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I finally decided to ditch the 4.56 gears that came in my 1968 convertible after 16 years. I've gotten a lot of help from several posts on this forum and, of course Gary (GTR1999) who has tolerated my long list of questions. I've switched back to a set of US Gear 3.73s (the car originally had a 3.70) and have gotten the pinion depth set spot on and have the checked the backlash at 10 spots with readings from .008" to .009" . I've run the gear pattern with load on the pinion, using a rag as several others have suggested, and would like some feedback on the pattern. I ran the pattern at three different locations and all are very similar.
Pattern looks good. The drive and coast are equal in length. Set up looks to be typical US Gear.
The lash is looser then I set with new gears, I would get that pattern with 5-7 lash and it will open up about 001 once broken in. The paperwork that comes with the new gears now has a paragraph explaining to expect some gear noise and this usually shows up in deceleration in the 45-55 mph range, it is very common to hear it with these gears now -more so then several years ago but they are still good and should not cause an issue.
Once the final preload and lash is set do a last pattern run and it should not change.
I would polish and radius the case better then I see but that is your call. Use socket heads in the caps for a little extra strength.
Thanks guys, especially you a Gary. Now just need to do the final details, check it one more time and reinstall. With all the help from the forum members and good old YouTube this wasn’t too bad. Just need to keep track of the details, check everything several times and have a few specialty tools. Of course the proof will be in how it performs so no celebrating yet 😀.
I finished everything up on Sunday and took her out for a test run and am happy to say everything performed great. The gears are quiet and the posi is operating smoothly. What a huge difference going from the 4.56s to 3.73s. Driveability is greatly improved. I haven't had it on the highway yet but it will be nice to cruise at 60 mph and stay under 3000 rpm.
I have read a few web sites that recommend changing the gear oil after 500 miles, however, US Gear doesn't say anything. Does anyone have any recommendations?
You should break in the new gears by driving short drives, no extended highway or hard usage. Drive 20-30 minutes and stop for at least an hour to let it cool down. I recommend doing this cycling 10 times, changing the oil at 500 miles and I change it again at 10k miles as part of maintenance but you probably can go 30k miles. Then again I have opened up diffs that sure were black and might have been original gear oil.
Gear Change Questions
