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Discussion Starter · #21 ·
I'll try it on Jack stands with the front line out, but at this point I don't think I want to swap engines. I will try putting it in neutral at 65 mph again to rule out the engine. I've had the transfer case out because some Gomer that had it before put the transfer case back together without a gasket and just used blue sillycone and it leaked like crazy. They didn't even bother to put the brace bolt back in the engine block. Total idiots.
 

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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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Be aware (maybe you already are) with AWD: running rear wheels off the ground with fronts on the ground, can only be accomplished by disconnecting the AWD fuse, or connector at the TC. This however, can cause transfer case clutch damage as there is pre-load on the clutches. On the other hand, if the front wheels are up in the air, they will typically still turn even with AWD disconnected. The front drive-shaft would still need to be disconnected to eliminate it as a suspect, but it sounds like you've already done this.

One way you can surely rule out wheels and tires is if you remove them.. then run the vehicle in the air to 60mph. VERY IMPORTANT: If you attempt this test.. be sure to tighten lug nuts over rear drums (if you have them).

I am currently dealing with a new issue of a newly (and professionally) built drive-shaft that was balanced (twice)... but has "runout" issues. It has not been determined the cause yet... if it's the driveshaft assembly, or an issue with one of the used yokes that were utilized. I have a hum at 60mph... and a very serious hum at 70mph. This happens both on the road, and just as bad in the air. The hum does not change with vehicle in neutral.. it is completely driveshaft related. I have temporarily put the original driveshaft back in, and the hum is gone.

If your vibration continues (while highway cruising with engine in neutral) .. then it can't be engine harmonics or torque-converter (since they both slow to idle). The drive-train however, continues to spin at full speed.

A note on torque-converters... it is possible to re-position them on the flexplate. If an engine had a minor imbalance issue, and the torque-coverter also has the same minor issue.. the harmonic vibration could be increased or decreased by changing the mated relationship of one to the other... essentially a counter-balance. This wouldn't be a cure, but might minimize engine/tc balance related issues... but it sounds like this is not your issue.

Accurately diagnosing when you get the vibration is critical to narrowing down the potential culprit, as to which parts are turning and which parts are not.

Here is a shot of me using a dial-indicator on the yoke, checking to be sure the output shaft is not bent. It showed no runout here. Same test on the driveshaft will show if you have driveshaft runout issues.

 

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The weird thing is how some of these vans have the phantom vibration/rumble and some don't.
When I was chasing mine, I was reading things online where people had swapped out everything in the van and the problem persisted. Almost like it was built into the van, like something happened on the assembly line. Really weird.
 

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Discussion Starter · #24 ·
With me getting on in my years,I have some issues crawling under vehicles like I did when I was younger. I don't really want to go as far as pulling the tranny to adjust the torque converter. I will try pulling all 4 wheels off tomorrow and running it up to speed. I thought I had the problem nailed a few days ago when I found an out of balance rear brake drum and balanced it with a bubble balancer. I really appreciate all the info you guys have given me.
I want to ad that one other thing I have always noticed with this van is when accelerating from a stop, I feel a vibration until I get to about 50 MPH. It has always done this since I've had it.
 

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I had the same vibration in my van (well its still there a tiny bit) what solved it for me was the pinion weight in the tsb. It made a huge difference for me. I also adjusted my driveline angle after lifting it and that helped a bit too

I found I could only accurately test for vibrations with the van lifted on the alignment rack. lifted by the control arms in the front and rear end in the back. this allowed the van to be at ride height and all the angles are correct

finding a shop with an EVA (electronic vibration analyzer) will be a great way to go. I used one to determine it was at drive line speeds and a 2nd order vibration
 

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Discussion Starter · #26 ·
albrow100 said:
I had the same vibration in my van (well its still there a tiny bit) what solved it for me was the pinion weight in the tsb. It made a huge difference for me. I also adjusted my driveline angle after lifting it and that helped a bit too

I found I could only accurately test for vibrations with the van lifted on the alignment rack. lifted by the control arms in the front and rear end in the back. this allowed the van to be at ride height and all the angles are correct

finding a shop with an EVA (electronic vibration analyzer) will be a great way to go. I used one to determine it was at drive line speeds and a 2nd order vibration
What is weight in the tsb?
 

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Hey all,

Just wanted to check in to see if there is any new information from anybody on this subject. I'm running into the same humming/vibration with my '98 AWD. I first noticed it a couple months ago when I got my van back from having the front diff rebuilt. That particular job took like 4 months to complete (don't get me started....) so I initially thought there was something wrong with the new diff.

I notice the noise at low speed when my foot is barely on the gas; i.e. low RPMs. In that situation the rumble seems to go away when I lift my foot off the gas.

Where it's way more noticeable is at 60+mph. In that situation, the rumble is consistent whether I have my foot on the gas or not. I can shift into neutral and coast and the rumble will not go away.

Anyway, just wanted to check in to see if anybody has learned anything in the 2 years since the last activity on this thread. I'm trying to decide if I'm better off learning to tune the rumble out. It's just one more thing on a list of noises I'm trying to track down and eliminate. I've dumped so much money and time into this van to get it to drive nice and quiet, it kind of makes me sick to think about.

Cheers.
 

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01 Astro RWD Cargo, 97 AWD Mark III
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I'm thinking about the balance shaft in the engine
That would be an engine issue that would disappear in the neutral coast test.
 
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