8-3/4 Noise After Rebuild..What's Normal??

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pastortom1

pastortom1

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Hey guys............

We took in an 8-3/4 for a rebuild a few weeks ago...actually a month ago....it was whining something fierce on deceleration....we've brought up the topic before on this forum.

Instead of just adjusting it, I had them put in a new ring & pinion set and bearings........I have it back now, after a month..... I think these guys had some trouble they're not telling me about, but it's over the dam now....

At any rate, there is still noticeable driveline noise now, but it's equally split on acceleration and deceleration, with just a slight quiet spot between.....it's still too noisy in my opinion, although it is definitely much quieter now than it was.

I'm also noticing gear noises when I corner sharply, and I'm wondering exactly what, under normal circumstances, I should be hearing....???

What's normal for this scenario? What's the best way to "break-in" these gears.........will they actually quiet down a bit more after a break in?..........will a better lube help the noise level, or help a break-in? Will figure 8's help when the gears are new?

I just haven't had enough experience with rear-ends to know what's right and wrong by "listening"..............

If some pro's could respond, I'd really appreciate it. :thumblef:
 
did you put friction modifier lube in it? even the sta-lube brand limited slip fluid needs more added. what brand of gears? some are noisier than others.
 
I was told that they're Mopar High Perf. gears, although they haven't produced the paperwork I was promised....They'd better pretty soon though.......

They've put no additives in the rear.......straight 90 against my wishes....I asked if they could put in the royal purple, but I guess they didn't have the time to monkey with it........(ain't customer service grand sometimes?...)

So, with a rebuild, new 3.55 gears set and bearings, what's normal?? What should I expect, and what about a "break-in"............will it quiet down a little more?.......................

Come on......I need input....................:drinkers:
 
You need to add some friction modifyer. I just installed a new 4.10's and a rebuilt Sure-grip in my 8 3/4, it chattered bad, especially around sharp turns. I added the sure grip additive, it has stopped! I have heard that 4,000 miles break in but I have hammered on mine since I put it in!! :burnout:
 
I installed a Auburn limited slip differential in my truck awhile back with 4.56 gears. Auburn gear says point blank no synthetic blend of gear oil of any kind it will void the warranty. I used the dino 90w. I put 500 miles on it and then changed the oil. Some drive it longer and shorter periods of time before they change it. I added Mopar limited slip additive and it has been fine ever since. I have no gear noise at all. You shouldn't either but I did change the gears out on a 8 3/4 that was in a Charger I had and it made a little noise on deceleration. But I mean it was just barely noticeable and I just lived with it. I believe it was better to use dino 90 in the break in period myself and go with synthetic. But Auburn gear is against it period for some reason.

I used Motive gears in my truck and Yukon in the Charger. I have always heard that Yukon are noisy.
 
Did you check the wear pattern when you installed the gears? At what speeds are you cornering? If it is above 30 mph or so, I do not think the noise would be the sure grip. The sure grip would not cause the noise when going straight either. If your cornering noise is at slow speeds then maybe friction modifier will help that. If it at higher speeds then maybe an axle bearing noise since corning puts more weight on the outside bearing, sometimes making it louder if the bearing is rough. As far as the noise on accel and decel, it sounds like gear noise since it is quiet on transition between coast and cruise. I have installed a couple of dozens of gears of different brands over the years and have never seen a gear set get quieter after brake in. If they are noisey when installed then they stay noisey. EVERYBODY manufactor of gears will have some noiser than others. I once while checking out a brand new Ford pickup with 2 miles on it, found very loud gear noise on decel only. Changed gear set and all was quiet. If you could not get a good wear pattern when setting your gears up, I would try another gear set. If two gear sets will not have a good pattern then you should get another case. I hope this helps, Ray
 
When you guys state "friction modifier", are you talking about the whale oil additive?.............and should I add it now, or drive the thing for a break-in, then drain and add or change the oil..........and what about the royal purple for the oil after some miles............I've heard this oil is the best from a lot of pro's..........BUT, need input from you guys...........:book:
 
pastortom1 said:
When you guys state "friction modifier", are you talking about the whale oil additive?.............and should I add it now, or drive the thing for a break-in, then drain and add or change the oil..........and what about the royal purple for the oil after some miles............I've heard this oil is the best from a lot of pro's..........BUT, need input from you guys...........:book:
Click to expand...

I would stictly use Mopar limited slip additive. I bought it at the dealership. All you need is 4oz of it for each oil change. I added the additive before break in and after so either way I was safe. I've can't help you out on the royal purple since I wasn't allowed to use it with the Auburn gear carrier so didn't use it but I know it is great stuff.
 
you need to add it now. and make sure that your gear oil is NOT synthetic. using lucas or stay lube +bottle of friction modifier. find out what brand of gears they put in it. what exactly is Mopar HIPERF gears?

actual breakin of how it was explained to me, in is about 20 minutes of driving and let cool for about 20-30 minutes then for 40 minutes let cool and hour. then change fluid at 500 miles.
 
pastortom1 said:
When you guys state "friction modifier", are you talking about the whale oil additive?.............and should I add it now, or drive the thing for a break-in, then drain and add or change the oil..........and what about the royal purple for the oil after some miles............I've heard this oil is the best from a lot of pro's..........BUT, need input from you guys...........:book:
Click to expand...

Pastortom, you need to get some of the limited slip/posi additive in that rear "ASAP" and both GMC and Mopar dealers carry it. You haven't mentioned how many miles you've got on the gears (I realize it's not much) but I'd give them at least 1000 miles to quiet down. Keep the builder in the loop so that if someting does go wrong they're still on the hook. Personally I've heard gears that had a slight whine like you can't hear the whine over the car radio and last for years.

terry
 
Maybe this will clear things up a bit. This is off RANDY'S RING AND PINION:

What is the break-in proceedure for a new set of gears?
All new gear sets require a break-in period to prevent damage from overheating. After driving the first 15 or 20 miles it is best to let the differential cool before proceeding. I recommend at least 500 miles before towing. I also recommend towing for very short distances (less than 15 miles) and letting the differential cool before continuing during the first 45 towing miles. This may seem unnecessary but I have seen many differentials damaged from being loaded before the gear set was broken in.
I also recommend changing the gear oil after the first 500 miles. This will remove any metal particles or phosphorus coating that has come from the new gear set.
 
Well guys, with all the input here, I should be OK..........Gotta call the shop that put them in and get on their case for the paperwork and details on the lube they used.

Thanks a bunch............ I'll keep the forum posted on how it develops...............:computer:
 
Guys, I've been running the car around town, not hammering it, just to get the gears broken in a bit..... the noise is equal on accel and decel, BUT, it whines abnormally (perhaps not for new gears, but I've never heard it before) when you corner tightly from street to street........both directions are equal whines, and definitely in the gearset.....kind of high pitched going around the corner.

BUT..........try to back out of a parking spot, and the gears try to lock up......bumping and grinding........really nasty........not when you back up straight, only when you turn either direction............

I don't think the gears are set up right, but I could be wrong........what's your first impression here from your experience???????

....................this is a good shop that did this.....racers themselves........I'm not sure how to handle this one..........if I just need a friction modifier to start making this slip freely, I'd hate to take the car back and give them a hard time...........................

Help......................:shaking:
 
It sounds like you better take it back. Some rear end noise is acceptable (according to my transmission rear gear specialist). I had mine checked, previous owner didn't set it up right.

Yours just doesn't sound right at all. Bring it back.

Just my opininon.
 
redfastback said:
you need to add it now. and make sure that your gear oil is NOT synthetic. using lucas or stay lube +bottle of friction modifier. find out what brand of gears they put in it. what exactly is Mopar HIPERF gears?

actual breakin of how it was explained to me, in is about 20 minutes of driving and let cool for about 20-30 minutes then for 40 minutes let cool and hour. then change fluid at 500 miles.
Click to expand...

Hey Red

What's the issue with syn lube?

The only thing I can think of is that the internal parts don't stay 'as coated' over time compared to dino.
 
If you're sure it's "gear" noise (which it sounds like), then all the posi lube stuff is just barking up the wrong tree. You'll potentially experience three types of gear noise: Accel, decel, and coast. If it's a high-pitched whining sound you're hearing on both accel and decel going straight down the road that changes frequency in direct proportion to speed which still persists after a a couple hundred miles of break in, then they are definitely not set up right. Probably excessive backlash.

My 3.73 gearset is a cheapie chinese version that has a coast whine to it. It shows good pattern both ways, and runs fine. Sometimes there's gona be a little noise, especialy with the less than quality gears. But yours definitely sounds like a setup problem.
 
It was NOT a good shop that built your rear end because a good shop doesn't just not put friction modifier in with the oil in a sure-grip rear end. Plus, they haven't given you the paper work AND they IGNORED your requests for certain things like the oil. I installed a set of 3.90 gears in my old 7.25" rear end about a year ago and didn't set them up properly and didn't break them in (I was too excited I guess and didn't realize the importance of proper setup and break in at the time) The gears whined LOUD on accel and decel, people thought the car was supercharged lol and were quiet when cruising at a steady speed like you describe. I lost a tooth off the ring gear after about one week. Anytime I had nasty grinding noises and gears trying to lock up while turning, it was because my spider (differential) gears were completely destroyed and broken apart. Forget "performance" shops. They are almost all the same. Their attitude is that they are racers and know everything about racing so specs (like pinion depth and backlash) can be done by feel because they are THAT good with racecars and they don't need to worry about paperwork and customer service because it's not a fleet service shop or dealership, it's a racecar shop and you're just an easy going guy with a racecar. That's total bullshit. Take your car to a dealership or OEM type well-known cahin shop where they will listen to your requests, use a dial indicator to setup your gears, check the wear pattern with grease on the teeth etc. and also provide you with you paperwork and give you a LONG warranty period. Just because it's a performance car doesn't mean it doesn't need to be setup using tight OEM specs etc. On the contrary, it needs to be done even better than OEM would have it. Often, guys in race shops have been building cars and racing for a long time, but have no ASE certification or other certifications. Guys at dealerships and well known chain shops will have proper training and do things right. They'll also treat you better. As you can see, "Ricky Racer" type guys piss me off to no end because they don't do things right. I used to be that way, but I only worked on my own car, not other people's cars. Get your money back and take the rear end to a place that'll do it right. My 904 trans was done at a race shop and it blew 3 sprags, needing a new case each time, and now it flares up when shifting from 2nd to 3rd gear under WOT. It's only behind 220 hp in a 3200 lb car....Not a huge challenge. Stick with a dealership or OEM chain shop that'll do it for you and you'll be much happier. If left much longer, I guarantee your rear end will blow up. It'll probably be under full throttle and will shock your transmission badly and blow your sprag clutch.
 
I'd take it back if i were you,set up properly there should be no noise coming from the rearend....
 
I called the garage, and they're taking it back in tomorrow morning....I just can't believe that after a month in that shop they still don't have it right.....and get this..... I told them I needed complete documentation on the gears set, and the tech states he "threw it out".....ON A GEAR SET HE CHARGED ME $477. FOR !!!!!!!

Just goes to show you how few these days can be trusted.....this shop has had a good reputation, but this has me frosted.....

I had 3 buyers lined up, and lost every one due to the time frame involved, and now this malarkey........

:angryfir:
 
on gears that are noisy, sometimes they can be setup correct and still be noisy. This is the case on a lot of after market cheap crappy gear sets. Seen this 100s of times since I was in the buis. back in the mid 70's till now.

So even if they tell you it is setup OK, then they need a new better gear set.

Sometimes it is cheap steel, somtimes the pitch of the teeth and and many other factors. But if it is noisy on coast and load most likely the gears are way to deeply meshed or bad... My 2 1/2 cents.

good luck!
:drinkers:
 
pastortom1 said:
I called the garage, and they're taking it back in tomorrow morning....I just can't believe that after a month in that shop they still don't have it right.....and get this..... I told them I needed complete documentation on the gears set, and the tech states he "threw it out".....ON A GEAR SET HE CHARGED ME $477. FOR !!!!!!!

Just goes to show you how few these days can be trusted.....this shop has had a good reputation, but this has me frosted.....

I had 3 buyers lined up, and lost every one due to the time frame involved, and now this malarkey........

:angryfir:
Click to expand...

Are you saying he charged you 477.00 for a set of gears,thats over 200.00 more then you should have paid..and as far as noise any center section that i've had setup or bought set up did NOT make noise,and they won't if they're properly set up...
 
I was charged $477. for the gear set, including bearings and a "rebuild kit" as he puts it........what he probably did was charge me for a Posi rebuild as well............there's no labor in that charge........:disgust:
 
That's not too bad a price "if" it included a good quality gearset along with "all" the rebuild parts. But in any case, I doubt it's properly set up. My Chinese no-name 3.73's are quiet except for a mild coast whine. My Yukon 3.91's are made in China, but quiet.

Noise bad. Quiet good. Pretty simple. I think you knew that.
 
477.00 for gears, bearings, and labor????? what??? out here you get charged at best 800.00.
 
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