EXP Jawa
Well-Known Member
- Joined
- Jun 9, 2014
- Threads
- 3
- Messages
- 1,011
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- Location
- Rochester, NY
- Website
- www.torsen.com
- First Name
- Rick
- Vehicle(s)
- 1999 Cobra Convertible, Electric Green
- Thread starter
- #1
OK, this is regarding my '99 GT, not an S550. But since this is the only Mustang board I'm on and its about time we had some real tech discussions here (in lieu of actual S550s to work on), I'm going to post here.
I've been chasing what I thought was a driveline vibration all summer. It comes and goes with throttle, so I assumed early on that I could rule out something like wheel or prop shaft balance. If the cruise is set at, say 65, on the highway, you can feel the vibration increase and as the throttle increases as the road rolls up little hills and then backs off as the throttle relaxes going back down, all while maintaining a constant speed. However, I should point out that this vibration seems apparent from very low speed up to highway speeds. It seems to come in and out of phase as speed increases. I know that there is going to be some inherent vibration in the chassis, being 15 years old, and a convertible with a V8. But I've been around working on NVH issues in vehicles enough that I can tell when something is distinctly out of place.
The first thing that occurred to me was U-joints, so I replaced them. I thought that with 90K miles, there was nothing to loose in doing it. But it didn't help. Some googling seemed to point to symptoms similar to a pinion angle problem, like truck owners run into when doing suspension lifts. But the pinion angle is fixed, and can't move much within the compliance of the trailing arm bushings, unless something is really worn and loose. So I spent some time with the car on the lift pushing and pulling on everything in the rear suspension, to no avail. I did find, however, that the tailshaft bushing in the T45 was worn in the vertical direction, and I could feel play in the u-joint yoke when I pushed it upwards. I replaced the bushing, but it didn't help the problem.
More recently, I realized that although the vibration is turned on/off with throttle position, it is far more excited within certain engine RPM ranges. If I merge onto the highway, at again say 65 mph, in 4th gear, there is no apparent vibration. As soon as I shift into 5th, bam, the vibration is there. At that point, the engine has dropped to about 1900 RPM, and it seems that the vibration is most active between about 1600-2000. If I accelerate fast enough to get to 2300 or more, it seems to calm again.
So, there you have it. Its a vibration that comes and goes with throttle, and seems tied to a specific engine speed range. That seems to point farther forward than I was looking before; toward the engine itself being involved. The only things I can think of are the harmonic balancer or the motor mounts. I'll also point out that it seems to have good days and bad days, though that might be a factor of how much time I spent at the critical speeds, I don't know. Does anyone have any advice they could offer? I'm pulling my hair out on this one (I'm nearly bald already!) and have been reluctant to drive it too far from home.
I've been chasing what I thought was a driveline vibration all summer. It comes and goes with throttle, so I assumed early on that I could rule out something like wheel or prop shaft balance. If the cruise is set at, say 65, on the highway, you can feel the vibration increase and as the throttle increases as the road rolls up little hills and then backs off as the throttle relaxes going back down, all while maintaining a constant speed. However, I should point out that this vibration seems apparent from very low speed up to highway speeds. It seems to come in and out of phase as speed increases. I know that there is going to be some inherent vibration in the chassis, being 15 years old, and a convertible with a V8. But I've been around working on NVH issues in vehicles enough that I can tell when something is distinctly out of place.
The first thing that occurred to me was U-joints, so I replaced them. I thought that with 90K miles, there was nothing to loose in doing it. But it didn't help. Some googling seemed to point to symptoms similar to a pinion angle problem, like truck owners run into when doing suspension lifts. But the pinion angle is fixed, and can't move much within the compliance of the trailing arm bushings, unless something is really worn and loose. So I spent some time with the car on the lift pushing and pulling on everything in the rear suspension, to no avail. I did find, however, that the tailshaft bushing in the T45 was worn in the vertical direction, and I could feel play in the u-joint yoke when I pushed it upwards. I replaced the bushing, but it didn't help the problem.
More recently, I realized that although the vibration is turned on/off with throttle position, it is far more excited within certain engine RPM ranges. If I merge onto the highway, at again say 65 mph, in 4th gear, there is no apparent vibration. As soon as I shift into 5th, bam, the vibration is there. At that point, the engine has dropped to about 1900 RPM, and it seems that the vibration is most active between about 1600-2000. If I accelerate fast enough to get to 2300 or more, it seems to calm again.
So, there you have it. Its a vibration that comes and goes with throttle, and seems tied to a specific engine speed range. That seems to point farther forward than I was looking before; toward the engine itself being involved. The only things I can think of are the harmonic balancer or the motor mounts. I'll also point out that it seems to have good days and bad days, though that might be a factor of how much time I spent at the critical speeds, I don't know. Does anyone have any advice they could offer? I'm pulling my hair out on this one (I'm nearly bald already!) and have been reluctant to drive it too far from home.
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