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Hello all,

As indicated, I am a newbie to these boards, but this seems like a great site. I plan to visit often, and will contribute whatever reliable info I can!

I have swapped a Tremec 3550 in place of the C4 that came with the car. I have an early 302, am using a matched-balance flywheel, a Windsor-Fox crossmember designed for this conversion, cable clutch setup (clutch is OEM 93 Cobra), and a Currie 8" TSD.

Since I've had this transmission in the car, I've battled vibration problems at highway speeds, starting right at 75. I don't make it a habit to drive 90 or anything, it just shouldn't vibrate. The vendor from whom I got most of the parts sent me a driveshaft that was too short (the yoke was scored) out of round, and out of balance. Not being a drivetrain expert, I took it to a local Classic Mustang shop. They stuck in a stock driveshaft (from a V8 67 with a C6 I think) with a stock yoke. They claim it's the correct length, but still I get some vibration, and furthermore I think the yoke bottoms out in the transmission sometimes at slow speeds, especially turning (ouch).

Can anyone help me to determine what the correct driveshaft length should be? I'm wondering what slip yoke I should use, how much travel it should have, how much (if any) should be visible, etc. I am almost certain that drivetrain alignment is not the problem. Getting a driveshaft that I knew was the correct length would answer that question, too. The clutch was installed properly, torqued uniformly and I did remember the three dowels :).

Any help would be sincerely and incredibly appreciated. This problem has persisted for far too long, and I don't know what to do at this point. The vendor is of no help.

Thanks!
Jason
 

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Since I've had this transmission in the car, I've battled vibration problems at highway speeds, starting right at 75. I don't make it a habit to drive 90 or anything, it just shouldn't vibrate. The vendor from whom I got most of the parts sent me a driveshaft that was too short (the yoke was scored) out of round, and out of balance. Not being a drivetrain expert, I took it to a local Classic Mustang shop. They stuck in a stock driveshaft (from a V8 67 with a C6 I think) with a stock yoke. They claim it's the correct length, but still I get some vibration, and furthermore I think the yoke bottoms out in the transmission sometimes at slow speeds, especially turning (ouch).

Can anyone help me to determine what the correct driveshaft length should be? I'm wondering what slip yoke I should use, how much travel it should have, how much (if any) should be visible, etc. I am almost certain that drivetrain alignment is not the problem. Getting a driveshaft that I knew was the correct length would answer that question, too. The clutch was installed properly, torqued uniformly and I did remember the three dowels :).

Any help would be sincerely and incredibly appreciated. This problem has persisted for far too long, and I don't know what to do at this point. The vendor is of no help.

Thanks!
Jason
Jason, welcome to the forum! :)
First, I believe that the stock length driveshaft for a C4 in 67 is 53.5".
As far as vibrations, this could be caused by a number of things.... did you know that few wheels are completely round? Your "out of round" tires could be a cause of the vibration you describe. Your vibration could be caused by your rear end, drive shaft, u-joints, clutch, etc. I think you correctly have excluded the engine and anything before the tranny, since it happens at certain speeds, rather than certain RPMS.
To determine if it's the drive shaft, you can determine balance in your own garage if you are careful. Block the front tires, and put the rear on jackstands. Have someone with a piece of chalk crawl under the car and while an assistant slowly speeds up the car in gear, put the chalk close to the driveshaft. If the shaft is out of balance, only part of it should be marked with chalk. This would confirm the out of balance shaft. You can also check at the same time for out of balance tires. Just be very careful.
One thing I'm sure of: the yoke shouldn't bottom out or even move when cornering, especially at slow speeds. You might be running into other issues.
Good luck with your search, and be careful out there.

Daniel
 
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