Odd engine vibration

[Jgreemo]

Hi all, on a recent run up to Mammoth, I was pulling 3100-3400 rpm up the mountain when I noticed an oscillating vibration, ocurring about once every 2 seconds or so. It seemed to be coming from the engine and when I cut back on the throttle to 2900-3000 rpm it stopped. Question is, for those who have had harmonic balancer issues, is this a potential symptom of a bad one?
This doesn't seem to be a new occurence and the motor is only about a year old. It also does effect performance as the thing runs smooth and strong. Just wondering what a bad harmonic balancer can do, besides generating a bad knock and broken crankshaft.

Thanks,
Jon

[dieselbegreat]

Question is, for those who have had harmonic balancer issues, is this a potential symptom of a bad one? YES! Even if visually it looks all right, it may have slipped on the crank. I had to have my crank keyway welded to re-time mine. Oscillating vibration (or "thrumming" as some say) is one sign. On the other hand, it could only be an a/c hose vibrating but an out of time or defective harmonic balancer could be disastrous.

[britannic]

I experienced something similar with a worn timing chain. Fitting DSG gears cured all of the weird vibration zones in the rev range.

[Jgreemo]

Turns out it's definitely the balancer. After looking it over carefully, the rubber is cracked in a number of places. As this balancer was purchased with the engine and installed just over a year ago I am wondering what kind of quality goes into making these things.

Thanks for the help!
Jon

[crew84]

Do not be too quick to decide it is the balancer. I still have the some of the same vibration though it is just barely noticeable. My engine had been completely balanced. The only item that was not balanced was the torque converter. It was worse before I had the rebuilt torque converter replaced with another one. I could not run it out of OD at 65 mph without it thrumming badly. It was more noticeable under load. I felt that I eliminated the balance issue as best as I could since I could not keep replacing Torque converters. BTW my balancer has less than 20K on it. Also all cylinders running equally makes a difference at higher RPMs.

[Jgreemo]

Thanks for the reply. This vibration is a relatively new occurrence, having started in the past few weeks. Could the TC some how get out of balance and still function normally?

I've gone through the hoses to make sure they are fastened down properly and isolated with rubber a few that looked like they might thrum. Hopefully this will take care of it, and besides, for about $100 in parts and a couple of hours of time, it's cheap insurance.
Jon

[crew84]

I have had my truck a long time. I got a vibration similar to the one that I have lightly now when I loosened some of the bell housing bolts to replace my starter heat shield. I decided to rewrap my wire harness also which meant loosening more bell housing bolts. So one day later this vibration started and I decided it must be something I overlooked. I crawled under and checked the bolts. They had loosened. I spent time making sure that they were torqued right this tme. The vibration was now gone. That is why I looked at the torque converter when the vibration started because I knew the bolts were tight. Also the vibration was getting worse with the converter. I figured maybe the bushing in it was getting loose from the vibration.

[britannic]

Replace the balancer pronto! Whether it's the cause of the vibration or not, cracks in the rubber are a major no-no!!!!!! I went to www.gmpartsdirect.com (http://www.gmpartsdirect.com) and got an OEM one for under $100.00.


Originally posted by Jgreemo:
Turns out it's definitely the balancer. After looking it over carefully, the rubber is cracked in a number of places. As this balancer was purchased with the engine and installed just over a year ago I am wondering what kind of quality goes into making these things.

Thanks for the help!
Jon

[ 02-16-2004, 05:51 PM: Message edited by: britannic ]

[Jgreemo]

I replaced the balancer today. As it's a daily driver, paid a bit over a $100 for it and took a couple of hours to put on. The old one looked ready to go. Also found a leaky power steering pump so time to replace that as well.

Thanks for the help guys.
Jon