1967 DeVille - knocking in my 429………. I think.

[Vossphoto]

https://youtu.be/MiXT8yzDPJ8


Hi all, Glad to be here (first post!). Ok men, I have a 1967 coupe DeVille with a 429.

The problem: when in drive, accelerating, a knock develops from the engine compartment.
To attempt to narrow where the problem stems from, we put the car in park, rev'd the motor and no knocking. Same result when in neutral. No knocking.

Then we put the car in drive, put my foot on the brake, and rev'd the motor ( see link above for the video ) and the knocking shows up again. It seems to me the noise is coming from the passenger side lower down the motor or possibly the tranny, not sure. Also I don't hear the knocking when idling. Any ideas of what the problem could be would be greatly appreciated. Thanks in advance

["Cadillac Kid" Greg Surfas 15364]

Hard to tell from that video. Check for exhaust leaks and listen close near the converter dust cover from underneath for noise coming from the flex plate. If all that is not the source and you have decent oil pressure the lower end (rods or thrust bearing) might be your culprit
Greg Surfas

[savemy67]

Hello Carlos,

Your post indicates no knocking when idling.  Is that when idling in Park, Neutral, or Drive?

In Park or Neutral, the transmission input from the engine is effectively separated from the transmission output to the driveshaft.  However, the flex plate, torque converter, and pump are rotating at engine speed.

Your test showed that with the rotational mass of the flex plate, torque converter and pump, there was no knocking sound when the engine was revved in Park and Neutral, but the knocking sound was apparent in Drive when the engine was revved.

So what happens when the transmission is placed in Drive?  The forward clutch unit is applied, which causes the turbine portion of the torque converter to apply torque to the mainshaft of the transmission, which in turn sends torque through a specific combination of internal, pinion, and sun gears, as well as a planetary carrier and output shaft to the drive shaft.

With your foot on the brake in Drive, the driveshaft and output shaft of the transmission cannot turn.  You are in effect trying to stall the engine with the torque converter..

I listened to your video, and to my ears the noise doesn't sound "heavy" enough to be a rod or bearing knock.  It sounds "tinny" to me.  I think that a rod or bearing knock would be apparent whenever a cylinder fired, hammering the piston/rod against a crankpin or main, regardless of what gear the transmission was in.  That said, given the load on the torque converter when you are trying to stall the engine, the knock could be emanating from the thrust bearing.

The knocking sound could also be from something simple to fix, like a loose flexplate to converter attaching bolt(s).  You may want to raise the car and remove the converter dust cover, and rotate the engine by hand checking all the converter attaching bolts, and checking the flexplate for cracks.  Let us know if you find anything.

Respectfully submitted,

Christopher Winter

[cadillactim]

Sounds like it could be rod bearing since it acts up under a load. Take all the plug wires off then slip them back on the plugs, but not all the way. Now make the engine act up like you do in the video. Pull off a plug wire one at a time. If the noise goes away when you pull off a plug wire that is the problem area, which would seem to indicate rod bearing.

The noise does not sound like loose torque converter bolts. To eliminate a cracked flywheel, rev the engine to about 2000 rpm in PARK, then turn key off. A cracked flywheel will usually make noise when you do this.

Tim

[Vossphoto]

Thank you, Gentlemen, for your much-appreciated input on my "knocking" issue. I'll be working on the car this weekend and plan to put your suggestions to use. Of course, I'll share the results here on the forum.

Also, Christopher, I'd like to answer your question:

"Your post indicates no knocking when idling.  Is that when idling in Park, Neutral, or Drive?"

The car doesn't knock when idling under any circumstance. I also tried revving the motor in park and neutral, with no noticeable knocking. The knock starts while driving and accelerating, or when in drive, with my foot on the brake ( car at a standstill) and revving the motor as seen on the video.

A sincere Thank you for your suggestions, Carlos

[vne247]

Could it be a broken spring on the exhaust manifold heat riser?  We fixed too much stuff on mine to know for sure, but I think that was making the noise that was driving me crazy.

[Matti R]

Hi Carlos,
Did you find the reason? Would be nice to hear how did you fix it.