I have this strange vibration when cruising in D at 2K rpm.
Over 2K and under 2K there are no vibrations.
If I shift to OD, the rpms drop and no vibration.
At 2000rpm in OD there doesn't feel like any vibration.
Before I start yanking anything apart, what should I check first.
My Formula has 3.23 gears, 16" wheels with stock size tires.
105K miles on the drivetrain.

Thanks

 

could be the driveshaft?

 

do u have poly motor mounts? i have this same vibration but i know it's because of the poly mounts. i never had the vibration until after the poly mount install.

 

I don't think so, but I'll check. I've only had the car 3 weeks.

 

i do recall having the same vibration with a broken stock mount as well. it looked ok but when i removed the mount, it was no good. it moved all around the clamshell very easily.

 

I'll look at that as well. I did put a poly trans mount in mine since I broke the stock one in two a week after I got the car.
Maybe that could have caused the vibration too since I recall hearing that on cz28.com with quite a few LT1/LS1 owners.

 

The trick Zeph is to use the poly engine mounts with the poly trans mount.. then no height/angle problem.

Not sure if you remember but the 82 vibrated pretty good around that speed too.. the new driveshaft made all of that go away.

 

1,2, OD no problem, 3 under a load there it is. Here is what NOT my problem,
trans mount (Ok near new)
DriveShaft (new)
pinion bearing (tight)
engine mounts (new stock)
everything tight
rims balanced


What else could it be and WHY in third only!!!!!!!!!!
converter??
something wrong with the 9bolt B&W (bearing, posi WTF???)
pinion angle???

 

Well, engine mount swap with the engine in the car isn't going to be fun. I'll probably swap them when I put the sbc 400 in there.

 

I have it too. It has occured since I put in a Poly Urethane trans mount. I'll bet thats why and you shouldn't worry. If your mount is poly urethane, it will cause a vibration where a rubber one wouldn't due to different properties. Better properties.

 

Ya, I just put the poly mount in there.
It's just weird that it is at 2K rpm in 3rd at about 42mph

 

flywheel bolts tightened?

 

I'll check the flywheel bolts today when I wake up.
edit: I thought you said torque converter bolts. I don't feel like dropping the tranny at the moment.

 

Zepher, I just had the poly trans mount put in tuesday (after I toasted the rubber one doing a burnout, scared the **** out of me THUNK! thought I lost my trans) and I have the same thing, smooth in OD but in 3rd and regular D around 2,000 I get a slight vibration. Its probably just the new mount but iff not I'd be willing to bet its the drive shaft from what I've heard they are notriously unbalenced from the factory even the 1LE aluminum I hear you get a nasty vibration from around 120mph

 

I have a friend with a mint 90 irocz 1le (only 6k on the odometer) and he said the first yr he had it he had like 3k on the motor and he was driving down the highway (287 for u NJ foke) and he was doin 155+ mph and said he had a vibration only when he got up in that high of mph.

Zepher put ina regular rubber tranny mount and then drive it to see if u get the same thing if u dont then theres the problem

 

One more thing to check if the mounts don't fix it.

Check your A/C unit under the bonnet..If you have a bad bearing or the mount is not stable it will cause vibration right through the car.

I'm not sure what the setup is on your year firbird, but if it has the same setup as an 85 Iroc then it will be the older style A/C unit. These units had a very poor mounting system and or if there is a slightly worn bearing it will feel like a driveshaft type vibration that you'll feel under your seat.

Hope this helps.

 

I'll look into those two options. My 88 has a serpentine setup, so it's only one belt.
To be honest, I don't know if the vibration was there with the stock rubber mount since I normally drive in OD all the time.
The stock mount broke a couple of days after I bought the car so I changed it the following day.

 

Is the driveshaft stock steel? I had a bad 'shudder' when I get the car over 80. This was caused by the rotational mass of the driveshaft. I got an aluminum one and my problem was solved. Don't know if this will help you or not. ALSO, are your wheel properly balanced. Just one being not quite right will do this too.

Don't take your car to PEPBOYS and let them do tires either, they can't balance right. Just something a bud of mine learned the hard way, twice!

 

Hey i wor at PEPBOYS and im an installer (tires , oil , etc.) and well i havent had a problem with people coming back becuz of there balence, ive had people come back time and time again becuz the other installers cant balence tires for crap. just depends on how the store is staffed.

 

I don't know if my shaft is steel or aluminum. I'll check it today and see.
It's not the tires since there isn't any vibrations at all in OD from 0 to 100mph just in D at 42mph at 2K rpm.

 

Hmmm actually my A/C compressor does make some noise... But why would this only start right after the poly install? ALso I have a theory I think "J's T/A" might have had it right when he said the kry is to replace the moter mounts at the same time... not really because they are polly but I think it might have something to do with the stock ruber mounts being or going bad... I mean think about it if the trans mount where bad chances are the moter mounts are two especially if you where like me and drive it for awhile after the trans mount broke I'm sure that would put extra strain ont the moter mounts.

 

Here is what you need to check:

Put the car in neutral and take it to the RPM which normally causes the vibration and see if vibration is still there while the car is stationary. It may not be a strong, but see if its there.

If it is then you can rule out driveshaft, drivetrain stuff.

If its not there while in neutral it probably is drivertain.

 

actually I noticed today that it seems to be not as bad, maybe those poly mounts need time to settle or something? I've been driving it on the new mount for a week and yesterday I was pretty harsh on it (few burnouts ect) and now it dosn't seem to make as much vibration as it was.

 

I have the same problem. From OD-3 shift at about 55-75 when I start on inclines. The TC unlocks and I get this weird vibration. I put my foot into it a little more, and it works fine, no vibration. I've been told on this board that it is TC Clutch chatter. I'm just ordering a new tranny/TC. Actually, It the new tranny should be here soon from Dana.

If Dana reads this thread, This is Kyle Jones. Just wanting to check with you on the tranny since I haven't heard anything from you since whe spoke on the phone when I ordered the tranny. It was the night of your doughters grad? I think it was.

 

Did it solve your problem

 

Yeah, the new tranny and TC fixed it.

They both work great together.:hail:

 

Prior to your replacement? did it ONLY vibrate in 3rd??? what about 1st or 2nd gear

Do you think the problem was the converter or the trans

 

hey timz2882, I work parts at pepboys in cinnaminson nj, badass job am i right? lol i am part time and i am workin 48.5 hoursa this week. stupid store.. oh yea, when u get a delivery how many tires u usually get?? we get a treuckj every weds and this week we got 419 tires, wut a pain....