high frequency vibration above 70mph but only on throttle

[ChriS2000]

Hey man, I'm actually in the process of messing with some pinion angles / vibration issues myself. 

Let me know if you need a hand, or want to go for a spin / compare notes on what's going on.

[gc3]

Hey man, I'm actually in the process of messing with some pinion angles / vibration issues myself. 

Let me know if you need a hand, or want to go for a spin / compare notes on what's going on.

what's your vibration symptoms?
how hard mounted are your driveline components?
a quick ride in a similarly set up car to compare vibration/noise might not be a bad idea.

[ChriS2000]

My vibration is more low speed, low load. 

I think it may be due to some driveline angle issues as well, but the side to side angle instead of up and down. 

I'm using the factory rubber diff bushings (f&r) and delrin subframe bushings.  The trans crossmember is using an energy suspension poly mount, as well as the engine. 

I measured 86.5 degrees on the yoke spline face on the trans, and 85 on the face of the pinion. 

I'd like to poke around your car anyway, as they're both set up for road racing / autox.  Let me know when you're free, maybe we can get some stuff sorted out.

[gc3]

hmm, i never measured lateral driveline angles, but mine looks pretty close to straight that i ignored it completely.
weird its a low speed/load issue for you. i think that might be harder to narrow down if it goes away with speed/load.

i'm 95% sure i'll make it to the season opener autoX at the silverdome on the 27th. that might be a good time to meet up, not sure how much free time i'll have before then.

[ChriS2000]

hmm, i never measured lateral driveline angles, but mine looks pretty close to straight that i ignored it completely.
weird its a low speed/load issue for you. i think that might be harder to narrow down if it goes away with speed/load.

i'm 95% sure i'll make it to the season opener autoX at the silverdome on the 27th. that might be a good time to meet up, not sure how much free time i'll have before then.

I used a magnetic angle finder on the surfaces to get those measurements, I got it at home depot for around $10. 

I'll be in the garage pretty much every weekend messing with stuff, just give me a shout whenever and we can meet up 

[gc3]

how are you measuring side/side angle with the gravity needle kind? (i assume that's what you're talking about?)

you should just plan on showing up at the autoX.
would be good to have some competition in the class for once too.

[ChriS2000]

I wasn't able to measure the side to side angle, which is why I suspect it may be the problem. 

I wouldn't mind heading up to that autox, i'm not a super huge fan of the surface at the silverdome (or autox in general for that matter).

[gc3]

i see, is it visibly off?
i cant imagine mine is more than a degree off side/side

and i prefer silverdome just because of the size of the lot. surface sucks but no other venue has the potential to hit 3rd gear.

once i safely complete this autoX i should be ready to start signing up for track days again.
but autoX is fun because it is actually competitive. track days are more like practice.

[ChriS2000]

It's hard to say for sure, I guess the best way to measure would be the distance from the tail shaft flange to each side of the trans tunnel. 

I did an autox at the silverdome a couple years back, drove me nuts trying to race on a surface that was that rough, covered in debris, and had weeds / crap growing in the cracked pavement.  Did a real number on my R888's as well 

[gc3]

im not sure the trans tunnel is square enough to measure. maybe a plumb bob and a straight edge on the ground might be better?

well.... the 600whp subarus keep tearing up the surface more, so just assume the condition to be worse off than before.
but i ride high enough that the lowered cars all mow the weeds and trees enough to not bug me.

[DDv8]

I ran a string from engine centre line through tail centre line to rear of car. Super easy to measure off set.


DD

[gc3]

well, managed to do more test runs over the weekend:
vibration is now gone up till 80+ mph, at which it seems to be more vibrate-y than last year, but not positive.
definitely dont feel like the driveshaft is going to fall off anymore, so the driveline angle adjustment seems to have fixed most of it.

got it up to 110 without much problem or worry, so it should be okay for track days, but i'd still like to eliminate all major vibrations.

i think the next step is to mount a gopro under the car and hope to see something shifting when it shouldnt be.

[scuter83]

Did you ever find other issues? I am getting a vibration 55-65mph while on throttle. Seems to lessen a lot when in coast. Have to double check driveline angles but thought they were pretty good. Not sure how much vibration from all Felton bushings is normal. I'm in a FC with T2 rear as well. First vibrations were bad wheel bearings but gave those fixed.