Well its on the 85 blazer, i just did the 383 swap in it. drove it for about 20 miles across town with open headers and around the business complex along with idling it in the shop. It was great to the exhaust shop, then when i went to leave, all of a sudden there was a harsh vibration through the entire truck. even the cups in the cup holders were rattling. it doesnt do it at idle, and only through a small rpm range, if i rev the engine up the vibration goes away.

I got true dual exhaust that has thrush turbo mufflers and 2.5 inch pipe. the system is bolted to the headers and ran back, then dumps down in front of the rear axle. and there are mounts that are welded to the back of the mufflers. so the exaust is only held on by the collector bolts and mounts on the mufflers that have a 1"x1" rubber isolator.

The biggest fear i have is that since its a 383 and externally balanced, that the motor isnt balanced right. i have a 400 flex plate and all that just to let ya know. But i would think that if the engine was out of balance that it would be shaking violently from idle all the way to redline, i wouldnt think it would only be at a certain rpm range would it??? and after 30 miles of driving that it would have thrown itself apart by now?

Could the way the exhaust is mounted be resonating that bad to create a vibration that rattles the windows?

Could it be the torque converter or tranny taking a crap soo soon? but it does it in idle and neutral too... i changed plugs and wires just to make sure and it still does it. The engine is running WAY rich but im not driving it anymore and monday a local guy is tuning the carb for me.

I unbolted the exaust from the headers and just rested it on the tranny crossmember and took the blazer for a quick spin, And the Vibration was gone. So i dont know if its the exaust creating the vibration, or if its the engine out of balance and the exaust is mutliplying it? or if the torque converter is junk and causing it? i dont know, help me guys!!! lol

If the engine was out of balance it would vibrate even at idle and get worse as the rpm's increased? how bad does an out of balance engine vibrate at idle?

Muffler installed backwards? I have seen it before.

Another guy suggested that... would it create that bad of a vibration? i mean, its bad enough that the windows vibrate and i feel like i have a massaging chair...

It would create a lot more backpressure on one side of the engine.

well, they are center/offset, i forget which way, ill check that and see if they are both on backwards maybe?

More often than not there is an arrow on the muffler indicating direction of flow

If that doesn't fix it maybe you could find some flex couplers.

Make sure the header bolts are tight to the motor and check all clearances around the pipes. Exhaust systems move around and need the space to do it. I'd also add another hanger or two to minimize the weight applied to the collectors. As is with the only mounts being on the mufflers and collector bolts it could shake something loose. As mentioned if you mounted one or more mufflers backward thet can cause engine vibration from backpressure. This can cause serious valvetrain issues. Did you add an h-pipe?

its bad enough that the windows vibrate and i feel like i have a massaging chair...


Take your girl for a ride.....she'll love the "new you".....:D

X2 on the backwards install.....check it out and leave a full report on our desks by morning....