Engine Vibration is Driving me Crazy!
Thread Starter
7th Gear
Joined: Oct 2019
Posts: 7
Likes: 1
Engine Vibration is Driving me Crazy!
Looking for any help here. I did a chassis swap- full 2000 C5 Corvette driveline (automatic)in a 1950 Pontiac Silver Streak. Has been on the road just under a year. It was running great until a week ago and then it developed a bad vibration. Shakes at idle and revving in P/Neutral. Also quite bad while driving. With the help of a local amateur LS guy, we checked the valve train first and it seems fine. No codes coming up. Unhooked the torque converter and it didn't get better, so we figured it must be forward of that point. Replaced the harmonic balancer on Friday and still a bad vibration. This afternoon I replaced both engine mounts and it still vibrates badly. I'm running out of ideas and I have to admit that I'm not a mechanic but somewhat mechanically inclined. For the swap i extended torque tube, with all new internals. I have been reading everything I can find online and nothing seems similar. Any ideas or if someone has had an issue like this before, I am kinda losing my mind trying to figure it out. Thanks in advance.
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Joined: Jan 2020
Posts: 61
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From: Northwest Indiana
Looking for any help here. I did a chassis swap- full 2000 C5 Corvette driveline (automatic)in a 1950 Pontiac Silver Streak. Has been on the road just under a year. It was running great until a week ago and then it developed a bad vibration. Shakes at idle and revving in P/Neutral. Also quite bad while driving. With the help of a local amateur LS guy, we checked the valve train first and it seems fine. No codes coming up. Unhooked the torque converter and it didn't get better, so we figured it must be forward of that point. Replaced the harmonic balancer on Friday and still a bad vibration. This afternoon I replaced both engine mounts and it still vibrates badly. I'm running out of ideas and I have to admit that I'm not a mechanic but somewhat mechanically inclined. For the swap i extended torque tube, with all new internals. I have been reading everything I can find online and nothing seems similar. Any ideas or if someone has had an issue like this before, I am kinda losing my mind trying to figure it out. Thanks in advance.
Thread Starter
7th Gear
Joined: Oct 2019
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Melting Slicks
Joined: Dec 2018
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From: Orange County, CA
Thread Starter
7th Gear
Joined: Oct 2019
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So, i am looking at pulling the torque tube this weekend. I think I have everything under control except for one thing... if I recall, I have to put in some extended bolts in the front housing to support the propeller shaft or something? For realignment I think. Can't seem to find a thread on that... if anyone can post a link I would be grateful. TIAdvance!
Thread Starter
7th Gear
Joined: Oct 2019
Posts: 7
Likes: 1
Well, pulled the torque tube this morning... im not sure if this would cause a vibration... should be okay. Im gonna put it back together and continue to try to find the cause of the vibration. Haha! I'm hilarious. So, to do the hassis swap, I had to extend the tt & shaft by 10.5". I wonder if the longer shaft made out of the same tube would have some flex, enough to tweak it? I will talk to driveline guy and maybe use a heavier tube. I have 1" of clearance in tt. Heavier is better right?
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Melting Slicks
Joined: Dec 2018
Posts: 2,647
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From: Orange County, CA
Dang, well at least you know.
A critical design aspect for the rotating machines I work on designing (as a Mechanical Engineer) is Rotordynamics - granted I don't perform the rotordynamic analyses myself.
GM surely heavily analyzed the prop shaft including for rotordynamic performance. One such aspect they would have analyzed is bending modes across the range of expected operating speeds, i.e. 800 - 7000 RPM. Their goal is to ensure any severe bending modes do not occur in that operating range.
I suspect that elongating the prop shaft by 10.5" may have caused a bending mode to occur at a lower rotational speed, now at a RPM the prop shaft has encountered.
Unfortunately I think the best option going forward is to have a custom length driveshaft made by a company like The Driveshaft Shop, since their off-the-shelf upgraded driveshaft solutions use more stout sizes/materials that may improve rotordynamic performance. Perhaps they're also able to provide rudimentary rotordynamic analysis.
A critical design aspect for the rotating machines I work on designing (as a Mechanical Engineer) is Rotordynamics - granted I don't perform the rotordynamic analyses myself.
GM surely heavily analyzed the prop shaft including for rotordynamic performance. One such aspect they would have analyzed is bending modes across the range of expected operating speeds, i.e. 800 - 7000 RPM. Their goal is to ensure any severe bending modes do not occur in that operating range.
I suspect that elongating the prop shaft by 10.5" may have caused a bending mode to occur at a lower rotational speed, now at a RPM the prop shaft has encountered.
Unfortunately I think the best option going forward is to have a custom length driveshaft made by a company like The Driveshaft Shop, since their off-the-shelf upgraded driveshaft solutions use more stout sizes/materials that may improve rotordynamic performance. Perhaps they're also able to provide rudimentary rotordynamic analysis.
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Dang, well at least you know.
A critical design aspect for the rotating machines I work on designing (as a Mechanical Engineer) is Rotordynamics - granted I don't perform the rotordynamic analyses myself.
GM surely heavily analyzed the prop shaft including for rotordynamic performance. One such aspect they would have analyzed is bending modes across the range of expected operating speeds, i.e. 800 - 7000 RPM. Their goal is to ensure any severe bending modes do not occur in that operating range.
I suspect that elongating the prop shaft by 10.5" may have caused a bending mode to occur at a lower rotational speed, now at a RPM the prop shaft has encountered.
Unfortunately I think the best option going forward is to have a custom length driveshaft made by a company like The Driveshaft Shop, since their off-the-shelf upgraded driveshaft solutions use more stout sizes/materials that may improve rotordynamic performance. Perhaps they're also able to provide rudimentary rotordynamic analysis.
A critical design aspect for the rotating machines I work on designing (as a Mechanical Engineer) is Rotordynamics - granted I don't perform the rotordynamic analyses myself.
GM surely heavily analyzed the prop shaft including for rotordynamic performance. One such aspect they would have analyzed is bending modes across the range of expected operating speeds, i.e. 800 - 7000 RPM. Their goal is to ensure any severe bending modes do not occur in that operating range.
I suspect that elongating the prop shaft by 10.5" may have caused a bending mode to occur at a lower rotational speed, now at a RPM the prop shaft has encountered.
Unfortunately I think the best option going forward is to have a custom length driveshaft made by a company like The Driveshaft Shop, since their off-the-shelf upgraded driveshaft solutions use more stout sizes/materials that may improve rotordynamic performance. Perhaps they're also able to provide rudimentary rotordynamic analysis.
Thread Starter
7th Gear
Joined: Oct 2019
Posts: 7
Likes: 1
Dang, well at least you know.
A critical design aspect for the rotating machines I work on designing (as a Mechanical Engineer) is Rotordynamics - granted I don't perform the rotordynamic analyses myself.
GM surely heavily analyzed the prop shaft including for rotordynamic performance. One such aspect they would have analyzed is bending modes across the range of expected operating speeds, i.e. 800 - 7000 RPM. Their goal is to ensure any severe bending modes do not occur in that operating range.
I suspect that elongating the prop shaft by 10.5" may have caused a bending mode to occur at a lower rotational speed, now at a RPM the prop shaft has encountered.
Unfortunately I think the best option going forward is to have a custom length driveshaft made by a company like The Driveshaft Shop, since their off-the-shelf upgraded driveshaft solutions use more stout sizes/materials that may improve rotordynamic performance. Perhaps they're also able to provide rudimentary rotordynamic analysis.
A critical design aspect for the rotating machines I work on designing (as a Mechanical Engineer) is Rotordynamics - granted I don't perform the rotordynamic analyses myself.
GM surely heavily analyzed the prop shaft including for rotordynamic performance. One such aspect they would have analyzed is bending modes across the range of expected operating speeds, i.e. 800 - 7000 RPM. Their goal is to ensure any severe bending modes do not occur in that operating range.
I suspect that elongating the prop shaft by 10.5" may have caused a bending mode to occur at a lower rotational speed, now at a RPM the prop shaft has encountered.
Unfortunately I think the best option going forward is to have a custom length driveshaft made by a company like The Driveshaft Shop, since their off-the-shelf upgraded driveshaft solutions use more stout sizes/materials that may improve rotordynamic performance. Perhaps they're also able to provide rudimentary rotordynamic analysis.
Cheers!
Thread Starter
7th Gear
Joined: Oct 2019
Posts: 7
Likes: 1
Wow! That's Quite the extension. I think I will need something similar. But I guess I just have to destroy this one again. Sounds like a challenge! Thanks for sharing.