[asrautox]

Originally Posted by cmitchell17

Where in the transmission is there this much slack/backlash? What about the slop in the rubber carrier bushing in the center support moving up and down?



You can make the same clunk happen when coasting and letting DFCO come on then press the gas and its loud enough its easily heard and felt driving. It drives me insane haha

Yeah, if you’re getting while already moving in gear then it’s likely a worn mount or u-joint.


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[oldman]

the u joint moves so little in this application, it would last 10 car lifetimes..

[6spdhyperblue]

Unless it was out of spec to start. That’s what I’m leaning towards. Something was manufactured incorrectly

[cmitchell17]

It's most likely just me. The slightest things drive me crazy, but when I compare my diveability to other manufacturers vehicles mine is definitely worse. If you get up under the car and move the driveshaft with your hands the backlash seems like it could never be enough to cause what I feel. It is amplified in 1st hear really bad. I feel it could have been mostly fixed with some sort of throttle follower and dampening at low speed stop and go traffic. I just don't think GM prioritizes it thinks diveability matters and their sales reflect it. Just like why iPhone sold way more because they paid attention the the user experience and made things respond like you would expect instead of pressing a button waiting, lag while scrolling in simple things, etc. Driving in stop and go traffic is embarrassing with a passenger you let off the gas and get thrown forward then try your best to apply the pedal as slow as possible to take up the slack but no matter how slow you still feel another clunk, then have to let off again and the transmission should slowly shift into second but ends up clunking and banging into first at inconsistent times.

[oldman]

Let me chime in, coming from performance cars over 40 years, there are drivability issues on all of them. Take the rear noise for instance, it is not science, clutch based diffs take different amounts of posi-quite. So Joe average that thinks a factory diff oil change is going to fix it... well it is not reality. Some diffs just need a little slippery fluid period.
Mopar 440 and 340 had one of the stiffer calibrated 727 trans, it just shifted firmer. I liked it, but people today would be complaining.

Hate to say this, if you want perfect NVH, V6 Lexus. Sure the IPhone sells but it cost at least twice as much.

[cmitchell17]

Originally Posted by oldman

Let me chime in, coming from performance cars over 40 years, there are drivability issues on all of them. Take the rear noise for instance, it is not science, clutch based diffs take different amounts of posi-quite. So Joe average that thinks a factory diff oil change is going to fix it... well it is not reality. Some diffs just need a little slippery fluid period.
Mopar 440 and 340 had one of the stiffer calibrated 727 trans, it just shifted firmer. I liked it, but people today would be complaining.

Hate to say this, if you want perfect NVH, V6 Lexus. Sure the IPhone sells but it cost at least twice as much.

Yeah I understand people these days, stuff that drives me crazy isn't the same as what I think GM things the average consumer would care about. The average consumer probably cares most things like wind noise and engine vibration, which were pretty carefully addressed.

I noticed if you drive up to a parking space to back in, before you come to a full stop to put it in reverse, if I put it in neutral, while I have my foot on the brake a little and the driveline is loaded up, while its still rolling forward a in idle, once you put it in neutral you can feel and hear the whole underside clunk and pop up. I agree with everyone and think the main culprit (and maybe the only one) is the horrendous amount of play/slack in the carrier support "bearing". I've heard its basically just a piece of rubber.

I'm going to try next time putting the gas on a little with the break still on and pop it into neutral to see if the clunk is more violent then, this should kind of prove the point.

I think (and I may have read this somewhere) that this middle carrier "bearing" was to smooth out and dampen some harmonic of the driveshaft at higher speeds. I can see why GM made this tradeoff, since people would freak out if there was even the slightest vibration. I would gladly take a little vibration to fix this clunk, to me it just makes the car feel like a cheap piece of crap haha.

[cmitchell17]

So I did confirm this. If you slightly hold the brake and load the driveline up by pressing the gas a little, then put it in neutral, you can hear the whole driveline violently bounce up and down and make a lot of noise, so to me its got to be the slop in the rubber carrier/isolator/bushing thing.

[6spdhyperblue]

My car doesn’t make that noise

My ‘14 GT did

[oldman]

Originally Posted by cmitchell17

is the horrendous amount of play/slack in the carrier support "bearing". I've heard its basically just a piece of rubber.

yep that is what it is, but if that were the case, people going to a one piece shaft should notice it go away. It could definitely be stronger.. Nothing liquid urethane can't fix.


Since this only happens in an auto, I would assume it is an auto thing.

[oldman]

Originally Posted by cmitchell17

So I did confirm this. If you slightly hold the brake and load the driveline up by pressing the gas a little, then put it in neutral, you can hear the whole driveline violently bounce up and down and make a lot of noise, so to me its got to be the slop in the rubber carrier/isolator/bushing thing.

The when I inch up a steep driveway with my manual it should do the same thing and it does not. It is the clutches and bands of the auto trans having a hard time dealing with being popped into neutral under slight load IMO of course. Make sure you are at idle before neutral and/or reverse...

[cmitchell17]

Originally Posted by oldman

The when I inch up a steep driveway with my manual it should do the same thing and it does not. It is the clutches and bands of the auto trans having a hard time dealing with being popped into neutral under slight load IMO of course. Make sure you are at idle before neutral and/or reverse...

I agree that the transmission is also part of the problem as well. I think GM intentionally programs the 8L90 to optimize clutch life, but at the same time sacrifices shift quality. You can hear and feel the same clunk/clang during downshifts when the transmission mistimes the offgoing or oncoming clutch and the whole driveline reverses for a second. Not allowing the torque converter to lock, especially on the 4-3 coast downshift helps the problem a little since the reversed torque gets absorbed into the torque converter instead of transferred to the drive shaft and differential. I think this is some trade off GM did since they think that the average consumer won't mind this sorry shifting that make people think something is broken. I've never noticed this in any ZF, Jatco, or Aisin transmission.

[oldman]

Had NAG5 in my Challenger....worked great!

[driven2exceSS]

So is there indeed a performance benefit from a Qa1 cf driveshaft, or aluminum driveshaft, or is "upgrading" the OEM DS solely for durability purposes???

[Joshinator99]

Originally Posted by driven2exceSS

So is there indeed a performance benefit from a Qa1 cf driveshaft, or aluminum driveshaft, or is "upgrading" the OEM DS solely for durability purposes???

To be honest, I like the idea that if the CF shaft breaks, it doesn’t become a battering ram on your car’s undercarriage. The few pounds of weight savings seems like a bonus.