Last year I had a 347 put into my67 Convertibleto replace my stock 289 and also had the C4 trans built with shift kit, servo, bands, etc etc to handle the increase in HP. I also put in a poly trans mount. I was getting a bad vibration between 35 and 50MPH and finally figured out that the poly trans mount didn't fit right, causing the driveshaftangle to be off which caused the oscillating vibrationand replaced it with a stock rubbermount and the vibration went away. I'd say I drove about 1000 miles on the poly one with the vibration, and did probably 20 pretty good burnouts over that time. I just replaced my trans mount today and coincidentally noticed over the last few weeks that I was getting a squeeking noise that didn't seem to be coming from the suspension at all and it has gotten progressively worse over the past few weeks. Well, long story short, replaced the trans mount today and noticed that I have a bad U joint on the trans side of the driveshaft and I think that is my squeak. Also, my car has been dyno'd and is putting just over 300HP to the ground...so:

1) Did the vibration and angle of the driveshaft being off kill the U joint or did the HP and burnouts? The U joint does not appear rusty and corroded and it also looks lubed well, just has play in it when you grab it and shake it...

2) Is there any upgraded U joint I can look into for the stock 8 inch rear/C4 trans car, or do they only make stronger U joints and/or yokes for 9 in rear end cars?

Thanks!

Mark

 

How old are the u-joints? Are there any grease fittings in them? How can you tell if they are lubed properly? Depending on the angle the driveshaft was in it could have placed the u-joint in a bind and added to the problem. But u-joints are a wearable item and most people never grease or inspect them unless there is a problem. If not lubed properly the pins inside the cups were out. I would just install two new u-joints and a driveshaft loop for safety.

 

I had beefed up my 289 years ago and broke several stock replacement ujoints mine was a 4 speed toplaoder.
I have replaced everything now and put in a supercharged 347 and a tko 500 going to a currie 9".
Check some driveline shops or just call curie #1330's are what im running and they are beefy!
Youll need to have the drive shaft end replaced and balanced and a matching saddle for the pinion end. If you going for the heavy duty stuff may be overkill but I like overkill. lol