I've read a few posts of people finding gears for their car at a junkyard, but I haven't found anything about whether or not you can install them by keeping all the shims where they were before. Do they need to be re-shimmed?

If its possible to install them just like that, I was thinking of looking for a 3.73 or 4.10 gear ratio out of a truck.

I know I could just replace the entire rear, but the only thirdgen rears with a 3.73 ratio as far as I know are the four cylinders and an 84? or maybe 85 5.0 HO manual. I want to avoid a rear thats gonna be about 20 years old. I don't think I could get a 10 bolt from a late model truck to fit in a thirdgen without modifying it, can I?

 

People have re-used the same shims that came w/ the gears, but really, those shims are worthless. The whole point in different thickness shims is to accomodate for manufacturing tolerances in the carrier and housing. If you take a carrier out of one housing, there is a very good chance that they will not be the correct shims for the new housing. Your best bet, if you absolutely insist on junkyard gears, is to find the ones you want, put a dial indicator on it and jot down the backlash reading. Then, when you set up the new rear, have the pinion depth gauge installed and find the correct pinion shim for the NEW housing, and install the pinion. Then, set up the carrier shims so that the SAME backlash reading is obtained. I would, however, keep the shims from the junkyard, and use it as a starting point, but NEVER would I just blindly put them in and "let it ride". Also a good idea to replace the bearings, seal, and crush sleeve. Once again, I know people have "gotten away" with re-using old stuff, but why half-a$s a job like this?

 

I was thinking of junkyard gears because if I could install them myself, I could have an extra $250 in my pocket from not having to pay to have them installed. I also like doing things myself whenver I can.
I've obviously never worked on a rear before, but if the only thing I need to keep an eye on is the backlash, that doesn't sound too difficult. So as long as I make sure I end up with the same backlash that I measured from the junkyard rear end I should be fine right?

 

You missed the whole part about setting the pinion, thats half the tooth pattern. Most use a .035" shim. I would probably use the pinion shim thats in the housing now, but you absolutely MUST check tooth pattern. I personally don't like setting up a rear w/o first measuring pinion depth w/ a guage tool, but I understand not everyone has access to one. Another critical assembly measurement is bearing pre-load. You have pinion bearing pre-load and total turning pre-load.

 

Again, I've never worked on a differential before, and this is all new to me. From what I understand so far, which may or not be what you meant, I would have to do everything almost the same as if I purchased new gears. If thats the case, then I guess I should forget about trying this myself. My reason behind wanting to try used gears is because I could install them myself from what I was told, but that seems to not be the case.

 

New gears or used gears, the fact remains that all housings have variations in manufacturing tolerances. Thats why each and every gear install should start from scratch, and set up the ring and pinion to the new housing. Ring and pinions wear and become a matched set, just like a camshaft w/ flat tappets. The only way you will get used gears to be quite, it to get the backlash exactly like it was in the old housing, and to get the pinion depth correct as well. Pinion depth is not measured w/ the pinion, its measured from dead center of the ring gear to the bearing races of the pinion, using a special tool to make these measurements. Once again, this is to account for manufacturing tolerances w/ the housing.

I understand you are trying to avoid having to do all of this, and there is an easier way to do it, but I won't garuntee results. Since the pinion is setup to the housing, you will need to re-use the pinion shim from the housing that you want to use. In order to replace the pinion shim, you will need to remove the rear (larger) pinion bearing. Install the pinion shim on the pinion you want to use and instal the pinion. If your re-using your old carrier and just swapping the ring gear, then use the "old" shim packs, and don't mix them up, the right pack must stay on the right and the left on the left. If you are also swapping the carrier, use the shims from the "used" carrier (the shims also account for tolerances in the carrier), but don't button it up yet! You will now have to acheive the same backlash as when you pulled the gears out. You will have to move shims left and right to acheive this. Once that is done, you will have to check tooth pattern. This will help verify that the pinion depth and backlash are correct.


Because of all the work needed to PROPERLY set up a rearend, I won't install "used" gears. I get new ones and start from scratch.

 

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