996 Front Differential Whining noise

Front Differential Whining noise, it's in the bench ready to strip down

P Thread 'C4 Front diff whine' 2 Dec 2020 I was hoping to delve into the collective knowledge base here. I was driving a 996 C4, similar to my own, today, and couldn't help notice that there was a faint whine from the front end. I mentioned it to the owner and she said that her garage had told her that it definitely was the diff and not wheel bearings. However, it wasn't worth bothering with as 1. it is very faint and 2. would be super expensive to rectify. It got me thinking, as I have never heard of anyone else with a similar issue, why would the garage say that it would be unreasonably expensive a job to consider? Is there... peterzoom Replies: 13 Forum: Porsche 911 996 (1997-2005) L Thread '996 C4 Transmission whine - what's the best way to identify?' 1 Jun 2021 I've recently acquired a 99 C4, there's a noticeable whine somewhere in the drivetrain (not engine as changes with road speed and not revs). Whines in all gears and if I dip the clutch, the gears seem fine and change nice and smoothly. From what I've read it's pointing to the pinion bearing however is there any way of determining this (or at least ruling other things out) before I send the box away for a new bearing? I'm doubtful it's a wheel bearing noise as doesn't fade in/out with changes in lateral load. And lastly, if it IS the pinion bearing who is best at sorting these? Cheers. Lightweight996 Replies: 27 Forum: Porsche 911 996 (1997-2005)

Hi Mine is a tiptronic when under acceleration or deceleration it's pretty quiet, when just coasting whit engine revs matching wheel speed there's a noticeable whining noise, I put sensors on the car at front, left and right wheels, on the torque converter, on the rear where the prop shaft enters and where the differential is at the front. It's the diff that's noisy. see video, Number 3 is the differential where the noise is coming from (middle LED lights) The video failed to upload, it was a set of "listening ears" and pinpointed the noises’ location immediately. Once the diff is stripped I'll post some pictures of internals/bearings condition. The car has only done 31,000 miles and has only been used gently.

I didn’t know you could rebuild these, well done

Video of listening ears sensors

Could it be your viscous clutch that's making the noise? Also, will you be doing anything with it whilst you're in there?

I replaced my diff on my C4 after it started to whine during my NC500 road trip, it didn’t sound like that. That sounds more like something loose, it’s a rattle rather then a diff whine.

The sensors are very sensitive and amplify the sound through a speaker in the car. The noise heard is a direct sound at the front differential when the diff has no load on it. I'm sure it's worn bearings displaying excessive backlash in the clearance between pinion & crown wheel. Once it's stripped I'll post pictures/videos

[Image-only or quote-only post; no author-written text.]

[Image-only or quote-only post; no author-written text.]

That's 4 bearings worn in my front differential, looking forward to completely dismantling, cleaning & rebuilding with all new bearings, seals etc. Didn't think for one minute it would be this bad!

If you play them all at once it's like a funky new sound depending on when you play the next in line. Alex could probably create some sweet dance tune from that lot.

31k miles that's crazy! Poor assembly at the factory? Does it have shims?

Somewhat related; I’ve just removed the 4wd on my 993 turbo. I’ve removed at least 7 bearings from the equation and the drivetrain is much quieter.

Crazy how much noise is coming from the bad bearing and how little from the good one

Quotes source post: 2835923

There's no difference one the airline is turned off or am I missing something?

The airline was used to get revs up, the 2 bearings that are worn come to a halt quickly.They should spin like the good one

Dismantled and ready for a rebuild once ALL replacement bearings and seals have arrived. The pinion nut was VERY tight. I ended up spark eroding the nut to weaken it and spread it apart, the nut is a shitty cheap soft one which seemed to glued on! The new nut I will install will be a specialist CNC ball screw nut with a locking facility. One thing I didn't mention is I'm a master toolmaker, have been in the trade for nearly 50 years and have full access to CAD CAM and a full range of specialist toolroom machinery.. A pinion spanner will be made using 3D scanning CAD and spark erosion to hold the pinion for re-assembly. I only really noticed the noise from the front differential after putting new quiet-rated tyres on, first of all I thought I'd made a mistake in the tyre sizes causing the diff to work overtime. Took Both front a rear wheels off and rolled them on a flat level surface to see it the rolling circumferences were different, they were all within 5mm of each other. It had to be the differential!

Quotes source post: 2836018

Master tool maker? You must be the only one left! Well done!

I had the 2 ball bearings in the support tube replaced some years ago as I also had a constant whine from the diff. Was afraid it was going to be an expensive job, but it was only about 70€ for the bearings and a few hours of work, including an oil change. Been fine ever since. I bet many people have not kept up with diff oil changes on these cars, as some of them will still be at relatively low mileage but already getting 20+ years old.

Quotes source post: 2836024

Forum's full of them.