I just bought a 2000 WS-6 with an auto trans and the vibration is driving me nutz.. First off, let me say that it does this in park and while driving down the road. It dosent matter what gear or speed so long as the RPM's are in the 1500-2000 or so range. It isnt throwing any codes so I dont think its a missfire or anything like that. I have changed the plugs and fuel filter and ran some seafoam through it so I don't think its maintenance related. If I start the engine and let it idle its fine but when I bring the rpm to 1500 or so to 2000 and hold it there while in park the engine goes through a reverberation process of quick fast vibrations for a sec or two then completely smooths out for a sec or two then right back to the vibrations again. Its similar to a bad universal joint or when the pinion angle is off, however, it does it when in park so I know this isnt the case. It does this when driving down the road also. I originally thought it to be drivetrain related and have checked and replaced a lot of things on the car trying to solve this issue. I don't know if it maybe the harmonic balancer or maybe the converter out of balance or flywheel bolts loose? It dosent make any odd or weird noises when the vibration is happening. The car starts right up and idles smoothly and has good power. I think the car has had the trans removed due to the ypipe being cut and rewelded a couple of inches after the cats. The car is 100% bone stock and no check engine lights. Im almost positive the cats are not gutted and that's what leads me to believe the trans has been removed and or replaced for whatever reason. This may or may not be related just thought Id throw it in the mix. I have looked closely at the balancer while the engine is idling and cant see any wobble or movement but we all know how that goes . Any suggestions would be great. Questions? Thanks.

 

Does the car have a poly trans mount? Car will vibrate with that installed

 

Check exhaust hangers, especially in the rear, Torque Arm bushing at the transmission and two long bolts on the back connected to the dif. Check trans mount and engine mounts for wear and/or replacement. Check drive shaft for damage, and get your tires balanced, i suggest Road Force balance as this is the best and most accurate way to do it,

 

It does this while in park and you can tell its comming from the engine or trans. Its not a rubbing sound its literally a vibrating feeling comming through the floor board and into the seats and doors of the car. Not so much into the steering wheel but more in the floor is where I feel it. The pass seat shakes back and fourth at the headrest about an inch or so with nobody in it. It also shakes going down the road at around 1500-2000 RPM. It dosent matter what the speed or gear just in tht RPM range.

 

Stock motor and trans mounts that are in good shape.

 

ive never seen a 2000 car with original engine mounts in good shape in over three years.

 

^^^Maybe he's just replaced the 14-15 year old factory ones with STOCK/OEM style aftermarket ones??

 

sometimes its hard to tell if mounts were broke... my car is in the shop getting a 418 swap and wen they pulled the motor both mounts were broke... i had no idea

 

I meant the ones there are the stock type rubber pieces. They may be the original ones or replacements. They don't allow the engine to flex much when torqued up in drive while holding the brakes and I don't hear any odd sounds so I assumed they were good. I will check them maybe this sunday. Im also gonna remove the converter bolts, push the converter back, and fire it up to isolate the engine from the trans to see if anything changes. Any other ideas are welcome and thanks for the ones already suggested.

 

Well, some new news today. I removed the converter bolts and fired the engine without the converter attached. The vibration all but went away. I then removed the acc belts and ran it again, no change. I then reinstalled the conv bolts and the vibration was back. I reinstalled the acc belts and called it a day. It looks like maybe the trans has been replaced and a reman converter was installed also. Im thinking the converter might not be balanced but I don't know if a trans shop could check that if it were removed. I cant tell if the flexplate is stock or not but it didn't appear to be loose or cracked anywhere. Any other ideas before I pull the trans?

 

Update: Pulled trans replaced converter. While I was in there fixed the massive oil leak. It was coming from either the cam sensor o ring or the top of the rear seal cover. If would fill the little void behind the top of the cover and run down the side of the block. Well I had to cut the factory y pipe about 6 in after the rear o2's because the mani bolts were severely rusted. I fired it up with out rear part of ypipe welded back and it was perfectly smooth. Welded ypipe back and the vibration is back. HMMM. Got to thinking about it and I did have to raise and slightly tug the drivers side pipe about 1/4 inch to get it to align back up. Found rear pass side catback rubber hanger was stretched and basically hanging with almost no pressure on the mount. Remember having to lift and tug the derivers side ypipe to re weld??? Ah hah!!! Tightened it up by bending the wire hanger on tailpipe and made the vibration a lot better. Im gonna go ahead and say its a combo of slightly worn mm's and exhaust hangers working in complete harmony causing chaos at its finest. Guess nows the perfect time to order poly mm's and those speed inc headers I have been eyeballing for some time. I already have a magnaflow cb waiting in the garage. ill report back when said items have been installed.. Wheww, Dayum what a ride. I have been chasing this problem harder than I did my wife before we got married. lol...

 

I would just go with factory mounts, the poly and solid mounts increase vibration felt in cabin. Good luck getting the transmission out when the engine doesn't move when you drop the trans crossmember.

My wifes trans am had a similar problem when we first got it. It was a combination of an incorrectly torqued flywheel, bad throw out bearing, and the transmission shop re welding the y pipe while the car was in the air causing it to vibrate against the drive shaft

 

How do you know the motor mounts are in good shape ? I thought mine were than I replaced them on just the off chance that something might be wrong with them and sure enough the inner rubber piece like disentegrated LOL

 

The engine and trans did move but not very much. The trans was far enough down that I could get to the bolts but I didnt feel it was sagging too much as to indicate worn or bad mounts. That may not be the right way to diagnose bad mounts though. I have tried stalling the car up to 2000 rpm and the drivers side cam e up a little but not a bunch. The y pipe was re welded but I call myself looking to make sure the catback part was clear of the ds and the tprque arm. Ill double check though. Thanks.

 

Not positive on them being good. I have had another fbody that had bad mounts but they were shot to the point you could stall it up to 1000 and the drivers side of the engine would lift like 3 in or so. You could also hear metal on metal when the clam shell hit the bolt going through it. You have any Ideas on how to check mm's without removing them? My mani to ypipe bolts are rusted bad so Im sure removing them would ruin the mani's. I was going to buy headers and do the mounts while Im in there. Hope this fixes the problem. Everything I have tried has fixed something but not the vibration problem.

 

WOW a little news today. Got new converter installed after fixing leaking rear cover seal and checking flexplate for problems. Had to cut stock ypipe where it had been previously cut (about 3 in behind each rear o2 sensor) in order to remove trans. got everything back on the car and decided to start it up before re welding the y pipe back together. Fired it up and it rad beautifully with no vibration whatsoever. I let the car run for 10 min or so while looking to make sure the leak was fixed and there was no trans seal leak. Welded the ypipe back thgether and the damn vibration is back in full force!!! WTF??? Only thing I can think of is the exhaust is vibrating under the car and or the mm's are a little worn. The pass side fit right up perfectly and we tack welded it in two spots to hold. I had to slightly force the drivers side pipe up and out about 1/2in or so to get the pipes to align up and tack welded that one in place. No biggie but IDK. I ordered LT's from Speed Engineering and poly mm's so we shalll see what that does. Hell, Its only money, right? Suggestions?

 

Got a code today for the first time. Bank 1 lean. Could bad injectors cause my symptoms and act up between idle and 2000 rpm enough to cause the engine to vibrate?

 

Little more info. Got misfire codes on every cylinder. No codes for misfires though. Gonna take it to a ls specialty shop to diagnose the issue as Im tired of messing with it. Looking forward to a good raping from them.

 

Missed the appointment due to not finished with installing poly mm's due to factory ones worn a little. I installed Speed Engineering headers and oryp since the factory crap had to come off to do mm's anyways. No change and engine is still running wierd. I have datalogged the LTFT's with a predator and they were straight +25% while ideling and at WOT. No KR was detected and the o2 voltage was 0.00v to 0.1v when Fuel trims were maxed. When crusing the LTFT's were between +19% and +22% while the o2 volts were back and fourth between 0.11v and 0.87v like they should be. New plugs, wires, and o2 sensors when headers were installed. Help, someone, Anyone.

 

You have a VACUUM LEAK someplace. Check all the PCV hoses and TIGHTEN THE INTAKE BOLTS<89 INCH< LBS<