rear end noise when cruising on highway

[JeffS197]

Hello,

I have a 2005 S197 Convertible that I picked up a few weeks ago. It has around 75K miles.

Its a 5-speed and the previous owner installed a set of 3.73s last year.

When I am cruising on the highway I notice a whining sound from the rear end whenever I am giving it any gas. Not sure if it is more prevalent than normal just because its a convertible, but with the top up it is very noticeable. Top down all you hear is wind anyways.

The slightest throttle (IE just cruising in 5th) causes the whine and as soon as I let off the gas it is gone.

Did not notice it until recently as I usually have the radio on but thanks to the wife having a headache I was driving with no music and then what do ya know, now its the damn whine from the rear end giving her a headache (dear god does it ever end with women?).

Do not really hear it driving around town or at all when decelerating or coasting, just when I am giving it gas on the highway cruising along in 5th. Its loud enough that when I have the cruise control on I can tell when the gas is being applied to maintain the set speed just listening to when the whine starts/stops. Hell it even drowns out the sound of my Ford Racing axle back when cruising it 5th at very light throttle.

This is my first Mustang and first rwd car for that matter so I am not sure how much noise (if any) is normal to hear from the rear end.

I figured that perhaps the diff fluid was not changed when the previous owner did the 3.73s so I checked the fluid and it seemed relatively clean.

Are there any known issues I should be looking into or anything in particular that I can investigate myself in my driveway before spending money on bringing it to a shop to diagnose?

From previous experiences with all types of cars most shops do not take the "I hear a noise" requests very seriously and do their best to humour you until something is physically broken upon inspection so I dont really want to throw away money for a shop to tell me "looks fine come back when its worse".

Thanks, Jeff

 

[07 Boss]

Gear noise during acceleration is usually and indication that the gears are worn and aren't meshing properly. This can be caused by being improperly set up during install, overloading or lack of lubrication. If fluid levels are OK then I think the only recourse is to replace them. Many might say gear noise is normal but I'm not one of those. But in that respect if it's not howling I might just leave them alone. If it bothers you, replace them.

 

[weather man]

3.73's are a tough gear set to keep quiet. I replaced mine with 4.10's.

 

[JeffS197]

ok thanks for the responses.

I can still make a nice big number 11 so I dont think its related to the clutches.

Its not so loud that I feel its going to blow up or anything so I will just keep an eye (or ear I guess) on it and if it starts to get louder will look into new gears. 4.10s would be a bit nuts for me as I commute over 50 miles a day on the highway to/from work. I already feel like the engine is revving high while cruising in 5th with the 3.73s. Too bad theres no 6th gear to drop the rpms.

I also found some info about a friction modifier additive I might try out if it gets worse. I got paper work for everything done when I bought the car and the previous owner had the 3.55s replaced last year with the 3.73s but cant tell from the paperwork if they reused the old fluid or added new fluid though it does look pretty clean.

I guess I could always call the place that did the work and complain or something but if its the norm for the 3.73s to whine a bit thats OK with me as long as the diff isnt going to blow up on me I think I will just live with it rather than risk them taking it apart and possibly screwing something up.

Thanks for the info guys.

 

[85GT 7.0]

Noise

Don't waste your money on the friction modifer it will not help the noise. Is's purpose is to keep the clutches in the differential from chattering when you turn.

 

[Wicked GT]

Have you replaced the factory driveshaft with a one piece? I have a small whine when cruising on the highway and think mine is due to the pinion angle being off a little as it started after my swap.

 

[JeffS197]

still on stock driveshaft and rediculous stock suspension.

You should see how high my rear end sits (my sig pic is deceiving, it looks alot higher in the rear in real life), it looks like I have a lift kit on the car in the back. really want to lower it to at least match the front but it sounds like alot of work as I would need panhard bar to center everything and adjustable upper control arm I believe to drop it over an inch.

was hoping I could just drop in rear springs and be done with it but I dont know if it is worth the risk of screwing everything up. maybe it would be fine Im not too sure I am still very new to the S197. I think I have alot more reading to do before I start spending any money.

 

[Sinister06gt]

I just had 3.73s put in my car earlier this month. They are FRPP gears and were installed by a local shop that does nothing but diff work. They whine a bit. Nothing I can't live with. The muffler deletes cover it up mostly unless I'm using cruise control and it's barely getting gas. I have BMR lower control arms I've been told they transmit the noise directly into car

 

[Fullboogie]

I've probably put 10 sets of 3:73's in 8.8's over the years, always done by a variety of very competent shops. Every single one of them whined like a 12 year old girl. The last set I installed in my GT500, I stood over the guy the whole time watching everything he did and verifying his work. Whine, whine, whine. Drives me crazy.

 

[Synyster06Gates]

still on stock driveshaft and rediculous stock suspension.

You should see how high my rear end sits (my sig pic is deceiving, it looks alot higher in the rear in real life), it looks like I have a lift kit on the car in the back. really want to lower it to at least match the front but it sounds like alot of work as I would need panhard bar to center everything and adjustable upper control arm I believe to drop it over an inch.

was hoping I could just drop in rear springs and be done with it but I dont know if it is worth the risk of screwing everything up. maybe it would be fine Im not too sure I am still very new to the S197. I think I have alot more reading to do before I start spending any money.

It varies car to car. I didn't need PHB on either my 06 or my 11. The 06 was lowered 1.5'' and the 11 was lowered 2.0'' in the rear. Neither drop made the driver side wheel kick out any. It's perfectly center. I haven't done UCA either. That's to correct the pinion angle and is more important on the 1 piece drive shafts than the stock 2 piece

But yes - I know what you mean about it looking like there was a lift kit on! lol

 

[drive_55_not]

I've probably put 10 sets of 3:73's in 8.8's over the years, always done by a variety of very competent shops. Every single one of them whined like a 12 year old girl. The last set I installed in my GT500, I stood over the guy the whole time watching everything he did and verifying his work. Whine, whine, whine. Drives me crazy.

The problem with gear installers is they set the R&P up with the correct backlash, pinion depth and pinion preload and call it good as it's in spec ... But the gear whine is all in the setup.

I started installing my own after the 4.10's I paid to have installed whined terribly, I redid it myself and found by setting the pinion depth centered on the tooth and the swipe toward the toe like tyhe lower left pattern from the Yukon setup, that eliminated the whine.

When I checked the 'expert installer' pattern it was centered like the upper left and it whined like a mother---

I've installed 3.15's, 3.73's, 3.90's [ all of those were used ] new 4.10's and 4.56's and was able to get them all to run quiet, and in spec.



.

 

[BruceH]

If the gears were the older Motives that frpp used to sell then they need to be set up with minimum backlash to be quiet.

I'd see it as a good reason to get 4.10 gears but that's me.

 

[JeffS197]

4.10s would be a bit nuts for me as I commute over 50 miles a day on the highway to/from work. I am usually cruising around 2400rpm in 5th right now. If it was a a second car for me I would definitely go with 4.10s.

 

[BruceH]

4.10s would be a bit nuts for me as I commute over 50 miles a day on the highway to/from work. I am usually cruising around 2400rpm in 5th right now. If it was a a second car for me I would definitely go with 4.10s.

If you do the math it's not that bad. Final drive in 5th with 3.73 is 2.54:1. With 4:10 it's 2.79:1. 5th gear is a .68 overdrive.

 

[oldVOR]

I've installed 3.15's, 3.73's, 3.90's [ all of those were used ] new 4.10's and 4.56's and was able to get them all to run quiet, and in spec..

Was it always the case to move the pattern towards the toe to get the gears to run quiet?

 

[Whipped05GT]

My 05 GT is my 10th mustang with different rear end gears and all of them have whined. Some worse than others.

 

[Kylar]

Just figured i would chime in. 2005 GT 25k miles, OEM 3.55 gears. Zero whine.