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Old 11-15-2014, 08:31 AM   #1
Hondo
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Default D20 popping-even when helld in

Made it back from panamint. Was going up a fairly steep, rough, rocky shelf road with a nasty drop off, believe they called it slate grade up near roger's pass above pleasant canyon. My d20 has been popping out of 4 low for awhile when it gets hot going uphill, but this time it was making a loud kung every few seconds while being held firmly in - all the way up the freaking grade. It's behind a close t19. It's fine in all other positions, maybe not 4 hi - never use it. It made it several miles back to the campsite in 4 low- mostly down hill, and all the way to the bay area in 2 high with no problems. Kind of scary on the steep grade though, mostly because was afraid it was going to grenade on me 3 hours in on the trail. Was definitely not having fun at that point. Any ideas what would cause this?
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1975 Scout II healthy 258, Wide T19 , 4:1 D300 3:54s,
1972 Real clean stock Scout II P/S, P/B, 345, T18, 3:73s
1969 Mach I. Balanced ported 351W, 650 double pumper, Super T10, Detroit locker with 4.11s. Lowered with racing springs, bars, Konis etc.
(Don't worry about getting arrested when I drive the Scouts).
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Old 11-15-2014, 08:42 AM   #2
ihpartsjeff
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Default Re: D20 popping-even when helld in

Sounds like you broke a tooth in the transfer case. I would pull the inspection pan off of the Dana 20 for a look at all the gears. We do sell just the pan gasket if you find nothing wrong and need to just put it back together.
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Old 11-16-2014, 09:19 PM   #3
Hondo
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Default Re: D20 popping-even when helld in

No completely broken teeth, a few pretty well munched. Don't know if that is enough to cause the kunging I was hearing and feeling. Maybe chip got stuck on a tooth face, or it wasn't fully engaging under load, even with me pushing. The big 4-low gear on the bottom left also has a lot more wobble on the shaft than I would expect.
Anyone wondering what happens when it pops out of 4-low, these pictures pretty much show it. The big gear on the left slides down (actually to the back) and engages the smaller gear in 4-low. The picture of the bottom of the transfer case shows where the gears would be just before popping out of 4 low. All the torque is concentrated on a very small portion of the gear tooth faces.
Attached Images
File Type: jpg just about to jump out of 4-low.jpg (101.3 KB, 159 views)
File Type: jpg 4 low fully engaged.jpg (83.5 KB, 163 views)
File Type: jpg drive gear tooth damage.jpg (83.5 KB, 170 views)
File Type: jpg shrapnel.jpg (68.3 KB, 157 views)
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1975 Scout II healthy 258, Wide T19 , 4:1 D300 3:54s,
1972 Real clean stock Scout II P/S, P/B, 345, T18, 3:73s
1969 Mach I. Balanced ported 351W, 650 double pumper, Super T10, Detroit locker with 4.11s. Lowered with racing springs, bars, Konis etc.
(Don't worry about getting arrested when I drive the Scouts).
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Old 11-17-2014, 07:19 AM   #4
ihpartsjeff
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Default Re: D20 popping-even when helld in

That low range gear doesn't look that bad. Not great, but not bad. Another thing to look at is the detent spring but that requires a full tear down of the transfer case.
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Old 11-17-2014, 08:04 AM   #5
Hondo
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Default Re: D20 popping-even when helld in

Agreed, but have the Dana 300 I bought on the bench getting cleaned up. The throwout bearing is also starting to growl at me intermitently, so looks like it's time for the t19 wide to go in as well. I was more concerned about the teeth on the smaller gear on the idle gear cluster. Think there are some hairline cracks out on the edges of some of the teeth, where more chunks are getting ready to break off.
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1975 Scout II healthy 258, Wide T19 , 4:1 D300 3:54s,
1972 Real clean stock Scout II P/S, P/B, 345, T18, 3:73s
1969 Mach I. Balanced ported 351W, 650 double pumper, Super T10, Detroit locker with 4.11s. Lowered with racing springs, bars, Konis etc.
(Don't worry about getting arrested when I drive the Scouts).
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Old 03-06-2015, 12:02 PM   #6
Knapp870
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Default Re: D20 popping-even when helld in

I had the same problem. It got so bad it was popping out when held in driving around in 4 lo. I have a twin stick and it seemed to be mainly the rear. I changed d20s, replaced motor mounts, got a Tom woods u-joint, tore both apart. I think it was probably a combination of detent springs and worn gear teeth.

However, what finally fixed it was switching to an almost new looking Dana 300. Now the thing is so tight you can hardly get it in and out. Sure beats the scary feeling of popping out going up a crazy rock face!!
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Old 03-06-2015, 06:43 PM   #7
Craig
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Default Re: D20 popping-even when helld in

The Dana 300 gears are machined different than the 20's

they made an offset in the machining of the main shaft.
This creates a pressure point which helps to keep the box in gear.



If you look close the one on the right is from pre 86 and looks to be offset.

The one on the left is 86 and up and looks more like tits on the gear.


Here is a close up



Here is a pic from jb conversions website and you can just make out the offset




Warn out slide rings could be an issue too.


Another good shot here
http://forums.IHPartsAmerica.com/tra...html#post78960
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Last edited by Craig; 03-06-2015 at 07:18 PM..
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