Help! Small block 360 has a knocking sound

[George Jets]

OK everyone, lets think about this being it is no longer the original engine in the car.

The 360 is an externally balanced engine.

The 904 automatic behind it needs the weighted converter to work correctly with the 360 with the stock mopar flex plate, or the half moon cut out after market flex plate to make up the indifference in balance to work with the 360.

Lets say he has the stock external balance 360 crank with a non-weighted 904 converter. Maybe it was an old 318 car with this 904 non-weighted converter.

Anyhow running that 360 with a non-weighted converter will set up all kinds of vibrations especially at the trans front pump bushing wearing it out, from the converter being out of balance.

Creating the Knock that you are talking about. 3/4s of the people on here are saying it's flex plate problem. Think it goes in a little deeper to a bad trans front pump bushing and or a cracked torque converter hub. From it being out of balance.

OP is saying it makes more noise in Neutral than in Park, that is because the front pump is only pumping when it is in neutral or in gear, not park. So if the front pump bushing is out it is going to make a lot more noise when it is under load pumping in Neutral, than when it is freewheeling in Park under no load.

My Vote:
Bad transmission front pump bushing.

 

[George Jets]

This diagnostic work on figuring out the Knock with this 360 and 904 transmission is like putting a Big Jig Saw Puzzle together.

All of the FABO members are putting pieces of this puzzle together along with some clues from the OP to keep things headed in the right direction to ultimately solve the problem.

 

[Cudafever]

I like your theory but if the bushing was bad it would(should) hang on the seal and leak atf
I say the imbalance cracked the flex plate.
My buddy, when he cracked the converter hub, it pissed a lot of atf when you shut the eng off.

I guess you could brake the pump drive instead of the hub and make noise and not leak fluid.

Pull the dipstick while it's running and hold it in the sun light and see if you find silver..................

 

[George Jets]

Cudafever, like your idea that the imbalance of running the non-weighted torque converter caused the flex plate to crack.

That makes sense.

Flex plate could be cracked up at the crank bolt area.

 

[George Jets]

Here is a question for the OP
@CheeseRules01!

What type of flex plate is behind your 360 right now.

Original mopar 318/904 Flex Plate

Or this Aftermarket B&M 360 to 904 Flex Plate # B&M 10239 for the 904s.

Then do you have the weights on your 904 torque converter ?
Or no weights at all (like used on the 318 / 904 applications).

Working to see if you have the correct Balanced Setup to work with your Externally Balanced 360 with the 904 trans.

The proper selection of balanced parts is what you need, otherwise the imbalance will cause problems like you are experiencing now as things fail, as with the Knock at the Transmission.

 

[diymirage]

This diagnostic work on figuring out the Knock with this 360 and 904 transmission is like putting a Big Jig Saw Puzzle together.

All of the FABO members are putting pieces of this puzzle together along with some clues from the OP to keep things headed in the right direction to ultimately solve the problem.

just dont turn all our pieces around or you might find the ones i have have a black back, yours might be green and the OPs are red

 

[AJ/FormS]

Those puzzles all start out the same...............

 

[CheeseRules01!]

I took the car for a drive the other day, and I am still convinced that it is in fact the transmission. If you wiggle the shifter around, the tone of the sound changes. Also when going up hill under a load, the transmission starts to slip and the knocking noise starts becoming a terrible rattling sound. I am not saying that everything you guys have told me is incorrect, but the transmission definitely has an issue. I checked the fluid, and it is full, not burnt looking or anything. Nice and cherry red. Not sure what the deal is, but it is toast. Also At this point I can't even start the car anymore, because the starter decided to die. I have another one, but with the headers on the car, it would take forever and not even be worth it since I have to tear it apart anyways. We have also been getting some nasty weather here lately, so the car is pretty much just a dead corpse in my driveway. I will get out in the spring and tear it apart to start checking things out and replacing things.

 

[CheeseRules01!]

Here is a question for the OP
@CheeseRules01!

What type of flex plate is behind your 360 right now.

Original mopar 318/904 Flex Plate
View attachment 1715456287


Or this Aftermarket B&M 360 to 904 Flex Plate # B&M 10239 for the 904s.
View attachment 1715456288

Then do you have the weights on your 904 torque converter ?
Or no weights at all (like used on the 318 / 904 applications).
View attachment 1715456289

Working to see if you have the correct Balanced Setup to work with your Externally Balanced 360 with the 904 trans.

The proper selection of balanced parts is what you need, otherwise the imbalance will cause problems like you are experiencing now as things fail, as with the Knock at the Transmission.

The Dart has the stock flexplate, and it has a properly weighted converter.

 

[nm9stheham]

Cudafever, like your idea that the imbalance of running the non-weighted torque converter caused the flex plate to crack.

Flex plate could be cracked up at the crank bolt area.

Mmmmm..... The 360's internal imbalance forces (in the rear half of the engine) are transmitted via the crank bearings to the block, and the imbalance forces from the external weights on TC or flexplate are transmitted to the trannie housing and engine block (via the crank flange/#5 bearing and the pump area). The two equal and opposite imbalances are tied together at the engine/trannie junction to counteract each other.

So actually, running the non-weighted TC or flexplate with a 360 wouldn't cause vibrations at the flexplate-to-crank junction....unless the bellhousing to engine bolts were loose. The external weights (TC or flexplate) are what put any stress on the flextplate.

Of course there are other reason that the flexplate can be cracked....

 

[AJ/FormS]

Come-on back in spring then. Don't leave us hanging.

 

[CheeseRules01!]

Come-on back in spring then. Don't leave us hanging.

Don't worry, I'll be documenting all of the work to the car on here. There will be plenty of pictures for ya to look at. Right now I am just in money saving mode. Trying to save as much as possible before spring so that I can do it right once I start putting her back together.