Mysterious shaking identified

Flywheel, Clutch, Transmission, Axles, etc...

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entirelyturbo
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Mysterious shaking identified

Post by entirelyturbo »

Remember the reason I wanted to get rid of my car? The mysterious shaking that I thought was a wheel bearing or possibly AWD binding? Well, it did it again today, and it stayed long enough for me to analyze it. The car tracked straight as an arrow, so it wasn't a wheel vibrating. It obviously isn't AWD binding, because I spent $400 on new tires to stop it!! :evil:

So after I disengaged the clutch and noticed the shaking immediately went away, I thought of something. I got home, jumped under the car, and tested to see how much the tranny mount would move. I had no problem shaking the entire transmission with my bare hands... So I'm pretty sure that's my problem...

I guess what happens is, when I hit a bump and the transmission is under stress from either accelerating or braking the car, the mount allows the tranny to move and then fall into a rhythm, I guess it has a natural frequency that occurs when I hit a bump just right...

Anyway, an OEM one is $130 :shock: Somewhere that I can get an STi one perhaps? Adam at Z1 Auto, maybe? I'll go ahead and shop around...
"Der Wahnsinn ist nur eine schmale Brücke/die Ufer sind Vernunft und Trieb"

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HomeSlice
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Post by HomeSlice »

i dont think adam has any sti mounts in stock. i talked to him like a week ago but he can prob get you one.
Cheers on the fix!
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vrg3
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Post by vrg3 »

It's the same mount as GD-chassis Imprezas, right? You could probably get one from a NASIOC member who has swapped his out for an STi mount for like $20 or $30. An almost-new OEM mount isn't the same as an STi mount, but it'll be very good for a few dozen thousand miles.
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Brat4by4
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Post by Brat4by4 »

search the internet for STi tranny mounts and find the place with the cheapest price + shipping. I ended up getting mine for about half of retail brand new. I even bought the dog-bone also for less than just the engine/tranny ones other places. Couldn't use it because of my future IC install and ended up selling it locally. I made out on that deal.

oh, and drop them a line to make sure they have them in stock. waiting for shipping from Japan can be a bear.
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turbonator
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Post by turbonator »

Did you ever get clunking sounds or did the car just shake??
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entirelyturbo
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Post by entirelyturbo »

Update: Someone on NASIOC sold me a OEM WRX tranny mount, since vrg3 suggested it :). The guy bought the engine and tranny off some genius that wrecked his WRX on the way home from the dealer :roll:, he was going to swap the drivtrain into his 2.5RS, and he didn't need the mount. He said it only had a few miles on it, and it was still shiny! $25, too :D

Anyway, I just put it in about an hour ago. Big improvement, fixed exactly what I wanted it to fix, car doesn't shake violently when I run over a big bump anymore. Clutch engagement feels a lot smoother, and there is probably a quarter horse more, again the whole wasted energy thing. It seemed to slightly help the hesitation, but alas, it definitely did not cure it :evil:...

Turbonator, I was hearing clunks, I was feeling shaking, everything! I distinctly remember making a right turn through a very bad series of bumps near my university, and the car shook so violently and clunked so much I had to pull over... I honestly thought the whole car was going to shake to pieces right in the middle of the road... Which leads me to the condition of the old mount: absolutely ruined. I was able to bend it almost an inch any way I wanted to with my bare hands with little effort...

So the problem that nearly drove me to part with my pride and joy has now been fixed! Woohoo! :mrgreen:
"Der Wahnsinn ist nur eine schmale Brücke/die Ufer sind Vernunft und Trieb"

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THAWA
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Post by THAWA »

wonderful that you fixed it
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mikec
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Post by mikec »

Tried to change my tranny mount, and all I managed to do was round the nuts off that hold the mount to the longitudinal member. :x

My brother and I put some polyurethane on the one thats already installed, hoping it'll set up enough to make a difference. I'm also hoping this solves the clunk I get, after reading this thread. Fingers crossed!
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Legacy777
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Post by Legacy777 »

I just ordered that urethane from mcmastercar.....so hopefully I'll be able to do the tranny mount soon, and see if how that works.
Josh

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ciper
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Post by ciper »

I think you just repaired a part damaged by another problem. It would be like replacing tires because the alignment is off.
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entirelyturbo
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Post by entirelyturbo »

I concluded that it simply couldn't be another problem. Nothing else in the car would move that much. I could not get any wheels to move side to side, all suspension pieces were bolted down properly, everything checked out except that tranny mount...

And the fact that the problem has not surfaced since the installation of the mount suggests that I fixed it ;)
"Der Wahnsinn ist nur eine schmale Brücke/die Ufer sind Vernunft und Trieb"

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ciper
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Post by ciper »

When the U-Joint is bad it causes it to angle to one side, so instead of spinning in a circle the transmission outlet moves around. This causes the mount to tear apart.
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Brat4by4
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Post by Brat4by4 »

Check-mate, match, Ciper. Get your u-joints checked out. If this is the case then that mount will shred again. And look into getting an STi mount. My stock mount was really flexible also and I think that will pretty much be the case with any OEM one after some mileage, unless it is STi, of course.
1993 WMP BC6 5MT EJ22T 9psi 3.9:1 213k 205/55R16

62.6 m/s @ 0.66 bar. Gotta love boost. :)
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entirelyturbo
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Post by entirelyturbo »

Is the U-joint loose, in which case it would shift and be out of balance only at certain times? Or are you saying it's bent, which would mean it's out of balance all the time? The car is smoother than my granma's 2003 Caddy CTS right now, so I know the driveshaft is at least straight the majority of the time. This horrible shaking has not occurred since.

I will get under there again and have a look anyway though...
"Der Wahnsinn ist nur eine schmale Brücke/die Ufer sind Vernunft und Trieb"

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Brat4by4
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Post by Brat4by4 »

Have a shop check it out. Someplace that would have seen lots of bad u-joint before. By yourself you'll see if it's bad when it tears your stuff up again.
1993 WMP BC6 5MT EJ22T 9psi 3.9:1 213k 205/55R16

62.6 m/s @ 0.66 bar. Gotta love boost. :)
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ciper
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Post by ciper »

"Is the U-joint loose, in which case it would shift and be out of balance only at certain times?" Yes

I inspected mine while installed on the car twice and didnt see it. It wasnt until I removed the drive shaft and laid it on the floor that I noticed one of the "races" was chewed up (meaning sometimes it would go crooked and shake everything).
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