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Old 02-15-2008, 09:51 PM
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New vibrations, not good vibrations

I have a 400SBC, 700R4, ford 9", tubbed, four link in a 92 S-10 extended cab. It has a two piece drive shaft with a urethane center carrier, Runs very well.

The last time we had it out, Oct. 2007, it developed a vibration after running it through the gears a couple of times. The vibration is like a harmonic, it comes and goes with a regular pattern. It does get worse with speed, but still comes and goes, like every 3-4 seconds. If I pop it up in neutral at say 60 MPH and let the engine go to idle, the vibration is still there. It doesn't matter if the converter clutch is locked or not. The balance weights are still on the wheels.

Today we pulled the axles and they are still straight and the splines looked as new. I ran the engine and trans through the gears to about 60MPH on the stands with the rear drive shaft off. The front shaft is running straight and could feel no vibration. The rear shaft looks good as do all u-joints.

Is there anything in the 700R4 that could cause this vibration? It is stock except for all the mods that could be done to it without changing any rotating hard parts.

The rear end is a stock ford trac-loc with 4.57 R&P. I have the housing tipped down a couple of degrees at rest, but it has been that way since day one.

Any help would be greatly appreciated.

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Old 02-16-2008, 02:46 AM
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well im just taking a guess here cause i hate vibrations it can someplace and the vibration traveling throu the frame. check the drive shift center bearing, u joints, trans mounts engine mounts . could be a front wheel bearings. u could do it the old fashion way run it till it brakes then u know where the problem was m guessing the center bearing for the split drive shaft
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Old 02-16-2008, 11:02 PM
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Iwould remove the whole drive shaft (both pieces), and physically check all the u-joints, and the steady bearing. Look for rust bloom around the cap seals, cracked seals, tight or "notchy" feeling movement, ect. My guess is you will find a joint with a tight spot.
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Old 02-17-2008, 09:52 AM
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Thanks guys for the suggestions. We are in the process of checking everything. Keep in mind that all parts were new last year, as we just got this project on the road in July 07.

I'm still trying to figure out if there could be anything inside the 700R4 that could be causing this.
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Old 02-17-2008, 11:02 AM
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The trans is not likely your problem. You stated the vibe was gone with rear shaft out of the truck. Have the rear shaft balanced and then be sure the ujoints are phased correctly. All 3 joints MUST be aligned when installed as an assembly. Pinion angle could be an issue also, as could the pinion itself. Start with the driveshaft.
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Old 02-17-2008, 11:39 AM
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Have the rear shaft balanced and then be sure the ujoints are phased correctly


To balance a two-piece shaft, both shafts must be assembly balanced together, and then installed the same way they were balanced. Try rotating the rear shaft 180 degrees to see if the vibe goes away. Also look for any spots where the shaft may have thrown a weight. Otherwise take both shafts in an have them checked for balance and straightness.
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Old 02-17-2008, 12:37 PM
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Good points all. Is the rear slip yoke suppose to be aligned with the front slip yoke or 90 out? Either way would align all u-joints.

As far as drive shaft balance, this truck was driven over 1000 miles until this vibration started. The drive shaft was never balanced to begin with. If the drive shaft was out of balance, it should have showed up day one I'd think.

To update, all three u-joints look and feel as new. Third member looks good. Pinion bearings feel like they did when I put it together.

Could it be a tire? Mickey Thompson Sportsman 31X18.5X15s on the rear mounted on Weld Prostar rims.
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