So my 02 Impreza 5MT is suffering from differential whine, which I see happens fairly often in these cars. I know this is only prolonging the inevitable, but is there anything I can do to keep it hanging on a while longer/keep it from getting louder? Special gear oil or anything? I've already got one very dead car in my garage that I'd love to put back together and drive out of said garage before I have to drop a transmission.

google it, and i mean that for a reason, not trying to pull a standard "i can't tolerate noob response".   

it probably varies too wildly to say "this is what you should do."   if it's a bearing failure that's different than a pinion gear failure which is different from a gear set or synchro's or a combination of things....how/why the bearing failed - defect, impact, driving conditions, localized overheating, poorly adjusted backlash or bearing preload, other failing components, running low on oil the first year the car was owned, someone previously dumping the wrong fluid into it by accident....there's just too many variables, failure modes to be very specific.  

 

which is why I would google it rather than rely on 3 anecdotal replies to what is not a common situation ("my front diff is failing, how can I still get it to survive, who has significant experience with this" type of question..).   people have tried a few things and reported on it and it should be easy to find.  i think they even call some mixtures "clocktails" so you can probably actually search for that term as a starting point.

 

1. change the gear oil for new oil and get the debris out of there

2. try a heavier weight synthetic

3. try a blend - a cocktail of oils/additives

 

if they don't help you can always switch back, a flush of oil isn't going to hurt. 

 

i recall a person that has torn these trans apart before (pretty sure he posted on here and he's from Australia or NZ) suggesting various oil concoctions may compromise other internal components even if it may help, or seem to help, existing issues.  so best to avoid that if you want to repair the current trans.  

It's probably the center diff which you can access easily without pulling the trans. It's a couple hours.

 

They are $586 and there's no way around that part. Used isn't an option they are all bad and you would have to buy a whole trans.

 

There could be other bearings going out but you will need the center diff most likely anyway so it's probably worth pulling and inspecting and if bad trying a new one before condemning the rest of the trans.

 

GD

Edited February 16, 20179 yr by GeneralDisorder

I would definitely inspect the bolt's magnet - it sits adjacent to the diff and actually is in a bad position to have 'chunks' from elsewhere in the trans. on it - there are internal bulkheads that make it difficult for mainshaft or driven gear pieces to get to it. Of course - more than 1/4 or 1/2 teaspoon of 'sludge' could be a bad sign - as well as a metallic particle sheen to the fluid.

 

if someone other than you has been maintaining the car - incorrect fluid may have been used in the trans in the past. normally it should be a non-synthetic GL-5.

 

(other fluids known to work for people which may have some type of synthetic substance in them are Walmart synth-blend gear oil, and Redline Lightweight Shockproof, Motul 300 has a following but I know nothing about it.)

 

Redline LW Shockproof quieted the front diff in our 03 H6 Outback a little.

 

I have Amsoil Severe Gear in my WRX's trans at the moment.

 

NO FLUID will repair something broken, but the right fluid can help the trans shift better and maybe last longer. Just based on what you've written, I might be tempted to run Redline LW or HW Shockproof while saving up for a used transmission swap. check LKQ or car-part.com

For best shifting the only two gear oils we have had success with is Subaru HPGO and Mogul Gear 300.

 

GD

(please excuse the quick hijack) Hey General..your PM box is full.

my Amsoil severe gear was put in by the shop that rebuilt my trans after 2nd gear was destroyed.(seeemingly not a wear-related failure - the shop said, and showed me, that even the synchros looked good - just that the 5mt's 2 piece case is known to flex too much, usually 3rd gear gets it, sometimes 2nd) Before that, I had Extra-S in it. Before that, I had RL LW SP. This Amsoil is in between the Extra-S and the Redline in 'feel'. But, I haven't run it during the summer yet so, kinda early to say if I prefer the Redline over amsoil. The Redline was like butter. Might not be thin enough though for northerners ??? Extra-S felt very notchy/scrape-y in the summertime.

 

many people like the Motul though, no question.

Edited February 16, 20179 yr by 1 Lucky Texan

Thanks for the input. Probably will try a synthetic gear oil and see how far that gets me. Any other symptoms to narrow down the front vs. center diff? I remember having binding issues when the center diff went bad on my 4EAT Legacy but I understand that's a whole different animal from a manual. Also- tips on the visual inspection of that center diff?

 

The whine sounds like it's coming from the firewall area, FWIW.

 

Edit- just realized after I posted that the center diff would be approximately next to my knee, so duh, of course the sound would seem like it's coming from in front of me.

Edited February 16, 20179 yr by Wagon Wagon

Maybe put it on four jack stands, run it in gear and listen with a stethoscope (or a long screwdriver with your ear to the handle) to both the center dif and the front dif areas, see which is noisier? 

Edited February 19, 20179 yr by lostinthe202

So just to be clear as far as the trans/drive with a 5 speed MT, there are three separate fluids that need changed front and rear diff and trans right? I had seen mention somewhere that the MT didn't have a front diff. I have a 95 legacy wagon. Thanks

Dam

Edited February 20, 20179 yr by 1997reduxe

the MT shares fluid with the front diff. GL-5 is the spec.

 

check your manual but I believe there's actually a different weight listed for trans vs rear diff - though many folks have probably used the same fluid in both locations. Rear diff can definitely use synthetic.

 

many people report some shifting problems if using full synthetic in the trans. supposedly the synchros spin too well with the improved lubrication.

 

automatics do, of course have their front diff separate from the ATF.

Edited February 20, 20179 yr by 1 Lucky Texan

Ah that explains it

Thank you

it's almost always the front diff and not the center diff if you're absolutely positive it's one of those two things creating the noise.

 

5 speed center diff failure results in torque bind. they can make noise in the rear extension housing, but it's not common.

 

i drove one to failure, my noisy front diff lasted 18,000 miles before it locked up.

Edited February 20, 20179 yr by grossgary