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Discussion Starter #43
the shims on GTO go between the rear pinion race and housing
so i would have to press the race out to reshim?

awesome.

well, i ordered a rebuild kit from gforce. looks like a hydraulic press from harborpoop will be in the works, as well.

emailed contemporary corvette, and they won't help me out or tell me exactly what they did. just reassured me their awesome mechanics and machinists were on the job, and i should run it and it will be fine.

ya, no, i'm not that stupid.

i've bought a lot of stuff from them, too. just lost a customer.

EVERYBODY, DON'T BUY CRAP FROM "FPARTS" ON EBAY. THEY SUCK.
 

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FPARTS is a junkyard, out here in Bristol PA. They simply remove stuff from wrecked cars and resell. So what came out of that car is what you likely got. I Don't think they have anyone in house than can R&R a diff.
I've bought many cores from them...I go and pick thru them to make sure they turn free etc.

For the rear race, you can knock it out with a punch from the front. There are 2 notches in the housing for this purpose. It is in there tight...if you have a press you can rig something up there too...but I normally just use a long brass punch and drive them out alternating between the 2 notches on each side.

If you put the shims under the pinion bearing on the gear, there is no way to re-shim easily as you can't get the bearing cone off without damaging it or destroying it. You can shim it there if you want though, same end result. I'd suggest buying 2 pinion bearing cones and making one a 'mock up' by opening up the ID so it is slip fit on your gear. Then you can shim by trial and error till you get it right and then press on your other new bearing cone. Same thing can be done with the rear race...the race is about a 1/3 the price of the cone FYI
 

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Discussion Starter #45 (Edited)
FPARTS is a junkyard, out here in Bristol PA. They simply remove stuff from wrecked cars and resell. So what came out of that car is what you likely got. I Don't think they have anyone in house than can R&R a diff.
I've bought many cores from them...I go and pick thru them to make sure they turn free etc.
this is not what was told to me in an email.

they said the original case was cracked, so they installed the gears in a new one.

i asked them what specific work was done, and they reassured me how they have mechanics and machinists on site and that it was set up properly, yadda yadda.

For the rear race, you can knock it out with a punch from the front. There are 2 notches in the housing for this purpose. It is in there tight...if you have a press you can rig something up there too...but I normally just use a long brass punch and drive them out alternating between the 2 notches on each side.

If you put the shims under the pinion bearing on the gear, there is no way to re-shim easily as you can't get the bearing cone off without damaging it or destroying it. You can shim it there if you want though, same end result. I'd suggest buying 2 pinion bearing cones and making one a 'mock up' by opening up the ID so it is slip fit on your gear. Then you can shim by trial and error till you get it right and then press on your other new bearing cone. Same thing can be done with the rear race...the race is about a 1/3 the price of the cone FYI
thanks for the info.
 

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this is not what was told to me in an email.

they said the original case was cracked, so they installed the gears in a new one.

i asked them what specific work was done, and they reassured me how they have mechanics and machinists on site and that it was set up properly, yadda yadda.



thanks for the info.

well they likely did swap the gears over...but I wouldn't expect it was done right. Only machinists I've seen there use sawzalls LOL

their mechanical guys are good at taking cars apart, without damaging stuff. I will say that..I've bought doors and all kinds of GTO parts there and all very nice undamaged parts.
 

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Discussion Starter #47
well they likely did swap the gears over...but I wouldn't expect it was done right. Only machinists I've seen there use sawzalls LOL.
that's the caveat for buying used parts on the internet, i suppose--you never really know what you're getting until you get it. it's not like you can physically check beforehand before purchasing something. at the very least this thing is almost worth in parts what i paid for it, more or less.

it's gonna be a fun project. :D

thanks for all the assistance, btw. not many shops will take the time and effort to help enthusiasts with their problems with no immediate return.
 

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Discussion Starter #48 (Edited)
figured i would give an update.

ok, diff #1. Stock diff.


diff #1 replaced the differential that was in my red car, since it was the best candidate for not sucking.

ended up working well. there was some initial noise that worried me, but as it turns out, the noise is gradually diminishing as i drive it. i noticed some light corrosion on the small roller bearings that support the stubs in the side adjusters, i think from the previous owner letting it sit uncovered for a long period of time. i will be sure to drain/replace the fluids after another few hundred miles.

diff #2, another stock diff.


i haven't messed with this one again. i got it as close as i could to a good pattern and set the side adjuster torque to about 25-30 ft lbs on each side. it may be too much as the carrier bearings are used (though they are in great looking condition). sealed it back up and stuck a pair of good stubs in it.

FYI, this was the original diff in my red car. I replaced it with another diff (#4, mentioned below) when it started to make clunking noises in turns that was not alleviated with a gear oil change + the proper amount and type of friction modifier. It also had a pinion seal leak. I decided to attempt a rebuild with a spring kit and new seals. It didn't need new bearings, as they were all immaculate when inspected. I have never gotten around to reinstalling, because I was never satisfied with the wear pattern.

IMG]http://www.ls1gto.com/forums/attachment.php?attachmentid=361970&stc=1&d=1433653945[/IMG]
this one, the cursed paperweight i bought from ebay, i ended up yanking apart. as mentioned in previous parts, the pinion depth is way, way off, so much that the teeth were only making contact on the very edge and there was no discernible pattern. now, upon close inspection, i can not only see the original wear pattern etched in the gears (which confirms my suspicions that they were indeed improperly set up by Contemporary Corvette, and were not ran with the horribly out-of-wack setup i bought them in), but the gears do look very beat on. The gear teeth are very shiny and smooth, the edges of the teeth somewhat sharp on the pinion gear. There are no machining striations evident at all. It doesn't look like much material has been removed, fortunately, so i'm not sure how bad off this gearset really is.

I recently purchased a set of 3.70 motives i am thinking of running with a stock diff, or with the trutrac currently attached to the 3.91 ring gear. the 3.70's may be a better ratio for what i want to do with my car.

I am debating using the 3.91 gears as paperweights, or trying to run them in blue and seeing what happens.

lastly, i introduce diff #4. This was the diff that i dropped out of my red car, replaced by one. It originally replaced #2 (as noted above, #2 was the stock diff that came with my red car)...
 

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Discussion Starter #49 (Edited)
As said above, i dropped the original diff (#2) in my red car several years ago and replaced it with a used diff (#4). This diff howled from installation, but i ran with it. The howl was initially only within a certain speed range, around 40 mph, so i figured these gears were just set up wrong from the factory like half of the other OEM GTO gearsets.

A year or so later, it began to whine on deceleration. I tightened the pinion nut 1/8th turn, and the whine went away.

It came back much later, possibly 6 months to another year. I don't quite remember. I knew my pinion bearing(s) were on their way out for good. Recently, it started to clunk at low speeds, only when slowing down to a stop, which i found odd.

I finally dropped it and refreshed the rest of my rear end. I replaced with diff #1, which is much, much better in comparison.

I took the cover off of #4 and examined. Very tiny metal pieces were evident in the oil--not the typical glitter, but small chunks about a millimeter or so across. The pinion was hard to turn at first, but after much cleaning with brake fluid it now turns smoothly. I can only assume these chunks were bits of pinion bearing material. The gears showed no evidence of galling, chipping, breaking, or excessive wear.

I was able to check the gear wear pattern and backlash the other day. I was correct in my initial assumption that the gear pattern was off.
 

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Discussion Starter #50
both the pinion depth and backlash are significantly off, as evident by the triangular pattern on the coast side and the pattern on the drive side being almost at the toe of the gear tooth.

backlash measured between .005"-.006"







i tried to remove the side adjusters, which so far has met with disaster. an entire can of PB blaster, heat applied to the case immediately around the adjuster, and beating on it with a 3/4 drive impact did nothing. it eventually broke all but one of the teeth on the tool i had made with a friend of mine to use on the side adjusters. (and no, it wasn't a flimsy oil filter wrench thing. it was quite a bit more stout than that). Enough torque to bend up the adjuster and break my tool, not enough to budge anything.

i never had this issue with any of the other diffs i've worked on so far. i don't drive red in the snow or rain and it doesn't sit outside, so not sure how this got so corroded that it is almost impossible to break loose.
 

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Discussion Starter #51
upon some more thinking, with #4:

was thinking the backlash was set correctly, as .005-.006 seems fine, that the pinion depth being off would throw the patterns off to opposite sides anyhow. seems like it needs a thinner shim (less pinion depth).

also thinking, if the pinion bearings are VERY worn, if the pinion would be pulled in farther, thus throwing off the gear setup?
 

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Discussion Starter #52
both the pinion depth and backlash are significantly off, as evident by the triangular pattern on the coast side and the pattern on the drive side being almost at the toe of the gear tooth.

backlash measured between .005"-.006"







i tried to remove the side adjusters, which so far has met with disaster. an entire can of PB blaster, heat applied to the case immediately around the adjuster, and beating on it with a 3/4 drive impact did nothing. it eventually broke all but one of the teeth on the tool i had made with a friend of mine to use on the side adjusters. (and no, it wasn't a flimsy oil filter wrench thing. it was quite a bit more stout than that). Enough torque to bend up the adjuster and break my tool, not enough to budge anything.

i never had this issue with any of the other diffs i've worked on so far. i don't drive red in the snow or rain and it doesn't sit outside, so not sure how this got so corroded that it is almost impossible to break loose.
just an update. don't have pics yet, but maybe when i have some time.

finally got the rear apart. i had someone at work cut the side adjusters out with a torch.

now that those are ruined and so is the case :gto_rage: i got a good look at the bearings and the gear set.

the gear set looks pretty normal. the only indication something was wrong was the lousy wear pattern.

both pinion bearings and races looked almost brand new, surprisingly. i was anticipating that they would be destroyed judging from the howling that was coming from the unit. one thing i did notice was how easy the pinion nut was to remove, however.

the side adjuster bearings were destroyed in the process, so i didn't get to examine them.
 

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Discussion Starter #53 (Edited)
so, some speculation here. let me know your thoughts

#1. The lake of torque requried to loosen the pinion nut may be indicate that the preload loosened up, causing the noise. The noise was most evident on decel, which is what originally had me thinking it was the pinion bearings, but lack of preload could cause the same noise. perhaps it did throw the pattern off slightly, as well.

#2. The diff may still have been set up poorly from the factory. The wear pattern seemed to indicate backlash and pinion depth were both off, but as the gears were worn, i suppose this pattern could be deceptive. That being said, .005-.006" does seem fairly normal. So I would think perhaps the pinion depth was off from the factory. Which would explain the "low mileage take-off" when i bought it--it was probably R&R'd by a dealer.

#3. I did find small chunks of metal in the diff when i removed it and examined it initially. There was no indication as to where these came from. Since i haven't examined the inside of the carrier, i am guessing the chunks came from the side gears/cones. Hopefully this is just from aggressive wear and not the result of cracked or broken gears. I was hoping to reuse the diff carrier. However, this might explain the clunking i heard from time to time coming to a stop (although i never heard clunking while turning or at any other time). The pieces were all smaller than 1mm in dia, fyi.
 

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Discussion Starter #54
was doing some research for another recent thread, and i figured i posted an update.

A few years ago I did rebuild the rear end i bought from fparts with a set of 3.70 motive gears that were used, but they seemed lightly worn. i set the pinion depth and backlash according to the measurements marked on the pinion face and ring gear, and the wear pattern seemed fairly close. i reused the old carrier bearings and races, since they seemed in good condition, but it has a new large pinion race and small pinion bearing and race. i forget what rotational torque i finally achieved to rotate the pinion yoke, but it's only a little tighter than a used stock diff.

I'm going to go back over it sometime in the next few months to make sure it is kosher, and try swapping it into my 2004. Will let you guys know how it works out.

swapped the #1 diff (shown in post 2 of this thread) in my red car, and it is running well, although it does whine when cold between 45-65 mph. it seems to go away, at least lessen greatly, after the differential warms up. i did change the fluid once after installing it, replacing it with redline synthetic and motorcraft xl3, and there is very little if any visible wear metal. i'll probably change it again over the winter to see.

#2 is still sitting in my garage as well. I really would like go back over this one and see how it runs in a car.

#4 has long since been junked. i sold the ring and pinion, as they seemed fairly solid and only worn. to the best of my guesses, the metal chunks came from the spider gears. I was unable to disassemble the LSD, so i will never know for sure, but the ring and pinion were solid when i removed them, and the bearings looked quite nice.

My guess with #1 and #4 where that they were of many that whined from the factory and were replaced, then subsequently sold on ebay. #4 lasted me a considerable amount of time, and likely would have continued to run (albiet with the whine) had the spider gears not cracked or broken.
 

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Thank you for your detailed thread. Im in the beginning process of building my first diff and am at a crossroad on whether I should reuse the stock gears and posi. Unfortunately, I didn't take a pattern or backlash reading before I tore everything apart so if reuse it I will likely have some amount of gear whine but I would think if I set it up correctly, it shouldn't be too big of a deal. Any tips or suggestions you have on that issue would be greatly appreciated.
 
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