Carbon fiber DS vibration fix

Todd914 · 12-31-2021, 05:07 PM

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 it’s 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.
I’m not a mechanic but I am a 70’s 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 wasn’t anything else on the car causing vibration because it was smooth with the OEM one on. I also knew it wasn’t 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.

YouTube

YouTube

https://spicerparts.com/calculators/...gle-calculator

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snow_bound26 · 12-31-2021, 06:36 PM

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.

REX_WGN · 01-03-2022, 11:25 AM

This is incredible work. Do you have pictures of where you shimmed?

K3rm1tth3fr0g · 01-03-2022, 12:57 PM

Cool stuff. Good job

Bansheeboy11 · 01-03-2022, 06:42 PM

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

Todd914 · 01-06-2022, 10:03 AM

Quote:

Originally Posted by REX_WGN

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.

K3rm1tth3fr0g · 01-06-2022, 07:04 PM

Quote:

Originally Posted by Todd914

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.

Welcome to NASIOC

JDMJNKY · 01-07-2022, 02:09 AM

Great find and a great share. Thanks and glad you fixed the issue.

fullah · 01-08-2022, 03:36 PM

Quote:

Originally Posted by Todd914

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.

murrdogg24 · 01-08-2022, 04:41 PM

I have always fixed vibration by clocking the driveshaft until the vibration is gone

car_freak85 · 01-10-2022, 01:49 PM

Quote:

Originally Posted by murrdogg24

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...

undyjr · 01-11-2022, 06:21 AM

I've had my DSS in two different VA chassis with no vibration in either. Did I just get lucky?

fullah · 02-19-2022, 11:06 AM

Quote:

Originally Posted by fullah

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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12-31-2021, 06:36 PM	#2
snow_bound26 Scooby Specialist Member#: 395793 Join Date: Jul 2014 Chapter/Region: Tri-State Location: SLC and Lake Placid Vehicle: 2005 92x Aero Beige	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.

01-03-2022, 11:25 AM	#3
REX_WGN Scooby Guru Member#: 107618 Join Date: Feb 2006 Chapter/Region: Tri-State Location: NY Vehicle: 2006 WRX Wagon 2009 FXT	This is incredible work. Do you have pictures of where you shimmed?

01-03-2022, 12:57 PM	#4
K3rm1tth3fr0g Scooby Specialist Member#: 508105 Join Date: Nov 2019 Chapter/Region: NWIC Location: Greater Seattle Area Vehicle: Link tuned 02 WRX EJ205 20G-XTR JDM 6MT E85	Cool stuff. Good job

01-03-2022, 06:42 PM	#5
Bansheeboy11 Scooby Specialist Member#: 182415 Join Date: Jun 2008 Chapter/Region: Tri-State Location: New York Vehicle: 1999 RS Aspen White	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

01-07-2022, 02:09 AM	#8
JDMJNKY Scooby Specialist Member#: 253498 Join Date: Jul 2010 Chapter/Region: SCIC Location: sOuL-CaLiFoRnIa Vehicle: 02 RSTI MURK'D	Great find and a great share. Thanks and glad you fixed the issue.

01-08-2022, 04:41 PM	#10
murrdogg24 Scooby Guru Member#: 50586 Join Date: Dec 2003 Chapter/Region: BAIC Location: Chiraq Vehicle: 64 Impala	I have always fixed vibration by clocking the driveshaft until the vibration is gone

01-11-2022, 06:21 AM	#12
undyjr Scooby Specialist Member#: 459692 Join Date: Dec 2016 Chapter/Region: South East Location: Hampton Roads Va Vehicle: 2019 WRX STI silica black	I've had my DSS in two different VA chassis with no vibration in either. Did I just get lucky?