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Old 06-10-2019, 05:25 PM   #1
'70_402
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NEED HELP... where's the noise coming from??

I have a growl/grind noise coming from what feels/sounds like the trans area of my truck when i let off the accelerator. This has been there since i swapped the LS and 4l80E into my truck... i have since completely rebuilt my transmission (new torque converter) and rear end. I have a new driveshaft that was built when i did the swap. Its only when i let off the gas.. i can roll on and off the throttle and it comes and goes. does it in gear and in neutral while coasting. I have trailing arm suspension so my pinion doesn't rotate while under/not under load....

The noise was there before and is still there through all the things i've changed out chasing this growl.

Any ideas???
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Old 06-10-2019, 06:28 PM   #2
tj1970cst
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Re: NEED HELP... where's the noise coming from??

A sprag (aka one way bearing) in the transmission can cause that symptom.

As well as many many other things.
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Old 06-11-2019, 06:28 AM   #3
rockyrivermark
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Re: NEED HELP... where's the noise coming from??

How old are u joints?
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Old 06-11-2019, 06:54 AM   #4
Sparky dave
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Re: NEED HELP... where's the noise coming from??

You got the driveline angles ok when the ls went in?
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Old 06-11-2019, 07:06 AM   #5
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Re: NEED HELP... where's the noise coming from??

Have you checked Rear Diff Bearings/Gears?
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Old 06-11-2019, 10:39 AM   #6
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Re: NEED HELP... where's the noise coming from??

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Originally Posted by Sparky dave View Post
You got the driveline angles ok when the ls went in?
I think this might be my problem... my trans output shaft is pointing down 5 degrees.. my pinion is sitting at 0 degrees.

What way should my pinion be pointing?? up or down?

But... my pinion is actually higher in truck than the output shaft of the trans because of the drop.
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1970 CST/10 LWB factory buckets, Air, PS, PB, Cruise, 468, th400 - Sold....
1968 Bel Air Wagon 6.0/4l80e "Family Cruiser" - Sold
2006 TBSS - Sold
1996 Chevy Z71 Daily Driver
Current project '68 SWB
Build Thread : http://67-72chevytrucks.com/vboard/s...d.php?t=757551
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Old 06-11-2019, 10:47 AM   #7
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Re: NEED HELP... where's the noise coming from??

Quote:
Originally Posted by '70_402 View Post
I have a growl/grind noise coming from what feels/sounds like the trans area of my truck when i let off the accelerator. This has been there since i swapped the LS and 4l80E into my truck... i have since completely rebuilt my transmission (new torque converter) and rear end. I have a new driveshaft that was built when i did the swap. Its only when i let off the gas.. i can roll on and off the throttle and it comes and goes. does it in gear and in neutral while coasting. I have trailing arm suspension so my pinion doesn't rotate while under/not under load....

The noise was there before and is still there through all the things i've changed out chasing this growl.

Any ideas???
It could be something as simple and normal as motor mount flex.. When you let off the gas, the mounts might be flexing just enough to allow an exhaust pipe, or some other component, touch the frame, thus amplifying a normal low level noise.. But that's just a guess on my part.

Diagnosing and locating the source of a noise over the internet is as difficult as emailing a piece of Mom's apple pie.. No matter how hard you try, you just can't do it.. All the posters have great intentions but they're just guessing. Nothing has been accomplished.. The worst thing you can do is throw some parts at it and hope "something sticks".. I suggest you take your truck to an experienced shop/mechanic and have them listen to it.. Then you'll know for sure..
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Old 06-11-2019, 11:29 AM   #8
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Re: NEED HELP... where's the noise coming from??

Quote:
Originally Posted by RustyPile View Post
It could be something as simple and normal as motor mount flex.. When you let off the gas, the mounts might be flexing just enough to allow an exhaust pipe, or some other component, touch the frame, thus amplifying a normal low level noise.. But that's just a guess on my part.

Diagnosing and locating the source of a noise over the internet is as difficult as emailing a piece of Mom's apple pie.. No matter how hard you try, you just can't do it.. All the posters have great intentions but they're just guessing. Nothing has been accomplished.. The worst thing you can do is throw some parts at it and hope "something sticks".. I suggest you take your truck to an experienced shop/mechanic and have them listen to it.. Then you'll know for sure..
I agree, but sometimes you get lucky and have someone who has went through the same exact issues and has a fix or an idea... right now i'm leaning towards driveline angles... that's my next area i need to familiarize myself with...
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1970 CST/10 LWB factory buckets, Air, PS, PB, Cruise, 468, th400 - Sold....
1968 Bel Air Wagon 6.0/4l80e "Family Cruiser" - Sold
2006 TBSS - Sold
1996 Chevy Z71 Daily Driver
Current project '68 SWB
Build Thread : http://67-72chevytrucks.com/vboard/s...d.php?t=757551
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Old 06-11-2019, 01:04 PM   #9
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Re: NEED HELP... where's the noise coming from??

Does it only do it when the Drivetrain is in motion or does it do it when coming off a load; if you put it under load (power brake it like you going to do a burnout) but dont actually let the drivetrain start turning, does it make the noise when you release the load?
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Old 06-11-2019, 03:24 PM   #10
'70_402
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Re: NEED HELP... where's the noise coming from??

Quote:
Originally Posted by Minkota View Post
Does it only do it when the Drivetrain is in motion or does it do it when coming off a load; if you put it under load (power brake it like you going to do a burnout) but dont actually let the drivetrain start turning, does it make the noise when you release the load?
It's when i'm coming off engine load while the drive-train is moving. does not do it while i'm stationary.
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1970 CST/10 LWB factory buckets, Air, PS, PB, Cruise, 468, th400 - Sold....
1968 Bel Air Wagon 6.0/4l80e "Family Cruiser" - Sold
2006 TBSS - Sold
1996 Chevy Z71 Daily Driver
Current project '68 SWB
Build Thread : http://67-72chevytrucks.com/vboard/s...d.php?t=757551
Gas Pedal Adapters For Sale http://67-72chevytrucks.com/vboard/s...d.php?t=746099
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Old 06-11-2019, 04:11 PM   #11
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Re: NEED HELP... where's the noise coming from??

Quote:
Originally Posted by '70_402 View Post
I think this might be my problem... my trans output shaft is pointing down 5 degrees.. my pinion is sitting at 0 degrees.

What way should my pinion be pointing?? up or down?

But... my pinion is actually higher in truck than the output shaft of the trans because of the drop.
That needs to be resolved before you do anything else.

Read here. From Inland Empire: Driveline. https://www.iedls.com/Power_Train




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Old 06-11-2019, 06:18 PM   #12
Sparky dave
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Re: NEED HELP... where's the noise coming from??

Quote:
Originally Posted by '70_402 View Post
I think this might be my problem... my trans output shaft is pointing down 5 degrees.. my pinion is sitting at 0 degrees.

What way should my pinion be pointing?? up or down?

But... my pinion is actually higher in truck than the output shaft of the trans because of the drop.
Think the angles should match if possible. Some people shim the u bolts ( see pic) or remove the welds and rotate, then re-weld. Also flipping the trailing arm bracket helps pinion angle on lowered trucks. Even if itís not the cause of the noise maybe it would put you in good stead for the future reliability
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