15 8 speeds does yours clunk?

paxtonman · May 16, 2015

So I was looking at the torque converter tables in the truck A8 last night and they are retarded. I copied and pasted the Vette A8 tables into the truck and have had smooth non-clunky shifting up and down for the whole morning.

I think a lot of the clunk we feel is the torque converter clutch locking or unlocking at the wrong time vs the actual shift.

Another issue is the A8 is a 4.56 first gear and there is a huge gap to second....Smoothing that out in an up or downshift can't be easy, especially under varying throttle conditions,

As I get more access to more tables in the A8, hopefully I can look into it further. As for now, get the Vette TCC lock and release table into your truck. You will love it.

How do we do this? Is this something the dealer has to do? Any affect on warranty?

Higgs Boson · May 16, 2015

How do we do this? Is this something the dealer has to do? Any affect on warranty?

you will need to have a tuner do this. a handheld style tuner won't work, you will need a custom tune. the dealer can't even do it. if you blow up your motor then GM will check for a tune and probably not cover the repair.

i tune all my new cars on the way home from taking delivery, i wish i could get a discount based on no warranty!!

where do you live?

Stoddard · May 16, 2015

you will need to have a tuner do this. a handheld style tuner won't work, you will need a custom tune. the dealer can't even do it. if you blow up your motor then GM will check for a tune and probably not cover the repair.

i tune all my new cars on the way home from taking delivery, i wish i could get a discount based on no warranty!!

where do you live?

Higgs, what tool has access to the 8 speed?

Higgs Boson · May 16, 2015

HPTuners is what I use. There is full access in the latest version for shift points and TCC tables. There are tables without values for shift pressures. There are generic enable/disable menus for some torque management items.

It is far from what we had for the 6 speeds but they are either still working on it or the 8 speed simply does not use/does not have the same type of logic as the older TCMs.

Don't know yet.

blwright · May 17, 2015

are you setting the parking brake?

if you stop, turn off engine, gather your things, let off the brake pedal and get out, the car might move.

No. I don't set the parking brake in my garage. I just turn it off and sit there. It moves.

BuyAmericanIron · May 17, 2015

Subscribed. I had the exact issue from post 1. After coasting to a stop coming off the freeway, the truck would have a very specific clunk upon accelerating. The sound was much more prevalent during cold weather. Did it from day 2. This week with 2400 miles, dealer installed a new transmission. So far with 200 miles on it, the noise is no longer present. Hope it stays that way.

Higgs Boson · May 17, 2015

No. I don't set the parking brake in my garage. I just turn it off and sit there. It moves.

going to need more info. does it slightly roll and rest against the transmission? does it power itself back up and idle forward? does it roll freely like a manual transmission in neutral? be specific about the circumstances.

just saying "it moves" doesn't mean a lot....most cars will move in park if there is a slight grade (even if you don't think there is). what seems flat is not always.

post a video.

jetfixer737 · May 18, 2015

Mine clunks slightly when cold and at low speeds (25mph max) If I push the pedal harder or travel at higher speeds though its smooth & quiet. However it is only 10 days since purchase and only has 1200 miles on the odometer. (April 2015 build) Also the first time in many years healing the old turbo-hydro 350 "Whine" in the lower gears. Kinda sounds nice. LOVE the truck.

Bill_F · May 18, 2015

No Clunks in min, built in January. Only thing I get is odd "hard shifts", but I think they relate to cold transmission and very slow speeds. I.e, When I leave work, and I am in my parking garage, it sometimes feels like the truck cannot decide if it should skip second, and it makes are hard shift, but it only happens at very low speeds (parking lots), when the truck has been parked for a long time (so its cold) - I noted that 30 seconds or so of idle, and this hard shift doesn't happen, so I am not remote starting it when I am getting close, and I don't see this much anymore. It may be gone because I have more miles on the truck, or it may be that the idling heats up the truck just enough, not sure. No audible clucking whatsoever - Just an annoying electronic sounding hum when in Auto.

I have had the truck since late Feb, but I am still under 1,500 miles, so pretty new in that respect.

jetfixer737 · June 12, 2015

I had my truck in to the dealer for a minor issue, and while there discovered there is a brand new software update that involves torque converter lockup.

Perhaps something related to this topic?

nadrojcote · June 12, 2015

5.3l does it too with the 6 speed. The problem is the rear leafs are too weak and cause axle wrap which in turn causes the yolk to thud when shifting.

Here's my fix for the issue. One other member did it on his 8 speed and said it worked for him.

Give it a shot. Did this on the weekend and took away all the clunking I had going on. Initially thought it was the tranny, had the update done for the 8 speed. The update made it worse if anything. Installed the shackle brackets on the springs like pic posted and it's gone for now.

http://www.gm-trucks.com/forums/topic/172777-clunkthud-while-acceleratingslowing-down/page-1