NV3550 Noise

[Jambi]

PLEASE perform some diagnostics before you drop the transmission. You have an opportunity to learn some valuable information before you get started.

Step 1. UNLOCK front hubs.
Step 2. Drive the Bronco in 2WD and make the noise. Determine whether the noise changes frequency with engine RPM, or with Bronco speed. (It's one or the other...)
Step 3. Shift the transfer case to 4WD. See if that changes anything.
Step 4. Shift the transfer case to 4Lo. See if that changes anything.
Step 5. Remove the rear driveshaft. Shift back to 4Hi. Lock front hubs. Drive in Front wheel drive (hi) and see if the noise changes.
Step 6. With hubs locked, Shift to 4 lo. Drive in Front wheel drive (lo) and see if the noise changes.
Step 7. Set the parking brake. Remove the front driveshaft. Shift to 2Hi. See if the noise persists if there are no driveshafts in it

Thank you for this post! Glad I saw it before I started taking things apart. I cut the audio file down to 10 seconds and was able to attach it. I'm in 3rd gear in the clip, but as I stated before it's also present in 2nd.

 

[jamesroney]

I couldn’t see anything in the video, but I could hear an awful sound. So I closed my eyes, listened three times, and said “who built that transfer case?”

You still need to do steps 2+ in my previous post.

 

[Timmy390]

Sounds like a screaming bearing to me.......

Tim

 

[jamesroney]

Sounds like a screaming bearing to me.......

Tim

Probably. But he said he went from C4 to NV3550, AND he swapped the output shaft. So he had to be in the transfer case. Might be a bearing, but also might be an extra long bolt thru the case rubbing against a gear. Also might be missing a bearing. (I've found all 13 rollers laying in the bottom of the pan before.) Also might be the tail shaft is too long, and crunching against the t-case input. But I'm guessing it's the output shaft bearing pre-load. Will know more when he posts the results of the diagnosis.

Certainly nothing to do with oil...

 

[Timmy390]

Probably. But he said he went from C4 to NV3550, AND he swapped the output shaft. So he had to be in the transfer case. Might be a bearing, but also might be an extra long bolt thru the case rubbing against a gear. Also might be missing a bearing. (I've found all 13 rollers laying in the bottom of the pan before.) Also might be the tail shaft is too long, and crunching against the t-case input. But I'm guessing it's the output shaft bearing pre-load. Will know more when he posts the results of the diagnosis.

Certainly nothing to do with oil...

Yes I was very generic in my screaming bearing statement. Sounds just like my Samurai trans when in 5th gear before I rebuilt it.....maybe the Sam was worse.....it was about to explode a bearing....

Oh oil is ruled out for sure unless it's lack there of .....output shaft preload is a good call IMO....lack of preload would mimic the sound of a bad bearing......

Tim

 

[Jambi]

PLEASE perform some diagnostics before you drop the transmission. You have an opportunity to learn some valuable information before you get started.

Step 1. UNLOCK front hubs.
Step 2. Drive the Bronco in 2WD and make the noise. Determine whether the noise changes frequency with engine RPM, or with Bronco speed. (It's one or the other...) Frequency definitely changes with speed
Step 3. Shift the transfer case to 4WD. See if that changes anything. Noise still there, but seemed quieter
Step 4. Shift the transfer case to 4Lo. See if that changes anything. Noise still there and seemed much louder
Step 5. Remove the rear driveshaft. Shift back to 4Hi. Lock front hubs. Drive in Front wheel drive (hi) and see if the noise changes.
Step 6. With hubs locked, Shift to 4 lo. Drive in Front wheel drive (lo) and see if the noise changes.
Step 7. Set the parking brake. Remove the front driveshaft. Shift to 2Hi. See if the noise persists if there are no driveshafts in it.

Finally had a chance to do steps 1 - 4 tonight; see responses above. I should be able to do the rest tomorrow.

 

[jamesroney]

Finally had a chance to do steps 1 - 4 tonight; see responses above. I should be able to do the rest tomorrow.

Re-evaluate step 4, and compare to step 2. At the exact same MPH, what is the frequency of the crunching?

As an example, if you are driving 20 MPH in 4th gear in 4WD-Lo, count the crunches in your head, or with a stopwatch. (or of course with audio on your video recording)
Then do exactly the same thing, driving 20 MPH in 2nd gear in 2WD-Hi and count the crunches.

"Louder" is nice to know, and important. But I want to know if the noise is "about the same" in frequency, or "about 2.5 x" in frequency.

Your diagnosis needs to point me either to the output of the transfer case, (frequency with Road Speed) or the input of the transfer case. (frequency 1/2 of road speed in Lo.) If it's the input side, then we need to isolate input of transfer case vs output of transmission.

Thanks.

 

[EPB72]

Re-evaluate step 4, and compare to step 2. At the exact same MPH, what is the frequency of the crunching?

As an example, if you are driving 20 MPH in 4th gear in 4WD-Lo, count the crunches in your head, or with a stopwatch. (or of course with audio on your video recording)
Then do exactly the same thing, driving 20 MPH in 2nd gear in 2WD-Hi and count the crunches.

"Louder" is nice to know, and important. But I want to know if the noise is "about the same" in frequency, or "about 2.5 x" in frequency.

Your diagnosis needs to point me either to the output of the transfer case, (frequency with Road Speed) or the input of the transfer case. (frequency 1/2 of road speed in Lo.) If it's the input side, then we need to isolate input of transfer case vs output of transmission.

Thanks.

How about shifting transfer case to neutral with wheels on ground TC input will spin , But output is not .. if noise is present , see if can pin point with stethescope,,,,

 

[jamesroney]

How about shifting transfer case to neutral with wheels on ground TC input will spin , But output is not .. if noise is present , see if can pin point with stethescope,,,,

100% yes.

 

[Jambi]

@jamesroney, unfortunately I didn't see your post #27 until after I removed the rear driveshaft and did steps 5 and 6.

I hope this doesn't confuse things--and it makes me want to reevaluate step 3--but for step 5 I have to be honest, I struggled to determine if I was hearing the noise or not. If it was there it was faint.

Step 6 on the other hand was a different story. Extremely noisy (sounded absolutely awful), clunky and I didn't go further than two houses down before turning around because I thought something serious was going to happen. Additionally, not sure if this makes sense, but I also felt like shifting the transmission was affected in terms of smoothness of shifting. I just kept thinking through step 6 that it seemed like something was binding up and my transfer case was on the verge of "blowing up inside".

I don't have a parking brake at the moment so I didn't do step 7.

 

[jamesroney]

@jamesroney, unfortunately I didn't see your post #27 until after I removed the rear driveshaft and did steps 5 and 6.

I hope this doesn't confuse things--and it makes me want to reevaluate step 3--but for step 5 I have to be honest, I struggled to determine if I was hearing the noise or not. If it was there it was faint.

Step 6 on the other hand was a different story. Extremely noisy (sounded absolutely awful), clunky and I didn't go further than two houses down before turning around because I thought something serious was going to happen. Additionally, not sure if this makes sense, but I also felt like shifting the transmission was affected in terms of smoothness of shifting. I just kept thinking through step 6 that it seemed like something was binding up and my transfer case was on the verge of "blowing up inside".

I don't have a parking brake at the moment so I didn't do step 7.

Step 7 does not REQUIRE a parking brake. It's just a convenience. Two wheel chocks, (pair of 4x4's) to keep your Bronco from rolling away. Once you pull both driveshafts...there's nothing to keep the Bronco parked.

Fortunately, you have isolated the problem, and it is in the front half of your transfer case. Your transmission is fine.

When you pull the transfer case, measure the actual spline engagement of the transmission output vs transfer case input. It's kind of hard to do if you are bench pressing the transfer case, while pulling it out, while measuring...but you can do it. Need to know withing 1/16 of an inch the exact depth of spline engagement. If you aren't sure, then pull the t-case, apply a bunch of white grease, or pattern compound, or something on the splines. Also put a daub on the very tip of the shaft...then re-install the t-case, and see how deep it goes. 99% chance it is good. 1% chance it is bottoming out.

 

[jamesroney]

Ok, this is where I’m checking out. You e got enough info to keep going.

I need to get back in the garage and get to work. So I won’t be answering anymore. I’m not mad, I’m just busy…

 

[Jambi]

Thank you @jamesroney, you've been a tremendous help!

 

[Jambi]

It was the front side thrust washer in the transfer case. I keep thinking, "how could I have not seen that the intermediate shaft wasn't through the trust washer when I put the tcase back together after the rebuild," but it must have slipped and I clearly missed it. So, when test driving the thrust washer had spun downward. Got it fixed and now there's no noise.

 

[DirtDonk]

Great! Good find.
Sorry you had to go back in, but glad it’s fixed.
Thanks for the follow up.

 

[bfoldy]

@jamesroney for the win! I’m impressed by the super-helpful instructions provided to the OP to diagnose and get his problem fixed.


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