T -case not shifting when moving

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greywolf

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I have a 1988 k1500 with an auto tran,350 with np231 t-case.When truck is in park or stopped the t-case shifts in and out of gear very smoothly. but when driving I can't shift into 4 Hi but it will shift from 4 Hi to 2 wd easily when moving,Any suggestions. Thanks
 

thz71

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Yah quit trying to put it into 4 hi when you're moving
 

ChristGilley

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To explain, you can't shift from rear wheel drive to 4wd while moving. You need to come to a complete stop. Because shifting into 4Hi makes your front wheels spin. So shifting into it while you are going down the road is both foolish and dangerous. Shifting from 4Hi to 2wd is different. It's just cutting off the front wheels so they are pushed along with the back wheels. So, you can't shift from 2wd to 4Hi while driving. Just like you can't just shift from Drive to Reverse


Sent while pulling out a Ford
 

thz71

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To explain, you can't shift from rear wheel drive to 4wd while moving. You need to come to a complete stop. Because shifting into 4Hi makes your front wheels spin. So shifting into it while you are going down the road is both foolish and dangerous. Shifting from 4Hi to 2wd is different. It's just cutting off the front wheels so they are pushed along with the back wheels. So, you can't shift from 2wd to 4Hi while driving. Just like you can't just shift from Drive to Reverse


Sent while pulling out a Ford
Yah what he said, sorry I'm in a bad mood lol
 

95Suburban

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Front wheels are already spinning at same speed as the rear. Drive shaft isn't, but tcase is synchronized, should bring it up as it's being engaged. Should be able to shift into 4hi at any legal speed. Older trucks with lockouts, not so much.

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ChristGilley

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Front wheels are already spinning at same speed as the rear. Drive shaft isn't, but tcase is synchronized, should bring it up as it's being engaged. Should be able to shift into 4hi at any legal speed. Older trucks with lockouts, not so much.

Sent from my 831C using Tapatalk

His is an 88, that's why I figured it wouldn't shift while he was moving. But if he doesn't have a lockout, then I don't know


Sent while pulling out a Ford
 

90W7

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GMT400's were born with shift on the fly, sounds like it's not synchronizing.

Obviously the front actuator works your just having to be stoped or a slow roll to engage the T-case. Sounds like it needs to be taken out and gone through.

Are you sure you don't have a Np241?
 
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