Author Topic: Noise problem under acceleration  (Read 432 times)

Offline Tiny

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Noise problem under acceleration
« on: May 10, 2017, 04:44:32 AM »
Hi all, I have a bad noise I just cannot seem to diagnose.  I have a 66 Coupe 289 Auto.  Under acceleration up a hill I get this real bad screeching/scraping/Grr sound relating to engine revs and when it is under load.  I have disconnected all fan belts and eliminated, power steering pump, water pump and alternator.  I replaced starter motor thinking this was the issue but sadly no.  The noise sounds similar to a starter motor being engaged after an engine has been started but I'm sure this is not the issue.

The noise is not present when car is stationary no matter how much i rev the engine, it is only there under load.  Its definitely sounds metallic and stops as soon as i back of the revs.

I have checked the the flex plate via the inspection hole, no sign of wear marks or similar.  Nothing on the starter motor either.  I was doing some research on flex plate balance weights and the 289 should have a 28 ounce weight.  Does the attached photo show a 28 ounce or a 50 ounce.  Could this be the issue??

Its got me stumped.  Anyone had any similar issues.

Thanks

Offline midlife

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Re: Noise problem under acceleration
« Reply #1 on: May 10, 2017, 08:00:08 AM »
Under load, the drive train will rotate a bit more than under no-load conditions, so check to see if there's any interference with the drive train with e-brake cables, mufflers, etc.  You may have a degraded motor or tranny mount.

Offline Tiny

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Re: Noise problem under acceleration
« Reply #2 on: May 10, 2017, 08:37:22 AM »
Thanks will have a look at that.  Its a real screeching sound rather than something rubbing and quite metallic.  Stationary I can rev the engine 4-5k RPM not a sound but as soon as I get some heavy load whilst driving the noise starts and is very consistent with the quick rise in revs rather than a steady build up of speed.

Offline svo2scj

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Re: Noise problem under acceleration
« Reply #3 on: May 10, 2017, 10:31:57 AM »
You were smart to eliminate areas (like the belts and starter) !   Was free right !!

I too would be looing at condition of mounts, as well as SIGNS of interferance (chaffing, clearancing).   Check the torque of motor or bell bolts especailly if trans mount is junk.   

Mark
P.S.  Get a look at the condition of the universal joints too (through the entire rotation)
1969 R Code , Sportsroof (non Mach) W Axle
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Offline mtinkham

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Re: Noise problem under acceleration
« Reply #4 on: May 10, 2017, 01:40:53 PM »
You mentioned inspecting the flex plate, did you check the torque converter bolts? How about the plate between the engine and transmission - any dents or warpage? Have you inspected the entire surface of the flex plate that is visible through the inspection opening?
1967 S-code Fastback, GT, 3-speed manual, Metuchen, Scheduled 04-21-1967 - Actual 04-25-1967

Offline jwc66k

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Re: Noise problem under acceleration
« Reply #5 on: May 10, 2017, 02:18:57 PM »
Hi all, I have a bad noise I just cannot seem to diagnose.

I have checked the the flex plate via the inspection hole, no sign of wear marks or similar.  Nothing on the starter motor either.  I was doing some research on flex plate balance weights and the 289 should have a 28 ounce weight.  Does the attached photo show a 28 ounce or a 50 ounce.  Could this be the issue??

Was the engine recently re-installed? If so, the flex plate is "keyed" to be installed to the torque converter and can be done incorrectly.
Jim
I promise to be politically correct in all my posts to keep the BBBB from vociferating.

Offline J_Speegle

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Re: Noise problem under acceleration
« Reply #6 on: May 10, 2017, 05:07:39 PM »
Just as a test you might get someone to either listen from the side with the hood open or act as operator while you place the car in gear with the brakes on (power brake sort of operation) don't break the tires loose but see if the sound returns and if so the person listening may be able to pin point the noise closer.

Make sure there is nothing for a long ways in front of the car, I would choose a road way rather than concert and never gravel ;)

Also watch to see how much the engine rises during the increase in load.

Since you have tested will all exterior rotating things disconnected (not rotating)  No belts, no fan, no pulleys except for the crank pulley of course and that the engine and trans  (at least internally) all rotate together and do not change in orientation with one another once placed under torque.

If you have grinding you surely have fillings and fresh clean surfaces where the metal is being removed.

Sounds and issues like this aren't not the easiest things to help with over the internet   ::) but lets we what we can figure out
Jeff Speegle

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Offline Tiny

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Re: Noise problem under acceleration
« Reply #7 on: May 10, 2017, 06:11:12 PM »
Thanks guys, will have a look at all your suggestions.  Will take a few days to test all avenues and I will get back to you and let you know how I go.

Cheers

Offline Tiny

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Re: Noise problem under acceleration
« Reply #8 on: May 13, 2017, 06:32:40 AM »
Hi all, well I inspected the mounts and found the passenger side mount and Transmission mount were fatigued so I replaced them.  I road tested the car and found that the noise has almost gone.  Sometimes under load the noise is not there at all but other times I can still hear it although not as bad as before.  Driving the car in a normal fashion now appears to be okay.  As I'm not a rev head I should be able to drive it sedately.

I'm still not sure how I can reduce the noise by changing the mounts as it was a metallic type sound.  But any it seems to have improved a lot.

Thanks to all of your responses and help.  Much appreciated.

Offline rrenz

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Re: Noise problem under acceleration
« Reply #9 on: May 13, 2017, 09:39:23 AM »
Is it possible that the bad mounts were causing the engine and drive train to move around under load into an un favorable position for the u joints causing the sound? Perhaps U joints need to be replaced?
1966 C Code NJ Springtime yellow
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Offline Texas Swede

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Re: Noise problem under acceleration
« Reply #10 on: May 13, 2017, 04:52:47 PM »
My friend Roland in Sweden had a similar noise under load in his 1970  GT350 Convertible with a FMX Automatic.
It turned out to be a looking seal in his transmission. Just a tip.
Texas Swede

Offline Tiny

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Re: Noise problem under acceleration
« Reply #11 on: May 14, 2017, 05:24:30 AM »
Hi all, this issue is still bugging so so I have done some more research and found a YouTube clip of the noise I am talking about.  Looks like it is probably more than likely the flex plate.  See the link below.  The clip doesn't rev the engine hard as it is stationary under load however its pretty well the noise I am getting.  I now have to find some time to remove the Transmission.

https://www.youtube.com/watch?v=IS-BBO4fvIg