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KELLY.ga
04-24-2018, 01:21 PM
Hi folks, this is my first time on this forum so, I am in conyers ga, I have completely restored 57 hard top, a 57 conv, a 40 ford coupe. The Conv and 40 are long gone, I only have the hard top now and it's been in the family 30 years now with on 23k miles on it. As you know I'm sure, you never get through with them. I have recently put a new 350,290 sbc in it and just put a Tbi on it which I really like. Now the problem, I have just recently put a 700r4 in it and I have a vibration at exactly 70 mph. I have had the tires rebalanced, they are 15 inche by the way, replaced one rear axle bearing and had the drive shaft rebalanced. Nothing seems to help, has anyone else had this problem. Any help would be greatly appreciated.

markm
04-24-2018, 01:59 PM
If you have a 700r4 someone had to shorten driveshaft my guess is that it is not straight and therefore its out of balance.

Rick_L
04-24-2018, 02:13 PM
Have a GOOD driveshaft shop chuck it up in a big lathe with proper fixtures for the u-joint and measure runout. If the vibration is really bad you can see the misalignment without measuring. The GOOD shop should be able to fix it. Doesn't matter how many weights you hang on a misaligned driveshaft.

markm
04-24-2018, 02:44 PM
The old boy who built shafts for me for 40 years always said if you built it right you don't need weights,

KELLY.ga
04-24-2018, 06:38 PM
Thanks to all you guys, that was my feeling also. Even though it has been balanced before I still feel it's the drive shaft.

WagonCrazy
04-25-2018, 06:31 AM
And check the ujoints too. Just to make sure....
I once had a vibration like you described, and it turned out to be rear ujoint was worn.