Knocking transmission

[Rackarboda]

I have this weird sound that started quite recently, a loud metallic one coming from (probably) the tranny. My initial thought was the flexplate bolts where I actually found a loose one but to no avail. It was a long shot since the noise only appears when in drive and a little less in reverse. I jacked up the car, put it in drive and tried to locate it, but it's not too easy to pinpoint. When I step on the brake the noise goes away.

Ideas?

 

[khryslerkid]

Torque converter bolt heads aren't too thick are they. This sounds like one of the bolts making contact with the engine block. Look for scarring and metal filings in the bell housing. Turn the crank by hand and feel for a spot that binds. Could be a bolt making contact with the dust shield too. Good luck.

 

[pnora]

Check the crankshaft end play. It is also possible the flex plate is loose on the crank. Do you have the thin head flex plate to converter bolts?

 

[Don Frelier]

It is also possible the flex plate is loose on the crank

I'm thinking loose flex plate on the engine as well. Sounds just like this and when you put the brake on the torque converter is loaded so it stops.

 

[Rackarboda]

I was unsure about the bolts on the flexplate when I assembled the machine after an overhaul some years ago, I think someone might have used some thicker ones and banged them down with a hammer or some, there are very clear marks from them in the block. After turning the converter by hand I couldn't feel any particular resistance at any point and I tightened all bolts when checking.

But if it was the bolts grinding up, wouldn't they be doing that also when in neutral? I have used the same bolts for the last five years and the sound appeared quite recently, I noticed it last autumn when I put the car away to hibernate. I can also add that the sound disappears when going over app. 30 mph and returns when going back and under no matter the RPM.

I had the same kind of sound on my Le Mans and at that time it was a flex plate bolt, but it made that sound even when in park or neutral.

 

[RemCharger]

I can also add that the sound disappears when going over app. 30 mph and returns when going back and under no matter the RPM.

I had the same kind of sound on my Le Mans and at that time it was a flex plate bolt, but it made that sound even when in park or neutral.

Don't let that fool you, the whole rotating assembly can float frontwards/backwards. Giving you the disappearing act. Look at each bolt head carefully for signs of contact.

 

[khryslerkid]

The fex plate does just that, it flexes, normally under load. In neutral not so much but it does moves in and out.

 

[black64]

Could your fan be hitting the radiator shroud under torque maybe a bad motor mount?

 

[oldbee]

Cracked flex plate? Rotate & look for a rusty crack.

 

[Dave6T4]

I had a noise like that develop in my '64 Polara 500 convertible. It turned out to be loose flex plate/crankshaft bolts. This also oblonged the holes in the flex plate, so I had to replace it. I learned a lesson; use only new crank bolts and Locktite them when torquing to factory spec's. Same with torque converter bolts.

 

[Rackarboda]

Thanks for all replies, I will inspect the flexplate and get some new bolts and hope for a quick recovery so I can get on with the rest. Have a good easter, guys.

 

[Rackarboda]

A brief update, I switched the bolts but the sound persists. What I could see from the flexplate, nothing was cracked or broken, but the view is quite limited without removing the transmission.
I might add that the sound only appears when the car is moving, or at least the wheels are turning like in the attached video. If I put it in drive and hold the brakes, there's no sound.

 

[Moms68]

1. I wouldn’t be driving that car until I found the issue.

2. Purchase a mechanics stethascope and use it to pinpoint the area of the noise. There appears to be a vibration while idling so it could be more engine related than transmission. It stops when under a load so I’d be looking for anything loose or broken.

 

[Mick56]

To check the bolts holding the flex plate to the crank, the trans has to be removed.

 

[Don Frelier]

I would have suggested trying to rotate the flex plate back and forth when you had the torque converter unbolted.
I still think the transmission needs to be removed and the crank bolts/flex plate holes inspected.