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Vibration at speed

billday

Active member
Joined
Dec 1, 2005
Messages
33
Location
Great Bend, KS
Corvette
1995 Yellow Coupe
My '95 6 speed Coupe has developed a strange vibration - only in 6th gear under power, especially above 70 mph. I don't get any vibration in 5th or any other gear. My gas mileage has dropped off lately, as well.

My first thought was u-joints, but it only happens in 6th gear, and physical inspection didn't show any obvious sloppy u-joint. I got new tires recently, but this vibration doesn't seem to be tire related. Is there any chance that I have a misfire that is only noticeable in top gear? Since it only affects 6th gear, do I have a transmission problem?

Thanks!
Bill
 

billday

Active member
Joined
Dec 1, 2005
Messages
33
Location
Great Bend, KS
Corvette
1995 Yellow Coupe
No codes - It really feels like a misfire, because it smooths out when I back off. I only feel it in 6th gear, but fuel mileage has dropped off, and it seems like power is down. I have decided to start with plugs, wires, & fuel filter, maybe air filter as well. I'm sure it's time, anyway. Then, I would suspect u-joints.
Are you getting any codes?
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
My C5 used to do that!!! Hunter 9700 Road Force Balance!!!! "Problem Solved"!!:upthumbs :lou :lou
 

6speeder

Well-known member
Joined
Jul 30, 2003
Messages
153
Location
santa cruz, ca
My C5 used to do that!!! Hunter 9700 Road Force Balance!!!! "Problem Solved"!!:upthumbs

Hey Jesse! ..... The Hunter 9700 balance machine corrected a misfire and declining fuel mileage on your C5? Must be a new feature on that machine.;)

billday..... a 'miss' at speed in high gear can be a symptom of a failing opti. I'm not suggesting that is your problem, only that it is a symptom.
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Hey Jesse! ..... The Hunter 9700 balance machine corrected a misfire and declining fuel mileage on your C5? Must be a new feature on that machine.;)

billday..... a 'miss' at speed in high gear can be a symptom of a failing opti. I'm not suggesting that is your problem, only that it is a symptom.
No !!! He said he had a Vibe Only in 6th. with No codes!! I just stated that My C5 had the same thing happen,It felt Like a Misfire!!!It acted Like a Misfire!!!! Wishuwerehere82 turned me on to a Hunter 9700 and Problem Solved!! But then again You are Right,Opti can do this too!! But so can a Plug Wire,Plug,EGR Valve, PCV Valve,Vacuum leak and even a Injector or even a Pinion or Carrier Bearing!! From the Symptoms He Described!! No codes is a Tough one to Diagnose,I never would have believed it was my Tires either, it felt Like a Misfire!! But it was!!!!!:upthumbs :lou
 

billday

Active member
Joined
Dec 1, 2005
Messages
33
Location
Great Bend, KS
Corvette
1995 Yellow Coupe
I know there are quite a few possibilities, I'm starting with the obvious, and cheapest. The vibration is only there when under power at 70+ in 6th, and stops when I back off.

Hey Jesse! ..... The Hunter 9700 balance machine corrected a misfire and declining fuel mileage on your C5? Must be a new feature on that machine.;)

billday..... a 'miss' at speed in high gear can be a symptom of a failing opti. I'm not suggesting that is your problem, only that it is a symptom.
 

6speeder

Well-known member
Joined
Jul 30, 2003
Messages
153
Location
santa cruz, ca
.......The vibration is only there when under power at 70+ in 6th, and stops when I back off.

Cheap/quick fix.... don't exceed 69mph in 6th, or shift down to pass:upthumbs

Your original post addressed vibration, engine miss, reduced fuel mileage.

Now you are only concerned with vibration... that MAY be solved with tire inflation, alignment, wheel balance. Take a tip from gmjunkie (jesse) and have your alignment checked on a Hunter machine.
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Cheap/quick fix.... don't exceed 69mph in 6th, or shift down to pass:upthumbs

Your original post addressed vibration, engine miss, reduced fuel mileage.

Now you are only concerned with vibration... that MAY be solved with tire inflation, alignment, wheel balance. Take a tip from gmjunkie (jesse) and have your alignment checked on a Hunter machine.
No actually I said have the tires Balanced on a Hunter 9700 Road Force balancer!!!! It actually puts 700-800 Lb of load on the Tire while balancing!! I do this to EVERY Car I buy for Resale before I start going over them for resale, It has literally Saved me $1000's,In Time and Parts!!!Chasing a Vibration or Pull in a Vehicle!!! As far as a Hunter 4 Wheel alignment Machine there Great,But it's to bad Most don't know or care how to use one Right!!! There what I call Toe and Go Artists!! It's Close enough Thanks for the $89.95,There just is hardly any REAL Front end Technicians anymore!! But Alignment and Tire Pressure WILL affect your gas Mileage!!:upthumbs
Dude's, I gotta Go Road Test this Car,I want to be sure it's Right before I put it up for Sale!!! Later!!:upthumbs :lou :lou
 

billday

Active member
Joined
Dec 1, 2005
Messages
33
Location
Great Bend, KS
Corvette
1995 Yellow Coupe
Well, I got the plugs and wires changed out. The top gear vibration seems to be gone! It is a good thing when the "cheap" repair does the job!

Bill
 

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