Diagnosing vibration

[mymontess]

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..

Sorry, didn't see "it does it in park..."

 

[565bbchevy]

I always you solid mounts through out, if your engine can't move there is no reason you would want the trans to have that ability.
Also if you have factory rubber isolators mounted to your trans crossmember where it bolts to the frame I would make solid spacers of equal thickness to replace those.

 

[565bbchevy]

I read where you did make the isolators solid though 1/4" sounds too thin this would only really affect your pinion angle.
If I remember correctly you have a complete Skip White balanced rotating assembly for you 496 so is this still externally balanced or internal.

 

[-83MONTESS-]

I read where you did make the isolators solid though 1/4" sounds too thin this would only really affect your pinion angle.
If I remember correctly you have a complete Skip White balanced rotating assembly for you 496 so is this still externally balanced or internal.

The Skip White assembly is from Scat and its externally balanced. My only complaint with that kit was the cheap "Pro Street" balancer. It is a nice looking piece and looks exactly like the high dollar balancer my dad uses on his Olds quality wise but im not crazy about using cheap no name sh*t. Any way to single components out to find out where the vibration is coming from or is it just a case of replacing parts til it goes away?

I dont have any isolators between the frame and crossmember. The crossmember bolts right to the frame except on the drivers side where my make shift frame extension bolts to the frame and the crossmember bolts to that. The extension I made is 1/4" flat steel and I have 3 thick washers on top of that for both crossmember bolts.

This week when im off im gonna get some square stock and make a better frame extension that I will weld to the frame and will allow me to bolt the crossmember to it without the bottom of the frame rail deflecting and letting the trans move.

When it comes to solid vs rubber im still not sure what im gonna do. I know a few racers that use a rubber trans mount with solid engine mounts. I figured if they are doing it with success I can as well. Who knows lol.

 

[565bbchevy]

If your crossmember mounting set up is flexing I would fix that first and see if the vibration goes away.
As far as the trans mount I would say a rubber or poly mount should be fine for your car, the only reason I am running a solid trans mount in my car is that with the cage it is very rigid and everything mounted to my engine is bolted directly to the body and roll bars underneath so I don't want anything at all to move.
I am also not a fan of the no name balancer, did you verify that there was a weight on it before installing it, some weights are machined into the hub and others bolt in so you can use the balancer on an internally balanced engine.

 

[-83MONTESS-]

If your crossmember mounting set up is flexing I would fix that first and see if the vibration goes away.
As far as the trans mount I would say a rubber or poly mount should be fine for your car, the only reason I am running a solid trans mount in my car is that with the cage it is very rigid and everything mounted to my engine is bolted directly to the body and roll bars underneath so I don't want anything at all to move.
I am also not a fan of the no name balancer, did you verify that there was a weight on it before installing it, some weights are machined into the hub and others bolt in so you can use the balancer on an internally balanced engine.

The weight is bolted on. The balancer itself seems like a quality piece but there isn't a brand just a sticker that says "Pro Street". Other than that it looks like the same thing my dad has and his was very expensive and by expensive I mean name brand top quality.

I have papers I got from Skip White specific to me showing the balancing of the rotating assembly so I can't imagine it's a crank or rod issue.

 

[pontiacgp]

You should run the same type of mount at the 3 points. The reason being is the engine and transmission are bolted together making them one unit. To have sold mounts in two locations and a poly or rubber in the 3rd location allowing that location to be able to move puts a strain on the 2 solid mounts. If you run a mid plate you can run without a transmission support.

 

[565bbchevy]

I also doubt that it has anything to do with the rotating assembly and I know Skip just bought that state of the art balancing machine a year or so ago.
But there is always the possibility that the guy boxing it up accidently gives you the wrong balancer or flexplate.
After you fix the crossmember situation and if the vibration is still there I would put it up on ramps, jack stands or a hoist and run it without the trans inspection cover and see if you see any odd movements on the flexplate.

 

[565bbchevy]

You should run the same type of mount at the 3 points. The reason being is the engine and transmission are bolted together making them one unit. To have sold mounts in two locations and a poly or rubber in the 3rd location allowing that location to be able to move puts a strain on the 2 solid mounts. If you run a mid plate you can run without a transmission support.

I agree, but after my first comment I looked around on some racing forums and it seems some racers have had trans case breakage issues running the solid trans mount with the solid engine mounts and many refuse to run anything but poly or rubber on the trans with solid engine mounts, which kind of surprised me since I have ran all solids on many cars (all Gbodies) for years without issues.

 

[pontiacgp]

we never ran solid mounts with our super stock cars. If you hit the wall or another car and tweak the clip with solid mounts you have a change of cracking the block. We hit the wall once hard enough to have the upper control arm put a nice dent int the headers but the engine was on poly mounts so it was saved.. I have also seen some guys use solid mount and they don't adjust the mounts properly and the car heads out the track with the block already stressed. Sold mounts will not break a block if properly installed and you don't run into anything hard. With our late model and sportsman car we ran solid mounts cause we use mid plates so the engine is sitting on 4 solid mounts We still used a transmission mount that was fabricated to the position of the transmission mount. I have seen a transmission that was hanging off the engine that locked up and that transmission was spinning around and smashing the tunnel while he was trying to stop the car.

and to get back on topic I don't have a good record of finding vibrations.....until something breaks. Solid mounts give you every little vibration so it's tricky to find what the problem is