Vibration at speed

[billday]

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

 

[Jeb]

Are you getting any codes?

 

[billday]

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]

My C5 used to do that!!! Hunter 9700 Road Force Balance!!!! "Problem Solved"!!

 

[6speeder]

My C5 used to do that!!! Hunter 9700 Road Force Balance!!!! "Problem Solved"!!

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]

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!!!!!

 

[billday]

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]

.......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

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]

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

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!!
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!!

 

[billday]

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