'18 3.73 PP Diff whine

[HourlyB]

I swapped in a Torsen 3.73 rear-end from a 2018 Mustang into my 2016 by Fortes in Framingham. (the input flange from the 2016 diff was swapped onto the 2018 diff) The diff was dry, so BG Ultra Guard 75w-90 with the slip modifier was put in.

Immediately on driving home, I noticed that the rear-end made a whining noise, really noticeable at highway speed and still present, but not as loud, at "suburban" speeds. (40-45 mph) No serious vibrations or grinding noises when shifting, getting on the throttle, getting off the throttle or cruising. It's just a steady whine.

Should I take this to a shop to get it looked at? I've heard that whine is relatively common with 3.73 gears, but also whine can be symptomatic of a issue in shimming.

Also, maybe it's just a thing of getting used to shorter gears, but I've noticed that with the new diff, it seems to be a lot more "hesitant" getting up to speed. Like, getting on the highway, I keep the car in 3rd gear at 4k, and get on the throttle, and the car only goes up to about 4.5k, that is until I go straight, then the revs/speed starts building. This didn't used to happen with my 3.15 diff, is that the TC kicking in or?

Sponsored

 

[shogun32]

do you have IRS or Diff mods?
If the clearances are a touch off (generally tight) you can get whine.

If TC is activating then a yellow symbol will flash. What you describe doesn't make much sense as far as acceleration.

 

[HourlyB]

do you have IRS or Diff mods?
If the clearances are a touch off (generally tight) you can get whine.

If TC is activating then a yellow symbol will flash. What you describe doesn't make much sense as far as acceleration.

I have a BMR IRS Cradle Bushing Lockout kit, Steeda rear lower control arm bearings, BMR Handling Springs, FP Track Shock & Strut kit and the wheels are 19x10 SVE R357's with 285/35 Firehawk Indy 500s.

And that's the strange thing, I'm not getting the big orange "YOU ARE GOING TO SLIDE OFF THE ROAD AND EXPLODE, DUMMY" light. It's just gutless, no warning light or anything.

 

[ice445]

I have a BMR IRS Cradle Bushing Lockout kit, Steeda rear lower control arm bearings, BMR Handling Springs, FP Track Shock & Strut kit and the wheels are 19x10 SVE R357's with 285/35 Firehawk Indy 500s.

And that's the strange thing, I'm not getting the big orange "YOU ARE GOING TO SLIDE OFF THE ROAD AND EXPLODE, DUMMY" light. It's just gutless, no warning light or anything.

The light only really comes in with extreme wheel slip, could definitely be power pulling. The 15-17 ratios are pretty short, so with a 3.73 rear end it's torque all the time lol

 

[TnWHTMARE]

If pinion depth/position is off, it will make a noise but if installed correctly it should be quiet. And your acceleration should be much better, not worse. Sounds like a data log is in order.

 

[HourlyB]

The light only really comes in with extreme wheel slip, could definitely be power pulling. The 15-17 ratios are pretty short, so with a 3.73 rear end it's torque all the time lol

If pinion depth/position is off, it will make a noise but if installed correctly it should be quiet. And your acceleration should be much better, not worse. Sounds like a data log is in order.

Hmmm, the diff was taken out of the PP at 8k, and looked pretty new when I got it, so I'm not sure if it came out of the factory with this sound or what.

I was hoping to avoid touching the engine & tuning for a bit. I was planning to do a Boundary OPG/CS with a LP Intake Manifold and CAI using a CMCV harness, and doing the spark plugs as well, guessing I should add a tuner? Given a shop is going to be doing the work anyway, should I bother going to Lund for a tune?

 

[shogun32]

ahh, so it was an assembly swap. The reason I asked about diff/IRS mods is that indeed mine does whine at low volume - windows up, radio off, best heard at 75mph on good pavement where tire noise is minimal. But I have replaced the diff bushings with WHiteline and braced/locked out the IRS.

There are other speeds where the resonance causes it to be louder but it's still very much a background noise quite subdued compared to a car with the various other DIFF solutions that cause a VERY obvious howl that comes and goes with sympathetic frequencies.

 

[TnWHTMARE]

I had an 18 with 3.55 (so not 3.73) but around 2k they started whining and by 5k they were getting worse. Took it to Ford and they had to replace the gears and bearings. Apparently the rear pinion bearing was faulty and causing movement. Quiet as a mouse after they replaced it.

 

[HourlyB]

ahh, so it was an assembly swap. The reason I asked about diff/IRS mods is that indeed mine does whine at low volume - windows up, radio off, best heard at 75mph on good pavement where tire noise is minimal. But I have replaced the diff bushings with WHiteline and braced/locked out the IRS.

There are other speeds where the resonance causes it to be louder but it's still very much a background noise quite subdued compared to a car with the various other DIFF solutions that cause a VERY obvious howl that comes and goes with sympathetic frequencies.

Yeah, it seems like something that increases with speed, but nothing else.

I had an 18 with 3.55 (so not 3.73) but around 2k they started whining and by 5k they were getting worse. Took it to Ford and they had to replace the gears and bearings. Apparently the rear pinion bearing was faulty and causing movement. Quiet as a mouse after they replaced it.

Yeah, I don't think even the part is covered by the warranty anymore, let alone it was hotrodded onto a earlier model year.

Would it be better to take it to a local shop or a dealer to try and get it shimmed? If I'm going to do the tune and power upgrade, then the one stop shop would be the better strategy imo.

 

[AZ_whippleS550]

The input flange nut sets pinion depth my guess is that it was not the same after the flanges were swapped. I had the same issue when I did mine I had a wine on decel so I had to tighten the pinion nut about 3/4 a turn

 

[spaz mk will]

Does a KAM reset apply here? The car should not have issues with that ratio but the computer is still expecting/calculating against the old ratio, might explain it pulling power. Pull battery for 30 minutes, unless you have a tuner with that option, this will clear the map.

 

[TnWHTMARE]

Does a KAM reset apply here? The car should not have issues with that ratio but the computer is still expecting/calculating against the old ratio, might explain it pulling power. Pull battery for 30 minutes, unless you have a tuner with that option, this will clear the map.

I wondered the same thing but ASSUMED it would learn based on what I have read.

 

[spaz mk will]

I wondered the same thing but ASSUMED it would learn based on what I have read.

I’ve seen the same, yes. KAM reset should at least shortcut that process a little, and doesn’t hurt to rule it out.

 

[andrewtac]

With the two piece driveshaft and rubber bushings I bet many factory rear ends whine people just don't notice it. I went full lockout, and one piece and my 3.15 whines. Probably could use adjustment

 

[HourlyB]

The input flange nut sets pinion depth my guess is that it was not the same after the flanges were swapped. I had the same issue when I did mine I had a wine on decel so I had to tighten the pinion nut about 3/4 a turn

Hmmm, if it's that, I should probably take it to the shop I got the work done at.

Does a KAM reset apply here? The car should not have issues with that ratio but the computer is still expecting/calculating against the old ratio, might explain it pulling power. Pull battery for 30 minutes, unless you have a tuner with that option, this will clear the map.

I’ve seen the same, yes. KAM reset should at least shortcut that process a little, and doesn’t hurt to rule it out.

So, negative terminal off for half a hour and then back on? Any other processes I should do?

Sponsored