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Well at long last i finally have the rearend in after several "issues", and it has culminated in dissapointment as the AAM gears seem to make some noise. It is a 91 posi-disc rearend with 3.73 AAM gears added. All bearings and seals replaced at the same time. I had a shop install them that a friend recommended. he has supposedly done multiple hundred gear jobs before and i thought with the premium price AAM gears were supposed to be really quiet?
It is not horrible loud where you need to crank the radio, but it is definitely there once you get up to 55-60mph. It only appears to be hile loaded and goes away when you let go of the gas. Is this something that can go away once broken in?
I understand the AAM gears are different (2 cut). If they were set up with the traditional backlash, could that do it or would noise be caused by something else?
So with our early winter and busy at work the car had to go into storage and i sadly don't even have it out yet......but i have been looking into things a bit again and one shop is telling me that with 3.73 you will always hear some noise because the pinion is moving faster. Is this true that this may be normal to expect when going with higher numerical gears?
Higher-# gears generally do tend to make a bit more noise, but it should be very minimal. AAM gears are generally a dependable product. Yes they do sometimes make noise when new and quiet down later, but not usually. It should never be enough to be obnoxious, in any ratio, with good quality gears.
Yes those backlash specs look about right. The exact # for it isn't critical - that is, it's not like, you set them up at .005" or whatever and they're noisy or otherwise wrong, but at .008" they're OK - so I wouldn't expect that to be a factor unless it's just grossly off. Personally I tend to set mine at the high end of the range anyway: gears GROW when they get hot, which means the backlash goes away under heavy use, which when 2 pieces of metal attempt to occupy the same volume, REAL BAD things start happening. Even slightly too little backlash can be MUCH worse than even ALOT too much.
Your noise may very well also not be the gears at all, but rather the pinion "head" bearing. (the big one) What do you know about how they were set up? How much shim is on the pinion? What was the pinion bearing preload set to? Is there any possibility the bearing got damaged during installation? How much preload is on the carrier bearings?
Last edited by sofakingdom; 06-13-2017 at 06:46 AM.
Even the Chevy dealer has had numerous complaints of higher ratio late model Camaro's that have gear whine. They have told some customers that it's pretty much normal, and that if they try to correct it they might even make it worse than it is.
Do a Google search for it. The consensus seems to be that some sets make noise, higher ratios (relative to ring gear size) are more likely to do it, and it isn't detrimental.
There are many opinions - some say no gear set should make noise, that its always the installers fault - I don't buy it since if that were the case the dealer wouldn't be having this complaint on productions vehicles, let alone telling customers its pointless to try to fix it. The guys that seem to have the most experience say it's very typical and in some cases, such as the 3.70 gears for my 9 bolt, virtually every single experience with them includes part throttle whining. Coasting or full throttle seems to be silent. Just part throttle cruise.
We have a saying around our shop - "Because race car". Stiff suspension, noisy coil overs, cabin vibration, gear set whine..... because race car. It's just the price you pay in some cases.
The 3.73 AAM gears should be quiet. These gears, along with 4.10 gears, were installed in countless S10 pick up trucks and Blazers with no problems. I'm still betting that they were set up like 5 cut gears instead of 2 cut gears.
Interesting. Mine are 5 cut Yukon gears . Pretty sure they are just rebranded yu-lick-long-ding-dong chinesium..... Recycled pinto fenders and the tears of orphans....
It would be nice if someone made some decent 9 bolt gears. It's stronger than a 10 bolt and now we have Torsen diffs from Australia. Seems like it shouldn't be that hard to do.
The 3.70 gears for the 9 bolt are pretty much all made by one manufacturer and put in someone else's box. I haven't seen one set yet that was quiet, no matter how well they were set up. AAM is the factory gear supplier for the 7.5/7.6 and 8.5/8.6 GM rear ends. Their quality is better than all of the others, and the price shows it. The AAM gears should be quiet when set up correctly.
Their quality is better than all of the others, and the price shows it. The AAM gears should be quiet when set up correctly.
Which is exactly why i am frustrated. I paid the premium because i wanted exactly that, quiet.......at this point, i feel as though it was wasted money and i should have just went with the motive gears like i was originally thinking of doing. I talked to another shop yesterday and didn't get a comfortable feeling that they are well experienced with setting up the new 2 cut, so i think i will give the original shop a call again to discuss first and see where that ends up.
SOFA - As for the actual specs of how he set it up, he didn't go into detail so i am not sure, but all new bearings were put in. For it being a bearing as opposed to gears, would bearing noise not be more consistent? This clearly completely goes away when off the gas and comes back when on. To me it sounds like gear noise when comparing to other failing bearing noises (eg. wheel) that i am used to.
The head bearing is loaded when the engine is pushing the car; the tail bearing when the engine is dragging the car. So their noise can change quite a bit accordingly. If the head bearing outer race got chipped during installation for example, it can make a moaning or whining type noise that's very similar to gear noise.
I agree, they should be mostly if not completely quiet... I have several sets of 3.73 gears in my driveway, of which I've done the setup on at least 3 that I can recall, and they're all pretty much like a new car in that regard. Very little noise if any. Not knowing how much noise yours are making, it's hard to guess whether it's enough to indicate a problem, of course.
So what's with the 5th gen Camaro gear whine complaints? Are those not AAM gears?
Not contradicting anyone cause you guys know a lot more than me - just curious. I had to learn a LOT about gear setup, tooth cut, hobbed vs. milled, 5 cut vs 2 cut, etc, etc when I did my 9 bolt. I wanted to be SURE I got it right. I was also pretty discouraged when the whining started shortly after "break in" (which I'm not convinced is even a thing for street gears), but after driving it for thousands of miles and seeing the gears a few more times during my carrier swap, and reading all the reports of 9 bolt 3.70 gear whine, I don't worry myself about it anymore. Apparently nothing I did could have avoided it.
Not knowing how much noise yours are making, it's hard to guess whether it's enough to indicate a problem, of course.
I agree, that's the problem. I am comparing it to the 3.42's that were in there which were completely quiet on accel and coast.....and that's with 200,000 miles on them too. there was a tiny bit of whine on decel at slow speeds gearing down (like getting ready to go around a corner), but when out cruising, nothing.
I have the 7.5/7.625 10 bolt with 4.10 gears. The first set whined and I lost that set due to the ring gear bolts loosening up. The second set I deburred the edges of every gear tooth (both ring & pinion gears) with a Dremel and a bit similar to a chainsaw chain sharpening bit. I used RED Loctite on the ring gear bolts. Backlash ended up at .010". BFL racing gear lube was used with NO additive. I have NO GEAR WHINE COMPARED TO THE FIRST 4.10 SET.
I'm not claiming anything here, this is just my experience. Can I set up a rear end better than anybody else? Probably not. This is just for info. Try it for yourself, if you wish.
I've had problems with the ring gear bolts with the 5/8 head backing out. I don't use them anymore. The contact area under the head is too small and they won't stay tight. I only use the bolts with the 3/4 inch head.
So to revive this thread and unfortunate experience, i got discouraged for a bit and then life just got too busy and the rearend has just sat there packed away in the garage since. So i pulled it out today after getting motivated again and cracked it open to first measure the backlash and put some compound on it to see the pattern before deciding to take it to another shop, and i found, what i would consider, an excessive amount of sludge in the bottom. This is only after about 30 miles or so. There wasn't much built up on the magnet though and the fluid looked fairly clear (other than the sludge) with no real glitter.
First of all, is this normal after new gears and new bearings? and 2nd, could this be clutch material? When i got the rearend used from a 91, it was fairly low mileage and quite clean in comparison inside. Is there something really wrong here besides the annoying noise?
You will have to do a complete tear down and inspection of this. First, take a pattern check before anything as recommended earlier. If this is clutch material, I would do a "run out" on the tires. They must be the same. This can wear clutches somewhat quickly, and is hard on the pinion gears in the posi.
[QUOTE=I would do a "run out" on the tires. They must be the same. [/QUOTE]
Do you mean check endplay on the axles?
Before it was ever put in the car I had to have the end of the new axle machined down because there was too much thickness on the other side of the C clip and I had to use a hammer to get the axle locking pin out.
Ok, so here's what i found........I checked backlash in 3 different spots and it seems to be .007 - .008". 7 in two of the 3 spots.
Here is the pattern check. As per above these are the newer style hob faced gears (AAM) and there is noise when on the gas / cruising. Perfectly quiet when you let off the gas.
I still suspect a bearing problem, not a gear one. I'd recommend changing the pinion bearings and re-using the shim that's behind the one, esp if it's .035" as it most likely should be.
I wonder if all that sludge in the housing is perhaps related to that carrier being a stock Auburn POS?
Isn't the drive/accel side too far to the heel? It's definitely not centered, and that is where the noise is. What would tightening the backlash a bit do given that it is a bit higher than AAM calls for? would it move both marks in the same direction?
Heel and toe don't matter in the slightest as in the above pictures of good patterns. What matters is that the pattern be centered between flank and face.
Your pattern is perfect. The whine is either a bearing issue or an artifact of the way the gear is cut. My 3.70 Motive (Yukon, but same same on a 9 bolt) gears are setup perfectly with a pinion depth gauge and the pattern looks very much similar to yours. I have the same whine at light throttle. No noise at coast and no noise (that I can tell over the engine) at WOT. I have about 7,000 miles on them now and have changed the gear oil twice and pulled the cover once. There is no indication of unusual wear or problems. That's just how they cut the gears.
Heel and toe don't matter in the slightest as in the above pictures of good patterns. What matters is that the pattern be centered between flank and face.
Your pattern is perfect. The whine is either a bearing issue or an artifact of the way the gear is cut. My 3.70 Motive (Yukon, but same same on a 9 bolt) gears are setup perfectly with a pinion depth gauge and the pattern looks very much similar to yours. I have the same whine at light throttle. No noise at coast and no noise (that I can tell over the engine) at WOT. I have about 7,000 miles on them now and have changed the gear oil twice and pulled the cover once. There is no indication of unusual wear or problems. That's just how they cut the gears.
My exhaust is loud. I don't care.
GD
Wow, there is some very confusing information out there then! I really don't know what to make of it all given that different sources out there say different things.. Interestingly enough some of the above pics I think are right from one of the gear manufacturers, yet pics from another gear manufacturer said adjustments are necessary if pattern it too close to the end. And then some tutorials online say the bottom third is good as under load the pattern moves towards the heel. Confusing! But thanks to you and others for your input and experiences.
If i would have known this was going to be the outcome though, i would have just went for the cheaper motive gears or something. Reputation of being quiet was the only reason i spent the extra on the AAM gears. In that respect i feel as though i wasted my money. I will double-check the bearings but i am quite confident it is gear noise as well as others who i had in the car at the time.
Now hopefully the excessive sludge in there isn't a serious issue of some kind........
Wow, there is some very confusing information out there then! I really don't know what to make of it all given that different sources out there say different things.. Interestingly enough some of the above pics I think are right from one of the gear manufacturers, yet pics from another gear manufacturer said adjustments are necessary if pattern it too close to the end. And then some tutorials online say the bottom third is good as under load the pattern moves towards the heel. Confusing! But thanks to you and others for your input and experiences.
If i would have known this was going to be the outcome though, i would have just went for the cheaper motive gears or something. Reputation of being quiet was the only reason i spent the extra on the AAM gears. In that respect i feel as though i wasted my money. I will double-check the bearings but i am quite confident it is gear noise as well as others who i had in the car at the time.
Now hopefully the excessive sludge in there isn't a serious issue of some kind........
Hey Eddie, came across this old post. I’m having similar gear noise on my 4.56 gears, trying to determine if it’s normal. Everything inside the rear end looks good. Did you ever check your bearings, what did you conclude on the noise? Thanks!
11-14-2016, 08:06 PM
