Buttercup grumbles

[jyinger]

Buttercup, my 1949 Coupe DeVille, is almost perfect.  Well, she is perfect until she gets to about 36mph.  The she starts to grumble.  Feels like your driving over a rough road.  More 'til 45mph, then I'm reluctant to drive much faster.  If I put her in neutral, the grumbling goes away.

Professionally rebuilt engine (L $ R in Santa Fe Springs),  professionally rebuilt transmission (L A Automatic Transmissions), all new front suspension parts, professionally aligned, professionally balanced drive shaft--re-checked that, new U-joints, new wheel bearings, new Diamond Back steel belted radials with wide-whites--balanced, checked and re-checked,  differential cleaned and checked, new brakes (discs in front, drums in the rear.....

We did take off the harmonic balancer and replace it.  No change.  We are stumped.  Any suggestions?

Jon Yinger  clc#26643

[James Landi]

I've so enjoyed your pictures of "Butter Cup" and sad that you're experiencing issues...   Here are some thoughts as follows:  Since the issues occur in concert with speed and likely with engine rpms, perhaps the entire drive train is somewhat out of alignment... and if this is the case, the rumble may develop an ever so slight whipping of the drive shaft.   Maybe you could use a laser beam to check this.

[Jon S]

If the "grumbling" goes away in Neutral, that eliminates the suspension, tires, wheel bearings, brakes, etc.  Does it feel like a harmonic resonance or chatter or just a grumble?

It may be too cold, but with the windows down and driving near a retainer wall does it get noticeably louder? If you drive it at the same grumble speed and go to a lower gear does the noise disappear or remain?

Need a little more information.

[savemy67]

Hello Jon Y,

Grumble or rumble?  When you say it feels like driving over a rough road, do you feel vibration through the steering wheel?  Do you feel vibration through the body?  Or is the experience at speed more a sensation of noise?

What happens when you apply the brakes or turn the steering wheel at the indicated speed?  Your post mentioned all new front suspension parts.  How were the King Pins replaced.  Was the rear suspension examined to see if it was in good shape?

These issues are hard to diagnose from afar, but try to isolate longitudinal rotating mass (engine/trans/etc.) from chassis/suspension symptoms as you narrow your search for the culprit.

Christopher Winter

[Smedly]

I know you mentioned new u joints but I would check them again. A ujoint vibration can go away when in neutral. Maybe the joint is just not quite seated right. Just a thought

[Ralph Messina CLC 4937]

Jon,

Many good questions above, but Christopher's are key to help us with diagnosis.

Grumble or rumble?  When you say it feels like driving over a rough road, do you feel vibration through the steering wheel?  Do you feel vibration through the body?  Or is the experience at speed more a sensation of noise?

It would be helpful to know how many trouble free miles you had before the grumble started. Did it start out barely noticeable and get worse incrementally, or all at once? I'd try to isolate the location of the noise. Put the car on a chassis lift and run the speed up cautiously - 20 MPH - in Drive. Look for driveshaft wobble and differential / axle / rear wheel bearing noise. See what changes when placed in Neutral. Do the same watching the engine.

Break-in issues like this after a meticulous rebuild are infuriating. I've found experienced professionals can make mistakes and new parts can fail quickly.....often leading to long sentences with many, many curse words.

[Jeff Rosansky CLC #28373]

This will be a good read as I have both a harmonic vibration and what I think is a bent wheel that vibrates between 50&60 and then smooths out.
Here are a few things I plan to do this summer......
I would suggest rotating the tires to see if anything changes. Then, drive thru water and then onto cement- see if your tracks look off.
Then I am going to try to borrow one of those go pro cameras and tape it to various places to see if anything is noticeable- such as the fenders to watch the tires, and then under the car to watch the driveshaft.

[jyinger]

Thanks for all of the responses so far.  It's really a rumble.  No vibration in the steering wheel, and no particular noise that I recognize.  I don't recall that it feels any different if I turn or brake at say 45mph.  But the rumbling does stop the moment I put the car in neutral. 

As I mentioned above, we've addressed every cause we could think of.  Replaced the harmonic balancer.  Checked rechecked the alignment.  Put it on the lift and ran it at 40pmh.  Removed the driveshaft and had it balanced (again) and installed new U-joints (again).

Even thought the transmission was rebuilt by a shop that we have had great service from, could there be a problem in the fluid coupling?  Would that be apparent to an experienced transmission guy?

That's what we're headed next.  Get another tranny, rebuild it, and replace the one that's in there now.  By the way, it's a dual range hydramatic out of a '52.

Thoughts?

[Scot Minesinger]

Jeff,

There is a procedure in the 1970 shop manual to diagnose vibrations and it is at the very beginning of it.  Very helpful.

If you think it is the wheels get them road force balanced and watch them do it so they don't put an unskilled inexperienced person on the job.  This will tell you if the rims are out of true.  They will be all not perfect, as my road-force balancer let me know all four of my rims were not perfect.  However, the car is smooth as glass now.

A bad rim is going to get worse as the car speeds up and not improve as you speed up. 

It may be engine speed related and you can put the car in 2 instead of D and test that theory out.  This is all outlined in the shop manual.

[Jon S]

Jeff,

It may be engine speed related and you can put the car in 2 instead of D and test that theory out.  This is all outlined in the shop manual.

Scot -

That was my initial thought, above.

[savemy67]

Hello Jon Y,

"But the rumbling does stop the moment I put the car in neutral."  I think this is a good clue.  Was the car at speed when you put the transmission in neutral?  And was the car accelerating slightly (or going up a slight incline), or was it coasting (or going down a slight decline)?  If coasting or going downhill when the transmission is placed in neutral, the engine will be under less load.  This may help determine if the grumble is engine/drive torus related or driven torus/transmission/driveline related.  You may want to have a look at the differential/axle bearings too.

Christopher Winter

[Jon S]

Christopher -

If the noise goes away in 2nd (or 3rd) assuming it's a 4 speed, then it should make the same noise in each gear at that same RPM.  If it doesn't, then I would tend to rule the engine out and focus on the transmission/drive train.  A logical starting point before throwing $$$ at it.

[Jon S]

I would suggest rotating the tires to see if anything changes. Then, drive thru water and then onto cement- see if your tracks look off.

Jeff -

Drive one of our classics thru water?  I try to avoid the smallest of puddles!

[cadman56]

Have you checked for wear on the drive shaft yoke & transmission tail shaft bushing?  Wear in this location will create a vibration frequency of multiples by differential ratio.  Sometimes the noise disappears when going into neutral or releasing gas, sometimes not.  Had this problem on two different cars.
Put on a different set of tires & was the front alignment set for steel radials?
Have you checked for defective/new engine & transmission mounts or incorrect ones or incorrectly assembly to the engine?  I know on a 56 the engine mounts can be mounted in the incorrect position.
Just some things to check.
Good luck, I have enjoyed reading about Buttercup.
Larry

[jyinger]

Thanks again everyone.  This really is a great forum!

I drove the car about 20 miles today.  Same.  Thanks Scott for recommending 2nd gear--I did that, and it rumbles  at about the right rpm (maybe 2800?), which we reach about 18-19 mph.  Same in 3rd gear---at about 27-29 mph.

The rumble goes away the moment I put it into neutral, whatever the speed.  I am leaning more to an out-of-balance or otherwise defective fluid coupling (there's no torque converter, of course, on a '49.

Jon

[Jon S]

Jon -

It could even be an accessory like the generator making that noise at a certain RPM.

[Tito Sobrinho]

JYinger:

In 1986 when I bought my 1949 Caddie, whenever driving at 50 mph I could feel and hear an awful vibration or grumble if you will.  The culprit was a thin" homemade" conical washer behind the harmonic balancer.
I went to a junk yard and got an harmonic balancer and  the thick conical washer behind it from a 1951 Fleetwood. Installed the washer in my car and the vibration... Gone! 

[Bob Schuman]

Another possibility is the water pump bearing. I once had a similar vibration in a Pontiac V-8 that took me quite a while to diagnose.
Bob Schuman

[Caddy Wizard]

I would really doubt an out-of-balance fluid coupling.  No way for it to get out of balance, basically.

Check the routing of the spark plug wires.  You could have a cross-fire miss induced in the plug wires if routed incorrectly.  The factory figured out that the wires would have this problem if not routed a certain way.  Jay Friedman has described this in a tech article in the SS, i think, and that references a small item in the Serviceman Bulletin from back in the day. This can make a big difference in smoothness and power.

[Steve Passmore]

Thanks again everyone.  This really is a great forum!

I drove the car about 20 miles today.  Same.  Thanks Scott for recommending 2nd gear--I did that, and it rumbles  at about the right rpm (maybe 2800?), which we reach about 18-19 mph.  Same in 3rd gear---at about 27-29 mph.

The rumble goes away the moment I put it into neutral, whatever the speed.

Jon

My monies on an engine problem. You have the rumble at the same RPM no matter what gear.    It go's away when you select neutral because you also take your foot off the gas and drop RPM.      If when stationary you slowly build the revs up to say 3000 and you get the rumble its definitely the motor.