glbeaty
Computer
- Jul 7, 2008
- 5
Hello,
I am preparing a C5 Corvette for road racing, and have come across an issue in the drive shaft that I need some assistance on.
For those not familiar with the car, C5 and C6 Corvettes use a rigid torque tube that positively locates the rear-mounted transaxle to the engine. The clutch is attached to the engine normally. Inside the torque tube is the drive shaft, which has male splines on the clutch side and female splines on the transmission side. Each side is supported by a bearing (there is no third or central bearing). Its a three-piece unit, with the main center shaft being connected to the splines on either end via rubber couplers (sometimes referred to as flex discs or guibos). These couplers are very similar to, and actually interchangeable with, the flex discs commonly found on BMWs. There are no u-joints.
Naturally, these discs are prone to failure under hard use. I can cheaply use some solid aluminum replacements and machine the assembly to keep run out in check, but I am concerned that this change might lower the drive shaft's natural frequency to something that might be encountered during operation (roughly 0 to 7000 RPMs).
My questions are, how would one go about guestimating the natural frequency of the system? What would happen if the natural frequency was reached? Would the drive shaft's bearings get destroyed? If harmonics are not a problem, why would GM have put rubber couplers in the drive shaft in the first place? (I am assuming machining the assembly straight enough to keep run out low without the use of compliant couplers would not be prohibitively expensive)
There is a (very slightly lighter) carbon fiber replacement available for the center piece, which I assume would have a higher natural frequency than the OE aluminum unit. It is commonly used in conjunction with solid aluminum couplers, but I don't have any data on failures of these (if any).
Some measurements are as follows:
Center drive shaft (aluminum): 102.9 cm, 2.5 kg, 5.51 cm dia (40.5", 5.5 lbs, 2.17" dia)
Clutch splines: 25.4 cm, 1.8 kg (10", 4.0 lbs)
Transmission splines: 11.4 cm, 1.9 kg (4.5", 4.1 lbs)
Each coupler: 2.5 cm, 0.5 kg(1.0", 1.0 lb)
Total assembly: 144.8 cm, 7.1 kg (57.0", 15.6 lbs)
Operating range: 0 to 7000 RPM
Some pictures:
The bearings and rubber couplers
Torque tube and transaxle assembly
Thanks in advance for any assistance.
I am preparing a C5 Corvette for road racing, and have come across an issue in the drive shaft that I need some assistance on.
For those not familiar with the car, C5 and C6 Corvettes use a rigid torque tube that positively locates the rear-mounted transaxle to the engine. The clutch is attached to the engine normally. Inside the torque tube is the drive shaft, which has male splines on the clutch side and female splines on the transmission side. Each side is supported by a bearing (there is no third or central bearing). Its a three-piece unit, with the main center shaft being connected to the splines on either end via rubber couplers (sometimes referred to as flex discs or guibos). These couplers are very similar to, and actually interchangeable with, the flex discs commonly found on BMWs. There are no u-joints.
Naturally, these discs are prone to failure under hard use. I can cheaply use some solid aluminum replacements and machine the assembly to keep run out in check, but I am concerned that this change might lower the drive shaft's natural frequency to something that might be encountered during operation (roughly 0 to 7000 RPMs).
My questions are, how would one go about guestimating the natural frequency of the system? What would happen if the natural frequency was reached? Would the drive shaft's bearings get destroyed? If harmonics are not a problem, why would GM have put rubber couplers in the drive shaft in the first place? (I am assuming machining the assembly straight enough to keep run out low without the use of compliant couplers would not be prohibitively expensive)
There is a (very slightly lighter) carbon fiber replacement available for the center piece, which I assume would have a higher natural frequency than the OE aluminum unit. It is commonly used in conjunction with solid aluminum couplers, but I don't have any data on failures of these (if any).
Some measurements are as follows:
Center drive shaft (aluminum): 102.9 cm, 2.5 kg, 5.51 cm dia (40.5", 5.5 lbs, 2.17" dia)
Clutch splines: 25.4 cm, 1.8 kg (10", 4.0 lbs)
Transmission splines: 11.4 cm, 1.9 kg (4.5", 4.1 lbs)
Each coupler: 2.5 cm, 0.5 kg(1.0", 1.0 lb)
Total assembly: 144.8 cm, 7.1 kg (57.0", 15.6 lbs)
Operating range: 0 to 7000 RPM
Some pictures:
The bearings and rubber couplers
Torque tube and transaxle assembly
Thanks in advance for any assistance.
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