jyeung528

Just wanted to see if anyone else has this issue or can offer their thoughts.

I have a vibration or rattle that sounds like it's coming from the rear, sounds like the tires or drivetrain, but my trunk parts and center console also vibrate, so it's difficult to pinpoint. Can't really feel the vibration, like you could feel pitted CV cups.

What makes this easier (or more difficult) to diagnose, is that it only occurs in a very specific situation.

Only at 70 mph, only during light/partial throttle.

So that means this does not happen outside of the 70 mph range, it does not happen on acceleration or deceleration or neutral (albeit if you're at the light/partial throttle it will happen if that light throttle accelerates or decelerates the car).

Because of the specificity of the condition that causes the problem, it makes me rule out CV cups and exhaust.

Thanks for the additional insights, if any.

jyeung528

bump.

Slowcrash_101

It sounds like an unbalanced driveshaft, but it could also be unbalanced tires. If it's the drive shaft, a machine shop can spin balance it for you.

jyeung528

Do you mean the propeller driveshaft that runs down the centerline of the car? or the two halfshaft driveshafts that connect the diff to the wheels? Or both.

jyeung528

In any event, if it were an unbalanced driveshaft or wheel, why would the vibration only occur at 70-75mph and only at light throttle? above 75mph and it won't vibrate anymore in any condition...wouldn't higher speeds accentuate an imbalance issue?

Car Analogy

Imbalance issues typically have a resonant frequency where the issue most makes itself apparent. This translates to a specific roadspeed that the condition is felt. Any faster, or slower, and the perception of the vibes quickly diminishes.

What happens if you apply light throttle, but enough to cause slight acceleration, and starting at like 60 accelerate up through to like 80? Do you find the vibes come on quickly, then drop away quickly, coinciding with passing across 70 mph?

jyeung528

At light throttle causing acceleration from 60 to 80, I will not feel any vibration.

Only at light throttle causing maintenance of speed or slight deceleration of speed from 70-75, will I feel the vibration.

Outside of the 70-75 range will be smooth.

What makes me think that it is not a balance issue is that if I'm in the 70-75 range, I will not feel any vibration if I accelerate or am off-throttle. I will only feel it at very light partial throttle (light enough to barely maintain or slightly decelerate).

This specific light throttle at a specific speed makes me think that it is the differential (backlash, or chipped gears, etc.)

It also happens irrespective of gear (I can be in 4th or 5th or 6th, as long as it is in the 70-75mph range).

Thanks for the thoughts.

At this point, I am going to conclude that it is differential damage (backlash, chipped gears, etc.) It got worse/more apparent after switching from LE-1605 (for 10 years, 200,000 miles) to Amsoil 75w110 recently. The Amsoil, after about 2,000 miles had significant metal shavings, bigger than I had ever seen with the LE 1605. I flushed that out and put in Amsoil 75w110 again, and flushed that out after 150 miles (only one day). Still saw a little big of metal shavings for one day of driving, same big size as the previous amsoil, bigger than I had ever seen with the LE 1605. Switched from the Amsoil to Valvoline syn-blend 85w140 last night and the vibration is still there, so I'm thinking the damage is done and just trying to prevent further damage.

jyeung528

my vibration has gotten worse, and because of that...it has become more apparent that this is the CV joint pitting/wear.

I'm going to use the spacers and see if that fixes it. (already swapped left to right 100K miles ago, so i'm going to swap back and use spacers).

s2000Junky

Very well could be, except I thought you said in other thread that it vibrated at idle? This wouldn’t be shafts then, however you could have two different situations going on here.

At any rate, as someone who has been through all the half shaft configs to extend their life, don’t swap your cups back now, just leave them where they are and add the spacers first, ( with any luck you got the two piece type) this will save you a lot of messy work that you potentially don’t need to do. If they still vibrate after adding the spacers, then swap the cups with the spacers, but from experience you typically wouldn’t need to once you already swapped the cups. Good luck

jyeung528

vibration at idle is not me. but thanks for looking out.

i already added the spacers and still have vibration, so going to try swapping with the spacers.

hopefully that fixes it otherwise i gotta buy new CV joints.