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Long standing pulsating vibration issue that I need help solving

Blue85 said:
It's a strange driveshaft. Almost like the slip spline and yoke aren't a matched set. I mean, what's the point of some of the spline always sticking out? It kind of looks blue-coated, but kind of not. Plus, you don't need much slip travel in the rear of a leaf-spring truck. If you can get any movement (besides linear, of course) in the spline it's going to put it out of balance.
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Normally these have rubber boot on but it's missing
 
Let me take it back off again and I'll give it a second look. I didn't notice the wear.


And what does that rubber boot look like
 
alright finally got the gopro slapped on. from what I can tell from the video my pinion angle hardly changes(track bars at work). I can post them if you all would like
 
I put the rear up on jackstands and can duplicate the vibration im feeling. Put the transfer case in neutral and its mostly gone.

gonna try and take the tires off and repeat and see what happens and work my way from there
 
The roller needle bearing under the input and output shafts will flat spot in np205’s and vibrate at high speed. I’ve seen it a few times when I used to work full time in a transmission shop as a rebuilder.

I’m not saying this is your issue. But if your transfer case hasn’t been fully rebuilt in a long time they may be worn like that. I’ve seen them ruin the input pilot as well. With a bad wear pattern that causes vibrations.

The picture below shows how many straight rollers are in an np205. And they will flat spot all over each one.

I see your first post says rebuilt transfer case. Did you replace all those rollers?

IMG_3587.png
 
CharlesC83 said:
The roller needle bearing under the input and output shafts will flat spot in np205’s and vibrate at high speed. I’ve seen it a few times when I used to work full time in a transmission shop as a rebuilder.

I’m not saying this is your issue. But if your transfer case hasn’t been fully rebuilt in a long time they may be worn like that. I’ve seen them ruin the input pilot as well. With a bad wear pattern that causes vibrations.

The picture below shows how many straight rollers are in an np205. And they will flat spot all over each one.

I see your first post says rebuilt transfer case. Did you replace all those rollers?

View attachment 498190
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I actually bought a new transfer case that was rebuilt. I can only assume that they replaced those bearings. Will note the vibration didnt change much after the transfer case swap as well
 
Took the drive shaft off and the vibration is still there with the transfer case in 2wd and in neutral.

seems smooth with transmission in neutral.

tried to put it in 2nd and 1st and given the same rpm(3000rpm) it seems smoother in 2nd and 1st
also noticed a ticking noise from the transmission.(took a stethoscope and probed around)
 
What would cause a vibration in a th350 in 3rd but not in 2nd or 1st?
 
Ramba_ral said:
What would cause a vibration in a th350 in 3rd but not in 2nd or 1st?
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Higher road speed from achieving high gear equals faster drivetrain RPM’s and in some cases less pinion deflection due to less throttle input as speed levels off.
Just some suggestions.
 
tarussell said:
Higher road speed from achieving high gear equals faster drivetrain RPM’s and in some cases less pinion deflection due to less throttle input as speed levels off.
Just some suggestions.
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Could be what I'm dealing with out on the road.
Right now I'm testing with the drive shaft off, transfer case in neutral and vehicle up on jack stands trying isolate where its coming from and can still feel it only in 3rd. Should rule out any sort of pin angle/deflection I would think.
 
Ramba_ral said:
Could be what I'm dealing with out on the road.
Right now I'm testing with the drive shaft off, transfer case in neutral and vehicle up on jack stands trying isolate where its coming from and can still feel it only in 3rd. Should rule out any sort of pin angle/deflection I would think.
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Gotcha, sorry that I missed the truck being up on stands with no rear shaft - been a while since I read the background on this thread.

Will it vibrate in high gear at any engine speed - as in using only enough throttle to allow the trans to up shift at minimum RPM’s v/s mimicking using the same throttle effort as if it was cruising down the road?
And does it get worse with added RPM’s ?
If I read back comments correctly you said that the vibration goes almost completely away when the T-case is in neutral - is this still the same while testing on stands or is the T-case in 2WD ?
 
tarussell said:
Gotcha, sorry that I missed the truck being up on stands with no rear shaft - been a while since I read the background on this thread.

Will it vibrate in high gear at any engine speed - as in using only enough throttle to allow the trans to up shift at minimum RPM’s v/s mimicking using the same throttle effort as if it was cruising down the road?
And does it get worse with added RPM’s ?
If I read back comments correctly you said that the vibration goes almost completely away when the T-case is in neutral - is this still the same while testing on stands or is the T-case in 2WD ?
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its starts at around 3k rpm in high gear and gets worse more rpm is applied
as per the t-case its there with the tcase in 2WD or neutral. it goes away when I manually put the transmission in 1st,2nd or neutral.
 
Ramba_ral said:
its starts at around 3k rpm in high gear and gets worse more rpm is applied
as per the t-case its there with the tcase in 2WD or neutral. it goes away when I manually put the transmission in 1st,2nd or neutral.
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3k rpm and more?
I don't know if this is not normal.
I try not to reach 3k at all, I bought a k5 with the th350 and cruising at 65mph it would be at 3k so I put a 700r4 with the overdrive to bring it down to 2600 rpm
 
May be an internal issue in the trans. Somethimg with the direct clutches?
 
Ramba_ral said:
What would cause a vibration in a th350 in 3rd but not in 2nd or 1st?
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Yes, as mentioned before, having the whole drivetrain and engine at the same RPM can magnify some harmonics. If cruising above 70MPH is planned regularly, OD is the real option. I can't imagine spending most of the time above 3000RPM is very comfortable and GM didn't design for those kind of speeds.

I think mine does a pulsing vibe thing in 3rd gear when accelerating sometimes, but it's no big deal because 4th gear comes in a few seconds.
 
It does seem to make a whine in reverse but ill admit I havent reved it up while in reverse.

If its internal to the trans the only way to to find out is to take it out of the truck and do a deep dive?

So right now the consensus is it might be internal to the transmission but if I'm going to do something about it i probably should get some sort of over drive transmission like a 700r4
 
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