71 Vibration over 50?

[djinva]

Just bought this 71 in Greensboro yesterday. It has a small block and a auto w/overdrive. It has a vibration over 50 mph. It had been sitting awhile and it got better as I went but it was always there(2 1/2 hrs home). It has a one piece driveshaft but I don't think its original. I thought it had a bad universal joint, but I took out the driveshaft today and it does not.

Did it come with a one piece driveshaft, it was orininally a 6 banger, I am not sure what tranny it had originally.

Any thoughts on the vibration?

Thanks

[71meangreenc10]

Sounds like you have the same problem I do, which with the one piece shaft your pinion angle is off. Youll have to measure the angles and get them close with some shims, or put the two piece shaft back in.

I have hurd rumors, but have never seen myself a factory one piece shaft for these trucks.

Smitty

[djinva]

Have you tried to correct yours?

I am planning on lowering it, I am curious if this will help the pinion angle or hurt it. I hate to work on the angle now only to lower it and have to start all over.

[71meangreenc10]

CPP has shims in their catalog for $19, I have a angle guage and am going to try to correct it with the shims, If it doesnt work, I have a 2 piece shaft to throw back in....


I dont think that lowering will effect a coil spring rear (could be wrong) But Id check it with the pinion guage.....

Smitty

[Blazer1970]

I would guess that you have a bad tire. Or maybe the tires were flat spotted if the truck sat for a long time.

[cparman]

I agree. If it were mine, I would have the tires rebalanced first, and then go after the hard stuff. I have a one piece shaft in my truck with a th400 and have no vibration. The truck is lowered with 2" springs and 2" blocks

Originally Posted by Blazer1970

I would guess that you have a bad tire. Or maybe the tires were flat spotted if the truck sat for a long time.

[djinva]

I really do not think it is in a tire, the vibration changes when you let off the throttle, so that is why I felt it was in the driveline.

[Monte Carlo Man]

Let's back the cart up a little here.

I can tell you that the older 3 on the tree six cylinder engines had a 2 piece drive shaft with a carrier bearing. Especially if it had a 8 foot bed.

I don't remember any of those trucks back then having a over drive transmission. There were times where people came out with all sorts of adapters that bolted to the back end of the transmission that added a over drive gear, but the automatic transmissions with over drive did not come out until something like 1982 with a 700R4 or the 200R4.

Now the 6 foot bed with the leaf spring suspension did have a one piece drive shaft as did the K/5 Blazers.

There is two ways to balance a shaft, static or dynamic. The process for balancing a drive shaft was patented at a place not far from my home - Corte's Drive Shaft in Brookville PA.

Before I did anything else, I would find someone that is a machinist that has a dial indicator to climb under the truck and measure the run out on each end of the drive shaft. Then I would check the run out in the middle of the drive shaft. Then I would look to see if the ears on the one end is 90* out from the ears on the other end. Then I would look at both ends of the drive shaft to see if there was some type of weight on the ends of the drive shaft.

If there was no weights, I would look to see if there was a place that looked like as if there was a weight at one time, where it either fell off or someone removed it. If I couldn't find anything wrong, I would move onto the next step which would be to put the truck on jack stands and run the engine in gear and watch the drive shaft spin.

Now thats not to say that you don't have a bent rim or a broken belt in a tire or some other problem. But I would exhaust all possibilities before I just blamed the drive shaft without looking at it first.

Maybe that is the reason why the last person sold the truck!

[djinva]

I agree it could be why the last owner sold it. It has a 200R4 (po said it was a 700R4)in it now and it has a 6' bed and coil springs. The driveshaft does have weights and there is no evidence any fell off. They look like 2 washers tacked onto the rear of the drive shaft. They are not factory weights.

I do not think it has anything to do with the vibration but I did discover the yoke that goes in the tranny is worn, so I took the bushing out of the tranny and I am going to replace the bushing seal and yoke.

The thing that really throws me is the fact it really improved over a 2 1/2 hour drive home. I am going to stick another set of tires/wheels on it and see if it makes a difference.

[vegaschevy]

Originally Posted by djinva

I really do not think it is in a tire, the vibration changes when you let off the throttle, so that is why I felt it was in the driveline.

I would still bet it is a bad tire....

[OhOneWS6]

Originally Posted by djinva

The thing that really throws me is the fact it really improved over a 2 1/2 hour drive home. I am going to stick another set of tires/wheels on it and see if it makes a difference.

My bet is a flat spotted tire from sitting. As the tire heat cycled from driving it the flat spot changed.

[djinva]

Replaced the yoke (it was worn) u joint, bushing and seal in the rear of the tranny, and its fine. I really didn't think I did anything to help it but its good.

[brad_man_72]

Originally Posted by djinva

I agree it could be why the last owner sold it. It has a 200R4 (po said it was a 700R4)in it now and it has a 6' bed and coil springs. The driveshaft does have weights and there is no evidence any fell off. They look like 2 washers tacked onto the rear of the drive shaft. They are not factory weights.

i see quite a few driveshafts, ive seen shops ballance just the tube! (this is about as effective as ballancing your hubs, then throwing wheels and tires on your truck and claiming the tires are ballanced)
driveshafts need to be ballanced as an assembely, our trucks his would include a trans yoke at the front and a 1310 ujoint at the rear. some shops do this properly, some dont.

[OhOneWS6]

Originally Posted by djinva

Replaced the yoke (it was worn) u joint, bushing and seal in the rear of the tranny, and its fine. I really didn't think I did anything to help it but its good.

Glad you got it sorted out. Thanks for updating.