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Old 12-03-2012, 04:04 PM
Telly Telly is offline
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Default Drive Train Thumping Noise

I've had my 78 FJ40 for a few months and I'm trying to diagnose a strange thumping/knocking sound coming from the transfer case or clutch area. It occurs when I'm turning with the clutch depressed. Prime example is when I'm backing out of the garage in a turn and coasting to a stop. Doesn't matter if I'm going forward or reverse. It's not a metal on metal sound...more like a sound of something loose...like "thonk, thonk, thonk" until I straight out and engage the tranny. I've checked all motor mounts, exhaust system and checked for any loose parts but found nothing. It does have a rear Aussie locker but the sound not coming from the rear axle but the locker may be culprit? It's not the front axle because the sound still exists after installing new bearings and locking hubs (that is where I though it potentially coming from prior to doing the rebuild). Thoughts? Thanks. Doug
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Old 12-03-2012, 04:11 PM
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Another potentially related deal is when I'm shifting a hard acceleration (like an on ramp) the rear of the truck shifts slightly, which would be flat scary on a icy road. I'm thinking Aussie Locker again?
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Old 12-03-2012, 04:33 PM
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Originally Posted by Telly View Post
Another potentially related deal is when I'm shifting a hard acceleration (like an on ramp) the rear of the truck shifts slightly, which would be flat scary on a icy road. I'm thinking Aussie Locker again?
that's the aussie locker.

it gives you one wheel drive till the other tire "catches up" so it'll tend to pull under acceleration.
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Old 12-03-2012, 04:41 PM
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Is the ebrake on a '78 behind the transfer case? Could your ebrake be grabbing the drum and causing a "clunk?"
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Old 12-03-2012, 04:46 PM
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I think the fact that this happens only when you are in a turn is the best evidence of what the culprit is...
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Old 12-03-2012, 05:20 PM
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I know the locker comes in handy in the rocks but I hate it driving around town. I've experienced the loud BANG a few times and it scares the $hit out of me.
That clunking can't be good on the t-case either. Doug
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Old 12-03-2012, 05:24 PM
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Originally Posted by Telly View Post
Another potentially related deal is when I'm shifting a hard acceleration (like an on ramp) the rear of the truck shifts slightly, which would be flat scary on a icy road. I'm thinking Aussie Locker again?
Thats called "torque steer" and the only way to stop it is to ditch the aussie locker.

Does it make the noise when you are turning if the clutch isnt depressed? Try backing up & turning like you do but put it in neutral, let the clutch out and see if the noise is still there while coasting.

As previously stated, its most likely the aussie locker as they are really noisy when turning tightly on pavement. They will thump and click pretty good, every now and then it will let out a loud BANG! and you'll think you broke an axle.
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Old 12-03-2012, 05:31 PM
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Thats called "torque steer" and the only way to stop it is to ditch the aussie locker.

Does it make the noise when you are turning if the clutch isnt depressed? Try backing up & turning like you do but put it in neutral, let the clutch out and see if the noise is still there while coasting.

As previously stated, its most likely the aussie locker as they are really noisy when turning tightly on pavement. They will thump and click pretty good, every now and then it will let out a loud BANG! and you'll think you broke an axle.
I did notice the clunking when decellerating on a tight, down hill off-ramp without the clutch depressed. The PO gave me the original rear diff parts so the aussie locker will be removed. I was planning to drive the rig some in the snow but I'd be in the ditch after the first "torque steer" hits me. Wish I had the funds for front/rear ARB air lockers
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Old 12-03-2012, 05:34 PM
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BTW Air Randy, I looked at a 1970 Boss 351 when I was 13 year old. Ended up buying a 68 Camaro RS, that now sports a 427 and a TKO 5-speed. Yeah...it's a money pit.
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Old 12-03-2012, 07:41 PM
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BTW Air Randy, I looked at a 1970 Boss 351 when I was 13 year old. Ended up buying a 68 Camaro RS, that now sports a 427 and a TKO 5-speed. Yeah...it's a money pit.
Yeah, but they are soooo much fun!
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