Thoughts on vibration

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scampy

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So I'm getting a vibration that comes in about the time I hit 3rd gear in the 1/4 is there for about apprx 400 rpm then is gone till i cross the finish and comes back breifly then is gone,so i feel it is speed related not rpm.It was just kinda weird its not really bad,like shake your eyes out, but there.Was waiting for it to get worse as i went faster then it was gone untill decel and only there for a breif time probably as it slowed to that speed again.
Looking for your thoughts on this,not use to one that comes in then goes away.
Thanks FABO
 
Does it happen in both lanes of the track?
 
OK so a bit more history if you will,we just built our stroker combo,see 340 stroker build will this make our goal and got 3 passes on it found the converter is a bit loose and running more rpm than i want.Run good except for too much trap rpm,no vibrations. Enter a new 4.10 gear set up,different case and all new pieces,bearings spool ring pinion,yoke and set up by our usual guy that also did the 4.30 coming out.Reinstalled and 1st pass out vibration/harmonics idk is there made 2 more passes no real change.I did notice after 1st pass one u bolt for the ujoint had more thread past the nut on the top than the bottom,was able to loosen nuts a bit and got it to move so apprx same but did not remove shaft,no difference.ujoints new at start of race season so was there 1st week and now have 6 runs.Probably leaving something out still so ask away.
 
Double check your pinion angle, and check the transmission mount...both could be the source.
 
Remove the shaft from the pinion yoke and spin it 180 degs. See if it goes away.
 
because nothing outside of the center section changed. My guess is it’s inside or the shaft rototated 180degs. Could be the spool is not true. The ring gear could be cockeyed. My limited slip case had a bunch of run out. Also the ring gear had high spots around the thread holes.
 
I'm gunna go a bit different direction with thought of a tire going bad. My reason for this is 430 gears we're enough to power threw the vibration you didn't notice where the 410 take a bit longer to get through and easier to notice. As far as trap vibration the tire could be flexing enough it goes out of round for a split second when the forward rotation is suddenly reduced. I'm assuming slicks of course. Just a thought from an ex tire jockey.
 
Well going to turn the shaft 180 for sure,would be great if thats it.Going to check balance on tires,bubble balance,any way to see this tire issue without swapping tires and yes bias slicks.The rear turned free by hand no tight spots but probably wouldn't feel that small of an amount.
 
Two thoughts here
Don't take offence, just spit balling
did a u-joint cap fall off during the gear replace and lost a needle or got a piece of trash in the cap?
or, did the slip yok, get remove and put back together out of faze. When you put the yok straight down, is the pinion yok straight down......or off a spline or two.......

This is kind of a cheese video, but if you fast forward to the 2:00 minute mark, it explains what i'm trying to say.
 
One more thought to go with tire/brake suggestions. Since the entire thing was apart would it be possible a rock or small amount of dirt got between rotor/drum and the axle when reassembly occurred. Also between brake and wheel. Should be able to check this fairly easy with car on stands rotate tires and check sidewall clearance between a known fixed point. Mite not be much 1/8 in or less but at speed could be an issue.
 
Cudafever said:
Two thoughts here
Don't take offence, just spit balling
did a u-joint cap fall off during the gear replace and lost a needle or got a piece of trash in the cap?
or, did the slip yok, get remove and put back together out of faze. When you put the yok straight down, is the pinion yok straight down......or off a spline or two.......

No Offense i've done that a few times trying to get the shaft in and lined up with the u bolts but it went really nice this time.THis shaft has been used the week before with no issues so not thinking any yoke phasing on the shaft issues.What I've been reading is that tire balance seems to be a vibration that comes in and out at a certain speed as opposed to something else this does not get worse the faster you go.Thanks and keep them coming,just trying to figure out what type of vibration or harmonic comes in then goes away as you go faster,then reppears on decel back through that speed point


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No Offense i've done that a few times trying to get the shaft in and lined up with the u bolts but it went really nice this time.THis shaft has been used the week before with no issues so not thinking any yoke phasing on the shaft issues.What I've been reading is that tire balance seems to be a vibration that comes in and out at a certain speed as opposed to something else this does not get worse the faster you go.Thanks and keep them coming,just trying to figure out what type of vibration or harmonic comes in then goes away as you go faster,then reppears on decel back through that speed point
 
Update,have gone over rear brakes,rotated pinion yoke 180 confirmed u joint position and checked tire balance still there,swapped to my spare wheels and slicks and still there.
 
I really don't what to pull the center section out again and put my 4.30 back in knowing I don't really want to run them,I just don't know what in the rear would cause this vibration,i'm not getting any noise from it,thinking of sending drive shaft out again for balance check,still gota check the trans mount,remove it, don't see anything mounted in frame,axle bearing???
 
scampy said:
I really don't what to pull the center section out again and put my 4.30 back in knowing I don't really want to run them,I just don't know what in the rear would cause this vibration,i'm not getting any noise from it,thinking of sending drive shaft out again for balance check,still gota check the trans mount,remove it, don't see anything mounted in frame,axle bearing???
Click to expand...
my car had a similar vibration. turned out that the yoke on the diff was somewhat loose up/down (radially) and i had to set-up the gear again with shims, meaning the pinion preload was off. it took a while before i found it out. wishing this could help.
 
flyfish said:
Double check your pinion angle, and check the transmission mount...both could be the source.
Click to expand...
So what kinda of play,if any should i be able to get at the trans mount,tailshaft,side to side,up?
 
scampy said:
So what kinda of play,if any should i be able to get at the trans mount,tailshaft,side to side,up?
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I'm not sure if there is a quantitative value you should be looking for (1/8 inch this way, or that way).... I just know that when I was chasing down a similar vibration years ago I was able to remedy it by replacing the bushing with something like this (polyurethane I believe). The one I removed was pretty worn out and cracked.

TMBT.jpg
 
flyfish said:
I'm not sure if there is a quantitative value you should be looking for (1/8 inch this way, or that way).... I just know that when I was chasing down a similar vibration years ago I was able to remedy it by replacing the bushing with something like this (polyurethane I believe). The one I removed was pretty worn out and cracked.

View attachment 1715184286
Click to expand...
Yea i can move it side to side and can push it up as well by hand prob closer to 1/4 inch,anyhow will be removing it tonight,hopefully and get a better look.I also have maybe a 1/16" of up down on the slip yoke in the trans,normal?
 
If the vibration comes in at 3rd gear for about 400 rpm, why wouldn't you consider something hanging up/ slipping in the trans? Or is that thinking the worst.
 
Cudafever said:
So did you ever find the vibrations???
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I can't say that I did,I've replaced the trans mount but still there,I just kinda gave up and ran with it,it has not gotten any worse. However I have replaced the whole center section this winter with new unit including case. Looked over the one removed did not see anything that stood out.My simple spidy sense said noticed it after the 4.10 went in thats where it should be but just did not want to change it out but now it is, if we get back to racing with the shutdowns and such.
Also I did send the shaft back out for balance check and he did say it was a little more than he like and made adjustment but no change.Its kinda minor there are times I don't notice it until i focus to listen/feel. I recenlty got a go pro and had some in car footage and can't even see or hear it.So i'm kinda hoping that its all smooth with this rear and see that my original thinking may be correct but????
 
Yeah my guess was that you went for 119 to 124 mph and the drive line was having a frequency problem at that point.
Run threw it at the top of the track, and then back threw it as you decelerated. Where before you never got there in mph(driveline rpm) to feel it..........

It not eng vibration, or you would feel it at every gear shift............is your shift RPM the same as your threw the trap rpm???
I guess if the vibration is minor and isn't getting any worse.

Is it possible that the transmission tail shaft bushing, is getting a little bit loose? or slip yoke has some wear on it. Drive shaft guy should have noticed that when rebalancing your shaft.
 
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