4L60E rattle noise just before 2->3 upshift, only when hot

[RiverGuy]

Occasionally, the transmission in my 2004 Olds Bravada makes a 'rattle' sound for 1/2 to 2 seconds just before upshifting from 2-3 (and maybe also from 1-2). I hear the rattling begin as the RPMs increase just before the shift is commanded and the rattle ends instantly when the shift completes.

• There are no negative symptoms associated i.e. no slipping, no 'end bump', etc, just a highly unnerving rattling sound.
• The problem started around 80K and the truck now has 98K miles on it.
• Never happens when manually up-shifting, even if I delay until several hundred rpms past the normal shift point.
• Happens more when tranny is hot -- don't think I've ever heard it with a cold tranny. A few hours towing a 2,000 lb trailer is sure to provoke it, but it does happen without towing,
• My Tech2 does not indicate any issues or transmission codes.
• Complete tranny flush/fill done at GM @ about 90K miles -- this had no effect on the rattling behavior.

Wondering if anyone else has experienced this, and maybe fixed it? Any ideas what it might be?

Thanks in advance!

 

[budwich]

How do you know its coming from the tranny... your ear is on the floor...

check your rear upper control arm.

 

[Mooseman]

Definitely check everything under the truck. Driveshaft, U-joints, suspension, exhaust, etc.

Did you check the transfer case? When was the last time the fluid was replaced?

What was the tranny fluid like? Any metal apart from the usual black sludge on the magnet?

A possibility is a cracked flexplate although this usually manifests itself all the time.

Since you have a Tech 2, try resetting the Trans. Adapts. Maybe the pressures are on the low side? And thinking of that, maybe one of the solenoids is getting weak?

 

[RiverGuy]

How do you know its coming from the tranny... your ear is on the floor...

check your rear upper control arm.

Thanks!
I know it is coming from the transmission because (see my third bullet above). That, and I am not stupid or deaf in either ear -- so with two good ears I can localize sounds somewhat reliably and by combining spatial and temporal senses and reasoning, I'm able to hear and think at the same time.

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;-)
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Interesting theory you suggest on the rear upper control arm, but it raises the question; how would the rear upper control arm know the difference between when I upshift 'manually' (no rattle) or when I let it upshift by itself (rattles)? As I mentioned above, the noise goes away when I upshift manually, no matter how high I let the rpm's go before shifting.

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LoL...reading your response, I had to double check to make sure I hadn't posted this to Trailvoy.com by accident!

 

[RiverGuy]

Definitely check everything under the truck. Driveshaft, U-joints, suspension, exhaust, etc.

Did you check the transfer case? When was the last time the fluid was replaced?

What was the tranny fluid like? Any metal apart from the usual black sludge on the magnet?

A possibility is a cracked flexplate although this usually manifests itself all the time.

Since you have a Tech 2, try resetting the Trans. Adapts. Maybe the pressures are on the low side? And thinking of that, maybe one of the solenoids is getting weak?

Thanks Mooseman!
Yes, everything's been checked out underneath. All fluids checked/replaced at about 90,000 miles when the flush was done. Tranny fluid was perfect -- no metal particles and surprisingly little sludge on the pan magnet compared to the other two Bravadas I owned before this one. Transfer case replaced about this time as well, but again -- the intermittent rattle predates all this and still continues.
-===========

- I think you are on the right track regarding weak solenoid(s) -- AlldataDIY points me in that direction as well.

 

[RiverGuy]

Thanks Mooseman!
Yes, everything's been checked out underneath. All fluids checked/replaced at about 90,000 miles when the flush was done. Tranny fluid was perfect -- no metal particles and surprisingly little sludge on the pan magnet compared to the other two Bravadas I owned before this one. Transfer case replaced about this time as well, but again -- the intermittent rattle predates all this and still continues.
-===========

- I think you are on the right track regarding weak solenoid(s) -- AlldataDIY points me in that direction as well.

...and thanks also for your post here: https://gmtnation.com/forums/threads/4l60e-tcc-questions.23700/
Right now I'm thinking the TCC is the root cause, I understand manually shifting disables TCC lockup, so that might explain why the rattle goes away when I upshift manually.

 

[Mooseman]

The TCC doesn't come into play until it's at least in 3rd gear. Manually shifting doesn't disable it as you can put in 3rd and it will lock. TCC only applies in 3rd or 4th while cruising. As you said, it does the noise just before shifting 2>3. There is also the possibility of a check ball that's bouncing just before the shift but would that even be audible? A buzzing solenoid maybe? I dunno.

 

[TJBaker57]

try resetting the Trans. Adapts.

I am pretty certain the service literature recommends to NOT reset TAPs except after an "internal repair".

I might be inclined to have a look at the values for clues though.

 

[TJBaker57]

happens when manually up-shifting, even if I delay until several hundred rpms past the normal shift point.

What sort of rpm are we talking about here? My shift points are pretty low as I am a serious lightfoot.

 

[RiverGuy]

What sort of rpm are we talking about here? My shift points are pretty low as I am a serious lightfoot.

Likewise, I'm a lightfoot. I'd be gussing to say the rattling occurs just before shifts happening in the 2300-3000 rpm range.

 

[RiverGuy]

The TCC doesn't come into play until it's at least in 3rd gear. Manually shifting doesn't disable it as you can put in 3rd and it will lock. TCC only applies in 3rd or 4th while cruising. As you said, it does the noise just before shifting 2>3. There is also the possibility of a check ball that's bouncing just before the shift but would that even be audible? A buzzing solenoid maybe? I dunno.

Thanks for that (I used to know these things .
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One reason I'm drawn to a problem in the torque converter is that the rattle sound is loud, clear and roughly consistent with what one might expect whan sharp vibrations are transmitted to the flex plate/flywheel.
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Also learning now that 4L60E manual shifts are hydraulic (not solenoid controlled), so the fact that the problem goes away when I shift manually points to a solenoid controlled function (as you suggest). I'm going to do some more sleuthing with Tech2 and probably drop the pan and check out the solenoids. Also wondering if this could be an ECCC related issue. Thanks (again) for helping me think this through...

 

[TJBaker57]

Likewise, I'm a lightfoot. I'd be gussing to say the rattling occurs just before shifts happening in the 2300-3000 rpm range.

My nearest interstate highway is a 2 hour drive from here. A fairly rural area, I seldom have any cause to accelerate briskly. I looked back over recordings from the past 6 months or so and found 2-3 shifts generally happening in the 1800 rpm arena!! Firmly seated in old fart-dom.

 

[budwich]

Thanks!
I know it is coming from the transmission because (see my third bullet above). That, and I am not stupid or deaf in either ear -- so with two good ears I can localize sounds somewhat reliably and by combining spatial and temporal senses and reasoning, I'm able to hear and think at the same time.

- ====================
;-)
- ====================
Interesting theory you suggest on the rear upper control arm, but it raises the question; how would the rear upper control arm know the difference between when I upshift 'manually' (no rattle) or when I let it upshift by itself (rattles)? As I mentioned above, the noise goes away when I upshift manually, no matter how high I let the rpm's go before shifting.

-============
LoL...reading your response, I had to double check to make sure I hadn't posted this to Trailvoy.com by accident!

glad you got good ears....

my "theory" comes from "experience"... having lost a control arm or two...
anyway, how does it know... it doesn't but it might depend on how much torque you are providing it between the two method. I believe my "vibration" was less when manually going thru gears (mostly 1-2... not so much 2-3)... whereas in "auto" it almost always showed from start up (ie. stop) to basically 2-3, was ok.

Anyway, if one of the control arms is "gone", then I think strange things can happen to the drive train. It costs nothing to check.... which you seem to indicate that you did (crawled under).

One other thing... what happens when you "kick down" ie. going to passing gear?

 

[Mooseman]

ECCC, aka: PWM, it is possible if it tries to engage the TCC before the shift to 3rd, but it shouldn't. What you could try to dispel this is to accelerate while lightly holding the brake pedal just to engage the brake lights but not engage the brakes. This will prevent the TCC from engaging completely. Would have to do this with no traffic behind you as you will totally confuse anyone while doing this.

 

[RiverGuy]

glad you got good ears....

my "theory" comes from "experience"... having lost a control arm or two...
anyway, how does it know... it doesn't but it might depend on how much torque you are providing it between the two method. I believe my "vibration" was less when manually going thru gears (mostly 1-2... not so much 2-3)... whereas in "auto" it almost always showed from start up (ie. stop) to basically 2-3, was ok.

Anyway, if one of the control arms is "gone", then I think strange things can happen to the drive train. It costs nothing to check.... which you seem to indicate that you did (crawled under).

One other thing... what happens when you "kick down" ie. going to passing gear?

Ok, thanks. It's definitely not drive-line torque related, as I said the noise never happens when I shift manually. In fact, it seems it happens more when I am going 'light-footed'. Detent (kick-down) downshifts are normal, heavy throttle applications and accompanying high-rpm shift points do not exhibit/provoke the noise.

 

[JayArr]

Could this be as simple as a broken "anti-rattle" spring inside the transmission?

It keeps the Low/Reverse clutch carrier assembly from rattling.

 

[RiverGuy]

Could this be as simple as a broken "anti-rattle" spring inside the transmission?

It keeps the Low/Reverse clutch carrier assembly from rattling.

Wow, after having owned three of these, one might think I'd have heard of an anti-rattle spring! Thanks for the tip! I'm wondering if it's referred to by a different name in the GM service manuals or on alldatadiy? Is there an easy way to check it? Again, it never rattles when I upshift manually, only during upshifts in DRIVE...

 

[JayArr]

It's a cheap $1 sort of spring clip but it's way inside the gear train so there is no easy way to check it. If the trans has been rebuilt I would wonder if maybe it wasn't put back in.

 

[RiverGuy]

Thanks. No, I've owned it since 52k and the noise only started at about 95k. Never rebuilt, and otherwise it's been solid as a rock.

 

[JayArr]

Here is a video of Brad rebuilding a 4L60E. Watch around 4:25 and you'll see him install the spring.

 

[RiverGuy]

Thanks (again). The problem is so trivial and very much intermittent, and I have other vehicles at my disposal, so there's no way l'd tear it out and tear it down with only 100k miles and no other concerns whatsoever. Maybe if I win the lottery and decide to fix the leaking right-front axle seal (another deferred-until-it-breaks repair) I might think about it again...