mullysd

I have a 1939 chevy coupe that has been built for 10 years. The drive line has 17.000 miles on it. I have a balanced 383/570 hp motor and Tremec 6 speed with a 9"ford 3:89 28 spline axles. This past summer I had a new clutch and balance flywheel in it. I am getting vibration around 60-70mph. As far as the drive line there has been nothing changed. The only thing I know is the pinion angle is off which I have shims to currect that. The drive shaft was out some this past summer and I fixed that too. I know my engine mounts are steel and rubber stock mounts with Heigts front cross member.I do know the engine mounts that back side of the rubber are cracked from heat transfer from the exhaust. I do have new ones to replace those. The trans mount is black Polyurethane that came with the T56 011 Tremec and is 10 years old.
My questions are should I not only change the engine mounts with a heat shield and the trans mount too. Been chasing this vibration all last summer. I even took my axles out this past summer the splines looked good and I didnt feel anything in the rear end when I had the axles out.
I warmed the car up this afternoon because it was above 50 today. Then took it out and noticed the viberation in the normal speeds like 60 or so. But today i ran it up to 110 and it was smoother. That said is it just the mounts that all of sudden got enough age and play toy abuse to them and now need replaced? Any help will be great! Thanks Steve

Darth_V8r

iTrader: (4)

In general, us F body guys will say use poly motor mounts and a stock rubber trans mount. Since you are already looking into your pinion angles, that would be next on the list anyway.

one thing to add to your list to look for is if the vibrations are really bad in 5/6 gear but seem to go away in 4th. There is a known issue on the 5/6 gear cluster causing vibrations when it is loose on the countershaft. Here's a link describing it for you and hoping that this is not the issue:

https://ls1tech.com/forums/manual-tr...vibration.html

mullysd

Thanks so much for responding to my post !!! This has been driving me crazy most friends that I have taken a ride with me don't notice it like I do. Today its going to be 58 outside so I will take it out and run it in other gears to see if I notice no vibration in all gears except 5-6th gear. Its great that we can connect with others to help solve our problems. Steve

BALLSS

Steve

was the vibration there before the clutch & FW were replaced?

If not than the FW/Clutch is likely not "zero" balanced. I assume your 383 is fully "internal" balanced motor

If this vibration was there before clutch/FW swap it likely is either DL angle is off or your failing motor mounts need replacing

As noted I and many others use poly engine mounts (I use the black Energy Suspension) and a stock rubber tranny mount

I have 2 factory shims under my T56. Every car will be different especially in your case with the 39 LT1/T56 combo

To me the fact the vibration seems to be a higher MPH vs constant it would be more a DL angle issue be it worn parts or angle of tranny & rear end not right

mullysd

Thanks for the info! I did notice that the trans mount bolts from the bottom side of the crossmember through to the mount are angled in position. I am not sure if they changed out my trans mount and the mount is not the right one. Because I got it up on my lift this afternoon and notice that. I don't remember it looking like that and it looks like the mount is hitting the front side of mount to the trans. Like it is too wide then pushing the mount backwards making the bolts not vertical like they should be. I don't think that is my vibration problem but I think I will replace it along with the motor mounts. Also change the rear end pinion angle too. I did turn the drive shaft this afternoon several times and did not feel anything. I did notice that when turning the drive shaft it has about 1/4 play in turning it left and then right (in the gears). I hope that is normal. I will post something if I get this solved. Thanks to all for your help. Steve