Drive train rumble - Ideas welcome (1 Viewer)

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I get it, phasing is simple but in my experience if its outa phase it rattles constant not intermittent. I would lay money its the wear on the slip spline.
 
It does have an OME lift - 2.5” maybe(? 33s fit). I measured angles before I replaced the U joints. The angles of xfer output shaft and the rear diff are within a degree or two. Drive shaft angle isn’t extreme.

I has a similar vibration and after process of elimination it ended up being the drive flange angles. I added a 4 degree steel shim from @orangefj45 and the problem was immediately solved. I thought it was driveline or rear third member related, but after I put in new u joints, had the shaft checked/balanced, new rear axle bearings, put in a new third member...the vibe was still present.

Can you post up photos of your drive flange angles with a digital angle finder? A degree or two can make all of the difference.
 
I had a similar problem problem, but only happened when I was pushing on the gas pedal. Sounded almost like a truck engine braking and came with a rattle/rumble. Castor shims fixed it.
This is almost exactly how I would describe the issue. Only it gets more pronounced at a very specific speed. Sounds almost like a jackhammer sound. If I grab the tcase knob I can quiet it down a little.
 
Got several possibles here: worn spline (some rotational play is ok, there should be no up/down play), out of phase yokes, and now maybe pinion angle interactions...

When under power the rear pinion rolls down. The 40s rear DS is so short that it doesn't take much pinion rotation to excite a DS problem, especially if the rear is already on the closed side of that few degrees of delta...

You've got some options. Will be interesting to see what does the trick.
 
Multiple possibilities.

I’d suggest starting by isolating the “issue” a little more.
If it’s noticeable in any gear at 2000 PRM and you think it’s engine related, what happens when you bri g the RPMs up to 2000 when not in gear ( sitting still )?!

Georg @ Valley Hybrids @ Cruiser Brothers
 
Got several possibles here: worn spline (some rotational play is ok, there should be no up/down play), out of phase yokes, and now maybe pinion angle interactions...

When under power the rear pinion rolls down. The 40s rear DS is so short that it doesn't take much pinion rotation to excite a DS problem, especially if the rear is already on the closed side of that few degrees of delta...

You've got some options. Will be interesting to see what does the trick.
This could be the case, but the front of the diff goes up under load. I would think, however, only under hard acceleration, climbing, or towing. Just cruising it shouldn't be torquing that much if at all. But, like you said, if it is already on the edge of being out of parallel, might happen.
 
Multiple possibilities.

I’d suggest starting by isolating the “issue” a little more.
If it’s noticeable in any gear at 2000 PRM and you think it’s engine related, what happens when you bri g the RPMs up to 2000 when not in gear ( sitting still )?!

Georg @ Valley Hybrids @ Cruiser Brothers
Engine is smooth as silk with no load. Timing is set at 7deg with an newish DUI and the Sniper is doing its job with fuel delivery.
 
Some annotated photos of angles. Looks like about 1.25 deg difference. These are looking at the gauge from the driver side.
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Engine is smooth as silk with no load. Timing is set at 7deg with an newish DUI and the Sniper is doing its job with fuel delivery.
Message me with your number and I’ll give you a call to help figure this out.

Georg @ Valley Hybrids @ Cruiser Brothers
 
This is almost exactly how I would describe the issue. Only it gets more pronounced at a very specific speed. Sounds almost like a jackhammer sound. If I grab the tcase knob I can quiet it down a little.
My bet is drive shafts out of phase, I forgot but I fixed that first, then did caster shim to improve steering. It is a super simple check/fix (phasing). But Georg will know, he's the expert. Very kind of him to lend some help. Good luck and be sure to report back on what it ends up being.
 
For the sake of documentation…driveshaft seems correctly phased to me. ??

Splines have just a slight amount of play. Can’t see it, but you can feel it just barely when trying to twist back and forth by hand.
26A099FC-FB22-4959-B7A2-577E0D6A6B43.jpeg
 
Thats short enough that the 2 deg may cause that vibe, but I am sticking with worn splines on the slip. Is the rear pinion loose ?
 
Thats short enough that the 2 deg may cause that vibe, but I am sticking with worn splines on the slip. Is the rear pinion loose ?
It has some rotational play - maybe a couple of degrees. No other looseness.
 
Thoughts on axle wrap? Was thinking I might put a camera down there and drive around to see what I see.

Here’s my logic:
- the diff is already angled up by 1-2 degrees relative to the tcase
- the symptoms occur only under load and maybe most pronounced in the torque-iest range
- when I hit the gas, if it is axle wrap, the diff would angle up even more

Eh?
 
Thoughts on axle wrap? Was thinking I might put a camera down there and drive around to see what I see.

Here’s my logic:
- the diff is already angled up by 1-2 degrees relative to the tcase
- the symptoms occur only under load and maybe most pronounced in the torque-iest range
- when I hit the gas, if it is axle wrap, the diff would angle up even more

Eh?
Or throw some shims on the spring pack to angle down. Whatever is easiest.
 
Is that a Mosley rebuilt motor? Traction bars if so! 😂
 
If it is still SUA it would only rotate under a healthy launch or load, like leaving the stop sign with boat in tow or hole shottin it, IMO if at all. How many miles on that driveline ? If you speak with Georg ask him if he has found a source for new oem slip spline or what he replaces them with, I'm in need of same. My rattle happens when lettin off for freeway offrampsit only happens from like 48 ish to 40 ish, dont hear it under throttle. I feared it would beat the dline to s***, its been same slip spline, original I believe from 1970, I had the tube changed to be longer and 188 wall.
 
Georg offered a phone call. You should take him up on this.
 
When under power the rear pinion rolls down. T

I think you meant "rolls up".

Or throw some shims on the spring pack to angle down. Whatever is easiest.

This.

You're already out of range to begin with. In my experience our SUA setups still get axle wrap unless your rear springs are pretty beefy. I'd aim for 2º lower than the transfer case output. That way when you wind it up at higher rpm the driveshaft will come into alignment. Slower speeds and lower rpm don't stress the u-joints near as badly as at higher revs.

Additionally, crank down the rear motor mounts pretty firm. The engine rotates longitudinally so jacking it up won't show any down play.

Third crazy thing is a wildly out of balance clutch & pressure plate. I have "heard" it can be an issue on other vehicles but not seen it mentioned around here.
 

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