Hey everyone,

Got another curve ball to throw at you. So I got a shop (VERY reputable guy) to install my new 4.777 final from a 09 into my rear...well.. the results were interesting. After three attempts, we cannot figure out why it is doing this.

1. Under throttle, even the slightest, it is very smooth and quiet and consistent feeling.
2. The SECOND you let off the throttle completely WITH THE GEAR ENGAGED...you hear a whining noise coming from the rear end, like whining down. The higher the RPM..the higher pitched the sound. We have absolutely no idea what it could be. We checked the service manual for something we may have missed, pulled it apart 3 times and still no dice. If ANYONE has heard of anything like this with any recommendation, or it just needs to be broken in (Already driven 70 miles with it making this noise) please let me know. It's annoying as hell and doesn't sit well in my gut.
3. My speedometer is incorrect.. I forgot what he said exactly (it was 1am when I picked up the car...) but I remember him saying it was now 107% ..so at 60, i'll be doing mid 50's. Does anyone know how to correct the speedometer? perhaps with Cobb? Or do I have to have the dealership do it?

Thanks everyone for the help... Now I'm heading to bed after all that driving. :/

 

Bump.. I really am hoping for some sort of answer or anything to this. Anyone?

 

Is your car an AT?
Anyway a whining sound might come from the gears not spaced correctly. You might hear a little whining during the break-in with shorter final gears but usually after a while it reall lows down or disappear (as in my case).
I had a "clicking" sound as a problem but that was due to broken bolts in the FEED final gear, a way poorer design and build quality in my opinion.

 

Gotcha. Sorry I should've specified. It's a 6speed Manual and it has a 09 RX8 ring and pinion in it. Stock LSD. It's only when letting go of the throttle completely while in gear that it makes this whining noise. I'm at about 85 miles on it now, whats the usual break in period?

 

I'm not sure about the usual break-in period but my sound stabilized after about 1000km.
I asked if it was an automatic because of the even longer final gear they have and your tacho offset.
I don't know how direct of a swap the final gear is with an OEM 4.777, i know for sure that we had to machine the ring spacer and the pinion collar on the FEED one. Did they do any machining at all?
Differentials tend to be pretty delicate to work at, they require a lot of precision and some skills with the proper tools.

 

More of a whining, that was my mistake. I wrote the post at 2am after 4 hours of driving..lol. Sorry Ray. But it's a whining. And thats funny because thats what the Mazda service tech has a hunch it could be as well.

Forgot to ask, is this damaging anything in the meantime..? Or am I okay until I can take it to him?

 

I didn't think much about the depth itself but you could either have to adjust it or to work the collar's height i think. Or both!

 

Sure but provided that the differential's interior is the same then adjusting the depth should be quite easy!
The point is: didn't the shop do any test before closing the box?

 

Yeah I guess it could be that then. Thanks a lot for the help everyone...I'll go rain on his parade and have him fix it for me. His mistake, not mine. I'm just a driver. :/ Hopefully thats the fix. Thanks again!

 

Gotcha. Thanks again for the help Ray.

 

If you read my 4.77 final drive post there is a pinion crush collar that directly sets the pinion depth spacing. You only get one shot to set the pinion depth with each of these collars since they crush to the correctly set depth. You cannot reuse the stock one.

Preferably have a transmission shop work on it, since they have the tools to do the measurements and adjustments correctly rather than a regular mechanic.

 

In otherwords I should take it to the dealership. lol. They have a diff specialist I know personally and he knows a lot. Good to know. I figured he was good considering he builds race cars all day for a living..and not just race cars as in takes a RX8 and strips it and does crazy things..race cars like.. well.. his cars look like formula cars basically. and he designs them and builds all the parts and everything.

 

Yeah, I guess I was trying to make good ties with a reputable race car driver/shop owner and all that.. big mistake it seems?

 

lol ..Not the guy I went to? :P Thats awesome to hear though, really looking forward to the results Ray. God only knows whats gonna happen here, it really sounds like I need to take my car to the dealership and basically pay another $800...

 

no its not incorrect from this mod

 

I know this old guy who's been building diffs for close to 50 years. He asked me "Why didn't that guy have his diff built by me. I wasn't sure how to respond .

Paul.

 

?? How so?

lol Paul, well I didn't know that was an option I had to buy a whole new rear end I think it's narrowed down to the crush washer needs to be replaced because he used all the old stuff. Can't do anything about it this weekend because he's in NY racing in SCCA Nationals right now, so we'll see I guess.

 

Vehicle speed is based on how fast the tires rotate (then multiplied by the tire circumference and you have speed). So messing with tire size can throw off the speedometer but not the rear gear,

 

Not so, the speed reading is taken from a gear in the transmission. So, changing the final gear ratio in the diff will change the speedo reading.

 

Huh? I would think they use a wheel speed sensor or the like. There is no speedo drive on the tranny.....or any wiring to anything that I remember?? The tranny drive gear thing is old school

 

You know it's funny because he said everything is engaged properly, he said he saw no defect with anything being put in improperly, so maybe I can drive it as I need to and just replace that crush washer that does the back lash and from there I could be set.. I don't know. Who knows. Just trying to be as positive as possible about this...

As for the speedometer, I was correct, rounded off, at 60 I'll actually be going 56 miles per hour. So not a big deal. For the most part, the car feels fine, no noise when I use the throttle and everything is okay, just like I said, I let off the throttle and I hear a whining noise from the rear that resonates to the outside. Not insanely loud, but loud enough to notice.

 

Just a heads up..it's gotten worse. Coasting on the highway, OUT of gear, I hear a quieter whining noise that goes with the speed of the tires. In gear, I hear a bit of a deeper sound that I can't really explain... So I have a feeling this is just getting worse. :/

 

dead on, not setup properly

you have to use a bluing dye on the ring teeth and verify the pinion tooth engagement pattern on the ring