Grinding noise a specific RPM

ghost_leader07

Original poster
Member
Dec 18, 2019
152
UAE
Greetings Everyone,

I would like your help regarding an issue that i'm facing on my 05 Trailblazer LT, I'm hearing a barely noticeable grinding/rattling noise whenever it reaches ~2800 RPM or slightly blow that especially before shifting into 3rd gear (slight delay on my 3rd gear) i don't hear it when shifting into 2nd mainly because it doesn't reach 3000 RPM usually shift around 2000 RPM at normal acceleration, you definitely can not hear it outside the car and seems to be coming off the driver side. what is strange though that you start the car while it's cold and let the RPM settle then give it a couple of revs or holding the RPM up to 2800-3000 RPM it doesn't show but driving for an hour or maybe less it'll come back again and stays even after parking and trying to hold the RPM at 2800-3000 RPM i can still hear it clearly but can't determine where exactly other than it seems to be coming from somewhere in the engine bay left driver side in particular, i had suspicion that it could be coming off the transmission but i went under it with someone in car and i couldn't hear it.

Sometimes it goes away by itself and couldn't hear it when shifting into 3rd gear it seems to be more RPM related than shift related since if i did a slow acceleration my 3rd gear would shift below 2500 RPM and wouldn't hear that noise it only happens when accelerating and reaching around 2800-3000 RPM mark and continues even after putting it into PARK it'll still be there for awhile until it cools off.

Sorry for the long thread i tried to be as detailed as possible, I would really appreciate any suggestions or tips to help me eliminate the transmission as a probable cause and track it down.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Have you tried shifting to 4hi? Could also be the transfer case.

The tranny in my 02 self destructed with grinding noises. Although I did not take it apart to find out what it was, I suspect the sun shell stripped and sent shrapnel everywhere. It did the noise at all RPMs however was worse while accelerating and wouldn't shift right.

 
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TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
My XUV does this too (its a V8 thou), and it was ruled a motor mount (which do need to be replaced).

The GMT360 line is known to failing motor mounts, so its something I would look into. They are easy to replace on the I6 motors.
 

ghost_leader07

Original poster
Member
Dec 18, 2019
152
UAE
Have you tried shifting to 4hi? Could also be the transfer case.

The tranny in my 02 self destructed with grinding noises. Although I did not take it apart to find out what it was, I suspect the sun shell stripped and sent shrapnel everywhere. It did the noise at all RPMs however was worse while accelerating and wouldn't shift right.


Thank you for responding,
My 4x4 switches between modes ok i guess but I haven't driven in 4Hi yet I was on 2Hi when the noise started but it was nothing like what you showed in the vid it was a brief grind that lasts about 1-2 seconds and whenever i try to do a hard acceleration the rattling noise appears around 2800rpm and goes away after 3000 rpm that happens without shifting into 3rd, it just appear around 2800rpm whether it's about to shift or not.
 

ghost_leader07

Original poster
Member
Dec 18, 2019
152
UAE
My XUV does this too (its a V8 thou), and it was ruled a motor mount (which do need to be replaced).

The GMT360 line is known to failing motor mounts, so its something I would look into. They are easy to replace on the I6 motors.

Thanks for the reply,
Well actually my motor mounts are quite bad and I'm going to replace them soon but i never guessed that they'd have something to do with the noise I'm getting.. I'll try to capture the noise on video though I'm not sure it'll pick it up because it's not that loud and a have a custom exhaust which is not helping in this particular issue lol
 

ghost_leader07

Original poster
Member
Dec 18, 2019
152
UAE
This sound like a transmission that is starting to wear out.

Seems unlikely because the noise coming from the engine bay driver side plus I've been maintaining it and has about 80k miles on it. Let's hope it's not the tranny. Fingers crossed
 

gmcman

Member
Dec 12, 2011
4,656
In addition to what's been suggested, does it feel like it has lost any power?

The delayed 3rd shift, does the tach needle rise slightly during the shift?

When the motor mounts are going bad, you can usually feel a vibration at idle @600 RPM, should be buttery smooth. Not discounting the motor mounts as your issue.

Curious about the 2-3 shift.

Also, the power steering lines run along thr area you describe. Since you said you can replicate this vibration in park, I would remove the serpentine belt for a short while, maybe a minute, and see if you can replicate that vibration again. At least rule out the steering lines.
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
Welcome to GMT Nation...

This is the Link to another GMTN Thread that has the "How to Change Out the Motor Mounts..." Information, plus an image from my "Flickr-Bucket" showing the ONLY ones to use. These are of course, made by ACDelco and while pricey and if you can find them, they'll last much longer than any Knock-Offs will after having to go through so much trouble involved with their R&Rs:


ACDELCOMOTORMOUNTS.jpg
 
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ghost_leader07

Original poster
Member
Dec 18, 2019
152
UAE
In addition to what's been suggested, does it feel like it has lost any power?
No it doesn't seem to have any power loss.

The delayed 3rd shift, does the tach needle rise slightly during the shift?
as a matter of fact it does rise slightly before shifting into 3rd i'm suspecting an issue with the 2-3 shift solenoid, already bought it and going to replace all of the solenoids and while i'm at it.

When the motor mounts are going bad, you can usually feel a vibration at idle @600 RPM, should be buttery smooth. Not discounting the motor mounts as your issue.
Yeah there's a vibration at idle and you can definitely feel it on the steering wheel and a lot more when turn off the car. i think my motor mounts are going out and i'm going to replace them and see if the issue persists.

Your analysis is pretty good you describe most of my issues lol, Thanks a lot and hopefully it's related to the motor mounts.
 

ghost_leader07

Original poster
Member
Dec 18, 2019
152
UAE
Something else just came to mind, small chance it could be your brake booster diaphragm.
I don't understand how is it related, can you explain? i'm carious since it'll only happen when accelerating and as i mentioned before around ~2800rpm.
 

ghost_leader07

Original poster
Member
Dec 18, 2019
152
UAE
Welcome to GMT Nation...

This is the Link to another GMTN Thread that has the "How to Change Out the Motor Mounts..." Information, plus an image from my "Flickr-Bucket" showing the ONLY ones to use. These are of course,

Thank you very much,

it seems like most of you guys suggesting a bad motor mounts as a probable cause for the noise i'm hearing.

These are of course, made by ACDelco and while pricey and if you can find them, they'll last much longer than any Knock-Offs will after having to go through so much trouble involved with their R&Rs:

Not a fan of getting cheap parts when it comes to engine parts so i'll definitely get ACDelco as you suggested.

Thanks again,
 
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gmcman

Member
Dec 12, 2011
4,656
I don't understand how is it related, can you explain? i'm carious since it'll only happen when accelerating and as i mentioned before around ~2800rpm.

When accelerating, you're changing the speed at which fluid runs through your power steering system. If you have lines that have deteriorated inside this could cause a restriction. These lines run on top of the LH frame rail behind the LF wheel to the steering rack.

In regards to your brake booster, this is less likely a cause, but there is a diaphragm inside that's operated by engine vacuum. If you have a hole in that it could fluctuate or possibly make a vibrating sound during changes in engine load but just something to check. Generally that would be more of an issue with the one-way valve outside the booster but something to check. The booster is mounted to the firewall behind the brake pedal.

Just giving you different possible scenarios if the issue is not with the engine mounts.
 
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gmcman

Member
Dec 12, 2011
4,656
as a matter of fact it does rise slightly before shifting into 3rd

When mine did that at around 160K, I had a check ball push through the seperator plate. You need to be easy on the shifts until you get this fixed. It doesn't take much to smoke the 3-4 clutch pack which is whats on the plate right now, and one of the most common failure points of the 4L60E.

I would look into a new seperator plate, 1-2 aluminum accumulator piston, new OE spring, new forward accumulator piston and spring, both shift solenoids won't hurt, easy to replace and could be a contributing factor if they are getting lazy, if not the sole contributor.

Removing the valve body isn't hard, just a little messy.
Yeah there's a vibration at idle and you can definitely feel it on the steering wheel

I missed this quote, and further solidifies the worn motor mount
 

ghost_leader07

Original poster
Member
Dec 18, 2019
152
UAE
I would look into a new seperator plate, 1-2 aluminum accumulator piston, new OE spring, new forward accumulator piston and spring

Is it possible to be done without taking the transmission off the truck?


both shift solenoids won't hurt, easy to replace and could be a contributing factor if they are getting lazy, if not the sole contributor

I think I'm going to try replacing the solenoids and Shift Position Sensor Switch first just to eliminate them and I'll check the parts you mentioned.

I missed this quote, and further solidifies the worn motor mount

Okay I'm going to replace them, now that i have some guidance on what to do to narrow some of the issues that i have.

Thanks @gmcman and everyone for your help 👍
 

gmcman

Member
Dec 12, 2011
4,656
Is it possible to be done without taking the transmission off the truck?


Absolutely, only removal of the valve body.

As mentioned, try the shift solenoids first. I would recommend changing them anyway if you are going to replace the seperator plate. That is the plate between the valve body and transmission case.

Also when you have the pan off, replace the filter (deep pan). I would get the plate, piston springs, solenoids from the dealer, as well as the filter but any OE filter would be good.

A dirty filter can starve the apply pistons and clutch pack and could contribute to a slow shift.

Either way, without removing the trans, there's only so much you can do. Sounds like you have a good game plan, just baby the 2-3 shift until you get it fixed, even just a slight coast for a second until it engages will help tremendously.

Filter and shift solenoids are easily changed with the pan off, just grab 5 quarts of ATF, Valvoline MaxLife is a great choice.
 
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