E350 - Droning Noise (from rear?) at deceleration

[E-350]

Update:
Have been at a junk yard today and checked some other RWD vans and trucks. All of them had some play on the slip yoke, partially more partially less than mine. So I took my chances:
took out an extension housing + slip yoke and brought it home.

Although I just changed my bushing the slip yoke I got from the junk yard had much less play.

So I installed the new slip yoke into the current ext. housing and put a new u joint in (front, Spicer greaseable) and the noise changed significantly. I can now drive >70 without that rattle and the vibrations while decelerating reduced a lot! But there‘s still „some“ noise.
Looks like the yoke/ bushing play is more important than I thought.

Will now replace the rear driveshaft u joint and check again. Then tire roration and check.

If still some noise I check the rear hub bearings and in case that‘s not successful I go back to my diff/ pinion.

[Lilnuts2]

Glad to hear (no pun) your making progress.

[E-350]

Soooo… did some more work: replaced the rear u joint and found the diff has some degree of free tilt. Once I find out how and where to upload a video I do so.

BUT: found something else.

I replaced my slip yoke with the one I got from the junk yard and now checked my old one again. I see scratches on the first ~25mm corresponding to the 25mm in my old extension housing bushing (copper layer was already fully gone in that area).
The other problem is that the bushing itself is ~40mm. Means I‘m missing at least 0.5“ in length after my 3“ rear lift. That means I don‘t have the designed „bearing area“ + I only transfer torque on 2/3 of the area!






So if I don‘t solve this permanently I guess I will have to do it again and again.

My idea is to get a driveshaft spacer. Axle relocation plates will not really provide the movement I need.

Anyone an idea where to get a 3/4“ spacer?

[Lilnuts2]

You mean like this?

https://superlift.com/product-detail/4310

[E-350]

Yes, "LIKE this". The one shown seems to be for Chevy/ GMC.

I found this one at 4WP, but still got to find our more about the dimensions. As this part would also center the driveshaft via the small collar it needs to fit my diff.

https://www.4wheelparts.com/p/fabtec...S92003#qstnAns

[carringb]

Have you verified the driveline pinion angle? J-Sweezy found this to be the root of his driveline vibration after he re-did his 4x4. More driveline info here:

https://madocumentupload.marketingas...16fdb&v5=False

A change in pinion angle can also affect effective driveline length.

[E-350]

carringb, I will work on the van again on Sunday and put the driveshaft spacer in (in case it fits... not sure yet). I have not checked the angle, but I would be really surprised to see a 3" rear lift not working. I have the feeling it's a fairly common lift and seems no one else has these problems after lifting...

But: let's see. I keep you posted on the progress

[E-350]

Sorry guys, took a bit longer as I first had to fix a water damage on a friend 1992 RV :-D

ok, so where are we:
As stated I replaced the bushing, I replaced the front U Joint. It got much better.
I opened up the diff and it looked good, though I didn't do more than a visual inspection.

Just Sunday I replaced the rear U Joint as well as added the Fabtech 92003 Drive Shaft Spacer. Perfectly fitted, came with longer screws, ...
--> noise changed again and it's not gone. But looks like I'm on the right track/ in the right area...

I think I'm going to a transmission shop, stop by and ask whether or not my play in the output shaft is normal. I somehow have the feeling it moving a bit more again and this causes the noise. Perhaps the output shaft came loose/ has play or whatever. Just to make sure I'm not playing on the wrong end...

Keeping you posted!

[Dearranged]

I've come across the same phenomenon as you re the vibration. I have installed a different yoke with the splines that are full length, the oem is counterbored the first 1 to 1.5". I don't know if that is going to 'fix' this drone or vibration yet. If not, I believe it is going to be the driveshaft tube itself. I get the same drone as you described, it changes harmonics from accel to decel. Dorman has a part number 976-059 that is a direct replacement I believe, pricey but I don't know how much it costs to retube a shaft at the moment. Also if you are lifted there is a ratio that works, something like 6 degrees inclination to 1.5 degrees pinion or something like that. You can google and find the info.

[Dearranged]

Also using the math on the spicer website, the driveshaft diameter should be at least 4" so the 1/2 critical speed harmonics are above the cruising speeds of 60-80 mph.