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Allison OEM Discuss repairing & maintaining an OEM Allison automatic transmission.

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Old 11-24-2019, 10:05 PM   #1 (permalink)
Jwhitecotton14
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Running out of ideas.. LML

Long post but I have read through a lot of threads about transmission issues and cant figure out mine here it is.
2012 Chevrolet 2500 4X4.
Autoray Code Scout code reader

Driving Home to NM on the interstate running 75 and transmission was fine. Stopped to get something to eat in the drive through it shifted weird from second down to first and flashed Range Inhibited message. Pulled it out of the way to a parking lot and seem to work fine. Started down the road and between 15mph and 20mph it would kick me out of gear and i would have to stop and put it into park then back into gear but it would be locked in 4th. Put it on a trailer and got it home and on my way home talked to a couple mechanics and all they would tell me was i needed a TCM. The Codes it threw was 751, 756, 761, 722, 843, 873, 877, 2771, and the 700 tcm code. i know what the codes mean except for looking at the TCM. I took it to the Chevy house and had them put in a new tcm and program it. Got it and headed home it was working just fine, got 5 miles down the road and started kicking me out of gear again and locked me in 4th. Limped it to the house and read the codes.. 843, 877, and the 700 tcm code. pulled the rear connector out and it was full of ATF. Cleaned the connector out with that connector cleaner spray and filled with dielectric grease and put back together. i cleared the codes and drove it, worked fine for a couple miles and messed up again. i checked the connector and it was dry. I cleared the codes and it would go to working just fine and shift through all six gear and it would kick me out of gear again and lock in it 4th. Got it back to the house and read the codes 843, 877, 700, and a new code 735-gear 5 incorrect ratio. Checked the wiring harness from the TCM to the transmission for breaks or exposed wires and checked connector again and had ATF in it again. I am ordering a new inner wiring harness and O-ring. When i get it in i will check to see if there is any material on the magnet but was wondering if anyone had another idea of what is going on or what else to check.

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Last edited by OkDually; 11-24-2019 at 10:12 PM. Reason: sig
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Old 11-24-2019, 11:01 PM   #2 (permalink)
Ron Nielson
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Old 11-25-2019, 03:19 AM   #3 (permalink)
davester
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Paragraphs. They are your friend.
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Old 11-25-2019, 10:34 AM   #4 (permalink)
Rvn4me
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This is just one of your codes.
P0735 usually means "Irregular 5th gear ratio" and is normally associated with toasted C3 clutches.
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Old 11-25-2019, 12:19 PM   #5 (permalink)
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Quote:
Originally Posted by Rvn4me View Post
This is just one of your codes.
P0735 usually means "Irregular 5th gear ratio" and is normally associated with toasted C3 clutches.
Ok, would they leave a lot of shaving on the pan magnet or do you have to pull the transmission to check them? Can you buy clutch packs for these transmission?
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Old 11-25-2019, 12:21 PM   #6 (permalink)
Jwhitecotton14
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With this inner wiring harness, do you have to pull the valve body out to get to it?
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Old 11-26-2019, 10:17 AM   #7 (permalink)
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Quote:
Originally Posted by Jwhitecotton14 View Post
With this inner wiring harness, do you have to pull the valve body out to get to it?
Valve body stays.
Step 3: Now the fun part. Undo all the clips for the internal wiring harness, and then using a pair of needle nose pliers or similar, carefully remove the wire spring clips holding the plastic wiring loom holder to the valvebody. DO NOT LOSE ANY OF THESE CLIPS! I strongly suspect from the design that these spring clips act as retainers for the solenoids underneath them. Also when disconnecting the harness plugs there is one small plug underneath the two big solenoids near the main connector, its kind of hard to see and hard to reach, but can be done I promise. I have huge hands and if I can get my fingers in there and unclip it I know you can too. Don't forget to plug that one back in when you reinstall the wiring also, and yes its a bit of a pain to reach again. Next you will need to remove the external connector leading outside the transmission. To do this, first disconnect the external connector, and then on the outside of the transmission the connector has a number of locking tabs that hold it in place and prevent the connector from being pushed inside the trans housing. You will have to push or squeeze these tabs with a flat screwdriver or whatever works for you while pushing with constant pressure on the connector until it goes through the hole. I had to get 3 of the big ones pushed in and then the connector pushed through. Now you can carefully snake the big connector out around the side of the valvebody and remove the wiring harness.

There’s step by step with pictures on the other site.

Other options
https://www.merchant-automotive.com/...ctor_Seal.aspx

You can just buy this for your fix
GM Part :24213704 ACDelco :24213704 SEAL $2.93 O-Ring

Last edited by Rvn4me; 11-26-2019 at 10:35 AM.
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Old 11-26-2019, 03:55 PM   #8 (permalink)
Jwhitecotton14
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Thanks for the help. Would y’all change any of the solenoids while you are there or would you put in the new harness and see if that changes anything?
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Old 11-26-2019, 03:59 PM   #9 (permalink)
Jwhitecotton14
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Quote:
Originally Posted by Rvn4me View Post

There’s step by step with pictures on the other site
What other site and where can I find those pictures?
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Last edited by OkDually; 11-26-2019 at 04:03 PM. Reason: repaired quote
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Old 11-27-2019, 12:41 PM   #10 (permalink)
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Quote:
Originally Posted by Jwhitecotton14 View Post
What other site and where can I find those pictures?
You might have to join to see pictures.

How To: Change the Allison internal wiring harness and pressure switch/temp sensor
https://www.duramaxforum.com/forum/h...mp-sensor.html


Last edited by Rvn4me; 11-27-2019 at 12:41 PM.
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