How do I replace rear end gears?

[bigcarguy]

There's a guy at work that needs to know how to place his son's rear end gears. It's an early 90's 4X4 with 3.42 gears in it. He needs to know everything he can before he starts working on it. Does anyone know of a tech write up on how to replace his gears?

[68 Suburban]

I would suggest if he does not know what he is doing, to have it done profesionally, or else he will be doing it again in about 500 miles.

[bigcarguy]

He's gonna do it himself, that's not my call. I'm just here to get the info for him. He's not the kind of person to pay someone else to do something for him.

[bigvinnie]

here's a link with some info on setting up a GM rear end...

http://www.tecinfo.com/~rsguy2/install.htm

[Michael A. K. G]

http://www.differentials.com/install.html

But I do agree that one should think twice about it.

I have about 20K miles on the Ford 7.5 inch I rebuilt (including a new gearset). I didn't save any money at all because of the tools I needed to buy (but that wasn't the point). Harbor Freight is a good source for very cheap tools. Like a <$20 dial indicator and magnetic base. But it only costs like $100 for a pro to set up a disassembled rear end, not including installing the rear into the vehicle.

You have to be really anal about getting every setting just right. And check the contact pattern with gear marking compound, and correct until it's perfect.

[bigcarguy]

thanks guys, I know I can always count on y'all for a speedy response. I'm in total agreement with everyone, I'd never attempt a gear swap by myself, but you know how hard-headed some of these older fellas can be. Thanks again.

[jku72]

Or, you could do what I did, and get some used gears, for 75$ and throw them in there and then drive 15,000 miles of trouble free driving. By using used gears, and getting the differential as a complete unit, the shims are already there, and you can get them pretty close. I used exactly 0"zero" special tools, and finished the job in about 2 hours. I then drove 3500 miles from Portland Oregon, to Portland Maine, then have driven another 12,000 since then, no noise, no nothing.
The biggest worry is not failure, but noise. The only way to make them fail, is to get dirt in there, or low oil levels, or overtorque the preload. I am sure to get heckled off this thread for this, but I have now done 2 ford rear ends this way, and one 12 bolt chevy, and they lasted longer than the rest of the truck,
If you use new gears, then yes, I imagine you would have to get all the special tools, to find the right shims, setup, blah blah, but when ever has a pair of rear end gears worn out if they are kept with oil? Meaning, junkyards are full of these gears, and if you inspect them, 99.9% of them look excellent even after 200,000 miles.

[Michael A. K. G]

Originally posted by bigvinnie
here's a link with some info on setting up a GM rear end...

http://www.tecinfo.com/~rsguy2/install.htm

An interesting and detailed site. But I think it has a major error. In effect, it tells you to back off the preload on the pinion bearings. If you do this, the crush washer will not be under any pressure, and it will have no effect. The pinion nut may work off, resulting in a floppy pinion. This will destroy the rear end if it gets bad enough to knock chips off the gears (it doesn't take very much).

The right thing to do is to tighten the pinion nut until you get the appropriate preload, as measured with an inch-pound torque wrench. If you overshoot, you have to remove the pinion and replace the crush washer with a new one, and start over. NEVER back off the pinion nut without replacing the crush washer.

[Michael A. K. G]

Originally posted by jku72
The only way to make them fail, is to get dirt in there, or low oil levels, or overtorque the preload.

No. Zero preload will also cause them to fail. So will contact at the edges of the teeth. Both are really easy to do if you aren't careful.

Even if set up correctly, lifting the vehicle (substantially) without adjusting the driveline angles, or severely overloading the vehicle can cause the rear end to have a short life.

Remember, the truck in question is a 4x4. I know most of them never see an unpaved trail, rock or stream, but that means it may see very severe service.

[Jmac05]

Take my word for it... tell him to have someone who knows what they are doing, do it for him.