vibration at certain rpm
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Joined: Feb 2014
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From: oklahoma
vibration at certain rpm
ok here is my head scratcher. have a 91 heritage and i've developed a bad vibration. since i don't have a tach i'll give ya some gear and mph readings. if i keep the rpm's down the bike runs great, but as the rpms come up a bad vibration starts. i mean bad enough that somebody in a car next to me could hear it!
5th gear at 70mph (on the speedo) all is great, at 72mph the vibration starts and won't stop until i drop speed back to 70mph. i'm gonna say this is around 3200 ish rpm. now taking off from a stop the vibration will start at about the exact same rpm in ANY gear.
the vibration CAN be duplicated with bike sitting on stand in neutral also. rev it up and at a certain rpm (same every time) the vibration starts. it sounds like it's coming from the front of the bike or from under the gas tank.
things i've checked. pulled windshield, pulled headlight, pulled spot lights. checked pegs, hiway bar, master cylinder cover, exhaust heat shields, pretty much everything on the front of the bike. i guess it comes down to pulling the tanks and checking under there.
any ideas what would cause this vibration?? i did pull the carb and rejet it but the vibration was there before but not as bad.
5th gear at 70mph (on the speedo) all is great, at 72mph the vibration starts and won't stop until i drop speed back to 70mph. i'm gonna say this is around 3200 ish rpm. now taking off from a stop the vibration will start at about the exact same rpm in ANY gear.
the vibration CAN be duplicated with bike sitting on stand in neutral also. rev it up and at a certain rpm (same every time) the vibration starts. it sounds like it's coming from the front of the bike or from under the gas tank.
things i've checked. pulled windshield, pulled headlight, pulled spot lights. checked pegs, hiway bar, master cylinder cover, exhaust heat shields, pretty much everything on the front of the bike. i guess it comes down to pulling the tanks and checking under there.
any ideas what would cause this vibration?? i did pull the carb and rejet it but the vibration was there before but not as bad.
Stellar HDF Member
Joined: Jul 2011
Posts: 2,583
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From: Boston, MA
HH,
1995 flstc here and I have vibrations from 2000++++. Solid mounted motor with no balancing mechanisms a la newer models (counter weights) and I'm 20 years old and you're 23.... I've learned to love it, to a point. I just went to rubber bushings on the risers. Your FLSTC will hide the ugly red polypropylene bushings but those worked awesome for me before I swapped the front end.
Tom
1995 flstc here and I have vibrations from 2000++++. Solid mounted motor with no balancing mechanisms a la newer models (counter weights) and I'm 20 years old and you're 23.... I've learned to love it, to a point. I just went to rubber bushings on the risers. Your FLSTC will hide the ugly red polypropylene bushings but those worked awesome for me before I swapped the front end.
Tom
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Joined: Feb 2014
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From: oklahoma
yeah i'm used to evo vibrations, i've logged over 100,000 miles on evo bikes. this is totally different. it just started last week, and it's a violent vibration at around 3200ish rpm. i'll check the upper mount tomorrow. i think i'm going to pull the tanks and check everything.
from looking under the tank bib it looks like the right side rear tank mount is either loose or the rubber grommet is broke. just looking for ideas of what else to check when i'm in there as i don't wanna pull the tanks several times!! lol
from looking under the tank bib it looks like the right side rear tank mount is either loose or the rubber grommet is broke. just looking for ideas of what else to check when i'm in there as i don't wanna pull the tanks several times!! lol
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Joined: Jun 2010
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From: Upstate New York
It's not unheard of for the top motor mount to crack. I think I'd pull the tanks and check it carefully.
I'd also replace the rubber grommets on the tanks if you haven't already.
Also, check the oil tank under the seat. If you've never replaced the rubber mounts that support the oil tank one of them might be broken. This happened to me a couple years back. I'd hear a rattle and feel a vibration at certain speeds. I'd have sworn the rattle was coming from the front. Turned out it was the oil tank/battery hitting against the vertical frame member (seat post tube). Check the clearance between the oil tank and the frame in front. There should be about 1/8 clearance between the tank and the frame. Any less, and you may have a weak/broken mount.
I'd also replace the rubber grommets on the tanks if you haven't already.
Also, check the oil tank under the seat. If you've never replaced the rubber mounts that support the oil tank one of them might be broken. This happened to me a couple years back. I'd hear a rattle and feel a vibration at certain speeds. I'd have sworn the rattle was coming from the front. Turned out it was the oil tank/battery hitting against the vertical frame member (seat post tube). Check the clearance between the oil tank and the frame in front. There should be about 1/8 clearance between the tank and the frame. Any less, and you may have a weak/broken mount.
Last edited by Uncle G.; May 19, 2014 at 07:21 PM.
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From: oklahoma
ok, haven't pulled tanks yet, gonna run it out of gas first. but i did pull the bib and the console off and have a look see. the throttle side tank (right side?) rear bushing is bad. will replace both while i'm in there. couldn't find anything else loose or moveable. oil tank is nice and solid has around a 1/4 inch between it and the downtube in the frame. battery is nice and tight. went over EVERY bolt i could get to today from the front wheel all the way to the rear light. didn't find any loose nothing out of place, except the washer on the right side rear shock. it's loose, but the bolt holding the shock on is tight. i taped the washer to keep if from moving for a test, still vibrating bad.
held the right side tank, tested and still vibrating. maybe it's INSIDE the motor? funny it would be at a certain rpm tho.
this week is super busy for me, but the weekend looks calm so i'll get the tanks dry and pull them this weekend and go over everything i can find.
one question,,, the top motor mount. bolt goes in from the clutch side of the bike, goes thru the bracket that bolts to the top of both heads. then thru the fram, then into a captive nut looking thing (is this right). now if i look from the carb side of the bike i can see the bolt sticking thru the brackets as there is a hole in this side of the bracket. now the bolt is NOT centered in this hole. it's offset to the front of the bike. it LOOKS like the end of the bolt is touching the bracket with the hole in it.
held the right side tank, tested and still vibrating. maybe it's INSIDE the motor? funny it would be at a certain rpm tho.
this week is super busy for me, but the weekend looks calm so i'll get the tanks dry and pull them this weekend and go over everything i can find.
one question,,, the top motor mount. bolt goes in from the clutch side of the bike, goes thru the bracket that bolts to the top of both heads. then thru the fram, then into a captive nut looking thing (is this right). now if i look from the carb side of the bike i can see the bolt sticking thru the brackets as there is a hole in this side of the bracket. now the bolt is NOT centered in this hole. it's offset to the front of the bike. it LOOKS like the end of the bolt is touching the bracket with the hole in it.
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Joined: May 2013
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From: Western NY
one question,,, the top motor mount. bolt goes in from the clutch side of the bike, goes thru the bracket that bolts to the top of both heads. then thru the fram, then into a captive nut looking thing (is this right). now if i look from the carb side of the bike i can see the bolt sticking thru the brackets as there is a hole in this side of the bracket. now the bolt is NOT centered in this hole. it's offset to the front of the bike. it LOOKS like the end of the bolt is touching the bracket with the hole in it.
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Joined: May 2013
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From: Western NY
Be sure to take a good look at your top motor mount. I've never had a broken one on either of my Evo's, but I have broken them on my Shovel. If it is cracked, broken, or loose you will definitely notice increased vibrations.
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Thread Starter
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Joined: Feb 2014
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From: oklahoma
hey thanks for the pic, mine looks exactly like that. no cracks, not loose. yeah this vibration is driving me nuts. if i shift it like an old grandpa at low rpms, and i don't go over 70mph (on the speedo) then it rides perfectly. but if i hit 72mph then the vibes start, OR if i run it higher in the rpms between gear changes. the vibe starts out low and then really gets going. it does NOT affect the handling of the bike, but it's very loud.
