Tips on changing rear end gears?
 

I finally got my set of 3.73 gears for my truck.

So this weekend I'll be jumping from a 2.73 to a 3.73. Im gonna be doing the install myself with the help of a weekend mechanic, but hes never touched a chevy rear end before.

Anybody have any write ups, articles, tutorials, tips, tricks, anything I need to know to make this go as smoothly as possible?

It's a 12 bolt. The gears came out of another 12 bolt, but Im not sure if I'm gonna need anything else or not?

Re: Tips on changing rear end gears?
 

Well I done this swap on my monte carlo, I went from 2.29's to 3.42's

I bought the carrier, ring gear attached, spiders, cross shaft, pinions, with it's bearing and shim already on it, his crush sleeve, and the spacers he had in his rear end and had him mark which side they were on. His was a factory 3.42 rear. Mines 2.29's factory.

I put ALL of his stuff in mine except for my pinion seal, and the bearing right behind the seal, and my axles, the rest was his stuff. I put the factory shims/spacers where they were in his, tightened up the pinion nut until almost all the play was gone, put everything back in, no noise nothing, it was perfect.

All you really need to be sure is an inch lb. toruqe wrench so you can set the bearings preload on the pinion, around 25 for old bearings, dunno how much for new ones. Then a dial indicator to check backlash, shold be between 9 and 12 thousandths. other then that just the socket to fit the big pinion/yoke nut, and the rest of the bolts. Some gear oil, cover gasket, or rtv, and some gear marking compound if you want.

I just put mine together and tried it out, working fine.

Re: Tips on changing rear end gears?
 

I recently swapped a 3.73 for a 3.08.

The most helpful thing I did was buy a copy of the dvd "Differential Rebuilding" by Paul Zank:

http://smartflix.com/store/video/135...ial-Rebuilding
http://www.technicalvideos.com/video...erential.phtml
http://www.technicalvideos.com/image...fferential.jpg

You will almost certainly need a "super shim":

http://i9.ebayimg.com/05/i/000/85/a0/8ec5_2.JPG
http://cgi.ebay.com/ebaymotors/CARRI...QQcmdZViewItem

when I did this swap, I took put some videos up on youtube about setting the proper bearing preload:

http://youtube.com/user/cellularmitosis

If you are lucky, you will only need to adjust things "side to side". If you need back and forth adjustment to get the proper gear wear pattern, that involves changing the shims on the pinion, and for that you will need one of these:

http://www.harborfreight.com/cpi/pho...2899/32879.gif
http://www.harborfreight.com/cpi/cta...emnumber=32879

you will also need a new crush sleeve, and you should really consider buying a new cross-shaft retaining bolt (if that bolt fails, the cross-shaft in your rear-end will slide out until it catches on the differential housing, at which point your carrier will basically explode):

http://www.markwilliams.com/images/58907-1.jpg
http://www.markwilliams.com/detail.aspx?ID=844
http://www.automedia.com/article/ima...0301rb_s08.jpg

removing my yoke was by far the hardest part of the adventure for me. The u-bolts were so rusted that they had completely fused to the yoke, so I had to cut them off and buy a new yoke. Also, the yoke will take an un-godly amount of torque to remove. If you don't have an impact gun, trust me, it's well worth the money. I bought mine from harbor freight, and although it is a cheap chinese tool, it gets the job done. If you catch it on sale, its only $40:

http://www.harborfreight.com/cpi/pho...5299/45252.gif
http://www.harborfreight.com/cpi/cta...emnumber=45252

In the end, the first rear-end I bought was too worn for me to get a decent gear pattern (I had that thing apart and back together again about 6 times). When I had it about as close as I could get it, I thought "well, maybe that's good enough". I put it all back together and took it for a spin around the block. That damn thing was so loud that people on the street were giving me looks. After getting it back home , I had worn it so badly in half a mile that the differential oil looked like it had glitter in it. I bought another used one and it was almost perfect the first time I put it in.

by the way -- are you considering selling off your used 2.73? I'd be interested if you are.

Re: Tips on changing rear end gears?
 

I changed my 12 bolt 3:42 gears to 3:73 gears and the change was really noticeablew in the traction department. I also did my son's truck and took it from a 10 bolt 3:08 standard rear end to a 12 bolt 3:73 posi rear end. The gain in performance was outstnding and the actual gain in mileage for his setup was around 2 MPG. The 3:08 gears and a 700R4 just did not work together well.

Re: Tips on changing rear end gears?
 

oh, you will also need a machinists dial and magnetic base:

http://www.harborfreight.com/cpi/pho...0699/00623.gif
http://www.harborfreight.com/cpi/cta...Itemnumber=623

http://www.harborfreight.com/cpi/pho...5699/05645.gif
http://www.harborfreight.com/cpi/cta...temnumber=5645

you use them to check the gear backlash, like so:

http://youtube.com/watch?v=-nYed9N32Zw

When I purchased my rebuild kit (it includes bearings, pinion nut, crush sleeve, marking compound, etc) from drivetrain.com, and I also ordered their machinist's dial and magnetic base:

http://www.drivetrain.com/tools.html

I paid $50 for those two tools, and very shortly thereafter discovered that they appeared to be the exact same tools which harbor freight sells for about $30. So if you buy them, get them from harbor freight.

Oh, you will absolutely *need* marking compound and brushes. The way you tell if the gears are lined up properly is you paint one gear, run it around a couple of times, and then look at the pattern which the paint makes on the other gear. This part of the process is absolutely essential, and if you get it wrong, you will wreck you rear-end in short order (however, you will likely know that you got it wrong, as it will be loud as all hell).

Re: Tips on changing rear end gears?
 

Holy crap...

I had no idea there was so much involved in it. I don't know the first thing about rear ends. (at least in the automobile department, that is ;)

Luckily, one of the techs at my dealership said he's done a hundred 12 bolt rear ends before, so for a 6 pack, he'd help me change them out and get everything I need.

Thanks anyways for the info fellas

Re: Tips on changing rear end gears?
 

this is one thing that you don't wanna screw up... you could ruin your gears, axle or more...

I suggest paying a shop $150ish to set them up and be done... another $100 will get you a rebuild kit (highly suggested) from Randy's ring and Pinion...

I took the easy way out and waited to find the right gears in the junkyard and replaced the entire rear....

ps I have a 12 bolt with 3.73's for sale but it's in PA... I found a posi unit for mine..

Re: Tips on changing rear end gears?
 

I thought you were getting a whole rear end. I had gears that I would have given you.

Re: Tips on changing rear end gears?
 

Damn! I wish I had known that. im trading this guy a set of heads for these gears. I wanted a whole rear end, but I'm settling for the gears for right now at least. I'd like to have posi, but Ill take what I can get.

We'll see though, if he doesn't get them for me tomorrow I'll let you know! :metal:

Re: Tips on changing rear end gears?
 

See that is exactly what everyone told me and ALMOSt scared me away from even trying to do a gear swap myself. All the tools and all the time of making it just perfect.


Yea you should do it that way, then you'll know you'll never have a problem with them again. if you can afford to have it done or buy the tools or have someone who has that stuff do it, then definately do it.

If you want to learn or can't afford it, or know someone who can, then you end up doing it yourself like I did. My dad kept telling me I'd be fine if I got my stuff from another monte carlo rear end and I did.

I guess I got lucky because it went together fine and had no noise at all whatsoever.

Re: Tips on changing rear end gears?
 

I even have a posi a board member gave me for those gears.

Re: Tips on changing rear end gears?
 

Update: I did a little negotiating today, and I'm gonna be getting the complete rear end now. So no more swapping gears for me!