The Project Pad

on my TDI b3 I have a poly rear diff mount, with rubber side mounts. Also, the subframe is on poly mounts and the control arm bushings back there are poly. Its not too noisy on the road, but at 60-70 there is a very noticeable hum. It really sounds like its coming from back there.

I actually swapped the rear diff, and replaced the carrier bearing and driveshaft u-joint. Noise still there.

Could be something in the trans, but it sounds like its coming from to far back.

Anyone else have this with poly mounts? Sounds a bit like the rear end noise from a big truck.

Rear toe good?

Sent from my SAMSUNG-SM-G870A using Tapatalk

scubagli wrote:Rear toe good?

Sent from my SAMSUNG-SM-G870A using Tapatalk

Should be, was recently aligned. Tires are wearing nicely. Does not sounds like tire, sounds just like a big rig gear noise from the pinion.

I had this problem with the 034 Delrin rear bushing. HRP bushing is fairly quite with 034 density mounts and solid SF mounts. The difs are noisy as hell, on a quite car like yours I bet that is all you are hearing.

audifreakjim wrote:I had this problem with the 034 Delrin rear bushing. HRP bushing is fairly quite with 034 density mounts and solid SF mounts. The difs are noisy as hell, on a quite car like yours I bet that is all you are hearing.

I think you're right. It probably is just the rear diff being noise translated through HPR rear mount and HPR subframe mounts. It resonates very noticeably from 60-70 when under load, and nothing above or below.

I even ran the thing on cruise control at 90mph on jack stands and checked for vibration from under the car. Terrifying to say the least.

Trying to nail down all things before roadtrip time....Today while driving to work, the camber adjustment started moving around on the driver side ball joint...thanks alignment shop.....

I'm with the others... I'll give 10:1 odds that everything is normal with the diff. You're just getting more noise transmitted into the body with the poly bushings. There's a reason they don't put those in at the factory!

elaw wrote:I'm with the others... I'll give 10:1 odds that everything is normal with the diff. You're just getting more noise transmitted into the body with the poly bushings. There's a reason they don't put those in at the factory!

Yessir. I put the yellow (track hardness) AK MS diff carrier bushings in my S6 and it is whiney.

Whining from the rear of high-performance cars can also be caused by passengers in the back seat. You should check for that.

I had a Delrin solid rear diff mount I discarded after a while. Doesn't mix with diesel vibration(doh). It was horrible. I replaced it with the 034 solid rubber mount that required a lot of grinding to fit.(grrrr)

oil_me wrote:I had a Delrin solid rear diff mount I discarded after a while. Doesn't mix with diesel vibration(doh). It was horrible. I replaced it with the 034 solid rubber mount that required a lot of grinding to fit.(grrrr)

Thanks for the thoughts gents. I guess I have always run factory mounts on the rear diffs of my other cars. I agree, things seem normal otherwise. For whatever reason, its not too loud or annoying, just present at that speed of 60-70. I plan on driving faster than that for the majority of my roadtrip, so I won't hear it.

That's the spirit. A fun experiment is to take the rear seat bottom out and listen to it. You should be able to hear it in much more detail.

audifreakjim wrote:That's the spirit. A fun experiment is to take the rear seat bottom out and listen to it. You should be able to hear it in much more detail.

good idea, i might just try that.

After rebuilding the driveshaft, I thought I might have lost my orientation (turns out I had it right). I had the car up on jackstands with the cruise set at 80mph with an open downpipe and crawled under and actually set my finger on the driveshaft....that shit was scary, but it was buttery smooth. The girlfriend saw what I was doing and her jaw hit the ground.

Holy shit.

Sent from my SAMSUNG-SM-G870A using Tapatalk

I've been under cars at speed on stands and it's hairy. Sure helps sometimes to find vibrations though.

ringbearer wrote:I've been under cars at speed on stands and it's hairy. Sure helps sometimes to find vibrations though.

Its one of those "WHAT THE FECK AM I DOING" moments. Actually had a nightmare about it last night where my car fell off stands and landed on someone.

That is somthing I have never had the balls to do. Somthing about being under the car with the wheels spinning at speed just says "dont do this!"

And yes, my rear diff whines with the full set of HPR I recently installed. Just annoying enough to notice.

I hope you were using your safety-stands for all above shenanigans

oh good god, the most shocking thing about that photo is that Berkltard is not under the car.

dana wrote: I had the car up on jackstands with the cruise set at 80mph with an open downpipe and crawled under and actually set my finger on the driveshaft....

YOU FVCKIN WHAT?

vt10vt wrote:I hope you were using your safety-stands for all above shenanigans

That is one of the more retarded things I have seen Audi guys do... Holy shit...
I'm suddenly feeling a lot less stupid for having a 90L fuel tank sitting unfastened in my spare wheel well.

There's a candidate for The Darwin Award.