Which diff is the culprit?

Frank

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The pinion and spur are moving fine but the rest of the truck isn't lol. Would that be the center diff? I took it apart and there were no broken parts so I put it back together but it's still doing it. It will move under very light throttle but when I give it more throttle it just makes a grinding noise. Hard to pinpoint exactly where the noise is coming from but sounds like the middle of the truck. Thanks in advance.
 

skeeler

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Have you checked the meshing of the pinion and spur? There should be one paper thickness between them.
 

Frank

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Have you checked the meshing of the pinion and spur? There should be one paper thickness between them.
Yes those are good. First thing I checked. Thanks.

Ch. to make sure you didn't shear one of the planetary gear pins that go to the drive shaft cups.
Are those the hinge pin looking pins? If so, those are good. I completely disassembled the center diff and it appeared good to me. Quite possible I'm overlooking something though.
 

tobyjoe

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Are your drive shafts turning? Any chance your spur is somehow not turning the center diff?
 

Frank

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Are your drive shafts turning? Any chance your spur is somehow not turning the center diff?
Drive shafts are not turning. If all gears look fine in center diff and both planetary gear pins are intact, what could it be? I'm gonna tear it back apart again and see if I see anything new.

Here's some pics of the center diff disassembled. For the life of me, I can't find anything unusual. But I'm sure I'm overlooking something. Thanks again guys.
 

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Rich Duperbash

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Drive shafts are not turning. If all gears look fine in center diff and both planetary gear pins are intact, what could it be? I'm gonna tear it back apart again and see if I see anything new.

Here's some pics of the center diff disassembled. For the life of me, I can't find anything unusual. But I'm sure I'm overlooking something. Thanks again guys.
If you pulled out all the gears from your center diff including both planetary gears and all gears and pins seem OK, the only thing I think is maybe the center cross pins are not seated. Other possibility is when you reset the spur side onto the diff cup, you might not have pressed down hard enough to fully mesh the spur side planetary gear gear into the 4 satellite gears. If that were the case, the 4 top screws would seem tight, but nut really be holding the gears in mesh. They might grab intermittently under low power, but slip with any further throttle. I'm wondering if the spur side planetary gear is lifting off the pin it rests on. That actually makes more sense in my book. Did you happen to put a Mugen shim behind the planetary gears? Shimming your diffs will help keep the gears meshed together better for sure.
 

Frank

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Embarrassed to say, and frustrated because I took apart all 3 diffs trying to find the culprit, it was the set screw on the rear input shaft cup. It came loose causing the cup to just spin freely. There must have been something going on in the center diff after I took it apart, maybe what @Rich Duperbash mentioned. Because the driveshafts weren't turning either. But after redoing the center diff and tightening the set screw to the shaft cup, she is ripping and a roaring again. Thanks for all you help guys.

The frustrating part is it could have been a 2 minute fix. I turned it into hours by taking apart all 3 diffs, center twice lol.

At least I got some experience in the diff teardown and reassembly.
 

Rich Duperbash

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This stuff can be very frustrating Frank. Don't be embarrassed, I've done exactly what you just described. These cups like to come loose, it's happened to me multiple times. In fact, I need to get more grub screws as the faces of mine show wear from breaking loose and spinning on the input shafts. Using Loctite blue 242 generously. Glad you solved your riddle.
 
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Bingy93

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Embarrassed to say, and frustrated because I took apart all 3 diffs trying to find the culprit, it was the set screw on the rear input shaft cup. It came loose causing the cup to just spin freely. There must have been something going on in the center diff after I took it apart, maybe what @Rich Duperbash mentioned. Because the driveshafts weren't turning either. But after redoing the center diff and tightening the set screw to the shaft cup, she is ripping and a roaring again. Thanks for all you help guys.

The frustrating part is it could have been a 2 minute fix. I turned it into hours by taking apart all 3 diffs, center twice lol.

At least I got some experience in the diff teardown and reassembly.
this has happen to me like 3 times bit anoyying took me ages aswell to find what was wrong. i check it every time i take it out aswell as the pillow balls n wheel nuts
 

Raji

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The pinion and spur are moving fine but the rest of the truck isn't lol. Would that be the center diff? I took it apart and there were no broken parts so I put it back together but it's still doing it. It will move under very light throttle but when I give it more throttle it just makes a grinding noise. Hard to pinpoint exactly where the noise is coming from but sounds like the middle of the truck. Thanks in advance.

He is rhight

Have you checked the meshing of the pinion and spur? There should be one paper thickness between them.

I had the same issue you only need to check the meshing of the pinion and spur.
Even if it seems ok. Do the meshing again.
 
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