Throbbing sounds at 45 mph plus!

[Rock TJ]

Hi all, I’m new to Jeeps. I’ve recently purchased a 2006 Jeep TJ 4 speed auto. 100,000 miles. Recent Reconditioned auto box. 2.5 inch suspension lift and 1inch body lift. 33” wheels / Tires (brand new Comforser at 25 psi). Yoke slip eliminator on it too. Also regeared for the 33” tires. Is well sorted for overland trips.

Issue: it’s pretty gutless and can just about cruise at 60 mph on a highway. Is this normal considering the mods. Also from about 45 mph and getting louder as speed increases is a throbbing vibration / sound that build and fades, builds and fades every second or two. Becomes too excessive at about 65 mph. Annoying and will be tiring over a distance. Any clues please. Thanks.

 

[macleanflood]

I get a little of that throbbing noise. How are your pinion angles and do you have adjustable control arms?

What engine, transmission and gear ratio?

-Mac

 

[Rock TJ]

I get a little of that throbbing noise. How are your pinion angles and do you have adjustable control arms?

What engine, transmission and gear ratio?

-Mac

4 litre petrol and 4 speed auto. Not sure what gearing it now has. I’ll try and find out from previous owner. I think most things on it are adjustable! I’ve been told it’s a “Jeep thing” but I certainly want to see if we can further improve on it! It’s useful to hear ides such as pinion angles as I can look into that. No such issues in my Volvo AWD!!!

 

[Steel City 06]

That does sound driveline related. Take some photos of your driveshafts and post them in here. Especially try to get ones that show the angles from the transfer case to the differentials for both front and rear.

If that “throbbing” actually is driveshaft related, it usually happens because both shafts are still spinning in 2WD and both are vibrating to a degree. In 2WD, it’s fairly normal for one shaft to spin ever so slightly faster than the other (usually the rear when under load), hence you get alternating periods of constructive and destructive interference in the vibrations you actually feel. Much like two musical instruments playing the same note but slightly out of tune with one another.

One easy way to test if that is the case is as follows: Go for a test drive on the highway, recreating the vibrations. As soon as you hit a low point in vibrations, shift into 4Hi. It should “pause” the pulsing at minimum vibrations. Likewise, shifting into 4Hi at peak vibrations will pause it there as well. Basically you’re testing this by forcing both driveshafts to go exactly the same speed, either in sync (peak vibrations) or out of sync (minimum vibrations) or somewhere in between. (Be sure to shift back into 2WD before making a tighter turn…)

 

[Rock TJ]

Thanks. I’ll give that a go on the highway. Will be a good pointer.
In the meantime is it an issue to be worried about. Is it causing damage or just an annoyance assuming it is this?

 

[Strizzo]

That does sound driveline related. Take some photos of your driveshafts and post them in here. Especially try to get ones that show the angles from the transfer case to the differentials for both front and rear.

If that “throbbing” actually is driveshaft related, it usually happens because both shafts are still spinning in 2WD and both are vibrating to a degree. In 2WD, it’s fairly normal for one shaft to spin ever so slightly faster than the other (usually the rear when under load), hence you get alternating periods of constructive and destructive interference in the vibrations you actually feel. Much like two musical instruments playing the same note but slightly out of tune with one another.

One easy way to test if that is the case is as follows: Go for a test drive on the highway, recreating the vibrations. As soon as you hit a low point in vibrations, shift into 4Hi. It should “pause” the pulsing at minimum vibrations. Likewise, shifting into 4Hi at peak vibrations will pause it there as well. Basically you’re testing this by forcing both driveshafts to go exactly the same speed, either in sync (peak vibrations) or out of sync (minimum vibrations) or somewhere in between. (Be sure to shift back into 2WD before making a tighter turn…)

I've thought about trying that but wasn't sure if it was a good idea to shift at 60+ MPH.

This sort of pulsing vibration is common after regearing for larger tires. Particularly with the 42RLE 4-speed automatic because of how deep you need to regear due to the fairly steep 0.69 overdrive. Others have reported the issue on totally stock TJs and LJs. You can see if the primary source of the vibration is coming from the front or rear driveshaft by removing the front shaft and taking a test drive. if the vibration goes away, you can reinstall the driveshaft and then remove the other and see if it comes back.

For many, the ultimate solution is to install a yukon spin free hub kit on the front axle, which lets you run whatever caster you need to, and stops the front shaft from spinning while driving down the road.

I have an 05 4.0 with the 42RLE and 33s. Re geared to 5.13, SYE, adjustable arms, etc. and i'm still chasing adjustments to get rid of the vibration.

 

[JMT]

Thanks. I’ll give that a go on the highway. Will be a good pointer.
In the meantime is it an issue to be worried about. Is it causing damage or just an annoyance assuming it is this?

Don’t shift into 4H at speeds exceeding 45mph

 

[TheBoogieman]

I’ve been told it’s a “Jeep thing”

It's not.

 

[JMT]

I’ve been told it’s a “Jeep thing”

That’s an excuse for not doing things correctly and using sub-par parts.

 

[TheBoogieman]

Yoke slip eliminator on it too.

View attachment 636327

So, it's not a Rubicon? They don't have a slip yoke to eliminate.

 

[jeepguy03]

That’s an excuse for not doing things correctly and using sub-par parts.

+1

Usually a description from sellers who know the entire front end is worn out but don't want to fix it.

 

[Steel City 06]

Don’t shift into 4H at speeds exceeding 45mph

As long as you have factory style hubs, you can shift at any legal speed. There is no wear on the transfer case in doing so unless you are currently on a curve or spinning the rear tires. All parts of the transfer case are already at the same speed.

Shifting to and from 4Hi under heavy load is not recommended. No load is best, but light load is also fine as long as the tires aren't slipping.

The caveat would be if you have YJ-style hubs or aftermarket locking hubs like the Yukon ones.

I shift to and from 4Hi at 70+ very frequently. Helps a lot in heavy rain or just to minimize annoying vibrations if my airbags aren't at the right pressure...

 

[JMT]

As long as you have factory style hubs, you can shift at any legal speed. There is no wear on the transfer case in doing so unless you are currently on a curve or spinning the rear tires. All parts of the transfer case are already at the same speed.

Shifting to and from 4Hi under heavy load is not recommended. No load is best, but light load is also fine as long as the tires aren't slipping.

The caveat would be if you have YJ-style hubs or aftermarket locking hubs like the Yukon ones.

I shift to and from 4Hi at 70+ very frequently. Helps a lot in heavy rain or just to minimize annoying vibrations if my airbags aren't at the right pressure...

I was wrong. The 2005 User Manual specifies shifting from 2H to 4H up to 55mph.

Of course, as you stated, the ratio doesn’t change so the gears will remain meshed together.