is my mechanic on acid?

1990 350 tpi. Okay well i bought my camero about a month ago and when i first had it on the road if i got over 3500-4000 rpms id get this massive vibration. At first it seemed like it was coming from infront of the dash....then it seemed more localized to from near the transmission like right beside my right leg but you can feel it through the shifter knob. My friend also said when he sat in the back he could feel the vibration too so ive had a tough time pin pointing it. The sort of vibration was similar to something turning over ie drive shaft it was like you get the heavy vibration for a half second and then off for a split second back on for a half second off for a split so the sort of vibration from something turning over (if you dont understand ill try to explain better)....the tranny mount bushing is still there and i replaced the u joints but that had no effect. Now the problem has gotten much worse to the point where i get the vibration during all acceleration and deceleration. Its really weird because it seems fine at first but as the car warms up it gets worse and worse and worse until the point where it becomes totally undriveable.

I took it to my mechanic and he took just a quick look at it and told me i wasnt getting the proper current coming off the alternator and that this would effect my computer and how it operates potentially causing the vibrations. Heres a couple of things.....one doesnt the computer just pull from the battery so even if the alternator isnt working at 100% shouldnt my battery just drain slowly i wouldnt think this could effect my computer. Second any way in hell the computer could cause this sort of problem because i really doubt it. Third my mechanic has been for a ride in it and knows what the problem feels like and im 99% sure it has to be drive train related.
Any chance it could be because of the alt.?

If youre still reading this thank you. Anyone have anything to check possibly towards the rear end of the car? i also hear a slight whirring coming out of the rear end but i think it just needs new gear lube. Any tips for things to check i am greatful for im at a loss and think my mechanic is a crazy man so hes not much help.

your drive shaft could be off balanced or hitting the exhaust mine was hitting the exhaust i could actually feel it in my gas pedal

no its definitly not hitting the exhaust and there is no noticeable vibration in any of the pedals. Im going to take it soon to get everything balanced/aligned and see if that does anything.

My guess would be to replace the u-joints. That's what it sounds like to me. I wouldn't think the exhaust bouncing off the drive shaft would cause the much of a vibration....although I could be wrong. I've only experienced that once....In an 83 Blazer. If you change the u-joints and it doesn't fix it, you're out 20 or 30 bucks...Big deal. Anyway...just my two cents....Good Luck!

Originally posted by doug791
the tranny mount bushing is still there and i replaced the u joints but that had no effect.... i mentioned that but its kind of buried in the middle there....i have replaced the u joints but it did nothing. I am losing respect for my mechanic by the second and want my car back in my own hands asap. I havent taken it to an alignment shop since i bought it so im going to do that. Im going to have all of the tire balances checked drive shaft balance checked and all of that.

Something i mentioned is i noticed a slight whirring noise coming out of the rear end. Its only at part throttle but ive been told this could be the sound of my rear end going. I have to swap the gear lube thats in there anyways how can i check to see if my rear end is going?

I was also wondering is headers/shift kit/3.73 gears enough to fry a 10 bolt? i doubt it but i thought id check.

How could it be the drive shaft or rear end of the problems arise around a certain RPM, and not speed?

You said around 4k rpms. What if you are going down the highway at 60mph but turning 2k rpms? Problem still there?

see thats whats throwing me that i cant figure out. Okay heres the cenario. If everything on the car is cold lets say its sat for 24 hours i can start it up and start driving no problems anything. If i get on the gas hard i feel it at higher rpms. However if ive been driving for even 2-3 minutes you start to feel it at anything over 50 kilometers and i feel it under breaking too. I cant figure out for the life of me what it is.

One thing I would not recommend is 3.73s...especially with the A4 tranny. As you probably know, TPI runs out of breath around 4800 rpms. Putting 3.73s will make your car rev out much faster and make your car come out of the powerband if you're accelerating all out. But then again...what do I know, I'm just a stupid 16 year old.

does it vibrate when the car is warm and not moving? like in park and you rev it up

Originally posted by Zrated383
One thing I would not recommend is 3.73s...especially with the A4 tranny. As you probably know, TPI runs out of breath around 4800 rpms. Putting 3.73s will make your car rev out much faster and make your car come out of the powerband if you're accelerating all out. But then again...what do I know, I'm just a stupid 16 year old.
rofl thanx man but i really dont care right now. All im concerned with at the moment is getting this stupid thing working.

does it vibrate when the car is warm and not moving? like in park and you rev it up Thats actually a really good question and im not sure. I dont get the car back from the mechanics until tommorow but when i do ill check that. That will at least let me localize it away from the engine/tranny.

Note: i just thought id add that i didnt put in the 3.73's they were already in when i bought the car but i love them. Not sure what it does to my 1/4 mile times but it makes the car absolutly haul when you hammer it from a light in the city. Although if i had a choice id probably step it down to some 3.43's or something but having them in is definitly not a bad thing.

Have you checked to see if you have any warped brake components? Another guess would be a broken flexplate...

wouldnt be the brakes. Could possibly be something to do tranny wise ie flex plate. I have to find a way to localize this problem to either by my tranny or by my rear end hopefully ill be able to so i can pin point the problem.

Easy way to pinpoint: hold it in first and drive it up to about 4500rpm.....if you don't get the vibration then its not engine related.

but if its solely rpm related if i drive it up to 4500 in 1st ill still get the vibration....the neutral idea seems better to me because in first i have the engine and drive train spinning so i cant pin point it. In neutral only the engine is running.....i think im right, please correct me if im not.

You are correct but it's also very possible that the vibration won't show up unless the engine is under a load. I see cases like that at work all the time (they usually turn out to be ignition related.)

do a burnout, engine will be under load, and it wont be moving

j/k :D

Remove driveshaft and problem might be solved. :D :D

Seriously, take it off and check the U-joints for notchiness. Also have the DS checked for balance.

Do a rear end service while you are at it and see if all the teeth in the gears are there.

I guess I might be the only one but it sounds like he snapped a motor mount to me. Either that or a tranny mount. Either of these can break and still look intact. Put in drive hold the brake and give a quick romp on the gas and you will hear a bang.

Just my .02 but if it is none of these things make sure to tell us what it was.

Brett

I would look at the driveshaft first. It doesn't cost anything to check it. If it only does it under load at higher RPMs that is your best bet.

UPDATE
Well i got my car back from my mechanic (will tell about that after) and ran the tests that were sugested. Drove the car around for a while until the problem started. Got it in my drive way and put it in neutral. Revved the engine up and around 3500 rpms i started getting the vibration. It was a little different unstead of it pulsing it was a solid vibration but that should just be attributed to the fact that my drive train was not turning over so i have basically pin pointed the problem to my engine.

The problem is a bit worse now. When the engine is at idle it rocks back and forth pretty good. I dont think there is anything wrong with the engine mounts i just think its just because i have a 350. When you get on the gas the engine stops shaking and goes pretty normal so i think all is well there.

As far as the problem with the engine im thinking one of the problems is i might have a leak on the intake side of my engine. When you get on the gas it feels like there is a slight sputtering and the car doesnt feel like it has all of its power. I had pulled off the plenum and egr and i think there is a chance the leak would be coming from the plenum due to some issues putting the plenum back on.

However that i know has nothing to do with my vibration problem because i had the vibration problem before i took anything off the car it just wasnt as bad.

My mechanic couldnt figure out what was wrong and said to take it to a gm dealership repair place because they have some scope? that he doesnt and some other stuff so they could better evaluate the problem. Any tips for things to check for the reason of my problem? What could cause a large vibration coming from the engine at over 3500 rpms?

(the problem i had when i put on the plenum is me and my friend are idiots and tightened it from front to back not from the middle out. Had some other problems but nothing that could be attributed to a vacuum leak.)

I would say, if it is in the engine and was there before,check the Harmonic balancer. They do get old and slip out of wack sometimes. I have seen them be able to be turned by hand,and I even had one on a old Thunderbird come off and hang on the crank shaft (ting,ting,ting)drove me nuts til I got home and cut it off with a torch.

T. :cool:

im kind of a newb. What does a harmonic balancer do/look like/where is it. My mechanic who is very sketchy he likes to make things up although he did say he checked it and said it was fine. Usually if he finds something thats broken hes very quick to tell me so he can fix it for me although i usually just fix it my self. Anyways dont think thats the problem. Its a severe vibration as i described in my last post so i wont do it again. Thinking maybe it could be a rod bearing? really not sure just throwing things out there. Its going to a different mechanics tommorow to see if he can figure out what it is.

To answer your questions,first it does just what it's name implies,balances and kills the harmonic vibations of the crank shaft. It is located on the crank shaft behind the crank pulley and is the thing you look at when setting the timeing (that is where the timeing mark is)it is basicly a flange with a rubber dough-nut around it and then another metal ring around that(the part with the timeing mark). They can slip and through your timeing off or even seperate. The only way that you yourself at home could check it would be to pull the valve cover and #1 spark plug,bring the piston(#1) up to TDC on compression (both valves closed)and see where the timeing mark is. It should be be somewhere between 0-10*,however this still doesn't mean it is ok,just means it hasn't slipped on the crank. Also check the rubber for big major cracks and missing chunks. This should get you started in the right direction.

T.:cool:


PS. Have you had transmission work done lately?

no i just bought the car....dont think its anything to do with the tranny because in neutral i still get the vibe. I should have some answers tommorow its getting looked at first thing by a second mechanic.

I take it you have a manual trans,the reason I asked is most of the time when work is done to the trans(ie clutch,throwout bearing,etc.) the pilotbushing is overlooked,even on an automatic this should be checked and replaced,this can be associated with vibration also.

T.:cool:

that actually sounds like something very possible. It is an automatic tranny (the stock 700R4 it has a shift kit not sure what else guy i bought it from was pretty car illiterate funny thing being he works on a gm assembly line). Anyways like i said earlier the vibration is a solid vibration when in park/neutral and when in drive it turns into a vibration that sounds like something turning over. What you said sounds like a very good idea to check. Like i said in my last post its going to be looked at by a mechanic first thing in the morning and well see what he says if not ill definitly give that a check.