Engine vibration in the 3000 RPM range? Smooths out if under boost.

[LEGACY_GN]

If I rev the engine to 3000 rpm range there is a steady throbbing or drumming vibration from the engine regardless if I'm in park or driving down road. If I accelerate under 5 or 10 pounds of boost in that range it seems to be smooth. Thoughts? Build is in my signature but it's a stroker with 5 disc stall and BHC harmonic balancer and JW flexplate, so I'm a bit dismayed at the vibration.

 

[Chuck Leeper]

"with 5 disc stall".
Since it is evident in park, neutral, pull the converter back, and see what you get.

 

[LEGACY_GN]

How do I pull the converter back? Because of the 5 disc it's tight up against the flywheel. No room.

 

[kidglok]

might be a long shot but maybe exhaust drone?

 

[LEGACY_GN]

No, I can feel the vibration pretty strong and it comes in waves like a fan or chopper.

 

[turbo nasty]

Unbolt converter slide back and try it like CL mention

 

[Amelio]

Also inspect your dampener very well

How long has the car been together since the build? How long after the build did you notice the vibration?

 

[dr_frankenstein]

i once had a simular deal...

my trans had lost a bellhousing dowel.

 

[LEGACY_GN]

What should I look for on the dampener. It's on there very very tight. We should have honed it as it went on hard and may never come off, lol. Built last october. Noticed last month. I did unbolt the motor mounts a couple of months ago to replace oil pan gasket. Jacked the engine way up due to girdle. Think something is lose now? Maybe a motor mount? I'll check the dowel pins too. I am fairly certain the convertor can't slide as it has no room. Its very tight.

 

[Chuck Leeper]

How do I pull the converter back? Because of the 5 disc it's tight up against the flywheel. No room.

It best not be a press fit between the pump and the flex plate. 5 disc or not, there HAS to be some space for crank end play. If not, the thrust brg will be toast in short order.
W/ the converter ALL the way back into the trans pump, there should be 1/8 to 3/16" space between the converter mount stands and the flex plate.
Take the bolts out of the converter, and shove it back..

 

[Mike T]

I did some work on a friends car that had a similar issue. It had a JW external balanced flex plate and a 5 disc Vigilante. We pulled he dust cover and found that the balancing weight had been welded on the converter side of the flex plate and it was sandwiched in between the converter and flex plate causing them to wobble.

 

[LEGACY_GN]

I did some work on a friends car that had a similar issue. It had a JW external balanced flex plate and a 5 disc Vigilante. We pulled he dust cover and found that the balancing weight had been welded on the converter side of the flex plate and it was sandwiched in between the converter and flex plate causing them to wobble.

wow, now that sounds probably. I have the JW and the 5 disc.What was the solution. Did they send you a new one? Will check tonight.

 

[Mike T]

The car was bought that way. We pulled the transmission and removed the flex plate, I carefully cut the welds that held the weight and relocated/rewelded it to the exact same spot on the front side of the flex plate. We put a new front seal in the transmission and reinstalled everything, it was fine after that. The part that I still don't get was that the starter sounded fine the whole time even with the flex plate wobbling 1/2 of an inch. I just noticed in your build that you have a stroker and it is most likely internally balanced and would not have the weighted flex plate.

 

[Mike T]

Chuck is right taking the converter loose would eliminate everything from the converter back. Another thought that comes to mind is that if you have the really hard poly mounts even a slight miss will feel just like a balance issue.

 

[LEGACY_GN]

I do have poly mounts but if it was missing wouldn't it be worse under boost. It smooths out with boost.

 

[Mike T]

I brought the mounts up because when I first built my motor I made the wrong chip selection in the Maft Pro and it caused a over fueling condition. About 45 minutes into the break in period I was sitting in the drivers seat trying to get a handle on what was going on and like yours mine had a vibration around 2500 to 3000. The car did not have a dead miss but it was obvious that the tune was off (my fault wrong chip selection) but besides that I really thought that the shop that balanced my crank had messed up and I was starting to think the motor was going to need to come right back out. As it turns out after making the correct chip setting the car started to run better and smoother with every mile that was put on it in fact it took about 500 miles before it was totally smooth ( maybe cylinders equalizing who knows). A few club members have sat in the car and commented on has smooth the motor runs. The point of all this is that I was certain that it was a balance issue but it only turned out to be a tuning problem exaggerated by the poly mounts which BTW I'm very happy with now.

 

[LEGACY_GN]

My motor is smoother than my Cadillac V with the exception of the 3000 rpm range. In that range its a harsh throbbing vibration that goes away with boost. I have dual poly mounts, poly body bushings, bhc dampener and jw flywheel. Up until lately never had a problem since the build. I don't think its the tune because it's new. It was smooth as glass before. I am concerned that I lifted the motor to swap oil pan gaskets and maybe something is loose. I'm going to check all the suggestions on here tomorrow and report back.

 

[Mike T]

If it was good before the gasket swap you are probably on the right track with something being loose or hitting. It's probably going away under boost due to torque moving the motor away from whatever it may be hitting. I Hope it's something simple

 

[LEGACY_GN]

Believe it or not I replaced the iac and cleaned the throttle body real well with carb cleaner and now the vibration is gone? Smooth as butter now.

 

[Mike T]

Good job