Gear Whine 3:73's

[chobracobra]

Latley my car has been making a smooth whining sound from the rear. At low speed and high speed the whining is apparent and pretty loud around 15 mph. I did a gear oil change with Lucas oil and the whining died down but is still there. is this just normal and unavoidable because of the higher number of teeth? or should i be worried about something? The gears look in great shape with no abnormal wear. thanks!

 

[srothfuss]

Who installed your gears? (I like to ask questions before I answer) There are two common causes of gear whine:

1) When gears are new (new teeth are straight cut) the teeth need to develop the wear pattern. This rounds the corners enought to quite the whine down.

2) The gears were installed incorrectly and there is too much play between the ring and pinion. This condition can be corrected by reinstalling the gears and properly setting the back lash

 

[bcd]

MY 99 did that when i had the 373s put in. i added a whole tube of limited slip additive and it never did it again

 

[tjm73]

MY 99 did that when i had the 373s put in. i added a whole tube of limited slip additive and it never did it again

Was friction modifier additive used? It should be with new gears and traction-lok clutch packs.

If it's real bad I'd suspect they were installed wrong.





bcd - I wanna see the full screen version of your avatar..............

 

[bcd]

found it at big-boys.com in one of the picture galleries. check it out some time. the one i use on the corral has a picture of a beaver and says happiness is a wet beaver i like that one pretty good too

 

[txstang84]

the friction modifier is for the clutch plates only-it keeps them from chattering around corners, it has nothing to do with quieting the gears

like srothfuss said, the gear noise is more than likely backlash setting, or part of the break-in.

let me add a question, what brand gears did you choose, FRPP's have a wonderful history of being very quiet if installed and broken in properly, I've also heard good things about motive from local shops who install gears regularly. Richmond on the other hand, has a long history of being a noisy gearset no matter how well it's set up...i do know that one from experience

Also, did you do a proper break-in? proper break-in consists of approximately 300 miles with periods of continuous use not to exceed 45min or 50mph....basically city driving.

another measurement which will make some noise is pinion depth, instead of backlash where there is too much or too little "play" between the pinion and ring gear teeth, pinion depth is too shallow or too deep gear engagment....but it can make a similar noise.

if the noise gets any worse within your next two tanks of gas, i'd take it back, and have whoever installed them, ck all the tolerances (backlash, pinion depth, and carrier, and pinion bearing preload)

good luck!

 

[bcd]

here is the link for my avatar
http://www.big-boys.com/pictures/picture1350.html

 

[chobracobra]

The gears have about 10,000 miles on them. I think the whining was always there, its just that up until recently it got worse. From my understanding, i do not need to add a friction modifyer because the gear lube claims to have it. Am i wrong? Please let me know and i will run out and add some if its needed. thanks in advance everyone.

 

[tjm73]

The gears have about 10,000 miles on them. I think the whining was always there, its just that up until recently it got worse. From my understanding, i do not need to add a friction modifyer because the gear lube claims to have it. Am i wrong? Please let me know and i will run out and add some if its needed. thanks in advance everyone.

Is that about 10,000 miles with you (ie used) or 10,000 miles since they were installed brand new?

 

[chobracobra]

No unforntutally i did not get to tackle the gears myself, but too be honest i am not worried about the break in because the guy who i bought the car from, really knew what he was doing and did a great job on everything else. I want to emphasize that the whining does not sound severe, it actually is a smooth whining that varies with mph and "almost" sounds like a tiny turbine at high speeds. maybe i am worried about nothing. anyone else on the friction modifyer question? thanks

 

[srothfuss]

If you buy the expensive gear oils, the friction modifier is already included in the bottles... If you buy the cheap stuff, then you need to add some modifier.


Edit: If your noise is getting louder you should really take the cover off and look for damage. Sometimes with new gear installs, metal shavings can get lodged in the differental and cause all kinds of problems.

And richmond gears are VERY loud! I had the same shop do a set of richmond 3.73's in an old F-body that I had... Good gear, too much noise for me. My FRPP's are quite.

 

[txstang84]

ummm, well, you should add the friction modifier since Ford recommends it, it can make the clutches in your trac loc chatter around corners...but once again, it has nothing to do with the gear noise.

if the gear noise is getting worse, and they've got 10k on them, you might want to have them ck'd. if you have a Harbor Freight nearby, you could pick up a cheap dial indicator and magnetic stand and ck the backlash yourself. they should be about 0.007"-0.009" for street/strip use (road race and autocross requires a little more lash since they are constantly beaten on)...much more than that, and they will make some noise. you could also see how much rotation you get from trying to spin the driveshaft by hand while the car is parked. if it feels at all sloppy, then your backlash is probably out

when you changed the fluid, did you happen to notice how the wear pattern looked on the teeth? was it centered on the ring gear teeth? did it contact the entire gear face? or was it shifted to one side...?

 

[chobracobra]

The wear on the gear faces looked normal and healthy, but srothfuss mentioned that Richmond gears are noisy, there is a possibility that they may be Richmonds, because the owner used FRPP on everything else but left out a brand on the gears. The metal shavings on the magnet were minimal, basically 10k's worth. maybe he changed the fluid after they broke in. by the way i used Lucas oil 80w/90

 

[txstang84]

no, i said richmonds are noisy...

if they are richmonds, they will say it on the ring gear right next to the tooth count...that's how mine came anyway.

well, like i mentioned before, if it gets much worse, take them in and have the tolerances ck'd. and as long as your diff isn't chattering around corners, then you won't need to put in the friction modifier.

 

[chobracobra]

alright cool, thanks everyone. i have a dial indicator and if it gets worse i will check those tolerances, maybe i shoulda asked here before i took the cover off.

 

[nosmatt]

Have you jacked up the car, and listened near the rear end?

gear noise is not "turbine" like, that is high pitch, gear whine is a lower frequency, and usually will be noisier on decel, or accel. a constant noise at speed, with silence at decel, or acel is a different problem, more likely pinion depth.
both too little backlash, and too much backlash will cause noise.


aod's are very likely to make noise as well, the roller clutches when takin a sh1t will many times make a very high pitched, constant whine.


i would try to isolate, and verify where it is comeing from.