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12 Bolt Video

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Old May 5, 2020 | 02:16 PM
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Default 12 Bolt Video

I have a truck 12 bolt that I put a eaton posi in. Check out the weirdness at the very start of the video, it does this in reverse or forward only once then I don't get it until I change direction again and hit it with some throttle. Feels like I don't get it if I ease onto the throttle.

https://photos.app.goo.gl/TqLJ9vQSt4ECUnx7A

When I took the rear apart both the ring and pinion gears were in great shape.

Any thoughts on what this is?
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Old May 5, 2020 | 08:11 PM
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I should have mentioned I installed a new tranny. Its a Hughes 4l80E Hughes 25-1bhd
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Old May 5, 2020 | 08:42 PM
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Just curious, does it sound as violent as it looks? I had an old school 12 bolt that pinion seal and bearing was trashed, that allowed pinion to move in the housing breaking the teeth off both gears. It made a lot of noise from a stop but was quiet down the road...for a little while LOL! Does that truck have a carrier bearing?

Last edited by Deguila; May 5, 2020 at 08:53 PM.
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Old May 6, 2020 | 04:15 PM
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It for sure has a thud to it, no carrier bearing, it's a C10 SWB.

I'm wondering if an over filled tranny may have caused the weirdness. Like could it have hit reverse/drive?
OR
if there something wacky with the posi unit which for the life of me I can't figure out what that would be.

The rotational play seen in the video after the initial weirdness does not alarm me and does not seem overly violent at all.
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Old May 6, 2020 | 06:27 PM
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Any luck figuring it out? Is that posi unit a clutch plate type or cones? Clutch type has to have the additive. Just a thought, Is U-joint trashed?
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Old May 8, 2020 | 07:08 AM
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It's an eaton posi so clutch style with stock spring pressure. I did put additive in as well when I re-filled it. Also the shaft and ujoints are new so no worries there either.

I'm starting to think this is more of a tranny problem. It's hard to see in the vid but it almost looks like the drive shaft is being twisted forward and back when I put it in gear. I'll drain some fluid and see if that helps, there might be too much fluid and while I don't know how that would create this problem I might as well dump some and see what happens.

If that doesn't work out I'll pull the diff cover and take a peek at ring gear and inspect the posi unit.

also I work slow so updates on this are gonna come in over time.
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Old May 8, 2020 | 08:13 AM
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LOL, gotcha. Take your time. I'm recovering from surgery so moving pretty slow myself.
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Old Jun 4, 2020 | 12:57 AM
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That does not look to be a differential issue. It recoils for a second hit, my guess is Tranny.

Miles
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