I recently installed a new 350 HO crate engine with vortec head, SDPC's intake manifold, new injectors, motor mounts and transmission mount, in my 87 TPI GTA. Since then I have been experiencing mild vibration when the transmission is placed in drive. In Park or Neutral the engine idles very smooth. The vibration is only felt when a load is placed in the engine. I took the car to a transmission shop and they told me it's not the transmission or converter and to look for my problem in the engine compartment.

My base timing is set to 8 degrees (in drive) and I was wondering if advancing the timing might smooth out any vibrations felt?

Thanks,

 

Just a couple of questions:

What design was the 350 HO - two-piece or one-piece rear main seal?

Which flexplate did you use with the engine?

What harmonic damper did you use?

 

Vader,

The GM engine I purchased was p/n 12486041 and it has a
one piece 4-bolt rear seal.

I used my stock 1987 5.7 Auto flexplate and I purchased a new
harmonic wheel balancer that was recommended for this engine
from GM.

The tranny 700R4 is the same and I used the same converter. My converter was replaced a couple years ago when I had this transmission rebuilt.

Let me know if you need any info. of if you have a answer to my vibration problem.

Thanks,

 

Does the vibration occur only while idling in gear, or while driving too? Also, does it vibrate when in park or neutral and raising the RPM's above idle?

 

No vibration is felt when the transmission is in either Park or Neutral, and raising the RPM above idle dosen't make any difference.

When you place your foot on the brake pedel and put the car in Drive, the vibration is felt at idle. While driving the car I can't really feel any vibration, but then I wonder if the higher RPM's dampen the vibration where it's not felt?

 

How/why do you do that? I was under the impression you need to disconnect the brown ECM wire, and Drive or Park wouldn't make any difference (as long as you aren't reving the engine up).

 

The underhood sticker does state that you should have the transmission in drive with the parking brake on while setting the timing. The engine will idle at a slightly lower RPM while in drive, which leads me to my next point. Since the vibration only occurs during idling conditions in drive, it has something to do with a load on the engine at such a low RPM. Is you engine stock? Aftermarket cam, heads? Check for a vacuum leak. What RPM does it idle at both in gear, and in park? I have noticed this in many cars with automatics and it will usually go away if you raise the idle slightly with the accelerator pedal while the car is in gear and your foot on the brake.