High Speed vibration, can't find what's causing it.

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RockinRobin said:
In the last month or so I started to notice the race car vibrating when I get above about 90 mph on a pass. Does it only while the car is still accelerating. When I let off it goes away.
It crosses the finish line 107-108 mph
No vibration during burnout or until 3rd gear (727)
So far I have:
Checked u joints and trans mount, also trans output shaft doesn't seem to have any side to side play.
checked motor plate
New front tires (was vibrating before the new tires)
front end alignment ( Stock front suspension. I do need tubular upper control arms as alignment is at its limit, but all ball and other joints are fine)
I would think that warped front rotors would show up before 90mph so I haven't looked at those
Suggestions??
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Could the drive shaft balancing be off? Maybe it is not turning true? Just a thought.
 
I’m curious to see what happens after Robin has his tires balanced. Something I haven’t mentioned and I don’t believe it’s been mentioned, is the high gear clutch can be also slipping causing the vibration. I experienced that years ago in my dads roadrunner. It’ll really show on a 1/4 mile over 1/8 mile. But just add that to the list of possibilities Robin lol.
 
Had the slicks balanced this morning. One of them took 18 ounces of weight to balance! The other took six. I am going into the weekend fairly confident that the vibration will go away. Will report after I make some passes Friday.
 
RockinRobin said:
Had the slicks balanced this morning. One of them took 18 ounces of weight to balance! The other took six. I am going into the weekend fairly confident that the vibration will go away. Will report after I make some passes Friday.
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You sure there isn't something (rock?) got INSIDE one of them?
 
RockinRobin said:
In the last month or so I started to notice the race car vibrating when I get above about 90 mph on a pass. Does it only while the car is still accelerating. When I let off it goes away.
It crosses the finish line 107-108 mph
No vibration during burnout or until 3rd gear (727)
So far I have:
Checked u joints and trans mount, also trans output shaft doesn't seem to have any side to side play.
checked motor plate
New front tires (was vibrating before the new tires)
front end alignment ( Stock front suspension. I do need tubular upper control arms as alignment is at its limit, but all ball and other joints are fine)
I would think that warped front rotors would show up before 90mph so I haven't looked at those
Suggestions??
Click to expand...
My Van would vibrate or shake over 90. I took it as the wind getting under it and just let it go. Possible you need to drop your front end a little. Other comments are also valued here, I'm just giving you a possible easy way out.
 
Swinger 340 said:
My Van would vibrate or shake over 90. I took it as the wind getting under it and just let it go. Possible you need to drop your front end a little. Other comments are also valued here, I'm just giving you a possible easy way out.
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I'll consider that if the tire balance doesn't work.
 
When they added 18 oz of weight to the one tire and wheel, did they try spinning the tire to eliminate the heavy spot. 18 oz is "way way" to much weight.
 
71Demon528 said:
Sounds like you may have lost a wheel weight on one of your rear slicks. If you balance them. It’s possible one of them came out of balance whether you balanced them when you mounted them or not. I have had to re balance mine after some usage in the past. I use a harbor freight bubble balancer, sticky wheel weights, and I duct tape all of my weights to the rim.

Not saying this is the problem, but it’s a possibility.

RJ
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This is where my mind went first.
 
RockinRobin said:
Ok I've learned my lesson. I'm due for new slicks at the end of the season and from now on they get balanced!
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I hear a lot of guy’s saying it isn’t necessary but boy it bites hard when it does bite you in the butt. I’ve tried it and went through bolts loosening up big time
 
RockinRobin said:
Ok I've learned my lesson. I'm due for new slicks at the end of the season and from now on they get balanced!
Click to expand...

Happy it’s fixed. It was interesting to see lots of theories and others’ suggestions. I’m happy it was something simple as I’ve often found, most of the time it usually is something simple. Especially if you have a solid foundation (meaning the car) to start with.
 
I was shocked at how much weight my et streets took to balance... they used stick on weights and of course they started falling off.. I foil taped over them (hoping i got them in the right spot) I didn't think they would be as far out as they were
 
Icetech said:
I was shocked at how much weight my et streets took to balance... they used stick on weights and of course they started falling off.. I foil taped over them (hoping i got them in the right spot) I didn't think they would be as far out as they were
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Got my ET Streets balanced yesterday and one took a lot of weight as well....................
 
I’d be leery of the balancing beads with the softer compound of a slick. It’s also a no go if you are coating the inside of the slicks to prevent leaks (old dish soap trick). I run tubes so bubble balance is my go to.
 
Not apples to apples, but the repro bias ply redlines consider being round as just a suggestion. Every time I have to remount them, I have to have them road force balanced. Match high spot on tire with low spot on steel wheel.
 
RockinRobin said:
Ok I've learned my lesson. I'm due for new slicks at the end of the season and from now on they get balanced!
Click to expand...
I have to pull mine when I get home from work and get them balanced before tomorrow's test and tune. Did you just get the regular balance.
 
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