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Old 12-31-2021, 05:07 PM   #1
Todd914
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Join Date: Dec 2021
Default Carbon fiber DS vibration fix

I bought a CF driveshaft for my 2020 WRX and after installing it, my car vibrated from 35-45mph and again at 80-100+. I sent the DS out for a rebalance and was told itís in spec. After searching the internets, asking on various forums and contacting some reputable shops, I was told, it Is what it is and to just live with it or put the OEM one back on.
Iím not a mechanic but I am a 70ís kid with a touch of OCD. So I decided to figure this one out on my own because after feeling the difference between the OEM 2 piece and the CF one piece, there was no way in hell I was going back. I was done trying to find someone with an answer and started to do some thinking on my own.
With the OEM DS the car was smooth as glass but with the CF DS it vibrated at two different speeds. I already knew it wasnít anything else on the car causing vibration because it was smooth with the OEM one on. I also knew it wasnít the CF DS because it was sent back to the manufacturer for a rebalance and inspection.
There was only one thing left to check and that would be the pinion angle. It had to have changed going from a two piece to a one piece. So I went to my friends shop and took some measurements and sure enough it was out of spec.
I was able to shim the rear diff with some SS washers to get the my angles within spec. Took it for a test drive and the vibration was gone.

-Depending on how much you need to shim the diff, you may have to mill the diff bracket to expose more threads on the bolts to get the nuts back on.

Here are some links to understand DS phasing/clocking, how to measure driveline angles and the driveline calculator to see if your in spec.



https://spicerparts.com/calculators/...gle-calculator
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Old 12-31-2021, 06:36 PM   #2
snow_bound26
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A lot of times if can be fixed by clocking the input shaft going into the trans. It's trial and error though. Go 2 teeth at a time until it's close then go 1 tooth at a time.
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Old 01-03-2022, 11:25 AM   #3
REX_WGN
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This is incredible work. Do you have pictures of where you shimmed?
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Old 01-03-2022, 12:57 PM   #4
K3rm1tth3fr0g
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EJ205 20G-XTR JDM 6MT E85

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Cool stuff. Good job
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Old 01-03-2022, 06:42 PM   #5
Bansheeboy11
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This is a huge problem on the older models, the diff mount bushings in the crossmember and the bushings for the front bar mount sag with age and cause problems with single piece driveshafts, you can use bushings on either side of the "T" bar to change the pinion angle
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Old 01-06-2022, 10:03 AM   #6
Todd914
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Quote:
Originally Posted by REX_WGN View Post
This is incredible work. Do you have pictures of where you shimmed?
Thanks, us old guys are good with our hands but suck at technology. I tried to do the picture thing. Not working for me today.
The shims go between the rear diff and rear diff bracket. Once you get under the car, it should be self explanatory.
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Old 01-06-2022, 07:04 PM   #7
K3rm1tth3fr0g
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Quote:
Originally Posted by Todd914 View Post
Thanks, us old guys are good with our hands but suck at technology. I tried to do the picture thing. Not working for me today.
The shims go between the rear diff and rear diff bracket. Once you get under the car, it should be self explanatory.

You need to use nasioc.img to upload photos using the BBcode and it has been broken since 2020 for new signups.



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Old 01-07-2022, 02:09 AM   #8
JDMJNKY
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Great find and a great share. Thanks and glad you fixed the issue.
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Old 01-08-2022, 03:36 PM   #9
fullah
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Quote:
Originally Posted by Todd914 View Post
my car vibrated from 35-45mph and again at 80-100+.
Love seeing threads like this--sometimes you know there is actually a problem when everyone else thinks your crazy haha.

Can you please give a little more detail on the vibrations? Were you getting it at certain speeds? certain rpms? did the vibration feel like it was more in the chassis or was it transmitting through the steering?

I watched that video you linked but since you measured on the VA wrx, can you please tell us what the specific angle that you were able to get after you did the washers? You have me curious now, I have a subtle vibration after doing the rear diff carrier bushings so I'd like to check my pinion angle just to rule this out.

Any specific info you can provide would be great.
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Old 01-08-2022, 04:41 PM   #10
murrdogg24
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I have always fixed vibration by clocking the driveshaft until the vibration is gone
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Old 01-10-2022, 01:49 PM   #11
car_freak85
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Quote:
Originally Posted by murrdogg24 View Post
I have always fixed vibration by clocking the driveshaft until the vibration is gone
Just installed my DSS carbon shaft and this /\ is my plan.

That's not to say worn out differential/transmission mounts and bushings aren't a problem. The rear diff bushings on SF Foresters are often torn or sagging the rear of the diff 0.5-in., or more, from where it should be sitting with fresh bushings. And folks seem baffled when they continually snap rear axles in them while off-roading...
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Old 01-11-2022, 06:21 AM   #12
undyjr
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I've had my DSS in two different VA chassis with no vibration in either. Did I just get lucky?
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Old 02-19-2022, 11:06 AM   #13
fullah
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Quote:
Originally Posted by fullah View Post
since you measured on the VA wrx, can you please tell us what the specific angle that you were able to get after you did the washers?
bump..where you at Todd? lol
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