Low Pitch Resonance at Highway Speeds (1 Viewer)

[CaptHamster]

Experiencing a really obnoxious low-pitch resonance in my FJ62 that starts at 65MPH . Lots of work done to the vehicle recently, which I will list below:

- H55F swap, transfer rebuild and rear driveshaft from Georg at Valley Hybrids in April of this year (4 months)
- BFGoodrich A/T K/O2's in 33x10.5x15 on stock wheels, mounted ~2K miles ago, recently re-balanced by local shop
- Knuckle job done 2 months ago with Sumo Gear kit, replaced one front axle spindle (driver's side), was damaged by overtightened bearing / water intrusion into hub (oops)
- 4° axle shims on rear axle, pointing pinion downwards; this made very little/almost no difference, debating removing them
- Old Man Emu deluxe heavy kit, done about 2-3 years ago, a little saggy now but still makes truck a little higher than stock

Not much vibration felt, whatever it is just makes the body resonate in such a way that it actually kind of hurts my ears. Below 65MPH, it slowly diminishes and is totally gone by 60MPH. I've tried speeding up past it, got to about 90MPH and it wasn't as bad but still present. Have tried clutch in, neutral and engine at idle speeds, still present, which leads me to believe it's driveline related. I can't imagine the recently refurb'd rear driveshaft is out of balance. The only things I can think are rear axle bearings or pinion bearing, all of which are factory original and never replaced.

Just want to make sure my thought process is right before I go throwing even more money at this thing trying to get stuff balanced right!

Also, recent pic included below, have to pay my IH8MUD taxes somehow

 

[pithicus]

Could it be diff related. Like a whine? 90mph! You got a turbo in that thing?

 

[cps432]

Experiencing a really obnoxious low-pitch resonance in my FJ62 that starts at 65MPH . Lots of work done to the vehicle recently, which I will list below:

- H55F swap, transfer rebuild and rear driveshaft from Georg at Valley Hybrids in April of this year (4 months)
- BFGoodrich A/T K/O2's in 33x10.5x15 on stock wheels, mounted ~2K miles ago, recently re-balanced by local shop
- Knuckle job done 2 months ago with Sumo Gear kit, replaced one front axle spindle (driver's side), was damaged by overtightened bearing / water intrusion into hub (oops)
- 4° axle shims on rear axle, pointing pinion downwards; this made very little/almost no difference, debating removing them
- Old Man Emu deluxe heavy kit, done about 2-3 years ago, a little saggy now but still makes truck a little higher than stock

Not much vibration felt, whatever it is just makes the body resonate in such a way that it actually kind of hurts my ears. Below 65MPH, it slowly diminishes and is totally gone by 60MPH. I've tried speeding up past it, got to about 90MPH and it wasn't as bad but still present. Have tried clutch in, neutral and engine at idle speeds, still present, which leads me to believe it's driveline related. I can't imagine the recently refurb'd rear driveshaft is out of balance. The only things I can think are rear axle bearings or pinion bearing, all of which are factory original and never replaced.

Just want to make sure my thought process is right before I go throwing even more money at this thing trying to get stuff balanced right!

Also, recent pic included below, have to pay my IH8MUD taxes somehow
View attachment 2754107

Rear bearings are easy to do. I’d do them soon if you just did the front end. Rear diff could certainly howl at those speeds if it’s worn.

I replaced my body mounts with a poly set from 4crawler.com and I was genuinely surprised how much of a difference it made in handling and sound absorption. Think about changing them too if you haven’t. Well worth it.

 

[OSS]

Rotate the tires and increase their pressure to rule them out

 

[CaptHamster]

Could it be diff related. Like a whine? 90mph! You got a turbo in that thing?

No, not a whine, more like a low pitch hum or resonating noise if that makes sense. No turbo, but a long stretch of downhill highway and a prayer got me as close to 90 as I could!

Rear bearings are easy to do. I’d do them soon if you just did the front end. Rear diff could certainly howl at those speeds if it’s worn.

I replaced my body mounts with a poly set from 4crawler.com and I was genuinely surprised how much of a difference it made in handling and sound absorption. Think about changing them too if you haven’t. Well worth it.

Rear bearings will definitely be added to the list. I know they've never been changed, and the more I listen to the noise, the more it possible sounds like a growling bearing. I just wasn't sure if I should be thinking rear axle bearings or pinion bearing.

Body mounts are a great idea, I've been meaning to do that to help smooth things out on bumps. I'll check out the poly ones.

Rotate the tires and increase their pressure to rule them out

Tires were rotated when they were re-balanced a few days ago, I keep pressures around 36 PSI. Will increase a bit here and there and see if it changes the noise!

 

[duncanrm]

Front hubs unlocked?

 

[cps432]

Front hubs unlocked?

Very good point...

 

[CaptHamster]

Front hubs unlocked?

First thing I checked! Definitely made that mistake before...noise is coming from the rear of the vehicle anyway.

Tires are pumped up to 45psi (just short of the max PSI of 50), I'll run those today and report back if the noise changes at all

 

[Godwin]

Park on level surface, set parking brake, transmission in neutral and driveline without any tension, then crawl under and check the driveshaft, pinion bearing, t-case output for looseness and wiggleness. Look closely at driveshaft bolts.

 

[portlandcruiser]

Update us once you get this solved. I have a similar hum after work was done on the transmission. I'm going to check the drive line this weekend.

 

[dbleon]

Ive got my money on either, Tcase output preload or ujoints

interested to see what you come up with

 

[tmxmotorsports]

Rear pinion bearing or rear axle bearings

 

[CaptHamster]

Have been driving for a couple days with tires up to ~45 PSI, changing pressures made no change to the noise.

As @Godwin advised, I just crawled underneath and checked for looseness/movement in the rear driveshaft and pinion areas. There was basically zero up/down or side/side lateral movement, which is good. A decent amount of rotational play in the driveshaft though, with a slight "tink" noise at either end of the rotational play. I do hear a noise similar to that when loading up the driveshaft and rear end (starting from a stop, changing direction from forward to reverse gears etc) but I don't think that's the source of the low humming/resonating at highway speeds. Driveshaft bolts are all tight, checked with torque wrench just to be sure.

Based on this, am I on the right path of narrowing down my search to pinion bearing and/or rear axle bearings?

 

[cps432]

Have been driving for a couple days with tires up to ~45 PSI, changing pressures made no change to the noise.

As @Godwin advised, I just crawled underneath and checked for looseness/movement in the rear driveshaft and pinion areas. There was basically zero up/down or side/side lateral movement, which is good. A decent amount of rotational play in the driveshaft though, with a slight "tink" noise at either end of the rotational play. I do hear a noise similar to that when loading up the driveshaft and rear end (starting from a stop, changing direction from forward to reverse gears etc) but I don't think that's the source of the low humming/resonating at highway speeds. Driveshaft bolts are all tight, checked with torque wrench just to be sure.

Based on this, am I on the right path of narrowing down my search to pinion bearing and/or rear axle bearings?

There is a bit of rotational play in a normal driveshaft, but that’s from the gears in the diff and t case. The u joints should be solid. Check them again to see if you have any play there. U joints can definitely cause the noise you’re hearing. It may be easier to get a feel for it with the driveshaft dropped. Alternatively, you could put a screwdriver in there and see if you’re able to move the u joint with applied leverage. It shouldn’t budge at the joint but rotational play in the gears is normal. I’d make sure it’s not u joints before you open up the axle. If you do pull the rear axle apart you might as well plan on replacing the rear bearings and seals. If your carrier bearings in the diff are worn out you’ll need to have it rebuilt. Seals and axle bearings are cheap. So are u joints. All easy and you can do it in a day.

If your axles seem to hang up when you install the new bearings hammer it in. Trust me, I know it sounds sketchy, but I went around and around for two weeks trying to figure out why my axle wouldn’t seat. Just had to man handle them a bit.

If you find that you need new pinion and carrier bearings, then call cruiser outfitters. They will send you a rebuilt diff that you can drop straight in. Should be around $600 for a rebuilt diff from CO.

 

[Godwin]

Have been driving for a couple days with tires up to ~45 PSI, changing pressures made no change to the noise.

As @Godwin advised, I just crawled underneath and checked for looseness/movement in the rear driveshaft and pinion areas. There was basically zero up/down or side/side lateral movement, which is good. A decent amount of rotational play in the driveshaft though, with a slight "tink" noise at either end of the rotational play. I do hear a noise similar to that when loading up the driveshaft and rear end (starting from a stop, changing direction from forward to reverse gears etc) but I don't think that's the source of the low humming/resonating at highway speeds. Driveshaft bolts are all tight, checked with torque wrench just to be sure.

Based on this, am I on the right path of narrowing down my search to pinion bearing and/or rear axle bearings?

Ruling out possibilities is good and now you can rule out the u-joints and driveshaft fasteners.

In my experience when rear semi-floater wheel bearings go out they do not make any noise. The tell tale sign is leaking gear oil at the wheel(s). As the bearing fail so does the seal.

 

[pithicus]

You could try a additive. Though I've heard the so called diff quietening additives are usually not much use.