Rear diff gear swap question

[mattrustable]

In order to swap my current 3.42 gear ratio to a 4.10 what else would I need to change? Like anything in the transmission or anything else in the diff and would it be smart to add something to the transfer case? I am putting 285/70r17s on my TB here in about a week. I am also having trouble finding the gears online so is there a list of what vehicles have the gears and anything else I might have to add with the bigger gears? With that list I can go to a junk yard or pick-a-part to get it.. Any advice would be greatly appreciated

[The Roadie]

Randy's Ring & Pinion is the go-to place for all those things, plus the usual places like Rockauto may also have them. ringpinion.com can give you the part numbers, then buy them there or search. You'll need install kits that include a variety of shims.

Don't neglect doing the front diff too.

No changes needed in the transfer case or transmission.

Don't underestimate how difficult doing the front diff is going to be. Read up.

[mattrustable]

Thanks for the reply Roadie. I will look into it furthermore

[TBYODA]

Thanks for the reply Roadie. I will look into it furthermore

Upgrade to a 8.6.

[mattrustable]

Thanks for the reply Roadie. I will look into it furthermore

Upgrade to a 8.6.

What are the advantages of that along with cost? If I stick with the 8.5 I'll just pull some off of an SS and save money

[djthumper]

If you are in a SWB I6 you only have an 8" rear end. If you go up to the 8.6" you will actually have a stronger rear end. Also if you are going up to 4.10 with what you are planning you may be better off just hitting 4.56 and be done with it.

[mattrustable]

If you are in a SWB I6 you only have an 8" rear end. If you go up to the 8.6" you will actually have a stronger rear end. Also if you are going up to 4.10 with what you are planning you may be better off just hitting 4.56 and be done with it.

SWB? lol but yes I6.. I guess I could do that.. Idk i just wanted bigger for my tires, 32s, I'm gonna put on but after looking at the gear ratio calculator, it would make sense to go with the 4.56

[djthumper]

SWB= Short Wheel Base. In order to go up to 4.56 you are going to need the 8.6" rear end. That will also open you up to much better lockers for the rear.

[navigator]

if you do a swap, you need to get one from a 2006+ because the sensors in the newer models are different than the older ones.

[Moots1288]

Thanks for the reply Roadie. I will look into it furthermore

Upgrade to a 8.6.

What are the advantages of that along with cost? If I stick with the 8.5 I'll just pull some off of an SS and save money

An SS 9.5?

[ErikSS]

I know of 3 trucks currently running stock differentials in SS axles. One those trucks has hardly left his driveway since the swap so he hasn't had time to develop an opinion. The other two love ours. There is also someone running an SS axle housing with a locker in it. All Trailblazer SS trucks had 4.10 gears. As Roadie mentioned, you have to match your front and rear gear ratio. So what change you make to the rear you also have to make to the front differential.
We typically refer to SS rear axles as 14 bolts.

[mikekey]

I think Erik is the only person to point out that you need to match the front differential to the rear. It hasn't been mentioned so lets not leave it up to assumption that the newb knows this. Front and rear need to be swapped. At the cost of doing the gear swap, it makes zero sense to swap 4.10's into a 8" axle. Find an 4.10 8.6" and swap the rear, then regear the front diff or just find a 4.10 front diff, as has been done. If you are regearing a 8.6" or 14 bolt to 4.56 double the cost and effort.

[Diacom]

I ordered my gears and master kits from these guys: http://shop.cruiserparts.net/index.php?main_page=product_info&cPath=805_812_814_821&products_id=11020

Some of the better prices I found and though they specialize in FJ's, they had a good selection and helpful staff.

[mattrustable]

Ok thanks everyone. I'll see what the junk yards have and go from there. So just to be clear, the way to tell if it is a 8.6" is to count the bolts on the diff plate? Which would be 14 bolts right? Again thanks

[ErikSS]

Ok thanks everyone. I'll see what the junk yards have and go from there. So just to be clear, the way to tell if it is a 8.6" is to count the bolts on the diff plate? Which would be 14 bolts right? Again thanks

No. There are three options. 8.0, 8.6, and the SS 9.5. The 8.0 and the 8.6 both have 10 bolts. The SS has 14 bolts. The bolts make the obvious difference between the 8.0/8.6 and the 9.5. Telling the difference between the 8.0 and 8.6 is a little harder. I've never owned either so research and see what you can find for physical differences.

[TBYODA]

I would see if the yard has the vin for axle then jonbo can run it for you to confirm. You also can open it (if the yard will let you) and count the splines and measure the ring gear. 8.6 have 30. 5.3l SWB and ext had the 8.6.

[TBYODA]

I think Erik is the only person to point out that you need to match the front differential to the rear.

Don't neglect doing the front diff too.

Don't underestimate how difficult doing the front diff is going to be. Read up.

Did you miss Roadie comment in the first post?

[Conner299]

I could be wrong, but don't you also have to have the ECM reprogrammed if changing gear sizes? I seem to remember reading that it will trip code lights, if you don't. If not, then I need to get my rear in gear, and get my diff's changed out. I have everything to do it.

[Cable810]

Since I swapped I get a ABS light cause of the gear change. I believe the code is for the wheel sensor but I'm not 100% sure.

[Shdwdrgn]

My limited experience is that the rear axle size is stamped into the cover. Both the original 8.0 and the new 8.6 had it stamped in, but I had to clean up the rust to actually see them. If you're changing things anyway, by far the easiest option is to get an axle that already has the gears you want... a few hours of labor and you can swap the rear axle by yourself.

You lose nothing by swapping from the 8.0 to the 8.6 rear. As far as I could tell, the difference in diameter was placed *above* the axle line, so you have exactly the same ground clearance. I have no experience with the 9.5.

Expect the front diff to be a multi-day project. If you have experienced help, it might not be, but expect it anyway! Also since everything will be apart anyway, you might as well inspect and re-lube your disconnect.

You have an advantage when it comes to reprogramming the gearing in your PCM -- tuners like HPT have the info available to make the change. Those of us with the older PCM aren't so lucky. However does anyone know if the newer models are still limited to stock gear ratios in the PCM, or if the 4.56's can indeed be programmed in?