The diff!!!......Surely not????!!!!

[phoenixv6quattro]

Hello again Gents. Got a strange problem(I think?) in the form of a noise.....Let me explain....
At the weekend some of the jobs I did included reinforcing the diff mounts(all 3, one main front and two small rear, this I did using polyurethane in a tube) and changing the diff fluid. I got the fluid from Audi, and came in 1ltr white bottles with "axle oil" written on it. I made 3 guys at Audi reasure me it is the right stuff, so I'm sure it is. Anyway the rear of the car was raised on ramps the whole weekend while I did some other odds and sods. After draining the diff(only 1.4 ltrs came out...I'm putting this down to the seals sweating oil for 11 years!) I filled it with 1.8 ltrs. I did this when the car was level and filled it untill oil started to pour out of the fill plug, as I was advised by an Audi Tech. Now before I changed the fluid the diff was not making any noises it shouldn't. As soon as I had it off the ramps on Monday, I took it for a test drive. Everything was A ok apart from a brand new noise coming from the Diff(as far as I can make out). Its very faint, almost like the whine of straight cut gears or driving your car in reverse. The noise is drowned out even if I put the heating on full whack. To add to this, its only noisy when you are applying the throttle(both under load or no load), and as soon as I lift off/rolling with no throttle the noise dissapears. The function of it is fine, doing its job as well as it always has. So far I have checked the level of oil in the diff, which is where it should be. I have also changed the wheels/tyres to make sure it wasnt road noise. I am 99.9% certain it is not a bearing because I know what a failed WB sounds like. All I have done is changed the oil and now I have this ****** noise!!! Can somone please help, and or advice. Any help will be immensely appreciated!

Cheers guys,

Ollie.

 

[adamss24]

I used the same gearbox oil when i filled me rear diff ! No noises at all but i have to fix me rear diff mount as i got the thump on a hard launch...

 

[Matt82]

when i read the title i thought it would be oil related. it has been extremely cold and the oil will have been thicker than usual etc but for it to occur when the new stuff went in is really odd

got the part number? maybe somone with etka or elsa can check if youve got the right bit in there to start with

 

[jcb]

what did you do to the diff mounts?
polybushing anything will make noise transefer more apparent

how loud are we talking? gets louder the more you accelerate or the faster you go?

 

[phoenixv6quattro]

Hello Gents. Sorry for the slack response....I've been smashing out 18 hour days/nights at work!!(Xmas debt!). Ref the part number I dont know as I have disposed of the bottles(will phone Audi and post one up soon as there open). I have filled a new OE diff mount(big front one under the exhaust mount arm) with sikaflex 252(which is just polyurethane in a tube, great stuff!). Really packed it in there, thing is almost solid now,like it was made entirely of poly! The noise isnt very loud. If I turn the heating on full whack or open a window I can't hear it. The noise is exactly the same tone/note as anyone on here would get from the whine on reverse gear, but a lot quieter. It does get slightly louder under load but not much at all. The main thing I took note of when trying to diagnise it is it stops as soon as I stop the throttle. When the car is just rolling, it is not there. This makes me think it isn't a wheel bearing? The point about noise transfer is a good/valid one. Also the other point Matt made about the oil thickness. The 11 year old diff oil I drained wad EXTREMELY thick. The Audi axle oil I put in was thin in comparison. Maybe the thick old oil was drowning out some noise?
Any feedback would be fantastic...

 

[yendall24]

hi mate i think you have had this noise for a while but now it is being transfered to the cars body through the stiffened mounts rubber mounts on there own would of absorbed the sound thats why manufacturers spend millions developing rubber bushes not just to support components but also to absorb vibration

 

[aragorn]

yep i agree, the lack of oil will have worn the diff bearings and the stiffer mounts are now transferring more noise to the chassis.

Craigs rear diff is a tiny bit noisey, and its got leaking seals too. We topped it up a fwe months back and it took around half a litre of oil, so it seeminly had a bit less in it than yours.

Thing is with oil it could do another 100k like that, or it might self destruct in 500miles, bearings are funny things.

Personally, i'd ignore it and just keep on top of the oil level.

 

[adamss24]

What is the difference between the gearbox oil and axle oil ? I have filled mine with gearbox oil, specs look very similar to me and no unusual noises as such ! Prices are about the same too...

 

[aragorn]

Basically nowt.

They're both the same 75w90 synthetic rating.

The only slight difference is the diff specifies GL5 and the tranny GL4.

If you google that you'll find its a MASSIVE can of worms, mainly stemming from early GL5 oils being very corrosive to the internals of some gearboxes.

GL4 seems to be hard to get these days, which would suggest to me that the issues are non-existant.

FWIW i put GL5 oil in the tranny of our 1.8T over a year ago, and its not ate itself yet.

 

[Broken Byzan]

Maybe i should ignore mine and never check it by the sounds, ignorance being bliss and all that !!

 

[phoenixv6quattro]

Hi gents. Phoned Audi today, and was re-assured once again, this time by the head technician (not being funny, but those parts guys sometimes don't know what their talking about when it comes to the older cars, especially when they are 17, and have only just started!!) that the axle oil is 101% correct, and as Audi intended for the application. So that rules that out.
I think your right guys, I believe it has been like that for some time, especially as the diff, when drained, only had 1.4 ltrs! Thats almost half a litre shy of what it should be!!! So the bearing wear makes for a sound conclusion. And yeah, the stiffer mount does make for more audible transfer to the chassis, so that explains why I couldn't hear it before. Think I will do as suggested, and ignore the noise. The diff is performing brilliantly, as it always has, so I guess its no biggie! Just to confirm though guys(this is a daft question, I apoligies, but I want to be 101% certain), if it were a wheel bearing, the noise would be constant wouldn't it? And not just audible under throttle?

 

[aragorn]

Wheel bearings tend to be variable, but usually with steering.

Ie when you turn and load up the bearing more, the noise increases etc.

 

[phoenixv6quattro]

Many thanks mate! Gents, cheers for all the advice/help.......Your all diamonds!

Ollie