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Hello, I'm trying to diagnose a 'chuck-chuck-chuck' noise on my '99 van. 116K miles, AAMCO rebuilt tranny at 85K 4yrs ago, 3.8L AWD. Driveability is fine, runs great, smooth changes, quiet, fresh ATF4+. However, at idle in park, turning A/C on will cause the noise to happen when the compressor clutch engages. Disappears when A/C off or clutch disengages. So it will cycle chuck-chuck-chuck for a minute, then disappear for a minute, then repeat. Slight revs (1000rpm) will also stop the noise, even if A/C is running.
Eliminated the A/C and all drive belt accessories by running without the belt fitted. By putting it in drive (low rpm) I can just hear the same noise, albeit much fainter. So I think the A/C pump, power steering, alternator, etc is not the cause.
So is this the "Bearing Knock" referred to below that is caused by crankshaft load? Anyone had any similar experiences? It's not top end noise, but hard to locate between sump/dust cover/tranny housing. Definitely bottom end though. Am I about to throw a main bearing :ask_wsign Is it easy to change No.1 bearing with engine/crankshaft in place?

http://www.rebuiltautoengines.com/dodge-caravan-articles.html

Many thanks for any suggestions that I might have overlooked.
- Clive
 

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Hello, I'm trying to diagnose a 'chuck-chuck-chuck' noise on my '99 van. 116K miles, AAMCO rebuilt tranny at 85K 4yrs ago, 3.8L AWD. Driveability is fine, runs great, smooth changes, quiet, fresh ATF4+. However, at idle in park, turning A/C on will cause the noise to happen when the compressor clutch engages. Disappears when A/C off or clutch disengages. So it will cycle chuck-chuck-chuck for a minute, then disappear for a minute, then repeat. Slight revs (1000rpm) will also stop the noise, even if A/C is running.
Eliminated the A/C and all drive belt accessories by running without the belt fitted. By putting it in drive (low rpm) I can just hear the same noise, albeit much fainter. So I think the A/C pump, power steering, alternator, etc is not the cause.
So is this the "Bearing Knock" referred to below that is caused by crankshaft load? Anyone had any similar experiences? It's not top end noise, but hard to locate between sump/dust cover/tranny housing. Definitely bottom end though. Am I about to throw a main bearing :ask_wsign Is it easy to change No.1 bearing with engine/crankshaft in place?

http://www.rebuiltautoengines.com/dodge-caravan-articles.html

Many thanks for any suggestions that I might have overlooked.
- Clive
Maybe the flywheel, better check it for cracks.
 

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I would get a mechanical oil pressure gauge to see what the actual oil pressure reads. Also it may be a wise idea to cut open the oil filter to look for bronze pieces in the filter, which would mean an eaten up bearing.
 

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You sure it's not the A/C compressor ?

As for the bearings, you can drop the engine pan and have total access to ALL the bearings. Just loosen the caps (rods and mains) and replace ALL, if you're worried. Easy as pie, use some white grease on the bearing surfaces as you replace them. Don't want to install them "dry" ..... :jpshakehe
 

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As I recall, bearing knock is most noticeable when you release the gas after acceleration. When you release the load, you hear it. Under load it keeps the rods in contact with the crank. That is what I remember from previous diagnostic discussions. But someone may correct me on that. Have you had the high pressure checked on your AC? Could a stuck H valve be creating excessive pressure on the compressor?
 

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It sounds like you are reporting a very common noise from the 3.3 and 3.8 liter engines, a noise that virtually all of these engines have (at least from Gen 3 vans), and a noise that doesn't affect the lifespan of the engine one bit.

FWIW #1, I first heard that noise on our 1998 DGC 3.8 back when it had like 30,000 miles on it. At the 170,000 mile mark (when I traded the old girl in), the noise was still there, no better, no worse.

FWIW #2, this noise has been debated here and on other forums for years, and while I don't think I've ever seen any definitive evidence that fingers any one component, the popular consensus seems to be that the noise emminates from the timing chain (or at least from within the timing chain cover).

Long story short, you've got nothing to worry about and at least a couple of hundred thousand miles of problem life left in your engine. ;)
 

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Does it make any difference(amount of noise) if the engine is cold or hot? I really doubt it is a crank bearing. Anyway, always assume the simplest/easiest things first. If a bearing, you will notice more knocking at hot temps. when oil thins and at higher RPMs. Also as mentioned, your oil pressure would be fairly low.

I had an old Ford, 289 engine that would do the "clunk, clunk, clunk" only at idle and only when hot. Turned out to be the camshaft spacer and was camshaft end "slap". Not saying that is it in your case but sometimes its the *craziest* "tings".

Also, remember that when a load kicks in (A/C compressor), the engine RPM may be changing (lower) and that aggravates the noise.
 

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Sounds like it may be a cracked torque plate. Remove the tin between the engine and the transmission and see if there is ANY play. Try to rock the torque converter back and forth. If there is ANY free play, the torque plate is cracked. You can't see the damage without dropping the transmission.
 

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Discussion Starter #9
Thanks for the responses! Not had time to pull the dust shield, but drove it today and it no issues at all. Ran A/C back at home, no unusual noises whatsoever. Could not make it repeat the chuck-chuck-chuck at idle. Which means what? A bad bearing can't fix itself can it? Maybe loose t/c bolts still that occurs intermittent? I'll see if cold/hot makes a difference (didn't think it did before), or if just-started (alternator draw) or long run (idle alternator).
 

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A sticky lifter could make a knock and if it cleared itself it could go away. Just monitor the engine and keep us updated
 

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Discussion Starter #11
Noise returned this am when engine cold, with A/C running. Barely perceptible with A/C off, requires a little throttle blip to hear it. Pulled the tin and inspected the flywheel/starter ring from the engine side. All 4 t/c bolts were a little loose, tightened them each about 1/3 turn. No cracks in the flywheel, no missing teeth. Can't view the crankshaft bolts. Would that 1/3 - 1/2 turn be my issue? Not fired it up - tomorrow will tell (after I replace the PCV hose I broke replacing the PCV).
Noted A/C kicking in drops rpms a little that's when I hear the noise at the lower rpm. Will it be there tomorrow?!?!
 

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Noise returned this am when engine cold, with A/C running. Barely perceptible with A/C off, requires a little throttle blip to hear it. Pulled the tin and inspected the flywheel/starter ring from the engine side. All 4 t/c bolts were a little loose, tightened them each about 1/3 turn. No cracks in the flywheel, no missing teeth. Can't view the crankshaft bolts. Would that 1/3 - 1/2 turn be my issue? Not fired it up - tomorrow will tell (after I replace the PCV hose I broke replacing the PCV).
Noted A/C kicking in drops rpms a little that's when I hear the noise at the lower rpm. Will it be there tomorrow?!?!
I still say you're chasing a phantom. All of the 3.3 and 3.8 liter Gen 3 engines that I've ever listened to have a very subtle knock at idle, especially when the A/C is on. Is it the timing chain? Don't know, and to me at least, it matters not. Like I said before, I first identified the noise on our 1998 when it had only 30,000 miles on the clock. After an additional 140,000 miles, the noise was unchanged and the engine ran as strong (if not stronger) the day I traded it in as the day I drove it off the showroom floor.
 

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Discussion Starter #13
Actually, that 1/2 turn on all 4 torque converter bolts was my issue. Easy to tighten after removing 2x10mm bolts + larger bolt to access behind the tin dust shield. Absolutely smooth again, no knocking whatsoever. Wouldn't think it could be cured so easily. Had imagined failing power-steering, bad crankshaft bearings, tranny issues. But I guess they either work loose over time, or AAMCO didn't torque them up correctly when the tranny was rebuilt 35Kmiles ago. Not braved adding locktite for fear of making removal if (when) tranny needs work again. I'll know what's causing the noise if it reoccurs. Not seen the inside of the flywheel, but the outer radius appears quite thick (5mm?) where the starter ring is welded on. Wouldn't think the ~200hp could crack that? Is it thinner at the crankshaft? Which piece 'flexes' - certainly not the outer radius!

Appreciate the help here guys, I know where to come back for the next issue.
 
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