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Keane165's 1970 LeMans

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harmonic balancer


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I've tightened up a lot of my suspension including body mounts. Now I notice vibration that continues even when I push in the clutch. My 77 Trans Am has low miles. I am considering replacing the harmonic balancer since it is probably original. Has anyone else done this and experienced a noticeable benefit? I am also going to look at engine and transmission mounts. Engine and transmission mounts would also be original.

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Does the vibration only occur at idle..?? Or Through a certain RPM range...?? While sitting in neutral only with the clutch engaged...?? Or driving down the road at different speeds..Etc..

If you could narrow down the specifics some...It will help in pointing you in the right direction...We like to help if we can....

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Thanks for getting back to me. The vibration seems to be the worst at around 50 mph. It's noticeable at lower and higher speeds but seems to be at it's max around 50mph. When the vehicle is stationary I do not notice the vibration in the pedals. When up to speed I've pushed in the clutch and the vibration is still there. At max vibration it's noticeable in the rear view mirror.

I've replaced bushings to include, upper/lower control arms, front/back sway bars, new upper/lower ball joints. Once I replaced the body mount bushings I noticed the vibration much more. I feel it in the gas pedal as well as in the Hurst shifter.

Prior to replacing the body mounts the vibration was not as noticeable. Prior to replacing the body mounts I would notice the vibration at about 55 mph and only until I hit 60 mph. Replacing the body mounts seems to have magnified the vibration. I expected some of that but I am concerned there's something wrong vs just more feedback from the engine as a result of poly bushings.

I believe the vibration is coming from the transmission forward. Any engine mount bushings or transmission support bushings would be original. The harmonic balancer is also original. Other than those three things I am not sure what else it could be.

I have also had it aligned and the wheels balanced.

 

 

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Any chance the driveshaft has lost a balance weight or the pinion angles are so bad between the transmission and differential? I am just thinking of another possible source of the vibration.

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I'd say yes those are definitely a possibility. I assume the driveshaft balance weights can just fall off over time. Sounds like those weren't on there very securely any how. Also rebalancing the drive shaft seems like an relatively inexpensive test. The pinion angles could be off as well. I've had the car since 86 and it has almost 30k miles on it. My cousin bought it new.

All are good ideas for what to cross off the list. I guess it's hard to determine the exact fix but more a process of elimination. 

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I've found out that my motor mount and my manual transmission mount are both old cracking rubber. That could be where my vibration is coming from so I plan to replace those. Now the debate is rubber or poly. Since I'm on a quest to reduce vibration I am thinking of rubber but could use some advice.

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Rubber typically is better at damping vibrations over poly.

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I agree with Frosty...That the root cause of the vibration issue is drive line related...And not necessarily the bushings and the mounts although the polyurethane body mounts will amplify any existing issue...Broken/worn engine/transmission mounts tend to have a very noticeable clunk when they are loaded and unloaded rather than a steady vibration under normal driving conditions...A couple of things to look at...Has the clutch been recently replaced...If so was the flywheel correctly resurfaced..??  If the clutch has not been replaced then that would be a moot point....I would definitely look at the drive shaft to see if there are any signs of missing weights...Also pay close special attention to the universal joints...On older low mileage cars that spend most of the time sitting...The needle bearings in the (U joint) caps can flat spot over time due to the weight of the driveshaft sitting on the needle bearings constantly in the same place without being rotated for extended periods...Even if they appear tight...if there are any flat spots it will cause a vibration as the joints will not work as smoothly as they should under normal driving conditions...Might be worth looking at...

Edited by TWO LANE BLACK TOP
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Thank you for all the great advice. I really appreciate it. The shop said that the universal joints were good and the drive shaft looked good. I need to get a confirmation that the drive shaft balance weights were still there. 

Thanks for the recommendation on rubber vs poly. New rubber engine mounts and transmission mount are on order. I am hoping that work is done by the end of the week. As soon as it's done I'll post an update.

Thanks again. I've attached some resent pics.

Young 77 Trans Am exterior side (6.11.21).jpg

Young 77 Trans Am interior note mileage (6.11.21).jpg

Young 77 Trans Am exterior side 2 (6.11.21).jpg

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Sweet looking ride. I hope you drive it look you stole it from time to time!

Another thought - tires and wheels. Are the tires and wheels balanced properly? Are they flat spotted at all? On one very rare occasion I had a steel belt separate on a rear tire and it would cause a vibration in the back end of the car at low speed (it was the driver rear at the time).

Are the front hubs on tight enough? Are the bearings in good shape and greased properly?

I'm still with Two Lane on this but I am thinking about other possibilities too.

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  • 4 weeks later...

I'd like to provide a quick update. The motor mounts and the transmission mount have been replace. The rubber mounts were totally cracked as they were original. As a result the vibration is completely gone and it drives like new. Thanks again for the excellent direction. I really appreciate it.

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We are happy to help a brother out. Thanks for providing the update. We appreciate it.

Edited by Frosty
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