Noise/Rattle From Underneath

[Jimjific]

Hello All,

Just got my 69 swb step and it drives great. The only weird thing is I have a rattle sound that shows up around 32mph and goes away around 37 mph. I have tried to figure it out and can't seem to locate it. I thought exhaust first but there is nothing loose and I would think that would show up with RPM not mph. I've put the truck into neutral and the noise is still there so it isn't the motor.

I have a split shaft drive shaft, which seems weird for a short bed, could it be the bearing? I don't feel any vibration just an annoying noise. This would make some sense since it would be based on mph.

Thanks for any help,
Jim

[brad_man_72]

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Make sure the driveshaft is still in time, the bolt on yoke is tight and all of the ujoints are installed properly and don't have and play.
Even if all of that looks ok someone could have turned parts 180* out and thrown the ballance off.
Only a driveline shop can ballance a driveshaft.
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[Jimjific]

Thanks for the reply. The truck only has 83K miles on it but I was thinking of replacing all of the u-joints and bearing anyway just so I know everything is new.
I will mark everything before I take it apart.

Jim

[Sammy]

If a previous owner has it 180 degrees out from prior u joint replacement you will not solve your problem by replacing the joints. Then it would need rebalanced as Brad said.

[Jimjific]

If it was out of balance, wouldn't I feel a vibration and wouldn't I feel it for more than just a 5mph zone? Right now all it is is an annoying rattle sound like a harmonic with no noticeable vibration.

Thanks again,
Jim

[Jimjific]

Thought I'd post an update on the noise issue. After doing some research I stopped by Advance Auto and got a new bearing. Figured for ~$20 what the heck. So I went to replace it I marked everything so I could put it back together the same. I took the back shaft out and then unbolted the carrier bearing and pulled the forward shaft out. Right away I noticed how different the new bearing and the old one was. The housing was about an inch shorter in the hanging direction and it would only mount using two of the four bolts. So I took the clam shell housing apart to get a better look at the bearing. I then realized that I was going to need to press this bearing out. I have a press but I really didn't feel like going through all of that since one, I didn't know if the bearing was really my noise issue and two, the old bearing seemed really good still. There was no play in it at all. So I cleaned it up and put everything back together and greased the shaft splines. Wouldn't you know, the sound is gone. I did about a hundred miles yesterday and everything is great. So I will be returning the bearing.

Thanks for the input,
Jim

[brad_man_72]

You have a slip yoke also, a lot of our trucks don't.
If greasing it helped, its worn out, and will eventually beat the rubber out of the carrier bearing. The slip and stub shouldn't have any hinge (up and down) movement. Torsional play doesn't create a vibration

You can cut the old bearing off with a cutoff wheel, its less likely to warp the shaft than using a press.

Yes its very possible that an out of ballance driveline will produce a vibration you can fee at certain speeds.
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