Yes another 8 speed transmission thread...but different

[SS502]

Okay, I believe I am starting to get the dreaded shudder. Long story short, I am getting a shudder from 68mph-90mph ONLY under throttle, smooth as silk when letting off the throttle. Truck is a 2018 Sierra SLT CCSB 6.2 8 speed with 4,058 miles. Only Mods (that might have a remote chance of changing the stock characteristics) done are 2.25 level, 275/60R20 BFG K02 tires, Borla ATAK Cat-back, Denali cluster (don't see how but figured I'd list it), RXP dual catch can, Range AFM disable and Pedal Commander (set at Sport+1). I want to get OPINIONS on a course of action. I am considering foregoing the warranty by having the complete fluid flush, buying an unlocked TCM, having it tuned and pressing on. Is this going to cure the shudder or am I just grasping at straws? I do not know how to tune in today's world of tunes, I just want the darn thing to last and function as it should. I remember @1SLOW1500 mentioning the transmission is "stuck in the middle of a fight with the engine management and ever changing trans software" and that makes sense to me. So will a properly tuned (and yes I will have to pay someone to do it right) TCM along with the flush help/cure the shudder problems or is it just somehow masking it? Please don't start a pissing contest, I am seeking opinions. I was always one to believe that this would not happen to me and this is a rare occurrence only being highlighted in the forums...it still may be a rare occurrence but I am now part of that minority.   

[Grumpy Bear]

Question. Does it matter how aggressively you are accelerating between those speeds or do you have to let completely out of it to tame the tiger?

[SS502]

11 minutes ago, Grumpy Bear said:

Question. Does it matter how aggressively you are accelerating between those speeds or do you have to let completely out of it to tame the tiger?

I was cruising at 65 (posted speed limit) and had empty roadway, so I gave it about 3/4 throttle and right at 68 all the way to 90 I had the shudder. As soon as I let off the gas it smoothed out, repeated several times and had the shudder each time. It happened again this morning (same scenario) and these are roads I am very familiar with. It has never done this before on these roads. Yes I completely got off the throttle, did not ease it down. 

[SS502]

16 minutes ago, Grumpy Bear said:

Question. Does it matter how aggressively you are accelerating between those speeds or do you have to let completely out of it to tame the tiger?

Oh and no I did not slowly accelerate, it was 3/4 each time.

[SS502]

38 minutes ago, Grumpy Bear said:

Question. Does it matter how aggressively you are accelerating between those speeds or do you have to let completely out of it to tame the tiger?

 

28 minutes ago, SS502 said:

I was cruising at 65 (posted speed limit) and had empty roadway, so I gave it about 3/4 throttle and right at 68 all the way to 90 I had the shudder. As soon as I let off the gas it smoothed out, repeated several times and had the shudder each time. It happened again this morning (same scenario) and these are roads I am very familiar with. It has never done this before on these roads. Yes I completely got off the throttle, did not ease it down. 

 

21 minutes ago, SS502 said:

Oh and no I did not slowly accelerate, it was 3/4 each time.

I am not one to discount a coincidence...I never had this problem BEFORE the Pedal Commander install. I will disconnect it tonight and see if for some reason it is having some sort of negative influence. While I love how responsive the PC makes the truck, I don't know if it plays nice with 3/4 or WOT inputs... 

[damnthetorpedoes]

How long have you had your KO2's on? I have almost the same setup as you with KO2's, level, and the 6.2. I don't notice anything at those speeds on good roads, but it can get a little rowdy on questionable surfaces at 3/4 to wot. 

[2017Darkness]

The shudder does not typically occur when on the throttle as much as you stated you were. It is usually light throttle, maybe 1/4 of pedal travel and when climbing a small grade or maintaining speed. The updated fluid and flush procedure takes care of the normal issue, but yours sounds very different from the normal complaint.

[Grumpy Bear]

An opinion eh?  

 

This is all very confusing. If it were a critical speed issue it wouldn't do it under acceleration. If it were a balance issue it wouldn't clear up when you let off. If it were a clutch pack slipping it would be worse the harder you hit it unless pump pressure is nonlinear which it could be. If fluid changes help it AND the new 'formula' fluid is different then it is a friction modifier issue they have identified. IF that's the case then it is slippage and at the mercy of the tuning. Primary of which would be servo apply pressure. Only one other set of things I can think of and that would be an apply piston bleeding off pressure or a cracked clutch cage preventing full clutch apply. These last two are Zebras. I opine you looking for Horses.

 

Would have, could have, should have and dime and your still short a cup of coffee. Do the fluid change. Then contact BB and ask about data logging. He's pretty good at finding things in data GM could care less about...or so I've heard.   

 

I will monitor with interest. I buy no more new GM until this sort of thing is history. Sorry to hear this is happening. Few care for their things as well as you. Best wishes. 

[redwngr]

Or, take it in and have run the shudder test/ install the newly recommended oil....

 

If you want the pics, use the link.

Otherwise it can be read here.

 

Article released Jan 331, 2019

 

https://gm-techlink.com/?p=11127

 

A new transmission fluid exchange procedure and a new formula of Mobil 1 Synthetic LV ATF HP transmission fluid have been released to address torque converter clutch (TCC) shudder conditions on 8L45 and 8L90 8-speed automatic transmissions (RPOs M5N, M5T, M5U, M5X) in some 2015-2017 Escalade, Yukon; 2015-2018 Silverado, Sierra; 2015-2019 Corvette; 2016-2018 CT6; 2016-2019 ATS, CTS, Camaro; and 2017-2019 Colorado and Canyon models.

The new fluid exchange procedure requires the use of the DT-45096 TransFlow Cooler Flush Machine and DT-52263 Transmission Fluid Exchange Tool Kit. (Fig. 10) The tool kit began shipping to dealerships at no charge in late January 2019. All GM dealerships should receive the tool kits by the end of March 2019.

Fig. 10

 

Shudder Test

The new service procedure addresses shake and/or shudder conditions during light throttle acceleration between 25 and 80 MPH (40 and 128 KM/H) at a steady speed when the transmission is not shifting gears. To ensure TCC shudder is diagnosed correctly, drive the vehicle on a smooth road with transmission sump temperature between 122°F (50°C) – 158°F (70°C). Constant throttle input on a smooth grade is needed.

A shudder condition may also be a chuggle, surge or vibration condition. Use GDS 2 or the CH-51450 PicoScope to confirm that the concern is TCC shudder and not a tire/wheel vibration or a driveline vibration, for example. A screen print from GDS 2 or the PicoScope showing the TCC shudder event must be attached to the Repair Order hard copy. (Fig. 11)

If TCC shudder is present, a vibration peak will appear within +/- 2 Hz of the frequency listed in Bulletin #18-NA-355. Refer to the bulletin for additional information, including required shudder test conditions for each vehicle being diagnosed as well as the fluid exchange procedures.

Fig. 11

 

Fluid Exchange

The TCC shudder condition is related to moisture content in the transmission fluid. The current fluid tends to be hydroscopic, or absorbs moisture, which increases the chance of TCC shudder. There are three different fluid exchange procedures to follow, depending on vehicle application, so that an acceptable concentration of the new HP fluid is achieved in the transmission.

The new Mobil 1 Synthetic LV ATF HP transmission fluid is now available to U.S. dealerships through your local GM Oil Distributor. The new Mobil 1 Synthetic LV ATF HP transmission fluid is available in quart bottles (GM Part Number 19417577) and, for a limited time, in 55-gallon drums (GM Part Number 19417904) in most locations. Drum production ended in January 2019. The GM part numbers are not on the product. The Mobil 1 Synthetic LV ATF HP fluid and the required tool kit will be available to all Canadian dealerships by the end of March 2019. GM Part Numbers for 0.946 liter bottles will be provided at that time.

TIP: Mobil 1 Synthetic LV ATF HP transmission fluid is required for all 8-speed transmission repairs regardless of the repair being completed.

Quart bottles, which can be identified by a new blue banner across the front of the bottle (Fig. 12), will be limited to 20 cases/120 quarts per dealer per week during the initial launch of the new product. The new bottles also feature the HP license number J-62120 on the back label. The use of the black label Mobil 1 Synthetic LV ATF HP fluid (GM Part Number 19355656) should be discontinued.

[SS502]

1 hour ago, damnthetorpedoes said:

How long have you had your KO2's on? I have almost the same setup as you with KO2's, level, and the 6.2. I don't notice anything at those speeds on good roads, but it can get a little rowdy on questionable surfaces at 3/4 to wot. 

Thank you for the response! I have had them on for about 4000 miles.

1 hour ago, 2017Darkness said:

The shudder does not typically occur when on the throttle as much as you stated you were. It is usually light throttle, maybe 1/4 of pedal travel and when climbing a small grade or maintaining speed. The updated fluid and flush procedure takes care of the normal issue, but yours sounds very different from the normal complaint.

Agreed and see the bottom reply please. Thank you for your inputs!

26 minutes ago, Grumpy Bear said:

An opinion eh?  

 

This is all very confusing. If it were a critical speed issue it wouldn't do it under acceleration. If it were a balance issue it wouldn't clear up when you let off. If it were a clutch pack slipping it would be worse the harder you hit it unless pump pressure is nonlinear which it could be. If fluid changes help it AND the new 'formula' fluid is different then it is a friction modifier issue they have identified. IF that's the case then it is slippage and at the mercy of the tuning. Primary of which would be servo apply pressure. Only one other set of things I can think of and that would be an apply piston bleeding off pressure or a cracked clutch cage preventing full clutch apply. These last two are Zebras. I opine you looking for Horses.

 

Would have, could have, should have and dime and your still short a cup of coffee. Do the fluid change. Then contact BB and ask about data logging. He's pretty good at finding things in data GM could care less about...or so I've heard.   

 

I will monitor with interest. I buy no more new GM until this sort of thing is history. Sorry to hear this is happening. Few care for their things as well as you. Best wishes. 

Okay, I do not like saying one of my Mods was at fault BUT...I disconnected the Pedal Commander, hooked up my throttle pedal (after waiting 15 minutes) and upon engine start, got a CEL. So shut the truck off, re-start and CEL is/was still there. Drove it to the dealership, code was for throttle signal error (soft hit) and cleared. Re--start no CEL. Drove back here to work on the same road. Did the same "test" WITHOUT the Pedal Commander hooked up and it was smooth as silk. Nothing, nada, perfect. So I think I found the culprit...not sure why or how but it was giving me that shudder or whatever you want to call it. Problem solved. Still would like inputs on the TCM/Fluid change thoughts...THANKS TO ALL WHO REPLIED.

[1SLOW1500]

I was busy today but was going to to tell you it's the pedal commander. It is changing the voltage values to the pcm and the tb. 

If it is still something in trans run the vin against the tab. And see that gm is telling the dealer to do. I say this because some say the flush and filter works, I think that is a band aid for a larger issue. Others have said everything from new updated converter to Tran to wiring harness. So take that for what you will. 

Once I read the tsb and talked to dealer I would decide if the best course of action for me was tune and test. I think it is but each his own. 

Its money but buy the unlocked tcm and get tuned and see where your at. 

I thing all the slip in the trans wears out the parts and fluid. That why the updated and stronger converter. The afm and DOD disable will help on the mast of the issues. Question no is what damage was done to the trans.

[SS502]

17 minutes ago, 1SLOW1500 said:

I was busy today but was going to to tell you it's the pedal commander. It is changing the voltage values to the pcm and the tb. 

If it is still something in trans run the vin against the tab. And see that gm is telling the dealer to do. I say this because some say the flush and filter works, I think that is a band aid for a larger issue. Others have said everything from new updated converter to Tran to wiring harness. So take that for what you will. 

Once I read the tsb and talked to dealer I would decide if the best course of action for me was tune and test. I think it is but each his own. 

Its money but buy the unlocked tcm and get tuned and see where your at. 

I thing all the slip in the trans wears out the parts and fluid. That why the updated and stronger converter. The afm and DOD disable will help on the mast of the issues. Question no is what damage was done to the trans.

Well, now my problem is I don't have a problem LOL....the truck runs, shifts, coasts, accelerates and stops just as smooth as day one. I still have the Range installed and did several "test" runs after PC removal with no issues at all. I am still inclined to get the unlocked TCM and tune but I now feel I should hold out until sometime down the road (post warranty) as I am not having any issues now. I hope I did no damage to the transmission, I only did 4 or 5 runs where it did the what I called shudder (although I no longer think it is what others are feeling based on @2017Darkness mentioned in his post above) and drove very easy with one exception. I wanted to see if it would do it with tranny fluid that was not fully warmed up and it did the exact same thing so I just stopped pushing things. I am returning it to Amazon, I don't want to sell it to anyone on here and have them dealing with this issue. Thank you Sir for your better late than never reply

[dieselfan1]

I'd get rid of it and go buy a Ford.....

 

NOT

 

just kidding I couldn't resist.

I would take it in for the flush and go from there. I feel bad for you this sucks with only 4000 miles.

[SS502]

15 minutes ago, dieselfan1 said:

I'd get rid of it and go buy a Ford.....

 

NOT

 

just kidding I couldn't resist.

I would take it in for the flush and go from there. I feel bad for you this sucks with only 4000 miles.

Well, it was the Pedal Commander doing it so I removed it...going back to Amazon!!! BTW your truck looks KILLER!

[dieselfan1]

15 minutes ago, SS502 said:

Well, it was the Pedal Commander doing it so I removed it...going back to Amazon!!! BTW your truck looks KILLER!

Thanks