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Rear diff clunk / knock

92K views 168 replies 61 participants last post by  scoobyrally 
#1 ·
I read some other posts about the diff clunking but I'm not sure if it was exactly what I am experiencing.

Basically, what I *think* is my rear diff, makes a clunk or more of a knocking sound quite a bit. In reverse, shifting from 1st to 2nd, sometimes even 2nd to 3rd and 4th to 5th (very very faintly), and even going over the small (higher speed) speed bumps.

Now that I think about it, clunk is really not a good description. It is more like a knock or a pop...

I never heard the noise on my 04 STi or either of my WRX's. There are ways of making it go away, such as taking 3-4 seconds to let the clutch all the way up going from 1st to 2nd, but even then, sometimes when you're not even shifting, just letting your foot off the gas in 1st or 2nd can make the noise.

I'm thinking about taking it to the dealership to see what they say. My TBE is going on in the next week or so, so I should probably go see them before then ;).

Does anyone else get this noise? I'm sure it's harmless. It's not THAT loud and it doesn't sound like something is broken particularly, it's just more annoying than anything else because I don't know what it is. I'm sure if I just put on the TBE and didn't see the dealer the exhaust would make enough noise that I would never hear it again :D.

If I had to guess, I would say it's a poorly shimmed ring & pinion, or perhaps even the entire diff housing moving slightly, but I have no idea.
 
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#2 · (Edited)
Another thing that occured to me:

The noise happens MORE often when you try to drive SLOW if anything. Generally, shifting at 5-7 grand won't make the noise very often. It's when you're specifically trying not to go fast (shifting at 3-5 grand) that the noise tends to occur.

Perhaps my car is angry with me when I am trying to obey traffic laws :(.

Also, this is not a clunk or knock that you can FEEL, it's just an anoying noise. The car feels completely normal when it makes the noise. I also know for a fact it's not a noise that could have been caused by any mods, as it made this noise the day I bought it with 5 miles on it and I didn't really think anything of it.
 
#3 ·
The only thing I've ever experienced that is similar to this is when creeping in traffic. I'll begin to let out the clutch, give some light throttle, and when I clutch back in I hear a soft clunk/pop. It sounds like a muted version of the rear-diff slap when you do a quick 1-2 shift at full throttle. It doesn't happen all the time and honestly I think it is just drivetrain slack (at least in my case.)
 
#5 ·
My STI is doing the exact same thing.

I first noticed it near the end of last week. Thursday or friday I believe. I thought maybe it was just something in the trunk rattling around so I cleaned the car out completely and the noise persisted. I also noticed that I cannot reproduce the noise by hitting the brakes but I can by downshifting. It's most noticable taking off slowly with the wheels turned, or just about anytime I go into reverse. I get the noise pretty much every time if I let off the gas after shifting.

Against my better judgement I went back to the dragstrip on saturday and made three passes. Car felt fine, and I ran my best ever 1/8th mile and 330ft. But on the way home I launched from a stoplight and felt the back end squishing around.

I am hoping this is an extreme case of rear strut clunk or worn out rear diff mount bushings and not a problem in the diff. Please Ben, bring your car into the dealer... I have a TBE, Intake, and Cobb Stg2... I don't want to return to the dealer unless I really have to.
 
#6 ·
I have it too. Posted a thread about it. I have now also observed this in my friends '05 STi. I think I found a way to reproduce this as well:

Jack the rear of the car, and rotate either rear wheel left then right. On my car, I could hear a milder version of the same knock. It is constantly reproducible when loading / unloading the diff. This is why we notice it in reverse or on downshifts.

I took it to a local trusted mechanic (Suby Specialties) and they told me it was not normal. I'm waiting on taking it to the dealer for now due to the lack of any local service that I trust. I have trolled here and NASIOC trying to find other people with the same problem, and hopefully even someone who has it who understands our diffs. So far, no luck. I guess I will only feel comfortable when someone cracks my diff, checks the lash and gears and says "it's within tolerances and is normal". I don't expect this from any of the local dealers though. :(
 
#9 ·
I may have the same annoying problem.

Ben, Chris or anyone in the LA/SFV area want to meet up and compare?
 
#10 ·
I'm going to go drive another brand new STi and see if it makes the noise and also have my mechanic at the dealer hear it. I'll let you know what they say. I'm in the valley if you want to compare noises. Just send me a PM.
 
#12 ·
Ben, I've got the same problem. I always described it as a knocking rather than the infamous strut clunk that everyone is talking about. Thankfully I haven't acquired that noise yet... Anyway, I spoke to the Suby dealership, and the resident "STi Expert" told me that it was probably normal, resulting from the construction of the rear diff. Also take a look at page 7-21 in your owner's manual, it mentions this "knock". I it says, "If you rapidly depress and release the accelerator pedal while driving at low speed, you may hear a knocking sound from the vicinity of the center differential. This sound occurs because of the structure of the center differential. It does not indicate a problem.
With all of that said, I am still taking the car into the dealership on 5/26/05 to have them take a look. I'll report back after their diagnosis or lack thereof.
 
#14 ·
I am going to take my car in next week. My main concern is that I wonder if any of the dealership techs knows if this is normal or not. Steve at Suby Specialties said it was not normal. If the dealer says the standard "it's fine" I may have him open it up and take a look.
 
#15 ·
Yeah I get that popping sound alot too. When I back up...put it in 1st and pull forward very slowly/turning to go in my lane or whatever I get a pop as soon as I start rolling forward. It's just the rear diff grabbing...I call it claking. It's normal. But take it in for sure to be safe.
 
#16 ·
UPDATE!

I just got back from the dealer and had my mechanic that I've known there for 5 years listen to the noise. He said it's normal.

I then took out 2 brand new 05 STI's with less than 5 miles on them and they both made the noise. I could make them do it by going in reverse and shifting from 1st to 2nd, just like in my car. The noise wasn't quite as loud, but it was very close, and definitely the same noise coming from the same place. I know when my car was new it made the identical noise and has gotten a tiny bit louder over time.

The solution? Get a loud exhaust or turn up your stereo :D I'm just gald everything is alright and I can start ignoring this noise!
 
#17 ·
Ben:

Thanks for the info. The report I just got from my dealer was classic: "It's coming from the aftermarket parts". I hoped against hope they would at least try to figure out the problem, but both of my local dealers now will blame any noise or problem on "aftermarket parts". :rollseyes:

I would pay $500 just for a local dealer that has 1/2 a clue and would at least make an educated attempt at diagnosing a problem.

I have an appointment with Suby Specialties later this month for a full inspection. I tend to think now that this is normal given Ben's response, but given my driving activities, I'd rather be 100% sure.

BTW, Ben, who is your mechanic?
 
#19 ·
jaygoesfast said:
I have a TBE, Intake, and Cobb Stg2... I don't want to return to the dealer unless I really have to.
theyre going to having a hard time refusing warranty on your diff with that list. make sure you unmarry your ap before turning it in for repairs just in case they decide to reflash it while they have it.
 
#20 ·
Met up with Ben today. It seems to be the same noise and happens under the same situations. Thanks again Ben!

ChrisF - What dealerships did you go to? I want to have things checked out, just for peace of mind.
 
#21 ·
xtian:

Thousand Oaks: Consistently lazy about troubleshooting and not at all mod friendly
Big Valley: said it was "aftermarket parts", but didn't indicate anything about mods on the car (better than T.O.)

I'm used to mechanics that take pride in their work and care about troubleshooting a customer's complaint / problem. Neither of these dealers did that. They immediately reached for the "not our fault or problem" line. So sad.
 
#22 ·
Might the answer to all of this be in our owners manual? Page 7-21

- If you rapidly depress and release the accelerator
pedal while driving at low speed, you may hear
a knocking sound from the vicinity of the center
differential and rear differential. This sound occurs
because of the structure of the center differential.
It does not indicate a problem.
 
#23 ·
And for some of you guys it may be the rear struts clunking. Subaru has made a new part # for the struts I got replaced under warranty. From what I have read, the problem arises either from the struts sticking because of lack of/incorrect lubrication or the tops of the struts have become loose and tend to shift when changing directions slowly or going over speed bumps. If it is your struts go to the dealership and they should be replaced under warranty.
 
#24 ·
The mechanic is Scott over at thousand oaks. I'm sorry if they are lazy or not mod friendly :( I've found with all cars in order to get any kind of service you have to devlope a relationship with the dealer. Just popping in once or twice because you have a problem is not going to motivate them to look at your car or want to deal with you. It's sad, but it's the truth.

I must say though, all of the people over at thousand oaks subaru are really nice and I have a very good relationship with the sales manager, the service department, etc.

Anyway, as for the struts, I know my noise and xtian's noise is definitely not a strut clunk. I don't even have the stock struts, mounts, etc, so there is no way it could be that. I think jaygoesfast's post says it all ;)
 
#26 ·
fadedSTi said:
i hear a clunking noise also. i hear sometimes when making a right hand turn or hitting a bump. also i can hear it clunking when im slowly rolling. i guess this is all normal?
That sounds a bit more like your rear strut(s).
 
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