1950s 1951 Caddy loud roar at highway speeds

[Mowerhoarder]

I feel like somebody posted about this before but I can't remember if they found a solution or not. The noise is kinda like a loud drone, almost like the car turns into a giant vibrating drum. It happens around 60-65 ish when going down the highway but it isn't a rear end thing as I can get it to do the same in my driveway by revving it a little bit. Maybe a transmission mount or something like that? Already did the engine mounts and it helped a little bit but not much. Sounds almost like it's revving way out on the highway even though I know it's around 2000-2500 rpm or so at that speed.

[dogbergs]

Really have no experience with this, but from how you explain

- fan blade?
- generator bearing?
- something torus related?

As you dont have a ps pump?

/ Best

[Mowerhoarder]

Yeah, no ps pump, the generator was replaced with a powermaster alternator so that should be alright, I really am thinking about the fan. Might take it off and run it down the highway real quick to see.

[dn010]

You'll be fine with no fan for a brief time. I'm running an electric fan that only kicks on at a certain temp, it doesn't run at all when driving down the road, even in the Florida heat, and you'd be amazed at how long it takes to come on while sitting idling.

[TJ Hopland]

IF you are going to do a no fan test for more than seconds you want to do it by removing the fan blade  but leaving the belt and pulley to still spin the water pump.  Without the water pump tuning it will overheat real quick especially if there is any load on it.

[Mike Josephic CLC #3877]

Since this "loud roar" happens both when you drive the
car and also sitting in the driveway you might want
to check the exhaust manifolds.  If the bolts are not
torqued properly, they will leak and the noise can
be quite loud, depending on how loose they are.

Mike

[Mowerhoarder]

Shoot I guess it could maybe be the manifolds. It's not an exhaust note per say but more of a really weird vibration that turns the whole car into a drum. I did put window seals in it and cruising with the windows up, it's so much quieter. The drone is still very audible but no wind noise should make it easier to figure out what it is.

[tcom2027]

Good morning Connor,

You've made a lot of assumptions and maybes. Let me offer the following:

Did it come on suddenly or gradually?

From what you posted, the noise is there at idle, does it increase to the same sound level as when driving, at say 2500 rpm?

Since it doesn't happen when the car is static it is very likely coming from reciprocating parts. That means it's from the transmission forward or a vibration from the exhaust system where it goes along the frame. 

You got a good start with considering the fan and you have verified that wind noise isn't the problem, You are going to have to do some serious troubleshooting, and it going to take a lot of work and time unfortunately.

Beginning with the water pump and alternator, new isn't always good. Remove the belt and run engine to see if the noise goes away. Drive it with them disconnected. But first spin them up by hand to feel for any crustiness.

Check the exhaust manifolds carefully, looking for cracks or mounting studs broken off especially at the rear. Make sure there is a good tight seal, Manifold to the down pipes. Get underneath and use good lighting,then the manifold pipe where it drops along the frame. If ok, then follow the pipe(s) back yanking on the hangers looking for looseness and points where it may be rubbing on the frame. Maybe not a great possibility but check it anyway.

Time for the transmission mounts as you said. Check the bell housing bolts, a reach maybe, but you want to be sure. Remove the inspection plate on the transmission. With good lighting check the flex plate for loose bolts or cracks as best you can for the latter.

If all that checks out, drop the driveline at the transmission and run it up through all the gears, PRNDLL. it could be the input bearing or something in the torque converter. ALso it may be the output bearing which would require disassembly. Don't bother to jack up the rear and run it, aside from being dangerous it doesn't help a lot as the rear end jumps around enough to mask the problem you are trying to identify. Use or borrow a good mechanics stethoscope and listen for any untoward sounds from the transmission.

Good news is you haven't fired the AutoZone/Kragen/RockAuto parts cannon, and only have time invested.

Good luck and I hope this helps.