Low RPM vibration that fades in and out at a constant pace
Nov 7, 2018 11:40:18 GMT -6
Toronado3800 likes this
Post by rustyshackleford on Nov 7, 2018 11:40:18 GMT -6
I seem to have a vibration that fades in and out at a constant pace. It's in a wave type format where if I hold the RPM steady at say 2000 RPM in Park, Neutral, or in gear, the vibration will act like this:
This seems to take about 2 seconds for the full cycle to complete and it happens in any gear at any speed or parked in park or neutral at any speed. It seems to be most pronounced when in gear at speeds under 20mph and again around 40-50mph and also when off the throttle, but it is most easily replicated when parked since I can easily control for road vibration and maintain a constant RPM rate. It occurs between approximately 1100-2600 rpms and then seems to be so subtle it is not easily discernable. I tried to take a video of the vibration in the mirrors, but it didn't show the vibration (it's relatively light at its peak). Although, now that I'm typing this I'm thinking about Jurassic Park, and I can probably put a glass of water in the cupholder and show the vibration in that.
Timeline of events:
This leads me to believe it's the harmonic balancer (unless a slight wobble at lower RPM is normal which I don't think it is) and since the AC compressor pulley is next in line that is probably taking the vibration from the balancer and killed the bearings/about to kill the clutch. The only other thing I could think of would be a warped/cracked flexplate but I don't know enough about that to troubleshoot it and I really don't want to diagnose that because if I have to pull the engine or transmission 1 month into ownership that will end my Aurora experience quickly lol.
I also took a video of the harmonic balancer, but it doesn't show the wobble (I cracked the screen on my phone somehow when replacing the fuel filter and had to go back to an old junker phone with a terrible quality camera).
For reference, prior to performing any of this maintenance I cleared the stored codes from the computer and no new codes have shown back up. No check engine lights displayed after replacing the alternator.
To sum it up, my question would be: Is the harmonic balancer the most likely culprit? If not, or if more info is needed what are my next steps?
My thoughts are to run the AC bypass belt (can't quite afford to replace the AC compressor clutch/bearing and we're heading into winter time, so that's gonna be a springtime ordeal along with a vac/recharge probably) although I've seen both the 740K6 and 745K6 recommended here for the Classic, so I don't know which is correct although it's only a 1/2" difference I don't want to mess up the belt tensioner. So, run the AC bypass belt and replace the harmonic balancer and see if that clears it up. If I do that, I can't seem to find the correct torque specs for the bolt on the harmonic balancer and have seen many numbers quoted for the Northstars online. I'd like to know what the FSM states the correct torque is for it for a Classic (1998 specifically if it makes a difference).
- Start of vibration cycle -- Smooth
- Increases into a vibration
- Reaches the peak of the vibration
- Fades out until smooth again
- Repeats the cycle
This seems to take about 2 seconds for the full cycle to complete and it happens in any gear at any speed or parked in park or neutral at any speed. It seems to be most pronounced when in gear at speeds under 20mph and again around 40-50mph and also when off the throttle, but it is most easily replicated when parked since I can easily control for road vibration and maintain a constant RPM rate. It occurs between approximately 1100-2600 rpms and then seems to be so subtle it is not easily discernable. I tried to take a video of the vibration in the mirrors, but it didn't show the vibration (it's relatively light at its peak). Although, now that I'm typing this I'm thinking about Jurassic Park, and I can probably put a glass of water in the cupholder and show the vibration in that.
Timeline of events:
- Alternator went out when driving vehicle home after purchase
- A few days after replacing the alternator the belt began to squeak, and AC issues started to appear
- Replaced the accessory drive belt and assumed the remanufactured alternator had a bad bearing
- Checked the pulleys while replacing the belt and found the AC compressor pulley bearing is shot and needs to be replaced (possibly also clutch, not sure how to check that)
- I did not check the crankshaft pulley (but I will) as I was only spinning them to check for bearing noise and didn't realize I should have wobbled the crankshaft pulley to see if it had play
- Checked the air gap on the AC compressor clutch and it appears to be just above .052" which I think is at the far end of acceptable tolerance
- At the same time as replacing the belt I replaced the gas cap (broke when I added gas the first time haha), fuel filter, air filter, PCV valve, spark plugs, and cleaned MAF and throttle body (didn't know about cleaning IAC Valve/EGR Valve until afterward so I will go clean those this week, maybe tonight)
- Plug wires looked newer, and plugs seemed fine other than the bit of oil on a couple of them, tested resistance on coil packs with a multimeter, and it came back 5.87, 5.97, 5.91, 6.11 but again, plugs look fine and no misfire engine codes.
- Noticed cam covers are leaking as well as some oil on plugs so the valve cover gaskets will need to be replaced (I don't think that would have anything to do with a vibration unless causing a misfire, just noting this for reference) Also, regarding these leaks it looks like the previous owner was using 5w-20 and I see the cap/manual calls for 10w-30 so I'm going to switch to 10w-30 high mileage + Lucas oil stabilizer after the next paycheck to see if that helps with the oil leak.
- Also replaced the front sway bar end links and cleaned mating surface of rotor to wheel of rust ridges and that seemed to kill any road vibration I may have had.
- Vibration in engine still remained as well as whine from accessory drive, watched pulleys again while idling and finally noticed from another angle that the harmonic balancer/crankshaft pulley has a slight wobble and smooths out when increasing RPM by moving throttle cable manually (didn't have someone to help so that was my improvisation to look at it)
This leads me to believe it's the harmonic balancer (unless a slight wobble at lower RPM is normal which I don't think it is) and since the AC compressor pulley is next in line that is probably taking the vibration from the balancer and killed the bearings/about to kill the clutch. The only other thing I could think of would be a warped/cracked flexplate but I don't know enough about that to troubleshoot it and I really don't want to diagnose that because if I have to pull the engine or transmission 1 month into ownership that will end my Aurora experience quickly lol.
I also took a video of the harmonic balancer, but it doesn't show the wobble (I cracked the screen on my phone somehow when replacing the fuel filter and had to go back to an old junker phone with a terrible quality camera).
For reference, prior to performing any of this maintenance I cleared the stored codes from the computer and no new codes have shown back up. No check engine lights displayed after replacing the alternator.
To sum it up, my question would be: Is the harmonic balancer the most likely culprit? If not, or if more info is needed what are my next steps?
My thoughts are to run the AC bypass belt (can't quite afford to replace the AC compressor clutch/bearing and we're heading into winter time, so that's gonna be a springtime ordeal along with a vac/recharge probably) although I've seen both the 740K6 and 745K6 recommended here for the Classic, so I don't know which is correct although it's only a 1/2" difference I don't want to mess up the belt tensioner. So, run the AC bypass belt and replace the harmonic balancer and see if that clears it up. If I do that, I can't seem to find the correct torque specs for the bolt on the harmonic balancer and have seen many numbers quoted for the Northstars online. I'd like to know what the FSM states the correct torque is for it for a Classic (1998 specifically if it makes a difference).