Technical Lets play what's that noise? 1955 Ford Mainline

So I am currently on my way back from Montana to Los Angeles in my 1955 Mainline with the 312 Y block (EDIT #3) With the 3 speed manual with overdrive trans . Engine is running smoothly but while I drive while deceleration, cruise or at idle there is a mild thumping that sounds to be the left front EDIT: it is an uneven rotational sound with a relatively slow interval when compared to a rod knock and much slower than a lifter tick. Does not occur while accelerating. When I pull over in neutral, and pop the hood there is no noise but when I am idling at a red light there is, confusing. Going to be in Salt Lake tomorrow, followed by St George Utah that night assuming all goes well. If anyone knowledgable on these fords is along the 15 freeway adjacent, or has a shop recommendation for a diagnosis I would be greatful.

EDIT#1: it is an uneven rotational sound with a relatively slow interval when compared to a rod knock and much slower than a lifter tick. Does not occur while accelerating.
EDIT #2 The engine oil has no metallic flakes or dirty contaminates that would indicate engine damage in it when I last checked a few hundred miles ago.

EDIT#3 the car is a 3 on the tree with overdrive

 

This is going to freak you out, but it sounds like a loose main bearing. Y-blocks are known to break cranks, particularly the 312.

 

Oof I dont like the sound of that. the sound is much more noticeable on the left side like when I heard it my eyes and ears were drawn to the left firewall basically

 

EDIT to main post : it is an uneven rotational sound with a relatively slow interval when compared to a rod knock and much slower than a lifter tick.

 

Fuel pump related. Either pump or internally in the engine?

 

Loose torque converter?

 

Sure sounds like a torque converter with the bolts that hold it to the flex plate being loose but I have no idea how a 55 Ford torque converter bolts up. Or if Blacktop-Ranger even has an automatic.
You might spend 10 bucks or so at a parts house and get a mechanics stethoscope to see if you can track down the noise.

 

My 55 torque converter was bolted to the flex plate with three bolts on each side, nothing like any of my later cars.

 

If that isn't convenient, a long handled screwdriver, socket extension, etc. held to your ear will work as you poke around. Hopefully can recreate the sound while in neutral and not moving - but if not, that's another clue towards something in the drive train.

 

Seen those flexplates like nosford posted crack more than once

 

3 speed manual

 

Let's go at it a different direction. What was worked on since the last time you drove the Car and the sound Wasn't there?

 

Good idea. This is the first mega miles trip ive run but at the start I refurbished my 6v generator, adjusted timing, did an oil change, and greased up the suspension joints. The adjustment in timing may have come undone to be honest, Ill have to check that

 

Could be ignition detonation for sure with todays garbage fuel and what that motor would like to have. Would for sure show up on accel. while loaded.

 

Did you check the motor mounts? Loose or separated mount will thump under acceleration, especially the left side mount.

 

Detonation generally sounds like ball bearings rolling around in a Tin Can.

 

My thinking has lead to there but I haven't checked it yet I will when im out of the snow roads and back on the highway.

 

I like the comments on the auto trans noises for a guy with a stick..

 

In their defense I did not specify in my in initial post. So I edited the post for clarity after the auto trans advice started popping in.

 

Scheduled an appointment for some lift/shop time later today

 

Wild as it may seem had main cap bolts stretch on a 302 and cause that sound. Luckily no damage to journals so replace the bolts an went on

 

And they were Oem bolts

 

I know this is of no specific help, but I've found the further I am from home, the louder those noises become, or the better my hearing gets.

Good luck, hope you find the source, and that it's something minor and/ or easily remedied.

 

If it were a loose main cap issue. @Blacktop-Ranger do you have a mechanical oil gauge? If so anything showing oil pressure going up on deceleration and down on exceleration?

 

Thrust bearing

 

Haha you got that right. especially in the cold out here noises become much more clear

 

No mechanical oil gauge which is a total oversight on my part. Just the standard oil light which has not come on

 

Check crank end play

 

I posted my torque converter pictures for Mr48chevy, he said he didn't know what the torque converter bolts looked like on a 1955 Ford Y Block. I would agree with several others that my first guess would be thrust bearing on crankshaft. Had one where I put my son inside and had him push on the clutch and release with the engine running, from under the hood I could watch the damper move in and out about 1/2". That was on a 289 with a 4 speed that at one time had a monster pressure plate which caused the failure I am sure.