Rear vibrations for days - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

FT86Z · 04-09-2019, 06:46 PM

Hello gurus,

Over 60mph i get insane vibrations. The rear windshield, drear deck area seems to be where the vibrations are the worst. I recently had a 4.88 final gear swap, DS Shop aluminum driveshaft, and Cusco motor mounts installed and the issue came immediately. The vibes are so bad that i feel like bolts may come loose. Under 60mph the car has slight vibrations that is 100 percent tolerable.

Other mods i have on the car (pre-vibrations) are: Cusco rear pillar brace, Beatrush rear subframe collars, Beatrush diff mount support brace, Beatrush subframe brace, Beatrush rear strut bar. These mods alone did not cause any harsh NVH.

First thing i did the following morning was swap in the OEM motor mounts. I also removed the rear pillar bar. The vibrations are still pretty bad over 60mph but marginally better. Im open to reverting any of the said mods with the exception of the DS and final gear (labor is $$$ and not something i can do myself).

Please give me some input as to what you believe the culprit may be. This is not my daily but it is a street car. Thanks in advance!

KL

DarkPira7e · 04-09-2019, 06:51 PM

Have you tried unbolting the driveshaft, rotating it, and bolting it back on? Some people report the need to do this with the aluminum shafts.

FT86Z · 04-09-2019, 07:03 PM

Quote:

Originally Posted by DarkPira7e

Have you tried unbolting the driveshaft, rotating it, and bolting it back on? Some people report the need to do this with the aluminum shafts.

That's great info. I will research to see if that's something i can attempt myself. Thanks.

x808drifter · 04-09-2019, 07:43 PM

Does it do it at high rev?

Or just at speed independent of RPM?

FT86Z · 04-09-2019, 08:02 PM

Quote:

Originally Posted by x808drifter

Does it do it at high rev?

Or just at speed independent of RPM?

It does it the entire rev range after 60mph.

new2subaru · 04-09-2019, 10:45 PM

Remove a single component at a time until you find the problem. Start with the easiest.

This is why it's best to change one thing at a time.

Turdinator · 04-09-2019, 11:10 PM

Sounds like a driveshaft imbalance. Was it new or secondhand?

FT86Z · 04-10-2019, 08:43 AM

Quote:

Originally Posted by Turdinator

Sounds like a driveshaft imbalance. Was it new or secondhand?

It was brand new and it was installed by a reputable shop. Perhaps it came bent or maybe it wasnt installed properly?

wparsons · 04-10-2019, 09:24 AM

Someone already said it, but it's very likely just needing to be unbolted and rotated. Not uncommon.

Turdinator · 04-11-2019, 02:12 AM

Quote:

Originally Posted by FT86Z

It was brand new and it was installed by a reputable shop. Perhaps it came bent or maybe it wasnt installed properly?

Try the unbolt and rotate as mentioned previously. It is possible, although unlikely, that the shaft got to you with a bad balance. Another possibility is with a 4.88 diff your driveshaft is spinning faster than stock for any given road speed, it could be its now spinning faster than the RPM range it was balanced for?

FT86Z · 04-11-2019, 05:29 PM

Quote:

Originally Posted by Turdinator

Try the unbolt and rotate as mentioned previously. It is possible, although unlikely, that the shaft got to you with a bad balance. Another possibility is with a 4.88 diff your driveshaft is spinning faster than stock for any given road speed, it could be its now spinning faster than the RPM range it was balanced for?

Will def rotate the DS as soon as possible and report back! Thanks

04-09-2019, 06:46 PM	#1
FT86Z Drift noob Join Date: Oct 2015 Drives: 2015 BRZ Sport-Tech CWP 6MT Location: Toronto Posts: 173 Thanks: 141 Thanked 36 Times in 20 Posts Mentioned: 0 Post(s) Tagged: 2 Thread(s)	Rear vibrations for days Hello gurus, Over 60mph i get insane vibrations. The rear windshield, drear deck area seems to be where the vibrations are the worst. I recently had a 4.88 final gear swap, DS Shop aluminum driveshaft, and Cusco motor mounts installed and the issue came immediately. The vibes are so bad that i feel like bolts may come loose. Under 60mph the car has slight vibrations that is 100 percent tolerable. Other mods i have on the car (pre-vibrations) are: Cusco rear pillar brace, Beatrush rear subframe collars, Beatrush diff mount support brace, Beatrush subframe brace, Beatrush rear strut bar. These mods alone did not cause any harsh NVH. First thing i did the following morning was swap in the OEM motor mounts. I also removed the rear pillar bar. The vibrations are still pretty bad over 60mph but marginally better. Im open to reverting any of the said mods with the exception of the DS and final gear (labor is $$$ and not something i can do myself). Please give me some input as to what you believe the culprit may be. This is not my daily but it is a street car. Thanks in advance! KL __________________ FT86Z 藤原とうふ店

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04-09-2019, 06:51 PM	#2
DarkPira7e Rust bucket enthusiast Join Date: Feb 2017 Drives: 2013 Turbo Firestorm FRS Location: Vermont Posts: 3,934 Thanks: 3,200 Thanked 4,095 Times in 2,045 Posts Mentioned: 31 Post(s) Tagged: 0 Thread(s)	Have you tried unbolting the driveshaft, rotating it, and bolting it back on? Some people report the need to do this with the aluminum shafts.

04-09-2019, 07:43 PM	#4
x808drifter LMGTFY Join Date: Mar 2016 Drives: 13 FRS, 91 Miata Location: Lava Town, HI Posts: 2,776 Thanks: 5,561 Thanked 3,646 Times in 1,625 Posts Mentioned: 15 Post(s) Tagged: 0 Thread(s)	Does it do it at high rev? Or just at speed independent of RPM?

04-09-2019, 10:45 PM	#6
new2subaru Weight Weenie Join Date: Aug 2015 Drives: 15 FR-S Location: Canada Posts: 2,586 Thanks: 5,016 Thanked 2,330 Times in 1,346 Posts Mentioned: 12 Post(s) Tagged: 0 Thread(s)	Remove a single component at a time until you find the problem. Start with the easiest. This is why it's best to change one thing at a time.

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