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Old 10-01-2018, 05:21 PM
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Grinding of left turn acceleration

Mu truck's running an '03 crown vic front & '96 T-bird rear. Ford 300-6 and small block C-6.
If I accelerate hard while making a left turn, I get a hellacious grinding noise. Right turn is OK. Straight acceleration is OK. Left & right without gas is OK. I replaced the left front hub-no change. I replaced the left rear bearing which was lunched-no change.
Motor mounts are new and there are no marks where anything rotating is hitting anything not. Wheels do not hit. Driveshaft does not move as rear is IRS.
My thoughts are: This is an 8.8 track lock diff. Running 75-90 synthetic w/friction modifier. Are the clutches chattering and if so, then why not on right turns? 2) Is the trans cavitating? Got plenty of fluid.
If it starts to grind, I can back off & it goes away but comes back with a little gas. Help!

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Old 10-02-2018, 03:55 AM
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If nothing is rubbing, then head off to a parking lot with a friend and have him/her stand next the car as it makes the noise and attempt to identify where the noise is coming from. Also hanging out the window to listen for the location of the noise might work as well. f course a bit of care and caution must be taken to keep from hurting yourself or your assistant.
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Old 10-02-2018, 05:21 AM
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I have had a starter problem cause something like this when whatever holds the gear away from the flexplate got sloppy. If the gear flops back and forth really easy, could be your grinding sound. Happened to me in a FWD car so it was mostly the turning not the acceleration and it was VERY loud. Starter gear tickling the flexplate. I stuck my camera under there with it running and jacked it up just enough to make the noise start. When I watched the vid it's audio helped me pinpoint the noise source. Took off the dust cover with engine off and found the gear not being held back firmly, it easily slid around with a finger. New starter=noise gone. Its another something to check.
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Old 10-02-2018, 09:49 AM
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I rebuilt the starter so I wouldn't have to fight the headers if it went bad but it's certainly worth checking out. It kind of has that sort of grinding sound. The rear bearing really needed replacing though so I'm glad that I checked that out anyway.
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Old 10-03-2018, 05:52 PM
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Pulled the starter. Had to do a Houdini to get it out. A 3/32 X 1 roll pin fell on the ground. Inspected the gear mechanism thinking that it came from there. The main pivot is about 5/16 and was intact. Retraction spring was strong so I don't think it's a starter problem. Reinstalled & drove it. Same problem. Nothing inside the bell has a roll pin so I'm baffled as to its origination.
Checked the left rear bearing and it's OK. Shock shield got crunched from a pot hole because it's a little too close to the A arm but that's from a right turn.
I wonder if it's the carb? It's an old Holley 465cfm 4 bbl with side pivot bowls. It sits on an Offy dual plane. It's mounted sideways. There's a pronounced whistle at off idle but I understand that it's not unusual for Holleys to do that. I don't have a whistle in the vent and wonder if I'm getting a bunch of fuel out the vent & the engine's not happy. Thinking of spinning it 180 and seeing what happens.
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Old 10-03-2018, 09:41 PM
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See if this helps you out:

https://www.hotrodders.com/forum/tra...es-136763.html

Pep
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Old 10-04-2018, 09:55 AM
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Quote:
Originally Posted by rip-tide View Post
I had wondered that too. I've only got 500 miles on it but the diff is OEM from '96. Heard some noise back there (probably that bearing) so I checked the diff & it was low. Thought I'd be nice & change the lube out. Went with valvoline synthetic & NAPA modifier. That could be very well what's happening. Got no leaking from the pinion & it feels tight. A bit of back lash but no big deal. Seems strange that it's only on left turns not right.
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Old 10-04-2018, 10:55 AM
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I run a 9" trac lock on my Ford and I get a scrubbing sensation on slow-tight left and right turns. The rear has maybe 5000 miles on it, just checked the fluid last week. I may dump the fluid, change it and add a bottle of friction modifier. The lube is Valvoline 75-90 and was okayed by Quick Performance that built the rear. They steered me away from using a synthetic oil. I would try a mineral-based product.
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Old 10-04-2018, 08:51 PM
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I have a crusty old stock 12 bolt from an el Camino in my car. When I don't drive it much, it gets clicky. Not loud, but you feel it too. An ancient GM tech (RIP) told me drive it in tight figure eights alternately in reverse and forward, slowly. Explaining that, he said it takes lubricant to areas that don't otherwise get it. Beyond that, he said change lube several times (it had sat for twenty years). Those things have always restored quiet operation for me. I know nada about gears. But sort of like how a guy periodically ought to do a few quick stops in reverse to adjust drum brakes, the figure eights work like exercise.
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Old 10-05-2018, 06:46 AM
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Just adding a thought or two. The rear operates normally as you think it should, the biggest part of the time. Only hard acceleration and a tight left turn produce the noise..

Think a track lock diff is not an OEM piece as mentioned, with that in mind. Try this, the hardware has a specific purpose and design.

A straight cut geared transmission whines like h ell to the average person, music to me.

Connecting the dots it is possible the track lock posy because of the design. Could make a noise under certain conditions.

A race piece is designed for hard duty, big power will have noise, and be perfectly functional.

I cannot speak directly about the track lock unit. The posy units I run are Eton or factory.

Taking the car out and doing a rain dance with it. I do not MO think it will prove to be a valid fix. The noise you here under a specific set of circumstances, just maybe normal .

Left axle when pulled on does not have excessive in/ out play. Not seeing gear oil around the backing plate, as it the axle were the wrong dimensions. Everything rolling free ?

Keep a close ear on it, if it's going to get hairy. The noise in a left turn will become more frequent, with less acceleration, the wider the turn.


Just saying,

Pep
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Old 10-25-2018, 04:32 PM
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F-me

As it turns out it was a broken motor mount. Not high on my list as it was new 700 miles ago. Either it was a faulty mount or the torque of the mighty 6 banger ripped it. I might steal a torque rod from the junk yard and fabricate mounts. Use to use a chain in the old days but noise transmission was horrendous. The actual grinding was from the water pump pulley bolts hitting the back of the electric fan motor.
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The Following 3 Users Say Thank You to belchfire For This Useful Post:
idrivejunk (10-25-2018), John long (10-25-2018), lmsport (10-25-2018)

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