What type of information with this provide just curious? I’m relatively new to working on cars (last 5 years) and self taught. But I’ve never downshifted to feel/hear the vibration, but I can tell you it’s worse in second under heavy load and then if you bump 3rd it goes away until the rpm reaches a similar point. But it’s definitely still related to speed more than rpm.
Vibration over 70 please help!
- Thread starter SamJam05
- Start date
I did rotate tires and they’re the same as before the rear gear change. I do appreciate the help a lot. I’ve gone to a few local mechanics about this and have changed everything they felt was the culprit that’s why I’m here. Started with “pinion angle is probably off” to the driveshaft is out of round, or the ujoints are bad. I’ve had a sneaking suspicion the entire time it was either rear gear or trans related, but I’ve checked the rear gear 3 times now. I’m slowly getting through my “broke more than a fixed” phase because I’m definitely still in that! Love that analogy. Again, I much appreciate the help.
I was unaware the internals could cause it to vibrate as well. Other thing I forgot to mention, if you turn the tires and listen to the transmission in neutral you can hear a click underneath the trans pan. Never heard it before, is that common?
if the problem only happens at a certain speed and it goes away, or happens, in a certain gear, then you know the issue is not just speed but also RPM related, whether it is engine or transmission. every clue that you can pick up of when, and when it does NOT happen, is a clue to getting it resolved. if it happens at a certain speed whether under load or not , that can help eliminate some potential causes.
If the vibration is only present under load as you described, then it’s in the driveline FER SURE. If it were a tire, front end component, axle, driveshaft, etc, then the vibration would be consistent regardless of load.
Since the only thing that is different from what you’ve described, is the the differential/ring and pinion. My guess is the backlash is too tight. A cheap, and relatively easy test is to increase the backlash by .002 - .004”. Pull the axles, then pull out the differential/ring gear and move .003-.006” of shim from the left side and put it into the right.
Gear setup is like rod and main bearings clearance - a little too loose and no one will know, but too tight and everyone (and you) will know. I run the backlash at the top of the spec or .001-.002” too much. The gears will be fine a little, repeat a little, too loose. Considering I’ve been doing this in the 800-1000hp range, I’m sure you’ll be fine. If you feel that this adjustment is over your head, but you can do basic repairs, then you’re wrong. The only tool needed is a budget caliper. The only parts needed are a rear shim kit (less than $50) and some silicone.
Since the only thing that is different from what you’ve described, is the the differential/ring and pinion. My guess is the backlash is too tight. A cheap, and relatively easy test is to increase the backlash by .002 - .004”. Pull the axles, then pull out the differential/ring gear and move .003-.006” of shim from the left side and put it into the right.
Gear setup is like rod and main bearings clearance - a little too loose and no one will know, but too tight and everyone (and you) will know. I run the backlash at the top of the spec or .001-.002” too much. The gears will be fine a little, repeat a little, too loose. Considering I’ve been doing this in the 800-1000hp range, I’m sure you’ll be fine. If you feel that this adjustment is over your head, but you can do basic repairs, then you’re wrong. The only tool needed is a budget caliper. The only parts needed are a rear shim kit (less than $50) and some silicone.
Eliminate the most you can. Not with new parts but with removing from equation.
If you have access to a drive on dyno. You can recreate the rpm and speed. This removes front wheels from the equation.
Run it on jack stands with the suspension loaded. Repeat with wheels removed and wheel nuts holding the drums. Repeat with no wheels and no drums but not touch brake pedal. Does the slip yoke have good engagement into the transmission?
When the car is up in the air, check tread runout. A balanced tire does not mean it's round.
If you have access to a drive on dyno. You can recreate the rpm and speed. This removes front wheels from the equation.
Run it on jack stands with the suspension loaded. Repeat with wheels removed and wheel nuts holding the drums. Repeat with no wheels and no drums but not touch brake pedal. Does the slip yoke have good engagement into the transmission?
When the car is up in the air, check tread runout. A balanced tire does not mean it's round.
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I disagree with that statement due to my own experience -- if the Road Force Balance of a wheel/tire combination is off, vibrations will rise as speed rises.
Yes, but it will be consistent with speed and independent of load. The OP is saying that when he lifts the vibration is gone/dissipates or is much less. A tire won’t do that.
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