Whining noise on decel 8 3/4 Posi

[72 charger]

Have a 8 3/4 that I just had a repo sure grip unit put in with a new hoosier ring and pinion gear 3.55 installed. All new bearings the whole shebang. Had it professionally set up and have royal purple synthetic gear oil in it for limited slip rears. But once you rear around probably 40 or so mph if you let off the throttle the rear end whines loud enough to hear over the exhaust. Called the guy who set it up says it may be from the brand of gears I bought. We also thought maybe its just because everything in the rear is brand new. Whats everyone's opinion?

 

[RustyRatRod]

The pinion gear depth is set incorrectly. It needs to be redone.

 

[72 charger]

The pinion gear depth is set incorrectly. It needs to be redone.

Is it to deep or shallow?

 

[RustyRatRod]

I cannot remember. It's one or the other, but I can never remember which.

 

[Powerflite]

This kind of noise can also occur if you have the pinion angle set too low. This is unlikely to be the cause unless the spring perches were moved from the stock position though.

 

[Supershafts]

Yeah Rusty got it, decel noise is usually to deep or sometimes BL is tight.

Which gear company did you use

 

[Cranky]

Yup, pinion is too deep....if BL is too tight, it will burn the gears up in short order.

 

[72 charger]

I bought everything as a kit order from a guy on ebay called Doctor Diff. The ring and pinion says Hoosier. I had the guy would set up the carrier come listen to the noise and he said it needs approximately .003 taken out. He also said that based on his experience he and a few other guys he knows tend to try and set them a little too deep because its supposed to "strengthen" the rear-end. He said he would take it out for me no problem but the only issue that it will have is the whining noise. I told him if that's it ill live with it for now rather than go through the trouble of tearing it all apart. Is he being truthful?

 

[RustyRatRod]

First things first. Dr. Diff is a great guy to do business with. You really scored when you did that. He is one of the most helpful people you'll ever run across.

Now, let me see if I can help you understand. When you purchase ring and pinion gears, they come with a "suggested" pinion gear depth setting. This is used only as a guide to get you close. Since each rear end and ring and pinion, bearings shims and the like differs just a little in production tolerances, those specs are only meant to get you in the ballpark. The installer is supposed to have enough experience to take it from there.

From what you've posted so far, I don't believe your installer is very knowledgable about setting up gears. That doesn't necessarily make him dishonest. There are a lot of mechanics out there who skate by and get away with it.

What should be done is, get it in the ballpark by whatever specs came with the ring and pinion. After that, look at the pattern. From there, adjust by the PATTERN. Get the pattern right and you'll not have a drop of noise.

 

[Supershafts]

Setting them deep runs the tooth contact more at the root, it doesn't necessarily mean it's going to be a guarantee it doesn't break,, it is a guarantee it is going to be noisey.
If you are racing and going to be setting 1.3 to high 1.1 60's with a overweight mopar and using the 8.75 then you play games with adjustments made for other reasoning, AND THAT's AFTER you have the ring and pin treated and go to the better AL case (if allowed for that classes rules).
If you aren't doing that then set them up correctly.

As RRR said you should start with what the gear manufacture says by following their depth and bl measurements, however always run a pattern check after, if it's not center of tooth heel to toe and center of tooth root to crown then you want to adjust to get it there.