Diagnosing vibration

[-83MONTESS-]

Alright some of you may have read my recent thread about trans issues but I have stumbled across another issue and I figured since it may potentially help others with similar problems I'll make another thread.

My problem is a vibration occurring under throttle above about 2k rpm regardless of gear or temp. It does it in park and driving down the road. No abnormal noises, oil pressure is good and no other symptoms of engine failure. Car has a big block with solid engine, body mounts and rubber trans mounts if it matters. Any idea on what could be the culprit? It did it with the old converter as well and when I replaced it I made sure flex plate bolts were tight. If anyone could help me diagnose this I will buy u a cyber beer for your troubles! Thanks guys.

 

[williamattop]

Man, you cant catch a break.
Ill give you my best guess. But for starters, solid mounts have been known to cause weird vibrations at different rpms. So you might want to disregaurd everything else Im going to mention.

Some possibilities could be either an out of balance (maybe a weight got knocked off?) flywheel or, get ready,,,,,,,,,,,,,, a cracked flywheel most likely by the crankshaft hub.
I say this because you stated it was doing this with the old converter also. So to me that would elimanate an out of balance TC although I guess it could still be possible you got 2 bad ones in a row.
Sounds like something is out of balance (even in park, which makes me think rotating) for one reason or another.

Just another thought, but is it possible you have a loose cover or heat shield or anything like that?

Of course this is just my opinion so lets wait till somebody more sober than myself comments before you start pulling that transmission again.

 

[-83MONTESS-]

Man, you cant catch a break.
Ill give you my best guess. But for starters, solid mounts have been known to cause weird vibrations at different rpms. So you might want to disregaurd everything else Im going to mention.

Some possibilities could be either an out of balance (maybe a weight got knocked off?) flywheel or, get ready,,,,,,,,,,,,,, a cracked flywheel most likely by the crankshaft hub.
I say this because you stated it was doing this with the old converter also. So to me that would elimanate an out of balance TC although I guess it could still be possible you got 2 bad ones in a row.
Sounds like something is out of balance (even in park, which makes me think rotating) for one reason or another.

Just another thought, but is it possible you have a loose cover or heat shield or anything like that?

Of course this is just my opinion so lets wait till somebody more sober than myself comments before you start pulling that transmission again.

No loose cover or heat shield, at this point im positive the vibration is rotating/engine related. I just don't know of anyway to narrow down the possibilities. I would hate to pull the trans again just to double check the flex plate and I would hate to pull the front of it all apart to check the balancer.

One thing I thought of is the trans mount. My car didnt have the frame extension on the drivers side and the crossmember I got requires the use of an extension. I made one out of 1/4" flat steel and spacers but when I lower the trans back onto the crossmember the under side of the frame where the extension is flexed. So maybe when I rev the engine the transmission is moving enough to cause a vibration?

 

[-83MONTESS-]

The more I think of it the more im leaning towards the crossmember. If I put a jack under the pan and lift it the trans will raise up a little with the crossmember. I never thought to even check it before but I will have to do more investigating tomarow. In the meantime any other ideas or ways to narrow the list?

 

[drogg1]

So you are saying your engine mounts are solid but your transmission mount is rubber? I have always heard/read it is best for them to be the same material. So solid with solid or rubber with rubber.

 

[-83MONTESS-]

So you are saying your engine mounts are solid but your transmission mount is rubber? I have always heard/read it is best for them to be the same material. So solid with solid or rubber with rubber.

Yes solid engine mounts, solid body mounts and a rubber trans mount. I have heard numerous different ways of doing it but it seems like most people say if you run solid engine mounts DO NOT use a solid trans mount. I guess I will have to do some more homework to see which answer is right.

 

[williamattop]

The more I think of it the more im leaning towards the crossmember. If I put a jack under the pan and lift it the trans will raise up a little with the crossmember. I never thought to even check it before but I will have to do more investigating tomarow. In the meantime any other ideas or ways to narrow the list?

This sounds like you may be on to something.
Im hoping this is your problem as this will be much simpler to check/rectify than any of the things I mentioned.

 

[Rktpwrd]

Let me know what you find out as well please. I am also running solid motor mounts with a poly trans mount. Want to know if I should anticipate problems with my setup as well.
Thanx
Donovan

 

[mymontess]

Just wanna throw a couple things out there- u-joints? Driveshaft / pinion angle?

 

[-83MONTESS-]

Just wanna throw a couple things out there- u-joints? Driveshaft / pinion angle?

I was gonna look at the driveshaft since I had it shortened but since the vibration is present even at idle in park or neutral I cant imagine that being the issue, at least not this issue lol.