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LOUD Vibration at about 3000 rpms

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gsm187

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One day I hope I'm able to offer help rather than constantly asking for it, but for now...Anyway, I am now getting a loud vibration and noise in every gear when I get to about 3000 rpms. Idle down and it's OK, more rpms and it's OK. It's hard to isolate where it's coming from, but sounds like below the engine bay. I don't have a catalytic converter anymore since I switched to twin SUs on my 80B. Anyone ever experience something ike this? Where should I begin to look for problems? I don't want to keep running her if I'm doing any damage, but would like to try and solve this myself first if possible. Let me know, thanks - as usual. Gary
 
Have you checked the heat shield behind the SU's for cracks? They can set up a "sympathetic vibration" at certain RPM's and it sounds awful. The other thing to check may be some loose exhaust fasteners (they can do the same thing), and if you've got a fan bolted to the water pump hub, it can make some scary noises if it gets loose... those are the things that come to mind immediately. HTH!!!
 
GSM187,
You mentioned that the fibration is at 3,000 rpm 'in every gear'. Does the vibration occur at 3,000 rpm with the tranny in neutral with the car not moving???
 
Ron - know where you're going....u-joints or thrust washer!
 
Yep
 
You got it....Does this make me a Yoda???? /ubbthreads/images/graemlins/smirk.gif
 
A small indication that the Force with you is! Only a small one...hehehehe
 
Can't blame me for trying....
 
Now, how about that vibration... in gear or out???
 
At 3,000 rpm's, it better be in gear! hehehehehe
 
Tony, I know that you are kidding /ubbthreads/images/graemlins/cheers.gif

... the 3,000 rpm out of gear only long enough to see if the fibration occurs...
OR
just check the condition of the u-joints. From under the car grab the drive shaft near the rear joint and see if there any lateral or vertical movement in the joint. Repeat the process for the front. I usually find that this type of vibration, when the car is in gear and moving, will produce a vibration... LOUD if the u-joints are really bad. Easy to check and easy to fix if that is the problem...
 
Ron - i agree...I've found the best way to check the thrust washer/bearing is to drive it up to speed...with car in gear a bad one will make terrible noise/vibration while under load...push clutch in & noise/vibration disappears.....same with U-joints.
 
Tony, For the effort involved in fixing the thrust bearing vs. the u-joint... I hope for gsm187's sake, it is the u-joint... If neither... clear the drawing board and think it through again...

Ron
 
Oh, I also agree again, Ron...before I'd change a thrust washer or bearing, I'd change the rear end!
 
U-J's would be rattling about at nearly all RPM's, wouldn't they?!?! I know there's a "band" where they'll be REALLY discordant, but if you let off the gas (in gear) and reapply, the vibration will change if it's a U-J... The other things I've mentioned are more RPM specific and "repeatable."
 
Before the bolts let loose on my Alfa's driveshaft (at the rear-end), it gave me very little noticable vibrations... until it was about 10 miles or so from letting go. I've also rode in a car (1978 Pinto Wagon) that let the U-joints go (front end of the driveshaft)... and it also had an increasingly harsh vibration that finally let go about 50 miles or so after it started. I've never ever gotten a long-term vibration from anything about to let go. Maybe that's just me?
 
DrEntropy, The last time I had a bad u-joint, as memory serves, it would vibrate like crazy when unloaded; that is when I took the foot off the gas... As we all know, there are many variables here that are undetermined. With this kind of problem I start with the most obvious possibilities and work from there. If the vibration is only when the car is moving then the drivetrain is suspect; if it vibrates at 3K rpm with the car stationary and in neutral; then it is probably a problem forward of the drivetrain. If the vibration stops when the clutch is depressed, then throwout bearing, clutch plate, pressure plate is suspect. ad infinitum. It could be an obvious fault or one of those insidious problems that drive us all nuts... /ubbthreads/images/graemlins/confused.gif

Anyway... Good luck...
 
Hey guys,thanks for the replies. Sorry I am late in replying but...unfortunately, when I went out to determine if the noisy vibration would occur in neutral, I had a no-start problem - the clock and lights don't work at all either. Jump start was unsuccessful, so I took the battery back to the chain store I bought it at about 13 months ago. It checked out fine and was fully recharged after a few minutes. I reinstalled it and ...nothing. I am wondering if the two issues are related, or if it's coincidental? Now what? I can't get further down the checklist for the vibration until I can figure out what this issue might be. Again, any help would be appreciated. Thanks, Gary /ubbthreads/images/graemlins/cryin.gif
 
For the no start problem, check the brown wires at the starter. Make sure the connections are clean and secure. Check to see if you have power going to the bottom fuse. If the brown wires are ok, then check the battery ground cable where it attaches to the body of the car.
 
Gary,
Keep us informed. We have thrown so many ideas at it and I am really curious...Oh, the joys of LBC ownership... /ubbthreads/images/graemlins/cheers.gif
 
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