Vibration.

[rhipsher]

Well I've just installed an upper A arm with new bushings. And tightened the C-beam bolts good. But something still doesn't feel right. I mean as you can see in my avatar just 5 months ago how fast I've driven it and it was fairly smooth. Now I won't take it past 130. It just doesn't feel safe. Ever since that last 11 runs at the drag strip. I guess those hard accelerations on a sticky track can really test your sheet. I've had cracked motor mounts on other cars and usually the engine just about jumps out of the car and bangs into the hood. I'm just not quite sure what to check anymore. So hear I am asking for suggestions.

[jonszr1]

ck your 1/2 shafts .it sounds like one of the u joints might have froze . had the same prob. with the white car .thought it was a tire had thrown a weight .but one of the u joints had froze

[Polo-1]

check all u-joints, not just half shafts if you launch it at the drags. I have to replace the yoke end of d shaft on mine every 2 years. My Z 30k on it.

[rhipsher]

I'll check the u-joints. But I'm starting to be suspicious of the motor mounts after all. I just got done tightening up the torque beam bolts and when I shift hard in 1st and 2nd gear I can see my stick move up and down. Not quite as bad as before I tightened the torque beam bolts, but it still does and my stick shifter never did that before. But a busted motor mount wouldn't suprise me especially if all the rest of my suspention bushings are all dry rotted and need to be replaced. So tomorrow I'll fire it up and apply the brakes and give it some gas and see if that LT5 moves excessively. If so good I'll just put new motor mounts on it. But man it feels like there's some heavy wieght shifting around when driving it. I don't think a bad u-joint is gonna cause that nor cause my shifter to jump up.

[XfireZ51]

Chunked the clutch? Is it speed or rpm related?

[karterdon]

What does the car feel like if you cruise @ 70 MPH?? Is the vibration thru out the entire car?? Does it seem to come thru just the steering wheel?? Does it feel to be in the back of the car or the front?? Could it be a bad tire - Look for bulges in the sidewalls (inside & out) - look for bulges in the tread - possible seperating from the casing.

Put the back end up on jack stands and run it in 3rd gear - try and make sure the axles are in as close to the normal ride angle as possible - listen for unusual noises.

If you have a bad motor mount - you should be able to brake torque the engine in a forward or reverse gear to determine a bad left or right side mount. - Remember - I do believe that the mounts were hydraulic so you should be able to determine a colapsed mount pretty easily.

All of the abouve is just food for thought.

Hope it helps

Don Yoakem
91 #267 Dark Red Met.

[rhipsher]

Originally Posted by karterdon

What does the car feel like if you cruise @ 70 MPH?? Is the vibration thru out the entire car?? Does it seem to come thru just the steering wheel?? Does it feel to be in the back of the car or the front?? Could it be a bad tire - Look for bulges in the sidewalls (inside & out) - look for bulges in the tread - possible seperating from the casing.

Put the back end up on jack stands and run it in 3rd gear - try and make sure the axles are in as close to the normal ride angle as possible - listen for unusual noises.

If you have a bad motor mount - you should be able to brake torque the engine in a forward or reverse gear to determine a bad left or right side mount. - Remember - I do believe that the mounts were hydraulic so you should be able to determine a colapsed mount pretty easily.

All of the abouve is just food for thought.

Hope it helps

Don Yoakem
91 #267 Dark Red Met.

Here's what I can tell you that I know for sure. My front tires are old and hard but still have alot of tread left. My rear tires are brand new. The weight shifting feeling is at all speeds. The vibration happens under hard acceleration or around 120mph and at 130 its down right scary kinda like if your drive shaft is out of balance or a tire has a bulge and the whole car shakes. Now there's one more thing I've noticed in the last 2 years I've had the car but has not been a problem or hurt the performance of the car. When I hit up around 120mph there has always been this low sounding hum which seems to be realated to the mph of the car. Not the engine or RPM's. When I take my foot off the gas its still there but as I let the car coast back down it starts to go away. I don't know if that could be rear gear noise. Sounds like a big 4X4 with mud tires comming down the road at about 40mph. Not near as loud but you definetely can hear it from the cockpit. I don't know if thats a common sound at high speeds. But you only start to hear it when you reach 120mph and up. Since I've never driven another ZR-1 I don't know how smooth they are suppose to run at those speeds. All I know is how mine is at those speeds. Its not what I would call the the most smooth or the most quiet ride on the way to 180mph but it damn sure gets there.

Is it really vehicle speed related or is it engine RPM related?

So at 120, do you get the vibration in 3rd and 4th and 5th and 6th?

[rhipsher]

Originally Posted by Jeffvette

Is it really vehicle speed related or is it engine RPM related?

So at 120, do you get the vibration in 3rd and 4th and 5th and 6th?

The vibration is definetaly rpm/hard acceleration realated. The hum is wheel speed realated because at 120 when you take your foot off the gas and press the clutch in the rpm's go back down to 800 but the hum is still there and starts to fade as the car slows down. I don't have a loud exhuast system so I notice every noise. I'll check all the u-joints today and the motor mounts. When I replaced the clutch a year ago I put a new u-joint in the main drive shaft. It was a Napa performance series. I noticed it had a grease sert in it but I said the hell with it and put it in anyway's. Now as far as I know the rest of the u-joints are the original ones. But like I said this really bad vibration didn't start till after the last visit to the drag strip.

If one of the u-joints are cooked how can I tell? I assume I'll be able to grab whatever shaft its connected to and shake it to see if its loose. I know if a drive shaft is out of balance just a little bit they vibrate bad. How much are spicer u-joint a piece and where can I pick them up if need be?

[lbszr]

The 4 by 4 sound your getting sounds like wheel bearings or maybe more than one problem with all the other symptoms.