Diagnosis Help - Rear Diff/Propshaft vibration/clunking
 

Hi all,

Got an issue with the scoob and need 2nd & 3rd opinion. Basically getting lot of mechanical noise / vibration when lift off throttle mostly noticeable on 4th and 5th when lifting off at speed and using engine braking. But also in lower gears when going around town. Being an impreza you always get some mechanical diff noise but not like a bag of spanners.

Had a decent look yesterday and it looks like noise/knocking is sourced at front end of rear diff where the diff/prop bearing would be. Also when turning rear wheels the prop shaft seems to have a small knock before turning. Joint feels tight, no movement up down sideways etc. But perhaps a little play when rotating..
Given everything if so tight the noise vibration may be coming from elsewhere. So just in case ive posted a video with this post to show what the noise sounds like, want further opinions before investing in be replacement diff :(
https://www.youtube.com/watch?v=eLlt...ature=youtu.be

Don't particularly want to drive it unless necessary at the moment until i get to the bottom of it.

Any help/ suggestions welcome!

check the bushes on the support bar that goes across car from left to right, it's located in front of the back wheels, the metal brackets touch the bodywork causing a horrible grinding noise, if you have had the car jacked up lately that is on of the causes, the bracket gets bent by the jacks

Hi mate!

good suggestion. Car get's lifted on a 2 post lift. I did check the bushes you mentioned. and seem ok. with still some polybush (upgraded from rubber few years back) sandwiched between support bar and chassis.

true enough swapping out for the polybushes did increase NVH but it's been significantly worse recently. Was thinking to try swap back in rubber ones when realised the extra noise from transmission.


Forgot to point out a key point, in my OP in that the gearbox was changed earlier in the year after loosing 1st, 2nd & 3rd in one full swoop! new gearbox feel much better and smoother (came from wagon blob wrx with lowish miles)

Update on current issues.

Swapped out rear diff, which did feel a little tighter but sound still exists. But definitely now more clearly coming from gearbox end of the car Possibly worn bearing in old diff was helping amplify the noise at the rear.

So in order to track down the noise further, removed prop shaft and rand the car idling in 5th gear. Noise still exists. so clearly nothing to do with prop/rear diff, sadly.. See video clip below for noise


But with engine sounding ok and no issues with clutch or gearbox feel when changing gears, putting power down, it appears to definitely be the gearbox somewhere, possible transferbox/center diff area?

So dug out my old broken gearbox and split it open to
a ) get some practice on opening the gearbox
b ) See what sort of a mess was made of it at the start of the year when it went bang!
c ) See if there is anything salvageable which i may be able to use to make one good gearbox out of two duff ones :(

See photos below for damage on original box.


So currently toyed between two options:
1) Try locate replacement gear set for the broken ones in the original box for low cost (if possible) and put original gearbox back in then remove newer(blobeye) gearbox and diagnose that on the bench. therefore at least still having a running car! then put newer box back in once issue diagnosed and resolved therefore having the smoother & stronger box).. sadly initial research doesn't look good for low cost repair..

2) Take newer gearbox out of the car strip down and try figure out what's wrong with it in the hope that out of two gearboxes on the bench I can get one good one!
The newer box does seem much better, gears are solid with smooth shifting, just the gawd awful rattle & clatter so don't think gears are knackered possibly bearing or centre diff issue!?! Hence why may be able to make 1 good out of two, then maybe build up old box and sell on as reconditioned..

Either way looks like it's going to be at least one more gearbox swap before it get's sorted :'(

Video Clip:


Old Gearbox Splitting

http://www.scouk.net/images/sidc/201...919_142920.jpg


Yup There be damage there..
http://www.scouk.net/images/sidc/201...919_150033.jpg



Definitely not how it should look Although surprising to see that's the only visible damage 3rd gear kaput
http://www.scouk.net/images/sidc/201...919_150040.jpg



The remains from bottom of the box.
http://www.scouk.net/images/sidc/201...919_151851.jpg