Rattling from underneath...

Rattling from underneath...

Postby Casey [OP] » June 4th 2009, 1:44am

'95 Astro w/94K. New to me in March, but I had a '90 for 3 years before that, so I'm semi-Astro familiar.

Here's the issue- I'm getiing a fairly loud rattle (well it sounds like a rattle to me) from the engine or possibly the TC. I had a loose honeycomb inside the cat-con, so that's not what's rattling. No exhaust rattling.

The rattle doesn't start until the engine gets up to about 160* or so. When I start and drive it cold, there's no noise. Once it's up to operating temp (210*), the rattle is present even at idle. The rattle is loudest just as the trans shifts gears under mid-full throttle. If I'm only on the throttle lightly, there's no audible rattle, or at least not nearly as loud as when I'm on the throttle.

When I re-did the exhaust I pulled the lower bellhousing cover and rotated the flexplate by hand. I'm 99% sure the van was in PARK at the time. Anyhoo, as I rotated the flexplate back and forth I could 'feel' some play, but I had no idea where it was coming from. I fear it's a rod knock I'm hearing, but I've never actually heard one live and in person, so I don't want to mis-diagnose it. The sound is a bit 'chattery' like a loose rocker arm would sound (I have a Slant Six so I know all about clattering valvetrain :D ), so I will be pulling the valve covers this weekend to have a look at them, but the sound sounds like it's coming from the lower and rear of the engine...or the front of the trans, right at the TC.

All of the TC-to-flexplate bolts were tight, as I did check those when I had the cover off.

The van had a decent maintenance record (regular oil changes, etc.) but was only driven a few thousand (like 4,000) miles over the last four years. This noise has developed in the last 3-4 weeks or so, but it doesn't sound like it's getting any louder. Oil pressure is 60-ish right after a cold start, then drops to 40-47 at cruise (2,000 rpm) when fully hot (210*). Hot idle oil pressure is 20 psi. I've changed the twice on the van in the 4,000 miles I've owned it, and it looked clean both times- I saw no metal or questionable material either time.

I did also change out the trans filter (was original w/90K miles) and fluid (probably original, too), and it looked pretty good (not dark red, not burnt, etc.), and added new fluid to the correct level. Trans shifts fine as far as I can tell and the van has no other issues. No SES light nor codes (did have a bad EGR which was replaced two months ago).

I'll probably drop the oil pan this weekend and check out the crank rod ends and bearings. Can the pan be dropped with the engine in place? I'm guessing I need to remove the oil pump pickup tube to get the pan fully off. Do I need to remove the lower trans cover, too, in order the get the oil pan off?

Comments and advice are welcome. :think:
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Re: Rattling from underneath...

Postby Matrixx » June 4th 2009, 6:54am

Hi Casey

The important thing here is to make sure where the rattle is coming from (externally or Internally). It could be the timing chain- or dip stick tubes broken from their mounts will rattle big time. If you could let us know if it's internal or external that would be great, thanks. A stethoscope would really help pin it down. :)
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Re: Rattling from underneath...

Postby Casey [OP] » June 4th 2009, 3:02pm

It's internal. I've checked everything external I can, and I see nothing lose.
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Re: Rattling from underneath...

Postby astro355 » June 4th 2009, 3:32pm

Casey wrote:It's internal. I've checked everything external I can, and I see nothing lose.


That really doesn't mean its internal. When someone says to me its a rattle, that's usually external. Internal noises are typical deeper in tone (bass) while external noises have a higher pitch (treble).

And how do you rotate the flexplate by hand with the van in park? Where the torque converter bolts removed? Were all four tires off the ground? :confused:
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Re: Rattling from underneath...

Postby Casey [OP] » June 4th 2009, 7:22pm

astro355 wrote:
Casey wrote:It's internal. I've checked everything external I can, and I see nothing lose.


That really doesn't mean its internal. When someone says to me its a rattle, that's usually external. Internal noises are typical deeper in tone (bass) while external noises have a higher pitch (treble).

And how do you rotate the flexplate by hand with the van in park? Where the torque converter bolts removed? Were all four tires off the ground? :confused:


Like I said, I've never heard a rod knock before, so what someone says is a rattle might actually be a knock to someone else. It could be something out of balance (TC) internally that's causing the rattling sound, but the TC balance weight was still intact when I looked. Yes, the van was in PARK and the parking brake was set with all four tires on the ground- I was working under the van on the exhaust system. As I said, all of the TC bolts were tight and looked to have never been removed.

I'm going to pull the doghouse this weekend and see if that helps me pinpoint to sound a bit easier. It sounds like it coming from the right side of the engine so I'll check things out.
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Re: Rattling from underneath...

Postby astro355 » June 4th 2009, 11:53pm

How were you under the van doing exhaust work with all four tires on the ground and able to turn the flexplate by hand with it in park? Am I missing something here?
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Re: Rattling from underneath...

Postby Casey [OP] » June 5th 2009, 3:52am

astro355 wrote:How were you under the van doing exhaust work with all four tires on the ground and able to turn the flexplate by hand with it in park? Am I missing something here?


Remove six exhaust manifold studs, remove exhaust clamp at joint rearward of cat-con, drop pipe. Remove lower trans cover, rotate flexplate by hand to inspect all bolts, verifying they were tight.

I'm just looking for advice or suggestions from anyone else who's had a similar rattling/knocking/hammering/call-it-what-you-like noise coming from their van that they felt wasn't external (i.e. loose exhaust, bad alternator bearing, etc.).
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Re: Rattling from underneath...

Postby gtkane » June 5th 2009, 4:01am

Broken flywheel.

It's VERY hard to see, but they crack around the 6 bolts that hold it to the crank. If you unbolt the converter and push it into the trans, pry the flywheel forward and back while watching. if it's cracked, you'll see or hear it.
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Re: Rattling from underneath...

Postby Matrixx » June 5th 2009, 4:12am

Hi Casey

Good advice given so far to check out. If you say it's on the right side, then might I suggest also you check the oil and transmission support bracket located on the passenger side intake manifold towards the front.

Mine broke, and it rattled to no end when I gave it gas. I used JB weld on it, and it has been good ever since (8-years ago now). Just another area to check as to what's already been mentioned.:)
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Re: Rattling from underneath...

Postby Casey [OP] » June 5th 2009, 4:45am

Matrixx wrote:Hi Casey

Good advice given so far to check out. If you say it's on the right side, then might I suggest also you check the oil and transmission support bracket located on the passenger side intake manifold towards the front.

Mine broke, and it rattled to no end when I gave it gas. I used JB weld on it, and it has been good ever since (8-years ago now). Just another area to check as to what's already been mentioned.:)


I checked that this afternoon, and the bracket is not bolted to the right front corner of the intake, but that isn't making any noise. I held it it firmly and throttled up the engine and still had the noise present. I wish it was that easy of a fix, but not this time. :(
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Re: Rattling from underneath...

Postby Casey [OP] » June 5th 2009, 4:48am

gtkane wrote:Broken flywheel.

It's VERY hard to see, but they crack around the 6 bolts that hold it to the crank. If you unbolt the converter and push it into the trans, pry the flywheel forward and back while watching. if it's cracked, you'll see or hear it.


Hmmm, I will be dropping the trans pan again this weekend and will ltake a look at the center of the flexplate. I guess if I had my choice, a cracked flexplate would be better than a rod knock...
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Re: Rattling from underneath...

Postby astro355 » June 5th 2009, 5:11am

Casey wrote:
astro355 wrote:How were you under the van doing exhaust work with all four tires on the ground and able to turn the flexplate by hand with it in park? Am I missing something here?


Remove six exhaust manifold studs, remove exhaust clamp at joint rearward of cat-con, drop pipe. Remove lower trans cover, rotate flexplate by hand to inspect all bolts, verifying they were tight.

I'm just looking for advice or suggestions from anyone else who's had a similar rattling/knocking/hammering/call-it-what-you-like noise coming from their van that they felt wasn't external (i.e. loose exhaust, bad alternator bearing, etc.).


How high does your van sit off the ground?
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Re: Rattling from underneath...

Postby Big_kid » June 5th 2009, 2:08pm

gtkane wrote:Broken flywheel.

It's VERY hard to see, but they crack around the 6 bolts that hold it to the crank. If you unbolt the converter and push it into the trans, pry the flywheel forward and back while watching. if it's cracked, you'll see or hear it.


I had this happen in a Caprice with an engine I rebuilt. It sounded like an intermittent lifter problem. I knew the cam, lifers, pushrods, etc were all new- it had me puzzled for a while. New flexplate solved the problem.

Word to the wise here- REPLACE THE SEAL AROUND THE TORQUE CONVERTER, EVEN IF IT'S NOT LEAKING!!! If you have a cracked flexplate, the vibration from it has loosened up the seal. I know this because 2 weeks after I R&R the tranny for the flex plate, I did it AGAIN for the seal that was shaken loose. Save the aggravation, spend the $12, and replace it at the same time. Nobody ever said to themselves " I wish I didn't have that new seal in there".

:chevy:
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Re: Rattling from underneath...

Postby Leeann_93 » June 5th 2009, 2:59pm

gtkane wrote:Broken flywheel.

It's VERY hard to see, but they crack around the 6 bolts that hold it to the crank. If you unbolt the converter and push it into the trans, pry the flywheel forward and back while watching. if it's cracked, you'll see or hear it.



The replacement motor for the Astro has this problem, and the noise the guy I bought it from described sounds exactly the same as what you've described.
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Re: Rattling from underneath...

Postby astro355 » June 5th 2009, 7:39pm

I can see a broken flywheel making a rattling noise. The flywheel that was connected to the 305 in my van was that way.

What I can't see is how you would have enough room to crawl under a van on the ground and have enough room to do a good inspection of the van to find the noise.
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Re: Rattling from underneath...

Postby Casey [OP] » June 6th 2009, 3:38am

Big_kid wrote:
gtkane wrote:Broken flywheel.

It's VERY hard to see, but they crack around the 6 bolts that hold it to the crank. If you unbolt the converter and push it into the trans, pry the flywheel forward and back while watching. if it's cracked, you'll see or hear it.


I had this happen in a Caprice with an engine I rebuilt. It sounded like an intermittent lifter problem. I knew the cam, lifers, pushrods, etc were all new- it had me puzzled for a while. New flexplate solved the problem.

Word to the wise here- REPLACE THE SEAL AROUND THE TORQUE CONVERTER, EVEN IF IT'S NOT LEAKING!!! If you have a cracked flexplate, the vibration from it has loosened up the seal. I know this because 2 weeks after I R&R the tranny for the flex plate, I did it AGAIN for the seal that was shaken loose. Save the aggravation, spend the $12, and replace it at the same time. Nobody ever said to themselves " I wish I didn't have that new seal in there".

:chevy:


Would this seal be on the backside, where the input shaft slides into the converter? :think: And is it a dealership part or can I find it at NAPA, etc.?
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Re: Rattling from underneath...

Postby Casey [OP] » June 8th 2009, 5:31am

I dropped the exhaust, trans shield, and oil pan today. After unbolting the torque converter, the flexplate checked out just fine. I didn't see any cracks around the crank bolts after I pushed the TC rearward the 1/4" or so.

Everything looked fine at the crank, but the big ends of the rods slide fore and aft (ditto for the small ends at the wrist pins), and that just doesn't seem right. It's been almost 20 years since I worked on a Chevy V-8/V-6 bottom end, though, so I pulled out my '90 Astro Service Manual and read the rod side clearance limits- .006-.014 for the 4.3L. Hopefully it's the same for a '95 4.3L, but either way, there was .010 of rod side clearance on four rod ends, and about .012-.014 on the remaining two rods. I should've unbolted a rod cap, but didn't since I wasn't 100% sure of the torque spec, so I didn't want to mess with it any further.

There was a tiny bit of crankshaft end play, and spec is .002-.006 ('90 4.3L specs again), and it was within spec. I recall I couldn't get the .006 feeler gauge in, but don't recall the exact measurement.

The oil looked good (was only 2K miles since the last change), but it's possible there was some extremely small bearing material in it. Nothing I saw jumped out at me, but I know it's not always going to be obvious.

When I had the TC unbolted and pushed back I ran the engine for a few seconds and the rattle was still there. Same thing when I removed the serpentine belt and ran the engine briefly- rattle was still present.

Once I had the pans and exhaust bolted back on, I got out the rubber hose (cheap stethescope) stuck it in my left ear, put an earplug in my right ear and crawled under to listen. :confused: The rattle sound was loudest at the rear flange of the oil pan, but it's hard to say if that's because there's no oil pan cavity there to absorb some of the sound or not. :shrug: It was noticibly louder, but not an "OMG, that's a lot louder" increase in volume.

I removed the engine cover/doghouse and confirmed the boss on the right front of the intake manifold is broken off, which explains why the brackets for the two dipstick tubes and the coolant hard line aren't attached to anything.

The one thing I noticed was some sealant smeared on rear face of the oil pan and on the flange at the rear main seal. It looks like the seal is leaking or did leak (semi-gooey oil residue, doesn't look fresh, though), so maybe someone smeared some RTV on there to try and stop it:

Image


Here's a pic of the bottom end:

Image


Cam appeared to have normal wear on it, too.

At this point, I may just buy a new flexplate as a Hail Mary repair and eat the $35 cost if it doesn't fix the rattle. I'm still going to pull both valve covers to elimnate that possibility, but my gut says it's not a valvetrain issue. I hope my gut is wrong...
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Re: Rattling from underneath...

Postby leifoliver » October 21st 2018, 3:11pm

What was it finally? I have the same issue with my 4.3l z-engine, helped the flexo plate xchange? I changed already rod_ and crank bearings, oil pump, checked the distributer at the lower end, set pushrod clearance like discribed in service manual, pushed the converter away and let the engine il run.. The rattle, the noise was/is still present...

It stays the flexo late and the camshaft.
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Re: Rattling from underneath...

Postby Mmusicman » October 21st 2018, 3:14pm

leifoliver wrote:What was it finally?

Your FIRST POST on this forum is to revive a 9 year old post??? :o
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Re: Rattling from underneath...

Postby leifoliver » October 21st 2018, 4:10pm

Yes sir. Let me know about your experiences.
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