What did you do to your NNBS GMT900 Tahoe/Yukon Today?
- Thread starter phattyford
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Those are the style i don't want if i can avoid it.
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Wow! You want functionality AND good looks. LOL
Yeah, odd i know but i got to be me!
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Just like the song. LOL
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I got my truck back today from my local tuner, who was working on eliminating a very hard downshift from 5th gear to 4th gear. He told me that he did his best, but he could not fully eliminate the hard downshift. Even though it is a newly rebuilt 6180 transmission, he believes that the root cause of the issue is something electrical, mechanical, or both inside the transmission. He gave me a referral to a local transmission specialist who would be willing to tear into the transmission to try to find the root cause of this issue. So, I will be reaching out to him in the near future.
@NickTransmissions, is there anything that comes to your mind regarding a hard downshift issue that occurs only when the transmission tries to downshift from 5th gear to 4th gear?
@NickTransmissions, is there anything that comes to your mind regarding a hard downshift issue that occurs only when the transmission tries to downshift from 5th gear to 4th gear?
Was the TEHCM replaced as part of the rebuild? If so, was it replaced with a brand new, GM TEHCM?
Were there prior issues of hard 5-4 downshift before the transmission was overhauled?
Was the valve body vacuum tested?
Any codes stored in the ECM?
when I had mine rebuilt, after multiple trips back to the shop they determined it was the clutch set they used and took it apart again and used a different clutch set.
just food for thought if nothing else works...
just food for thought if nothing else works...
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Thank you @NickTransmissions for your quick reply.
This was a newly rebuilt transmission purchased from GM. As such, I don't know what happened to it prior to my acquiring it. This issue has been present since day 1.
There has been no physical testing that I am aware of, other than the tuner plugging in his HP Tuners device, and whatever that device can do.
There are no transmission-related trouble codes in the ECM.
One other oddity with this transmission is that it takes 4-5 seconds for reverse to engage, and when it does it is a bit harsher, than when it shifts into 1st gear.
I've copied the notes from the tuner, in case there is something in the verbiage that resonates with you:
"Datalog and Drive truck, modify areas of trans tune to soften the 5-4 hard downshift. Made several changes, I'm only able to soften, not remove the harsh downshift. Tried changing data in trans tune one by one, ended up rewriting trans tune and shift points and pressure to make the hard downshift best as possible."
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Thank you for your suggestion, and I will note that for any future work done on it.
Is it under GM’s powertrain warranty?
If so, restore the factory tune to the TEHCM and start the warranty claims process with GM.
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Thank you, @NickTransmissions. Much appreciated.
You're welcome, Joseph.
From swapping the radiator, hoses, t’s and belts? C’mon now…. I had to break a wire somewhere… ffs fml
Bad ground.
@PG01
It looks like the ground is shared with the MAF part of that combo sensor, so I think if it was the ground, the ECM would report that, too. My assumption might be wrong.
I finally put everything in Saturday morning, filled the overflow, started it and it was running like crap so i shut it off. I looked to be sure i plugged the maf back in because thats all i unplugged. It was in so i cleaned it real quick, plugged it back in and started it again and still running like that so i put some more coolant in and shut it off, grabbed my small scanner and got those codes. At this point it started raining and i didn’t feel like getting wet so i closed it up, locked it up and walked away. Ill poke around today a little.
Thank you @Fless for looking that up for me.
Ty @SpareParts for your input.
Sir_Hiro
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Nothing like getting your monthly costco run done to figure out your rear lift struts decided they did not want to retain fluid anymore.
Ordered the finest Chineseum Struts and the lift gate is good...for about 6 months when I think those will explode.
Ordered the finest Chineseum Struts and the lift gate is good...for about 6 months when I think those will explode.
Probably the maf unplug it and see if it runs any better, it wont run good but it puts it in speed density mode and then kind of relies on the map sensor, it might cough or sputter a bit at first
lowh07
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Alright, I got a micrometer to check installed spring height. The mic didn't fit over the integrated seat/seals, so I measured those separately and factored that into the height. These PAC dual springs call for 1.810 installed height, and I was getting between 1.854 and 1.914, so it makes sense why my retainers were hitting my rockers. They're sitting up higher because of the valve job on these heads. I had installed different comp cams locks that were supposed to be OEM specs. I decided to try some OEM ones, and it turns out they're different so they lowered the installed height by about .036 for all of them..... so that's one issue solved. On the one I've checked, it technically clears but just barely, and I haven't even checked the tallest valve so I thought I would need to do something else.
I ordered a completely different set of springs, seats, seals, retainers from BTR which should be here today. These have an installed height of 1.780, and from what I've found, they should work with my Texas Speed cam. The spring pressure will be a little lower than the PAC springs at 1.780, so I think 1.770 is the number for me to shoot for. I'm not sure how much of that height difference is accounted for with the retainers, so I'll just need to install and see. I might need to get some -.050 locks. I have some shims on the way also to make up whatever difference I need. But that should give me at least an extra .040 clearance, plus it looks like the BTR retainers have slighter smaller OD, so hopefully this is good..
Remember when I posted about the heads earlier and said "finally something that took less time than I expected!".......... this is fighting me every step of the way but I'm learning a ton.
I ordered a completely different set of springs, seats, seals, retainers from BTR which should be here today. These have an installed height of 1.780, and from what I've found, they should work with my Texas Speed cam. The spring pressure will be a little lower than the PAC springs at 1.780, so I think 1.770 is the number for me to shoot for. I'm not sure how much of that height difference is accounted for with the retainers, so I'll just need to install and see. I might need to get some -.050 locks. I have some shims on the way also to make up whatever difference I need. But that should give me at least an extra .040 clearance, plus it looks like the BTR retainers have slighter smaller OD, so hopefully this is good..
Remember when I posted about the heads earlier and said "finally something that took less time than I expected!".......... this is fighting me every step of the way but I'm learning a ton.
