**(FIXED)** 2016 gmc Yukon 6l80 issues after rebuilding

[Maatttyyy12]

Hey guys, long story short I’m at end of road here with this 6l80. I’m very mechanically inclined and have my own shop but do not dabble in transmissions much. I bought a 2016 Yukon with a bad 6l80. Thing was smoked, I decided to rebuild it my self. This is a family hauler for kids and wife, isn’t for performance or anything. Any how I rebuilt it, new bellhousing and stator assembly, all new bushings, all new pistons, new gm clutches, zip kit installed, new 35r drum, new 456 drum, new sealing rings, new teflon rings, new pressure switches… reverse, 1st, 2nd, 5th all slip under load. Normal light throttle everything seems perfect, give it more the 20% throttle in those gears and she just revs. Also has a binding when it attempts to downshift from 5th to 4th, but only under load. If just cruising (no throttle input) and manually downshift from 5th to 4th is smooth. What am I doing wrong here? Had it apart twice now. Clutch clearances all came back in spec, 456 was a little on tight side .058, that was with thinnest snap ring and oem clutches. No codes, I feel like I have a faulty techm! @NickTransmissions please help lol thanks guys

 

[mikeyss]

I think there is a re-learn procedure for the TCM that has to be done.

 

[Maatttyyy12]

I think there is a re-learn proceesure for the TCM that has to be done.

Yes I forgot to add that to the post but I did that as well.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally assist you with your issue, but @NickTransmissions and other members of this Forum much more knowledgeable than me in this area will chime in.

 

[NickTransmissions]

Did you replace the TEHCM? Thinking not since you mentioned replacing pressure switches (which is not possible to do-you a replace the diaphragms and seals, not the switches themselves).

What were the vacuum test readings for the pump stator support and valve body castings?

Did you machine the pump body/bell and pump stator support?

 

[Maatttyyy12]

Did you replace the TEHCM? Thinking not since you mentioned replacing pressure switches (which is not possible to do-you a replace the diaphragms and seals, not the switches themselves).

What were the vacuum test readings for the pump stator support and valve body castings?

Did you machine the pump body/bell and pump stator support?

Nick ended up being the tehcm. I replaced it last night at 1 am with one that had the identical part number, resets the shift adapts and she is shifting and holding every gear absolutely perfect now. But yes I did mean diaphragm and seals just mis worded it. Now I feel confident in having to rebuild another if I ever have to since I rebuilt it correctly but it was a bad techm causing my issues. Weird it didn’t throw any codes, however I had my suspicions due to the original transmission being completely toasted beyond believe. There was metal in everything. I appreciate your response

 

[Joseph Garcia]

Nick ended up being the tehcm. I replaced it last night at 1 am with one that had the identical part number, resets the shift adapts and she is shifting and holding every gear absolutely perfect now. But yes I did mean diaphragm and seals just mis worded it. Now I feel confident in having to rebuild another if I ever have to since I rebuilt it correctly but it was a bad techm causing my issues. Weird it didn’t throw any codes, however I had my suspicions due to the original transmission being completely toasted beyond believe. There was metal in everything. I appreciate your response

I'm glad to read that your issue is resolved. Please add the word "FIXED" or "SOLVED" to your thread's title, to let others who are experiencing a similar issue know that this thread has an identified solution.

 

[Maatttyyy12]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally assist you with your issue, but @NickTransmissions and other members of this Forum much more knowledgeable than me in this area will chime in.

I appreciate your welcoming and I do plan on visiting this forum and trying to help others out when needed! Where should I post photos of my family hauler? Very new to the whole forum thing in general. Thanks again!

 

[Maatttyyy12]

 

[NickTransmissions]

Nick ended up being the tehcm. I replaced it last night at 1 am with one that had the identical part number, resets the shift adapts and she is shifting and holding every gear absolutely perfect now. But yes I did mean diaphragm and seals just mis worded it. Now I feel confident in having to rebuild another if I ever have to since I rebuilt it correctly but it was a bad techm causing my issues. Weird it didn’t throw any codes, however I had my suspicions due to the original transmission being completely toasted beyond believe. There was metal in everything. I appreciate your response

Glad you were able to get it fixed. I never reuse TEHCMs in my 6L builds, for that reason.

Do you still have that bad TEHCM?

 

[Maatttyyy12]

Glad you were able to get it fixed. I never reuse TEHCMs in my 6L builds, for that reason.

Do you still have that bad TEHCM?

Yes I do have it. It was my understanding that they rarely go bad. The weird thing is my unit threw no codes at all, so it was a hard thing to diagnose. I just knew that I had replaced all common failure points and the tehcm was the last thing. I also have a core 6l80 that I was planning on rebuilding to sell just so I could recoup some of my money. I already have a machined pump assembly, but now will need to source a new tehcm so I can sell it complete

 

[NickTransmissions]

Yes I do have it. It was my understanding that they rarely go bad. The weird thing is my unit threw no codes at all, so it was a hard thing to diagnose. I just knew that I had replaced all common failure points and the tehcm was the last thing. I also have a core 6l80 that I was planning on rebuilding to sell just so I could recoup some of my money. I already have a machined pump assembly, but now will need to source a new tehcm so I can sell it complete

It’s not super common but not super rare either. It happens often enough for me to mandate replacement on all overhauls. There are other builders who reuse them, citing low likelihood of them going bad (in the builder’s warranty period - the part left unsaid).

I’d love to test that TEHCM - I have the Bosch TEHCM test block so should be able to confirm or deny it’s bad (I’m sure it is but would be cool to show it in a video).

Would you be willing to send it to me if I paid for the shipping each way, assuming you want it back?

 

[Maatttyyy12]

It’s not super common but not super rare either. It happens often enough for me to mandate replacement on all overhauls. There are other builders who reuse them, citing low likelihood of them going bad (in the builder’s warranty period - the part left unsaid).

I’d love to test that TEHCM - I have the Bosch TEHCM test block so should be able to confirm or deny it’s bad (I’m sure it is but would be cool to show it in a video).

Would you be willing to send it to me if I paid for the shipping each way, assuming you want it back?

Yes I am actually all for that. I would love to actually see the cause of failure for it to make it slip in reverse,1st,2nd, and 5th. I went down a rabbit hole of looking for bad stator sealing rings, bad teflon rings, cracked 35r, torn lip seal. All because of the tehcm. I do believe when the torque converter completely fails and then the metal goes through out them is when the failures of tehcm happen. I believe if the transmission is just showing signs of failure( brown fluid not black and no metal just clutch material) then they probably end up being fine.

 

[NickTransmissions]

Yes I am actually all for that.

Cool - I sent you a PM...Take a look when you have a few moments and we can go from there.