Driveline vibration help needed - 94 Cobra

[94Cobra]

I am looking for some help on how to isolate the problem. At or above 75mph in 5th gear ONLY, I get a repeating, cyclical driveline vibration. If I push the clutch in or put the car in neutral, the vibration goes away. I also noted the rpms the vibration occurred at in 5th gear and the vibration does not happen at the noted rpms in 4th, 3rd, etc. I do have energy suspension poly motor and trans mounts. The trans mount has several washers between it and the cross member to raise the rear of my tremec 3550 to get the pinion angle within spec. I had ASAP measure my pinion angles since my car is lowereed 1 inch and they are within spec. I have a brand new FRPP aluminum driveshaft and a metal extension to compensate for the shorter 3550. I just had the tires balanced with no help. I did notice the right side O2 sensor is almost touching my FRPP safety bellhouse, but I don't think that is the problem or the vibration would be happening in all gears. Any advice on how to determine if the problem is in the 3550, rear axle or driveshaft would be appreciated.

[Viper_ed]

My 03 Cobra did the same thing at 85 in 6th. It was the driveshaft that was out of balance. Dealer replaced it and all was good after that.


BTW, I have heard ALOT of bad stories about ASAP, just beware!

[gmkillr]

Did you index your bellhousing?

Maybe try your driveshaft on a different set of bolt holes?
I know as long as I have my driveshaft installed the same exact way everytime I dont have any problems. Maybe try rotating it to the next set of bolt holes & see if that works. Its worth a try & probably only takes 10min. to do.
Good luck!

[94Cobra]

I did not index the bellhousing. I will try rotating the driveshaft to different bolt holes.

Anyone else have input on how to determine if the problem is in the driveshaft, tranny, or rear axle?

[burntire]

I did not index the bellhousing. I will try rotating the driveshaft to different bolt holes.

Anyone else have input on how to determine if the problem is in the driveshaft, tranny, or rear axle?

Index and rotate the drive shaft to start. Try every possible position to see if you get rid of it. Sounds like my 99 cobra.

[Viper_ed]

Sounds like my 99 cobra.

Must of been the same POS Driveshaft they stuck on my 03.

[burntire]

My 99 was bad. They had a ford engineer come in to get it fixed.

[Steve-0]

My 99 was bad. They had a ford engineer come in to get it fixed.

Wow, you were special!


Sounds like a driveshaft imbalance to me too, but guess you will have to see.

[burntire]

Wow, you were special!


Sounds like a driveshaft imbalance to me too, but guess you will have to see.

After the 10th visit I guess they got tired of seeing me.

[94Cobra]

If it were the driveshaft being out of balance, wouldn't the problem still exist when the clutch is pushed in or it is in neutral? The driveshaft is still spinning since the tires are turning, which is why I was assuming it is a transmission problem.

[gmkillr]

Id get someone besides asap to index your bellhousing for you. Id try Tim @
Rodeheaver's or Lou @ Luarel Mountain.

[Viper_ed]

If it were the driveshaft being out of balance, wouldn't the problem still exist when the clutch is pushed in or it is in neutral? The driveshaft is still spinning since the tires are turning, which is why I was assuming it is a transmission problem.

I assumed the same thing with mine, but it was just one of those things that there just isn't a explination for I guess.

[Rodeheaver's]

I will say this, i have seen driveshafts do some pretty spooky stuff, i had my driveshaft balenced in my 460 car because i vibrated and now it doesnt vibrate but at 120mph it starts singing me a song, but no more vibration is felt, this is called harmonic vibrations, I think i will live with it... but this is why the factory puts a rubber/steel balencer on the factory drive shaft

[bgblockelcamino]

i would try drivesahft first too. there is a place in neville island that can balance it for you. Island Spring and drivline. they have done a few drivesahfts for me. had great luck with them. it is cheap easy thing to check that way you can rule it out.