Strange Vibration on a 1951 Dodge car. Could it be something wrong with the fluid coupling?

[48ragtop]

I've got a vibration that has been driving myself and my friend that actually worked for GM as a field engineer diagnosing driveline vibrations nuts. 

Originally the car had several issues I took care of including a new ball and trunnion Ujoint with housing as both were run dry and damaged.  Well that took care of my consistent vibration.  Now I have one that comes and goes.  Can come in bad at slow speeds or high speeds and then can go completely away so the car is smooth.  Temperature doesn't make a difference, road conditions don't. It seems to be pretty much isolated to the engine fluid coupling assembly.  (once i got everything else fixed we are finally able to get to this). 

I have drained and refilled the coupling with the recommended fluid you can only get in the 5 gallon pail and it still does it.  I added a vibration damper it didn't have and that didn't fix it.  Just sitting in the driveway with the car in Neutral I can rev it over and over carefully and alot of the time you can feel the vibration, trying to match the rpms each time and make note of the vibration as to when it comes in and and and if it does.  Occasionally it is completely gone when I go back to idle and bring the revs up.  Then repeating the procedure I can get it to come back. It does it more often than not but it may be vibration free for a few cycles in a row.  

Now I did actually unbolt the rear mounts and lift pressure up on the engine just to make sure my problem wasn't motor mounts and that made no difference.  They look in good shae and are good and soft but firm enough as any Motor mount I have ever had my hands on. 

Is there any chance something might have come apart inside the Coupling, throwing it out of balance and as it gets thrown around in the coupling it occasionally finds something close to it's home spot so it balances? The coupling seems to perform as designed with no excessive slippage when I drive it. 

Could the engine be out of balance and the coupling actually occasionally balances it out?  

Any suggestions or diagnosing techniques welcome. 

My wife just believes the car is possessed and there is no fix. 

[48ragtop]

I do want to mention the vibration has a cyclical or droning to it if that helps at all. 

[Sniper]

i would inspect the exhaust system, look for rub marks.  Make sure it has rubber hangers

[maddmaxx1949]

Are all the nuts tight on the coupling? May be a basic answer but doesn't hurt to double check

[Plymouthy Adams]

as you rebuilt the trunion....look again to this and make sure all is right and tight...suggest clocking the driveshaft ...

[Merle Coggins]

I once had new tires mounted for a truck and they messed up the balancing. When driving the truck the vibration would come and go. I could even feel it change and move front to rear, left to right, or go away all together. I noticed that it would change or move around any time there was even a slight curve in the road. I went back to the tire shop and got them all rebalanced. They actually sent me to a different shop to get them balanced. Apparently their balance machine couldn’t center up my wheels properly. The vibration went away. All 4 tires were out of balance and would come in and out of phase with each other any time there was a curve or corner. I was happy to get that one resolved. 

Edited July 16, 2021 by Merle Coggins

[48ragtop]

Being I can get the vibration to come and go with it in neutral sitting in the driveway just revving the engine , we can eliminate probably everything from the tranny back. Atleast the driveshaft back as none of those are moving at that point.  Good ideas to check though if i do get this "stationary" vibration fixed and develop anymore when I get it back out for a test drive. I did actually mount and bubble balance the wheels/tires  myself.  We did run the car on jack stands initially before I found the bad joint and checked for tire run out as well.  All was good with the wheels/ tires from what we could see.   I didn't put the coupling or clutch plate in the car.  That work was done before me.  Is there any way to check those without pulling the engine / tranny?  It's a Wayfarer roadster so it has a huge X member that makes alot of work under the car more difficult and from what I see,  it may not be possible to pull the pan in the car as I tried that to drain it,  but couldn't figure out any way to get it out, so I pulled the plug through the fill hole and rotated the engine by hand until it completely drained then rotated it back and forth some after letting it sit to make sure I got all the fluid out. 

Keep the ideas coming though.  If nothing else I'll file them for the next car I get that someone else gave up on.  Getting close to that point on this one. 

[Dodgeb4ya]

You need to remove the clutch housi g cover and look/watch while running any wobble of the FD or the clutch driven plate and pressure plate.

Is the FD tight to the crank...does the FD look newish-like rebuilt, or old & oily.

There are two input shaft bushings in the FD. If worn a vibration will occur.

If the front bearing in the FD coupling is worn...vibration will occur also.

[48ragtop]

Does anyone know if it's possible to pull that cover in the wayfarer roadster with the engine in the car?  Maybe I missed something when I was under there and had the bolts out.

 It's weird when I was out road testing it, one time I stopped,  long enough to put the top down as I had never driven it with it down after test driving probably 10 miles,  when I pulled out on the road and drove back to town another 5 miles the darn thing was as smooth as could be all the way back.  I was running along at 55, lots of corners I slowed down in a few hills to accelerate on,  and even drove it through town on the way back stopping at a couple of lights.  No real vibration at any time.  That was the puzzling part. I originally thought maybe it had the wrong fluid (maybe too thick) in the Coupling and when it finally heated up from engine heat sink (from the time it took me to put down the top) it flowed properly so it wasn't working as a slug in there like the colder oil might have. (you try to think of anything when you get to this point)  That was the original reason I changed the fluid in it as who knows what they had filled it with. 

Edited July 17, 2021 by 48ragtop

[Dodgeb4ya]

I doubt it had the wrong understanding in the coupling.

That bell housing cover can be removed even with the convertible X member frame.

[48ragtop]

I'll have to give it another look.  Maybe I missed something.  It dropped down but seemed attached across the back, but that's buried in the member.  We'll see.  Hopoe for the best.  Gonna wear out my jacks and stands from the number of times i have had this thing up in the air. 

[joecoozie]

Did you check the front motor mount?

Also, just because a motor mount looks/feels good doesn't mean it is good.

The rubber can dry from age and separate from the metal part of the mount and you may not be able to tell by looking at it.

[48ragtop]

Wouldn't a bad motor mount do it all the time? There is not a good way to check the front as there is no way to properly jack the motor to take pressure off it.  Now the 5 mile drive at varying speeds over bumps and around fairly sharp corners should have shifted something if it was a motor mount to make the problem come back.  That's the odd part a long drive under those conditions and the problem wouldn't present itself.  Yet the same trip today and it wouldn't go away but did occasionally change in severity. 

I'll have to get it in the air later today and try to get the cover off.  Loose bolts could cause that problem thinking about it,  but again seems like it should be more consistent. 

Keep the ideas coming though.  

I wish someone had had a similar problem as I'm in the wild ass guessing phase now.  Short of pulling the engine and going over it and the coupling,  which really isn't an option I'm starting to run out of things to check. 

[JBNeal]

I concur on the input shaft bushing and bearing wear...I had a Dakota 5spd that had a very similar vibration, but without any FD coupling.  I could feather the clutch to get the vibration to go away at low rpms when in stop'n'go traffic, and it would disappear while on the highway.  My thinking was that engine braking would help to force the input shaft to re-center itself, temporarily eliminating the vibration.   With the longer FD input shaft, bushing and bearing wear that cause vibrations can be more pronounced.  The droning noise also can be indicative of a worn bearing.  Engine balancing issues would be repeatable at noted rpms as the only parts that could vary would be timing chain related, but that would produce a different sound as well as engine performance issues.  The engine to transmission engagement is an area where there are several moving parts that need proper alignment for vibration-free operation.  The variation here is the clutch, pressure plate and FD coupler, as anything out of tolerance will cause engagement issues.  If there is a contact circle larger than the clutch diameter, that is indicative of a clutch that is sorta walking around in there as it is not staying centered.

[48ragtop]

I'm going to get it up today and see if I can get the cover off for an inspection. I'll post back as to success or not and what I find.  It's odd how it could stay smooth through so many cycles  and then get completely off through so many cycles. (revs and clutch in and out sequences) Will definitely be one to keep in the long term memory if one ever runs across this scenario again.  

[James_Douglas]

12 hours ago, joecoozie said:

Did you check the front motor mount?

Also, just because a motor mount looks/feels good doesn't mean it is good.

The rubber can dry from age and separate from the metal part of the mount and you may not be able to tell by looking at it.

I spent MONTHS with an odd vibration that I could not run down. Turned out that the left front lip of the motor mount would contact the block side mount. It would do it at idle.  If you look real careful at the way the mount is designed, if the rubber gets old and compresses just a little the two side can make contact. I had to grind some clearance into the mount. You can see stress marks from the press if you have it in your hand. Also, if you have two or three of them that radius edge on the drivers side is different on all of them. Check that out real well before you do anything else.

 

As to the Fluid Coupling. If you still have the bottom plate out, drain it. Turn it back up to the fill point. Take a screwdriver and carefully turn the inner around until you line up one of the large holes with the threaded outer plug hole. You will have to take a drill bit to gauge the inner hole size as I don't remember what it was. Then take a BOLT that is threaded to the plug hole pitch and size. Turn the end of the bolt so it will go through smooth the inner hole. Screw the bolt down. Now drive it like a stick easy around the block and see if the problem goes away (Assuming it was not the mount). If it does then you know it is the coupling. If it does not then it is not the coupling.

 

An old timer taught me that trick years ago. He said to keep a bolt like that in the glove box on long tips. Just in case the fluid coupling seal dies or the bearing dies...you can stop, let it cool dump the oil, and screw in the bolt in place of the plug. Then drive it like a stick to get where you are going. He said he drove one like that for a year and it never caused an issue.

 

James