350 ticking noise but only at idle. What would it be?

[SnS C10]

I posted this in the suburban forum but thought it may be more of a question for here

Hey guys long time member. My name is Shaun. I recently traded a toyota corona I had for awhile for this 1986 suburban. its a 2500, 4x4. engine is a crate 350 from Goodwrench with im told 40,000 miles on it and same for the transmission which im told is a th400 although i have not verified this. The engine runs beatifully and sounds great with its dual flowmaster mufflers. its all stock as it needs to pass california smog which it has.

My issue at this point is there is a ticking/knock noise. While in Park it will make the noise but with the slightest raise in rpms, say 100rpm, the noise goes away. There is no noise while driving or revving. Seems to only be right around the park rpm. Kind of sounds like the flexplate tapping against the cover but what do you guys think? I didnt think it sounded like a catastrophic problem and if it were i believe i would hear it more often at different rpm ranges. Thoughts? heres a link to a video

https://www.youtube.com/watch?v=QQvgLrDh0fA

[SnS C10]

Here’s a picture of the new toy

[SnS C10]

double post

[SnS C10]

seems strange to me that it goes away with only a an extremely slight variation in rpm. Never hear it while the truck is moving either. Just when I sit at a light after the engine has been warmed up. Do you guys think it sounds like a noise from the oil pan or the torque converter area?

[geezer#99]

Search for it.
Make a megaphone from an old piece of garden hose with a funnel stuck in the end.
You’ll be able to pinpoint it then.

Sounds like a lifter to me.

[SnS C10]

the noise is much much quieter on the top of the engine. its at its loudest basically where the video is taken. If i put a rang between the oil pan and flex plate cover the noise gets a little quieter

[geezer#99]

It’s quieter up top because you have a lot of cast iron to muffle it.
Only a metal pan on the bottom which amplifies noises.

[68gmsee]

Since it seems to be coming from under the vehicle and at park or idle I would use a long section of stiff garden hose (maybe 4 to 5 ft piece) as a stethoscope and see if you can pin point it that way.

I used that method to isolated a drive shaft noise by lifting one tire off the ground, shocked it really good and had someone idle the truck. Just be careful and not get under the truck. The hose should be long enough to reach the area that you suspect.

My brother had a similar noise on his car one year and it turned out to be a hairline crack on the flex plate where the bolts are.

[BigRandy]

I would look at the flex plate.

I had an 86 with a 305 that did the same thing about every 40K miles. It was on its 3rd flex plate at 124K miles when I sold it. Each time the symptoms were the same. In park it would clatter like a cheap dinner bell but in gear or at increased RPM it was silent, and each time I found the flex plate had cracks between the crankshaft bolts.

Is it gradually getting worse? Mine did. If it is I'd suggest checking it quickly so the converter doesn't wobble around and damage the front pump and send trash through the transmission.

It's a pain but not a huge deal to fix. As to why the bolts would be breaking? I suspected crank walk with my 305 but didn't care to dive in because I wasn't in a place where I could do anything about it.

You might find something simple like a loose converter bolt. If so then it's a quick fix.

I wonder if you could pull the dust cover and put a cheap bore scope camera up there and look around? eBay has them for phones and laptops for about 5-10 bucks. https://www.ebay.com/itm/7mm-Android...ZIWRIhYr9H2fqg

[SnS C10]

thanks for those responses guys.

An update- I drove the truck on my lunch break and when i got back to my parking spot i could hear the noise again. So, i got out a new 5/16 hose that i had and got under the truck and put one end of the hose on the oil pan and one end on my ear and the noise was not any louder at all. Then i put on the flexplate cover and same, not any louder. Next, i put the hose right on the weep hole opening on the very bottom center of the weep hole cover and wow it was twice as loud right there. So its coming from inside the flex plate cover....

I also was listening to the engine as i shifted from drive to neutral to reverse and back and forth a few times. When the trans engages to reverse the noise gets more prominent. I can make the noise by shifting thru the gears like this. So probably next step would be pull the cover? Is it safe to drive like this or should i just park it? The engine and trans feel fine, but i also dont want to hurt anything

[BigRandy]

Originally Posted by SnS C10

thanks for those responses guys.

Is it safe to drive like this or should i just park it? The engine and trans feel fine, but i also dont want to hurt anything

Based on your findings I wouldn't. If the flex plate is cracked then it isn't spinning true and neither is the torque converter. The risk is damage to the pump and trash in the transmission.

I'd pull the cover and take a look at the bolts. You might get lucky and find one that's just loose.

[68gmsee]

If the noise is louder through the weep hole, just remove it and with a good flashlight carefully check every bolt in the flexplate. On my brother's car it was very visible after we removed the cover and rotated the engine.

[Coley]

I would agree with the flex plate. The sound seems 'external' to the engine and in the trans/housing area....which points to the flex plate.
Regardless....it doesn't sound too serious, just something that needs a little elbow grease to fix.
Coley

[SnS C10]

another update-

i pulled the flexplate cover. I noticed that one of the bolts for the cover was resting on the exhaust pipe so i thought i lucked out and that was the vibration. Wrong!! The inside of the cover is very marked up from the flexplate making contact with it. Also, this cover seems heavy duty. Its very thick and rigid. Ive seen others made of sheet metal. Anyways, all of the bolt looked and felt fine for the flex plate. But you can see in the pictures where its contacting the cover. I did find a crack also which i posted a picture of.

As far as replacement, i read that i can unbolt the engine and trans but put longer threaded rods thru the bottom holes for a guide. At that point i should be able to slide the trans back a few inches to get the flex plate out and without having to take off the cooler lines, driveshaft, etc...is this correct?

[geezer#99]

Did you run it with the cover off?

[SnS C10]

i did run and drive it with the cover off. Feels smooth and no more noise at all. No vibrations or anything

[geezer#99]

IIRC there are two different covers available.
You likely have the wrong one or it was modified to fit.

[Dead Parrot]

Possible the added strain of rubbing against that cover caused the flex plate to crack.

2nd the suggestion to get a different cover.

How are the seals on the transmission? Might make more sense to completely pull the trans and have new seals installed while you replace the flex plate.

[BigRandy]

Originally Posted by Dead Parrot

How are the seals on the transmission? Might make more sense to completely pull the trans and have new seals installed while you replace the flex plate.

Agreed. A cracked flex plate will cause the converter to wobble which would explain the wear mark on the dust cover. Also, if you're going to back the trans out you might as well get it on the ground, inspect the front pump and change the front seal. A wobbling converter could have damaged both. Maybe not if you're lucky. I caught mine early enough and got away with a seal change.

[mattfranklin]

Fascinating discussion and diagnosis. Great pictures, too! When I first started reading, I was going to suggest going to a heavier viscosity to see if the sound changed, but as I read further you guys homed in on it and nailed it. Great work!

[kwmech]

Check the crankshaft back and forth for end play. Should be no more that say .015.

[SnS C10]

With the cover off I can still hear the noise. When the engine is cold it’s much harder to hear. Fully warmed up it’s more noticeable. I assume the drop in rpm is making the noise more noticeable. Anyhow going to try and replace the flexplate within the next week

[Dead Parrot]

It is possible you have two noise sources. One, the rubbing on the cover which you found and a 2nd one. Might run your noise finding hose around any nearby exhaust joints.

[SnS C10]

alright guys so on saturday i tackled this job. I started around 3 in the afternoon. All 6 engine bolts out, converter bolts, trans mount and cross member. I was able to leave the drive shaft in, i just put a jack stand underneath it. Also put a jack stand with a block of wood under the oil pan on engine. Floor jack was under the trans pan with a block of wood. I was able to get the engine and trans to seperate about 1.5 inches or so.

I had a hard time with two of the bolts for the flexplate as they seemed to be extremely tight. I had just enough room to fit a 6 point socket in there. The other 4 bolts were also tight but came out easier as i just used a regular box end wrench for those. I got to the point where the flexplate was removed and called it quits. The next morning around 9 i got back on it and i had the truck driving at 11:20am. Not too bad on time. Noise is gone now so im pretty stoked about that

[BigRandy]

Originally Posted by SnS C10

alright guys so on saturday i tackled this job..................

.....and i had the truck driving at 11:20am. Not too bad on time. Noise is gone now so im pretty stoked about that

That's great news! It's a good feeling when you know you fixed it Did you check the crankshaft end play or decide to just let'r roll? Hopefully it was nothing more than defect in the flex plate or just not tightened correctly.