Front end knocking/rumble in 4H (1 Viewer)

[largenfirm]

Found a new symptom over the weekend.

Subject vehicle: 1982 FJ40, 2f, 4 speed, stock axles and drivetrain, new springs.

Running in 2H, all is happiness.

Put transfer case in 4H, but do not switch in hubs, and I get a knocking/rumbling sound from under the truck that varies with speed, and quits when stopped.

Quick visual inspection under the truck reveals no (obvious) looseness of bolts on the front driveline flanges, nor any visible issues with the u-joints.

Haven't tried 4L, yet. Wasn't doing this a couple of months ago, last time I used 4H/4L. Work done since then includes new springs (2.5" lift), and installation of OEM power steering, neither of which seems an obvious candidate for causing knocking, unless the lift changed the third member angle enough...naw, not likely.

Any way of distinguishing whether the problem is the front part of the transfer case, the driveline, the third member, or the axle proper, without tearing into it?

Thanks,
Kirk

 

[Degnol]

Is your front propeller shaft in phase?

Ed

 

[too tall]

The lift you installed is in fact the obvious candidate as you changed your pinion angle .Did you install caster shims in order to correct this ?

 

[largenfirm]

The lift you installed is in fact the obvious candidate as you changed your pinion angle .Did you install caster shims in order to correct this ?

No shims, as the lift was so small. The old springs were very tired, though.

<sigh> Guess I'll be looking at driveline angles, next. Sure hope it is that simple.

Kirk

 

[largenfirm]

Is your front propeller shaft in phase?

Ed

Yes, the driveline hasn't been out since the frame-off, and phase was preserved then.

Also, the noise wasn't present two months ago, and the driveline hasn't been molested since then.

Kirk

 

[Degnol]

The lift you installed is in fact the obvious candidate as you changed your pinion angle .Did you install caster shims in order to correct this ?

Wouldn't shims installed in the front in such a manner as to correct pinion angle also have a detrimental effect on handling? Caster correction shims are installed with the big end forward, thus pointing the pinion down, not up.
Ed

 

[Degnol]

You might try putting the TC in neutral, unlock the hubs and spin the propeller shaft by hand and feel for any binding and/or listen to see if you hear a clunk and isolate it.
U-joints have been greased, I assume. A dry u-joint can cause that, too.

GL

Ed

 

[largenfirm]

You might try putting the TC in neutral, unlock the hubs and spin the propeller shaft by hand and feel for any binding and/or listen to see if you hear a clunk and isolate it.
U-joints have been greased, I assume. A dry u-joint can cause that, too.

GL

Ed

Well lubed u-joints, yes.

Good tip, I'll give that a try.

Kirk

 

[muddy12]

Any difference with the hubs locked? Might help narrow it down to a problem in the hubs?

 

[Degnol]

Another thought.....see how much of your slip shaft is engaged. IIRC, you need at least 1" of engagement. If not, the shaft may be wobbling at the slip shaft. I lifted mine 3.5" and the engagement at the slip was minimal. I'm pretty sure if I got twisty it may have come out.

Ed

 

[Degnol]

Another test. Engage the lockout hubs and leave the TC in 2H, see if the noise is the same with the front axle passively spinning the shaft. If the noise is the same, it almost has to be in the driveshaft.

GL

Ed

 

[Pin_Head]

This is one of the things that you have to just bite the bullet and put all 4 wheels up on jack stands, start it running in gear and get out and listen to localize where the noise is coming from. Stay out from under and in front of the truck and it is not a bad idea to have someone in the cab to control it just in case.