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4L80E Im lost!

Kevin22497

New Member
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Location
Delaware
Thread starter #1
Hey guys. New to the forum but thanks in advance for any help. 1997 K3500 6.5. Just put a new reman 4L80E in and found out that the shifter shaft isnt long enough for my MLPS. Ok so I need to swap the shafts. The bigger problem is that when I manually shift the trans from under the truck I cannot get any reverse. The big round plug is plugged in and everything Ive read seems to me the MLPS not being present wont effect this. Im lost. Only other difference is the new trans has two speed sonsors instead of one. Thanks for any help here.
 

Will L.

Well-Known Member
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#3
Welcome Kevin.
Iirc the ones with the shorter shaft had both trans lines close to the front and the newer ones had one trans line farther back and had the oong shaft for the mlps/ nss.

I guess since a rebuild, the other shaft could have been installed?

No clue why no reverse. Need a real transmission guy for that one : @THEFERMANATOR

You might be calling back the trans shop That did the rebuild. If the trans has to come out, I would bring them the whole truck at that point for their error in shaft and no reverse.
 

Kevin22497

New Member
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Location
Delaware
Thread starter #4
Hey Will. Thanks for the welcome and response. I should have been more clear. I installed a different trans, did not have mine rebuilt. Not knowing much about them I didnt notice the short shaft on the new one. If you (or someone else) can confirm, am I correct that the MLPS has NOTHING to do with gear selection internally? My understanding is that the bigger plug is for neutral safety/back up and the small plug simply goes to the PRNDL
 

THEFERMANATOR

FRANKENBURBAN
Staff member
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Staff #6
The nsbu is only for the gear display, nuetral safety, and reverse lights, the pressure manifold switch internally is what tells the ecm what gear is selected. That said, I'm pretty sure reverse is a hydraulically selected gear meaning no shift solenoid change is needed for reverse, it is controlled hydraulically via the manial shift valve position. The only 2 arms I know of is the 91-94 shift arm which had a box on the end for the mechanical shift linkage connection, and 95+ shaft designed for nsbu switch. Being a used trans, who knows what itis out of though. Theres alot of issues that can cause no reverse. Does it try to move at all, or just nothing?
 
Messages
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Location
Delaware
Thread starter #7
Thanks for the help THEFERMINATOR. So I had a chance to play with it again today and the symtoms are crazy. Being that I have the neutral safety jumped, it will start in any gear. With the truck running, in park, reverse, and neutral, when you hit the gas it feels like its in gear but binding up. The ONLY way i can get the engine to free rev is if i start it in neutral with the transfer case in neutral. It seems like something isnt meshed correctly. When i put the trans into drive it does move forward. Did I miss something on the install?
 

THEFERMANATOR

FRANKENBURBAN
Staff member
Lead Moderator
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Staff #8
Sounds to me like you got a cobbled together mess. The manual shift shafts should all be the same from 95+. Have you pulled the rear cooler line fitting out of the trans to make sure it is the special long fitting? I know there has been issues with people installing the wrong fitting which causes all the cooler return flow to dump straight to the pan. This can cause low line pressure, but the bigger problem is all the fluid that libricates the rotating assembly is from that cooler return. So if the wrong fitting gets installed, the trans is running dry and will weld itself together internally causing it to drag like you describe. Once this happens, the trans is toast, and must come back apart. Sounds like you need to do some in depth diagnoistics on this trans you put in.
 
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