the rear axle is related to the speedometer - the speedometer is driven by two gears in the tailshaft housing of the transfer case - those gears do need to be matched to the final drive ratio in the axle.

The "teeth" on the carrier are most likely part of an ABS (anti-lock braking system) speed sensor - and it would be extremely unusual for them to wear since nothing is supposed to come in to contact with them - nevertheless - carriers do wear and are replaceable.

If that 95 Tracker had been a 95 Sidekick I would have been only too happy to provide you with the part numbers, and a dealer who would probably have them in stock.

You are correct on getting a new "advisor" it is the carrier that has to be replaced. the teeth are all perfect its the CENTER HOLE that is "wore out" i will have to post pictures to better explain myself. never the less, is there ANYWHERE that you know of that i can get this part. i called a dallas, tx rear end place and they said i can not get just that part it has to be the whole housing and it will cost me 700 bucks...no bueno. =(

its the round part with teeth and the 12 bolts in it. The CENTER of that part is wore out. That is what needs to be replaced. Im a girl, and im learning about my tracker, so please, bare with me...i want to be able to work on this thing myself, Something that i can be proud of and say I did it (with yalls help of course)