Noise when foot off the gas

[feddomw]

I have been chasing down a sound that has been driving me nuts. Hopefully some one will chime in that feels my pain.

I am not a mechanic.
I tried to record the the sound but I can't get it clearly.

I have had it for a while: basically when driving at any speed, when I take my foot off the accelerator I hear a sound that is not whining, nor grinding, just a "gearing" sound. The best way I can describe it is that it is similar to the sound of a very heavy truck coasting. It does not sound like something is wrong per se, but my previous 100 did not have it for sure.
It's a resonating humming type sound.

My current truck has 90K miles more mileage though.

T-case and front and rear diff have new fluids, drive shafts are greased (I have the clunk though, but that's another matter). Transmission recently flushed, it's smooth.

Because it's only present when I take my foot off the gas, I think it is unlikely that it's a wheel bearing. My best guess is that it's a drivetrain/freewheel issue because I only hear it when there is no "drive" on the drivetrain.

My shop (Cruiser specialists, but 100's are very rare here and they have more 40's and 80's than anything else) thinks it's just "wear". I currently have 255K kilometers, when you add up all the wear on all the driveline parts this creates room for slop and noise, that is their thinking.

I don't buy it.

 

[Trunk Monkey]

U-joints. Most commonly heard when decelerating.

 

[feddomw]

U-joints. Most commonly heard when decelerating.

Google seems to point out u-joints too. Good to hear a Mudder confirm it, thanks. That or driveshafts.

I don't have the time or space to fix it myself unfortunately, does anyone know what the time to replace them is? And while the DS are pulled, good excuse to regrease the splines I guess.

 

[C6H12O6]

If you have space to park your truck, you have space to pull the driveshafts. Time and tools might still be an issue, but it's only a few bolts on each end to pull the shaft. Take the whole shaft in to a driveline shop and they will swap the u-joints, clean it all up, and balance the shaft for you. Very much a 1 job. You might want to order OEM joints and print out the page from the FSM so they can see how it should be phased/lined up when they're done, but very painless process.

 

[spencer arndt]

It's a pain...but dude i did it in like 2 hours with X2 14 mm box wrenches, a hammer, pliers and a vice.. Check Cruiser Outfitters for U-Joints i dont know if they would have them for the 100 but if they do they'll have the the best service, highest quality parts and best price you can get.

 

[bamabrock]

my advice is to never let up!

 

[Trunk Monkey]

@cruiseroutfit has them, that's where I got mine.

 

[looking4lc]

i have same sound you mentioned,

which U-Joint should be replaced? all?
what other things I should be doing " while its out" ??

 

[feddomw]

i have same sound you mentioned,

which U-Joint should be replaced? all?
what other things I should be doing " while its out" ??

Stealership wants around 220 Euro's for each u-joint. Ouch. That's just the parts, not the labor.

If the DS is off, I would pull them apart and clean and re-grease the splines. I say this like I know what I am or will be doing, but I really don't. I think it will be pretty clear though once I have the parts in my hands.

The bolts connecting the DS flanges to the diffs should be fine to re-use, as I understand it.

 

[Trunk Monkey]

There's an easy way to tell if it's the u-joints and which one(s) it is. Remove one driveshaft, lock CDL, go for a drive, see if the noise is still present. If it's gone, you've maybe got your culprit. Still there, replace DS, remove the other one, repeat.

 

[feddomw]

There's an easy way to tell if it's the u-joints and which one(s) it is. Remove one driveshaft, lock CDL, go for a drive, see if the noise is still present. If it's gone, you've maybe got your culprit. Still there, replace DS, remove the other one, repeat.

By removing a driveshaft, you are effectively forcing the transfer box (or center diff) from "driving" only the other drive shaft, effectively creating a 2WD vehicle? Why lock Center diff? Forgive my ignorance if this is a stupid question, I am eager to understand this.

 

[2001LC]

You can inspect each of the four spiders (AKA U-joints) for play.

If replacing keep in mind; FSM recommends marking propeller shafts (AKA drive shafts) so they can be assemble in the exact alignment they were in.

 

[abuck99]

Ujoints will have a low sounding resonance & vibration. T-case will be higher pitched whine- & more noticeable when it's cold.

Do you notice the noise all the time, or more when it's cold? Do you sense any vibration in the drive line?

 

[feddomw]

Ujoints will have a low sounding resonance & vibration. T-case will be higher pitched whine- & more noticeable when it's cold.

Do you notice the noise all the time, or more when it's cold? Do you sense any vibration in the drive line?

Vibration in the driveline is there, but I am picky. Others might say "it's barely there".

The first feedback was the best: I hear it only when coasting/decelerating. It is not really a vibration, it is a sound. Ideally I would like a perfect diagnosis but I have no reputably shop nearby, nor do I have a way to lift the wheels off the ground. I will crawl under the car later and check the U-joints for play while it's parked.
The shop that did some work on it recently charged me for greasing spiders and slide yokes, I will assume they know what they are doing and would have noticed if something was REALLY wrong..... They are not in the "grease until it flows past the seals" camp, BTW.

 

[Trunk Monkey]

With one DS out, the open diff t-case will send the power that way, truck won't move. Locking the center sends power to the other end and you can drive. I've never been much for the whole "checking for play" in the u-joints. You'd have to have a hell of a lot of slop to be able to detect it by bumping the DS around by hand. Mine that was basically a dry joint had no "play" in it.

Bad u-joints sounds like you're driving the rumble strip on the side of the road when you let off the gas. Goes away when you step on the gas again.

Careful if you do remove one DS that you have the wheels chocked or CDL already locked, again with the open diff, truck will roll.

 

[FranceJohnson]

When my U-joints went bad it sounded a lot like being on shaky concrete road when I let off the gas. If you have a grease gun, might be worth greasing one point at a time along your drive shaft and see what *temporarily* dampens the noise. I would suggest not waiting as long as I did. My rear u-joint was on its last leg by the time I figured it out. If it brakes loose, you will give a wrecking-ball drive shaft under your truck, which is going to cause A LOT of damage. Not a bad idea to just replace them all while you in there.

 

[2001LC]

It seem we're speaking of different parts. Per FSM: Front drive shaft DS & PS (AKA front axle's, AKA CV joints), inboard & outboard tulips (AKA CV U-joint). Propeller shaft front & rear (aka front & rear drive shaft) spider joint (AKA U-joint).

 

[feddomw]

It seem we're speaking of different parts. Per FSM: Front drive shaft DS & PS (AKA front axle's, AKA CV joints), inboard & outboard tulips (AKA CV U-joint). Propeller shaft front & rear (aka front & rear drive shaft) spider joint (AKA U-joint).

Good point. I am assuming we had been talking about prop shaft and spider joints.

 

[04UZJ100]

It was front wheel bearings on ours.

 

[fst aslp]

Did you ever resolve? Mine is making a similar noise. Still very faint