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Old 11-05-2018, 02:20 PM   #1
70chevelleSS
 
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Clunk when shifting between reverse and drive

I have recently had my car (a8 ss) develop a pretty rough shift from reverse to drive and vice-versa. My car does have the shudder currently and I'm going to take it in for the flush soon. Are these two things related? The shift is pretty jerky and the "clunk" is very audible. Once it is in drive or reverse however, it is fine. No odd shifts or noises, normal and smooth apart from the shudder when it gets good and warm.

I have read that a "Fast Learn" procedure can help smooth this out...any input?
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Old 11-12-2018, 05:38 PM   #2
cmitchell17

 
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Mine does the same thing, but its attributed to a reverse "placebo" effect. After a while of driving the car new then getting used to it, more imperfections get noticeable and start bothering me.

I want to try to get a go-pro up underneath and look at how much the carrier bearing is moving. Its not only the clunk and overly violent bump, but the sound is way too loud, especially with as good a job as they did with wind noises and other NVH things only to ignore something that seems trivial like excess play and slop. GM I think has always had a problem in putting way to much backlash into the differential, I have yet to be able to get under my car and move the driveshaft back and forth and confirm how much play is in it. I think the carrier bearing is just supported in rubber.

I think the fast learn may make it "seem" better since resetting it will make it worse then smooth out over time, so it make it seem like its better.

I haven't actually logged the trans gears to see if it does a "garage" shift at normal operating temps when shifting from drive to reverse to neutral. The clunk and sound is also audible when shifting into neutral from a gear which is weird as well. I'm pretty sure at low temperatures and high idle it does a "garage" shift where it shifts into 2nd gear first, then quickly shift to 1st to lessen the bang when the car is at high idle.
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Old 11-12-2018, 11:24 PM   #3
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My rpms also rise to around 900 while waiting for reverse to engage. I can’t get the hp tuners fast learn to work. It gets stuck in the “learning d” them aborts.
I have a very audible clunk and a pretty violent jerk as well. Mine is not bad at all shifting into drive. The real issue for me is when shifting into reverse. Takes a a while to engage and rpms rise, then bangs into gear.
I’m going to take my car in for the shudder issue to get another flush and when I do I’ll ask them about it.

I’ll probably get the whole “it’s normal” run around.


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Old 11-16-2018, 06:04 PM   #4
cmitchell17

 
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Quote:
Originally Posted by 70chevelleSS View Post
My rpms also rise to around 900 while waiting for reverse to engage. I can’t get the hp tuners fast learn to work. It gets stuck in the “learning d” them aborts.
I have a very audible clunk and a pretty violent jerk as well. Mine is not bad at all shifting into drive. The real issue for me is when shifting into reverse. Takes a a while to engage and rpms rise, then bangs into gear.
I’m going to take my car in for the shudder issue to get another flush and when I do I’ll ask them about it.

I’ll probably get the whole “it’s normal” run around.


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Yeah I have the same trouble with it. I recommend putting in a support ticket, maybe if we put in enough tickets we can get it fixed and working right.
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Old 12-04-2018, 06:55 PM   #5
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I've noticed this with the A10 on my 18' ZL1 too.

Figured it was just normal, since it's the first auto car I've ever owned.
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Old 12-04-2018, 06:59 PM   #6
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I've noticed this with the A10 on my 18' ZL1 too.

Figured it was just normal, since it's the first auto car I've ever owned.


I did the trans fast relearn with HP tuners and followed the learning procedures. It helped noticeably. Still not great but it’s better.

My 2006 duramax with 240k miles shifts much smoother. Haha

Guess that’s just how it is. Guess it’s a trade off; After getting the trans tuned, it is an absolute beast when you open it up.


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Old 12-05-2018, 06:04 PM   #7
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I used to have a 05 Duramax and the Allison had the same horrible shift quality. Of course you can't expect a truck like that to have as quality of shifts, but the Allison would randomly for no reason shift unnecessarily hard and clunk and bind on rolling downshifts. It also had an extreme amount of backlash that made the problem worse. Low speed stop and go traffic was the worst, you would let off the pedal and your head and body would be thrown forward, then when you press back on the gas it would clunk and throw you back. The Camaro does the exact same thing I really need to daily drive a different vehicle to see if this is just a GM problem. I don't think ive had enough seat time in another vehicle to take notice if this is a problem with other cars.
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Old 12-05-2018, 07:49 PM   #8
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Quote:
Originally Posted by cmitchell17 View Post
I used to have a 05 Duramax and the Allison had the same horrible shift quality. Of course you can't expect a truck like that to have as quality of shifts, but the Allison would randomly for no reason shift unnecessarily hard and clunk and bind on rolling downshifts. It also had an extreme amount of backlash that made the problem worse. Low speed stop and go traffic was the worst, you would let off the pedal and your head and body would be thrown forward, then when you press back on the gas it would clunk and throw you back. The Camaro does the exact same thing I really need to daily drive a different vehicle to see if this is just a GM problem. I don't think ive had enough seat time in another vehicle to take notice if this is a problem with other cars.


That’s odd, my duramax is butter smooth. Of course your 05 was an LLY which had the five speed allison. Mine has the 6 speed so maybe they have improved it.
My duramax (246k miles as of today) is much smoother shifting than my Camaro, and I think it has a lot to do with the fact that the torque converter on the truck doesn’t lock unless you’re in fifth or sixth at cruising speed.
The Camaro starts locking the torque converter very early on


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Old 12-07-2018, 06:20 PM   #9
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How is the differential backlash? The 14 bolt in my Duramax was so bad you could almost count the seconds from when you hit the gas to when it took all the slack up and clunked and the wheels started to move. I guess you would expect a heavy duty rear end to have more backlash than any differential to reduce excess heat while towing. I tried to experiment with my Duramax and my camaro by increasing torque at zero throttle cruise and by increasing rolling idle speed. I was trying to keep positive torque even when off the throttle to try to keep the driveline loaded so you wouldn't have the clunk, slam, and jerk.

Unfortunately like a lot of other stuff, either it didn't work or do as I expected, or the TCM/PCM just ignores those tables or either hptuners/efilive is writing the wrong tables. I swear both of them were almost undriveable to me compared to other cars especially in stop and go traffic while you just get tossed back and forth from just pressing the gas and letting off. Its embarrassing when driving other people around haha. It drives me insane and I can't believe how no one else cares about it.
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Old 12-07-2018, 07:36 PM   #10
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Quote:
Originally Posted by cmitchell17 View Post
How is the differential backlash? The 14 bolt in my Duramax was so bad you could almost count the seconds from when you hit the gas to when it took all the slack up and clunked and the wheels started to move. I guess you would expect a heavy duty rear end to have more backlash than any differential to reduce excess heat while towing. I tried to experiment with my Duramax and my camaro by increasing torque at zero throttle cruise and by increasing rolling idle speed. I was trying to keep positive torque even when off the throttle to try to keep the driveline loaded so you wouldn't have the clunk, slam, and jerk.

Unfortunately like a lot of other stuff, either it didn't work or do as I expected, or the TCM/PCM just ignores those tables or either hptuners/efilive is writing the wrong tables. I swear both of them were almost undriveable to me compared to other cars especially in stop and go traffic while you just get tossed back and forth from just pressing the gas and letting off. Its embarrassing when driving other people around haha. It drives me insane and I can't believe how no one else cares about it.


My duramax does exhibit the behavior you are describing.. but it’s not very pronounced. I can make it clunk like that but it doesn’t do it badly. The AAM 11.5 axle that they use is damn near bulletproof. The G80 is junk though. I have had my 06 LBZ since new and never had any significant issues with it.

My dad had an 03 LB7 and now has 14 LML and the 03 had. A little bit of clunky similar to mine. The 14 doesn’t have any at all. At least none that i can perceive.

My Camaro doesn’t really do what you are talking about when driving... The only time it clunks is when I’m stopped or rolling and into drive or reverse.. I think it has to do with the clutch pressure and apply adaptations (or lack of adaptation)

I have messed with unlocking the converter before in my Camaro by commanding unlocked with the VCM scanner. It smooths it out significantly. I have considered working up a tune where the converter only locks in the 8th gear. Might try to make one up this weekend and try it out.


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Old 12-07-2018, 10:35 PM   #11
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Quote:
Originally Posted by 70chevelleSS View Post
My duramax does exhibit the behavior you are describing.. but it’s not very pronounced. I can make it clunk like that but it doesn’t do it badly. The AAM 11.5 axle that they use is damn near bulletproof. The G80 is junk though. I have had my 06 LBZ since new and never had any significant issues with it.

My dad had an 03 LB7 and now has 14 LML and the 03 had. A little bit of clunky similar to mine. The 14 doesn’t have any at all. At least none that i can perceive.

My Camaro doesn’t really do what you are talking about when driving... The only time it clunks is when I’m stopped or rolling and into drive or reverse.. I think it has to do with the clutch pressure and apply adaptations (or lack of adaptation)

I have messed with unlocking the converter before in my Camaro by commanding unlocked with the VCM scanner. It smooths it out significantly. I have considered working up a tune where the converter only locks in the 8th gear. Might try to make one up this weekend and try it out.


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I verified the same by forcing it to be unlocked with hp tuners. I wonder how hard it would be to readjust the backlash in these differentials? Probably a pain in these haha, I think GM just doesn’t care about driveline and axel quality considering how much effort they put into wind noise, build quality, etc. then forget about the most basic stuff haha


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