Rear prop shaft causing vibration when coasting? (1 Viewer)

[tohox]

Hi,

I've noticed a hum when coasting from highway speeds. The sound will often appear as soon as I depress the clutch but once it has started the hum will remain even if I release the clutch and but will disappear if I accelerate or slow down enough. The sound becomes a vibration and eventually a loud rattle when coasting from lower speeds and can also be triggered by driving over a bump. At first I though I heard it coming from the front driver's side but this is happening in 2WD with hubs disengaged so I doubt it is actually coming from anything at the front of the vehicle (I've confirmed the hubs were indeed disengaged).

My first thought was that there might be something wrong with the rear prop shaft so I compared the front and the rear and there is definitely some play in the spline of the rear prop shaft while there is none at the front. Hard to quantify as it is only a fraction of a degree but it is still quite noticeable when I twist the shaft holding it from both ends. This play appears to be only when twisting along the spline axis which corresponds to the spline teeth backlash. No movement radially so I expect very little runout if at all (I haven't removed the prop shaft yet).

I've had a look in the RM183E body/chassis manual and while it mentions maximum runout and bearing axial play it says nothing about spline backlash...

Do you have such play in the spline of your rear prop shaft?
Any experience with such noise/vibration/rattle when coasting?

1991 PZJ91-MNS

Thanks!

 

[Sundowner]

That's an interesting place to have wear/movement in the manner you describe...

I haven't had that kind of thing happen on any of my rigs. I've had an imbalance in a shaft that led to a vibration, and I've had a damaged shaft effectively do the same thing. I've also had joints start to wear and cause it, and I've had bad pinion angle cause it...but I haven't had splines cause it.

 

[tohox]

That's an interesting place to have wear/movement in the manner you describe...

I haven't had that kind of thing happen on any of my rigs. I've had an imbalance in a shaft that led to a vibration, and I've had a damaged shaft effectively do the same thing. I've also had joints start to wear and cause it, and I've had bad pinion angle cause it...but I haven't had splines cause it.

Thanks for the feedback! I'll investigate further once the prop shaft is removed.

 

[FJBen]

Have you greased it lately?

That’s an easy one to start with. Don’t overgrease the splines.

You can also grab towards the Ujoints and shake back and fourth. There shouldn’t be a lot of movement at all. That can cause vibration.

 

[tohox]

Have you greased it lately?

That’s an easy one to start with. Don’t overgrease the splines.

You can also grab towards the Ujoints and shake back and fourth. There shouldn’t be a lot of movement at all. That can cause vibration.

When I first imported the truck I had to change a rear diff. seal after which I had a very hard time reinstalling the prop shaft as I couldn't extend or retract it. I brought it to a local shop and they noticed it was packed solid with grease. They managed to empty it with compressed air and parts cleaner (what a mess that made!) before reapplying fresh grease and it has been working fine since.

So the last grease application probably dates back 3-4 years. I just regreased it as well as the joint bearings earlier today which made no difference on the perceived backlash. I'll drive it tomorrow to see if that changed anything.

Thanks!

 

[tohox]

Hi,

I've noticed a hum when coasting from highway speeds. The sound will often appear as soon as I depress the clutch but once it has started the hum will remain even if I release the clutch and but will disappear if I accelerate or slow down enough. The sound becomes a vibration and eventually a loud rattle when coasting from lower speeds and can also be triggered by driving over a bump. At first I though I heard it coming from the front driver's side but this is happening in 2WD with hubs disengaged so I doubt it is actually coming from anything at the front of the vehicle (I've confirmed the hubs were indeed disengaged).

My first thought was that there might be something wrong with the rear prop shaft so I compared the front and the rear and there is definitely some play in the spline of the rear prop shaft while there is none at the front. Hard to quantify as it is only a fraction of a degree but it is still quite noticeable when I twist the shaft holding it from both ends. This play appears to be only when twisting along the spline axis which corresponds to the spline teeth backlash. No movement radially so I expect very little runout if at all (I haven't removed the prop shaft yet).

I've had a look in the RM183E body/chassis manual and while it mentions maximum runout and bearing axial play it says nothing about spline backlash...
View attachment 3713858

Do you have such play in the spline of your rear prop shaft?
Any experience with such noise/vibration/rattle when coasting?

1991 PZJ91-MNS

Thanks!

So! driving around with the rear prop shaft removed made no difference at all but I did find the source of both the high speed noise and the low speed vibration+rattle!

Turns out I had removed my roof top tent a few days ago and hadn't driven at highway speeds since removing it. With the tent removed the rack starts singing with a surprisingly loud low pitch hum around 90km/h which is why I noticed it when decelerating.

The vibration and rattle at low speed were caused by a rotten exhaust hanger which would sometimes start shaking at idle or when I hit a bump.

While I have the prop shaft removed I'll take it apart to see how much grease is left and what the spline looks like inside.

Voilà!

 

[Sundowner]

Weird, how sounds resonate and seem to come from strange places; easy fix, though, in this case!