Posted by Dan on April 21, 03 at 17:21:31:
Howdy!
First time poster here. Y'all seem in-tune with Subs, so I figure I'll see if someone here can help me.
Vehicle History: Originally a 1994 Sub 1500 2WD 5.7 4L60E tranny.
In the 741,000 miles on the truck, I've upgraded to a Vortech supercharged 383, custom programming, intercooled, HD 4L60E, 8-bolt front suspension and 14 bolt full floater 4.56 gears, plus other upgrades.
Since the upgrades were installed, I've developed a number of persistent vibrations. I can feel them in the steering wheel and in my seat.
It's not the tires and wheels as I've done sufficient replacement and swapping to verify that. I've got Firestone R4S that seem to be about as perfect as one can get and are perfectly smooth on a friends truck and my Sub still vibrates with his on.
Furthermore, at one point, last last set were "rounded" on a machine to make them nearly perfectly round by shaving the high spots while mounted on the vehicle. No change.
The front suspension has been checked by several mechanics with no faults found. It's "tight as a drum" by their description. Bilstein shocks are new. All bushings are new (most are poly.) Steering box is tight.
Also, rotors, drums and rear hubs have been replaced. Braking does not affect the vibration, though.
The driveshaft was suspected to be a source. Replaced. No change. The vibration is road speed... not a high speed vibration.
The transmission was suspected (shuttering or out-of-balance) and was swapped. No change.
(BTW, PATC / www.transmissioncenter.net in the Shreveport, LA area is an excellent tranny source that I highly recommend.)
The vibration is at highway speed and seems centered around 65 mph. At 40 and 100, it's smooth as glass. Yes, that sounds like tires...
Here's a key point: It's only about 75% consistent. Furthermore, it actually "comes and goes" at regular intervals. For example, at 70 mph, it will shake for about 8 to 10 seconds and then smooth out totally for another 8 to 10 seconds. And then some (rare) days, it's smooth as glass.
This truck has been worked hard with heavy loads and towing. I've wondered if there were any weaknesses in the frame that might need to be checked.
Well, I apologize for the length of this post as I tried to be as complete as possible.
Any thoughts or ideas would be GREATLY appreciated.
I still enjoy the truck and cannot see any (other) reason to buy a new one. Still looks good and drives well (vibration not withstanding.) Besides, I enjoy the 6.6 second 0-60 runs... hehe
If I think of anything else, I'll add it to this post.
Dan
(If you choose to email me directly, please remove the capital letters from the address)