18GTSC
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Spacer? Mine is for the A10...no spacer I guess.
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Gregor12
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I tried dropping my trans mount about a 1/4 of an inch but there is still some vibration. I bought the spacers/adapters separate so I may just have to get it all balanced together. DSS needs weeks to balance a DS because they have so many orders. But I found someone local who makes custom driveshafts and balances driveshafts as well. We shall see if it truly is the pinion angle or just the DS being out of balance.
Angrey
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Firstly, you have to understand that there's several things that can cause vibration in the drivetrain associated with the driveshaft.
1) An imbalance in the shaft. Although it's not uncommon, this is always the first diagnosis and blame. Most manufacturers balance the shaft to very high rpm (higher than most cars will experience). It's certainly possible and wouldn't be the first time a shaft needs to be properly balanced, but generally speaking, the better companies rarely send out a shaft that isn't balanced properly.
2) Critical speed. The critical speed of the shaft is that speed at which the rotational forces begin to constructively act like a guitar string and give the shaft a vibration/resonance. Generally speaking, the longer the shaft, the lower the critical speed. (short is good, long is not as good). The material strength plays a part. The thickness or profile plays a part (thicker is better in resisting harmonics, but also more challenging to balance).
In MOST cars, the fastest rpms the shaft will encounter are in the 1:1 gear at redline. In this condition, the motor is spinning at say 8k rpms. The transmission is transferring that torque same speed. The rear end, is then multiplying that torque by the ratio (say 3.73:1).
In every other gear, the transmission is splitting/multiplying the engine input shaft speed. So unless the vehicle "drags" out at redline in the 1:1 gear, redline in that gear will be the fastest speed the shaft will see.
3) Half critical speed. This one is a bit complicated to explain, but it's USUALLY the culprit with a lot of drivetrain imbalances. Most older cars use what's called a "universal joint." This joint allows angle and flex in two different components. However, one of the drawbacks is that as the knuckle rotates, it moves slowly on one side of the rotation and then whips very quickly on the other side of the rotation. This joint is very simple and robust. The other common joint is called a "CV" or constant velocity joint. Unlike the U joint, the CV joint does not have the change in velocity, making it a smoother affair. However, it's more expensive and more complicated and generally not as strong or robust as most U joint applications.
For cars that feature a U joint, the half critical speed comes into play with a bad vibration, particularly if the working angle of the motor-transmission to driveshaft isn't EXACTLY the same and opposite angle as the driveshaft to rear differential. (so imagine a situation where the front joint is 2 degrees and the rear joint is 5 degrees, this creates a very bad situation for the half critical speed resonance and vibrations).
Ideally, the joint needs at least 1/2 degree angle to keep it working lubricant. So the most ideal setup would be 1/2 degree in the front and -1/2 degree in the back. Perfectly matching, just enough angle to keep the joints from drying out.
Keep in mind, that it's ASSUMED by most people that the longitudinal angles are zero (meaning your motor isn't offset to the side or the rear diff). Although there can be slight angles here, it's usually not enough to be a relevant factor.
If you've read through ALL that, if you're getting vibrations, there's a few options. Send the shaft back to be balanced. (spoiler, most manufacturers won't tell you or admit if the shaft is off, they almost always send it back saying it's balanced, even if it wasn't). If the problem still persists, a typical old school trick is to try to flip the shaft 180 for the attachment bolts. If there's an imbalance in the shaft, sometimes this helps to counter balance it (kinda like spinning an out of balance tire around an out of balance wheel to see if they help cancel each other). Sometimes it works, sometimes not.
If that doesn't work, check your working angle. There's plenty of websites that cover how to do that. Quality shops will also be able to help set it right (using shims or spacers for your trans mount if possible).
The reason that Ford went with a 2 piece driveshaft for the S550 is that the length was so much that they couldn't get the proper critical speed rating out of such a long shaft. The 2 piece with a CV connector resolves that problem that's created by having a short transmission with no tail section.
1) An imbalance in the shaft. Although it's not uncommon, this is always the first diagnosis and blame. Most manufacturers balance the shaft to very high rpm (higher than most cars will experience). It's certainly possible and wouldn't be the first time a shaft needs to be properly balanced, but generally speaking, the better companies rarely send out a shaft that isn't balanced properly.
2) Critical speed. The critical speed of the shaft is that speed at which the rotational forces begin to constructively act like a guitar string and give the shaft a vibration/resonance. Generally speaking, the longer the shaft, the lower the critical speed. (short is good, long is not as good). The material strength plays a part. The thickness or profile plays a part (thicker is better in resisting harmonics, but also more challenging to balance).
In MOST cars, the fastest rpms the shaft will encounter are in the 1:1 gear at redline. In this condition, the motor is spinning at say 8k rpms. The transmission is transferring that torque same speed. The rear end, is then multiplying that torque by the ratio (say 3.73:1).
In every other gear, the transmission is splitting/multiplying the engine input shaft speed. So unless the vehicle "drags" out at redline in the 1:1 gear, redline in that gear will be the fastest speed the shaft will see.
3) Half critical speed. This one is a bit complicated to explain, but it's USUALLY the culprit with a lot of drivetrain imbalances. Most older cars use what's called a "universal joint." This joint allows angle and flex in two different components. However, one of the drawbacks is that as the knuckle rotates, it moves slowly on one side of the rotation and then whips very quickly on the other side of the rotation. This joint is very simple and robust. The other common joint is called a "CV" or constant velocity joint. Unlike the U joint, the CV joint does not have the change in velocity, making it a smoother affair. However, it's more expensive and more complicated and generally not as strong or robust as most U joint applications.
For cars that feature a U joint, the half critical speed comes into play with a bad vibration, particularly if the working angle of the motor-transmission to driveshaft isn't EXACTLY the same and opposite angle as the driveshaft to rear differential. (so imagine a situation where the front joint is 2 degrees and the rear joint is 5 degrees, this creates a very bad situation for the half critical speed resonance and vibrations).
Ideally, the joint needs at least 1/2 degree angle to keep it working lubricant. So the most ideal setup would be 1/2 degree in the front and -1/2 degree in the back. Perfectly matching, just enough angle to keep the joints from drying out.
Keep in mind, that it's ASSUMED by most people that the longitudinal angles are zero (meaning your motor isn't offset to the side or the rear diff). Although there can be slight angles here, it's usually not enough to be a relevant factor.
If you've read through ALL that, if you're getting vibrations, there's a few options. Send the shaft back to be balanced. (spoiler, most manufacturers won't tell you or admit if the shaft is off, they almost always send it back saying it's balanced, even if it wasn't). If the problem still persists, a typical old school trick is to try to flip the shaft 180 for the attachment bolts. If there's an imbalance in the shaft, sometimes this helps to counter balance it (kinda like spinning an out of balance tire around an out of balance wheel to see if they help cancel each other). Sometimes it works, sometimes not.
If that doesn't work, check your working angle. There's plenty of websites that cover how to do that. Quality shops will also be able to help set it right (using shims or spacers for your trans mount if possible).
The reason that Ford went with a 2 piece driveshaft for the S550 is that the length was so much that they couldn't get the proper critical speed rating out of such a long shaft. The 2 piece with a CV connector resolves that problem that's created by having a short transmission with no tail section.
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