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Pinion Bearing Noise (I think)

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3MAX

1/2 ton status
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Feb 24, 2009
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Location
North Alabama
I just finished my build and got my Blazer back on the road, but it seems I've got an issue to sort out.:doah:

I get a grinding / whining noise when I let off the throttle going over 30mph. It only lasts a couple of seconds, and it only does it after being on the throttle. I can cause the noise at will by feathering on and off the throttle over 30mph.

I'm certain it's coming from the rear end, and according to internet diagnosis, this is pinion bearing noise caused by lack of preload.

The axle is a 14 bolt semi-float that I rebuilt. I'm 100% certain that I set the preload correctly during assembly. I even purchased an inch-lb torque wrench specifically for this purpose.

Tonight I set the rear end on jack stands and dropped the drive shaft to check the pinion for any play. Nothing. Nada. even checked it with a dial indicator - I couldn't get any end play or side to side movement, even when hitting it with a dead blow hammer.

So... what now? Could there be another issue causing the noise? I just hate to go through the rear end again before checking all possibilities.
 
I've had that round "oil slinger" thing on the yoke come loose from the yoke ,so it could spin on it,and it make some strange noises only during a coast from about 30-40 mph...
I tack welded it onto the yoke and the noise stopped..hope its somthing simple like that in your case..
 
If there's a tin slinger take it off the throw it away . Is there any lift on this rig ? It kinda sounds like gear rattle and that's from to much angle . Jess
 
I have the same noise in my truck, but it's coming from my transfer case. Mine is a NP208 and I have 6" of lift...
 
38377k5 said:
What transfer case is in the truck? What kind of truck and how much lift?
Click to expand...

It's a '90 K5 with a 700R4, 241, and 4" lift. The differential is set to the same angle as the output shaft (6* I believe). Using the stock driveshaft, not getting any vibration except a little along with the noise. I'm not certain what the working angle of the drive shaft is, but it's pretty steep.
 
Really its a driver annoyance , and in the long run bolts may loosen , and or other things may go south . Jess
 
Checked the drive shaft angle tonight - 28*

Is this pushing the limit of the stock shaft & u-joints? Will running at this angle typically lead to noise as described above?
 
3MAX said:
Checked the drive shaft angle tonight - 28*

Is this pushing the limit of the stock shaft & u-joints? Will running at this angle typically lead to noise as described above?
Click to expand...


It's very probable. Every truck is different, but at that kind of angle you might want to be looking at a CV driveshaft. Even if you have both u-joints in phase, I wouldn't imagine stock u-joints would have a long life under those conditions.

You also have to look at the maximum operating angle of your u-joints. Generally, conventional wisdom is that in an ideal situation u-joint angles on each end should be equal, and maximum operating angle of 3 degrees or less. That's a relatively conservative number, though.
 
After putting several more miles on the Blazer this weekend, I no longer think the noise is from the rear axle or drive shaft. I'm pretty sure it's the transfer case, and it seems to be getting worse. It sure sounds like a bearing rattling during coast / deceleration.
 
3MAX said:
After putting several more miles on the Blazer this weekend, I no longer think the noise is from the rear axle or drive shaft. I'm pretty sure it's the transfer case, and it seems to be getting worse. It sure sounds like a bearing rattling during coast / deceleration.
Click to expand...

That's always a possibility, just make sure you've eliminated all the "easy" and more common possibilities. A plus is that the rear output bearing in the TC is pretty easy to get to and inspect.
 
I had trouble getting rid of vibrations in my driveshaft with 13* in the joints. By your measurements you have 22*. That's really a lot for a standard joint. Do you have the 1330 at the T-case and adapter U-joint at the pinion? Is this a stock driveshaft or have you had it lengthened (or custom built)? How far is the slip yoke sticking out of the t-case?
 
Blue85 said:
I had trouble getting rid of vibrations in my driveshaft with 13* in the joints. By your measurements you have 22*. That's really a lot for a standard joint. Do you have the 1330 at the T-case and adapter U-joint at the pinion? Is this a stock driveshaft or have you had it lengthened (or custom built)? How far is the slip yoke sticking out of the t-case?
Click to expand...

Actually, 28* is the working angle of the joints, not the angle of the shaft itself.

This is the stock, un-modified driveshaft with the conversion U-joint at the pinion. I don't remember for certain how far the yoke is out of the t-case, but I did measure it after the lift and it has plenty of engagement. I suppose the longer pinion on the 14 bsf axle compared to the original 10 bolt helped out with the standard length drive shaft.
 
My plan is to replace the output shaft bearing when I have time in the next couple of weeks. I've rebuilt everything else on the truck, but haven't been into the t-case yet. What's involved in replacing the bearing?

I see two bearings (front and rear) and a bushing listed for the output shaft. One bearing is a roller bearing and the other is a needle bearing. As long as I can get to them, I'd like to replace both while I'm there. Any other suggestions while I'm at it?
 
3MAX said:
Actually, 28* is the working angle of the joints, not the angle of the shaft itself.

This is the stock, un-modified driveshaft with the conversion U-joint at the pinion. I don't remember for certain how far the yoke is out of the t-case, but I did measure it after the lift and it has plenty of engagement. I suppose the longer pinion on the 14 bsf axle compared to the original 10 bolt helped out with the standard length drive shaft.
Click to expand...

I bet you it's the two things that have already been talked about. First is you probably need a CV shaft. Even a 4" lift will reach the limits of a stock 2-joint shaft. Plus, you have to look at your angles too. 2-joints like the output of the tcase and the pinion of the axle to be parallel with the ground. A CV wants the pinion to be pointed right at the tcase output. Do you have some pictures of the set up? That can help to see what angles you are working with.

Second is even if you think you have enough engagement on the slip yoke, you probably don't. I was getting the exact same thing as what you are talking about in mine with a NP208, stock shaft and 4" of lift. As soon as I went with a SYE NP241 with a CV shaft....smooth as butter.

3MAX said:
My plan is to replace the output shaft bearing when I have time in the next couple of weeks. I've rebuilt everything else on the truck, but haven't been into the t-case yet. What's involved in replacing the bearing?

I see two bearings (front and rear) and a bushing listed for the output shaft. One bearing is a roller bearing and the other is a needle bearing. As long as I can get to them, I'd like to replace both while I'm there. Any other suggestions while I'm at it?
Click to expand...

I don't think this is your problem. If it was, I would imagine the seal would be bad too and you would be leaking out the rear output
 
The out put seal is brand new, so its not leaking. Even with the steep angles, I get no vibration under load or cruise. Only when I get off the throttle or coast down hill (drag on the drivetrain) do I get noise. Its not really a vibration, but a grinding / rattling sound of a bad bearing that you can feel. I don't doubt that a CV shaft would improve my set up, but I'm not convinced its the shaft angles that are causing this issue.
 
I went through the exact same thinking you are going through right now. And I had the exact same noises you are having in the exact same situations, to where I couldn't think that it was the driveshaft/slip yoke being pulled out to far. But when I changed my setup....like I said....smooooth. The last thing I like doing is throwing money at parts that are not necessary
 
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