1931 CM6 vibration

[EThomas]

It’s been a journey getting her roadworthy and reliable to daily drive. The cooling system is sorted with new hoses and a tightened water pump. The soft fuel line from the fuel hard line to the motor is new (that was fun). The hydraulic brake switch is new. All the electrical connections are cleaned and tightened. 
 

I’m now on to an issue that is perplexing. There is a noise while driving over 25 mph. I initially thought it was a brake issue as the passenger drum was a little warm after a quick drive. After preparing for a brake job, turned out two lug nuts had fallen off behind the hubcap. Tightened them (and all the other nuts) and tried again. The noise is there. It’s a thumping noise. In first, second and third gear under 25 mph, no noise. Over 25 mph, it starts. There is no vibration I can feel under me or in the wheel. It seems to be independent of any gear (first, second or third) - that seems to rule out transmission and axel. It’s all speed dependent and only over 25 mph. 
 

I suspect U joint or motor mount. This morning, under the car, I see this. It’s a suede boot with a leather and metal tie around it. It’s on both ends of the U joint. Should it be there? I don’t want to remove it if something is supposed to cover the joint. I’ve made a couple if minor errors applying modern thoughts to this. Most small issues have been resolved by a little tightening here and there and some use.

 

Any thoughts or insights? Does this replace a cover? Would the metal tie bind the joint?

[JFranklin]

The boots are beneficial to keep things clean. Has your car been lubed recently? It all looks real clean. 

[EThomas]

It was restored in the early 2000’s and was in two museums till early this year. I’m guessing about 20 years total just sitting. It has less than 500 miles total since the odometer was reset at that time. Most of what I’ve dealt with is dry rot and corrosion from sitting.
 

I’ve greased up all the places based on the owner’s book. I’m obsessive about clean so I’ve tidied up behind myself. That said, it was super clean when I got it and I haven’t taken it on a dirty road or any weather. 

[viv w]

Those leather boots are correct for those ball and socket UJ's.

[Narve N]

Try to wiggle the propeller shaft. If it has noticeable sideways slack, you should put it on a repair list. I had my driveshaft fitted with "modern" universal joints at an acceptable price. The guys at the shop said Chrysler shafts are notorious for their shafts enabling longitudinal movement at both ends (same principle also 30 years later). You should also try to take the car up to 25 mph+, push the car in neutral and maybe switch off the engine to eliminate vibrations from the engine/gearbox.

The main culprit for vibrations on my 1929 was the wheels. After some attempts to balance them without much success, I bit the apple and had new rims made. That also sorted the fear of having a sloppy locking ring fell off at speed (happened once).

But I still have vibrations, and believe there is something inside my gearbox that starts wiggling around when I get past 40 mph. Anyone having dealt with such before?

[hchris]

Having sat for a lengthy period, have you considered a flat spot or out of round tyre ?

[Gunsmoke]

These propeller/drive shafts have what is known as ball and trunnion joints at end, which also have stiff springs to prevent shaft from sliding back and forth. They are relatively easy to fix if you can find a new kit. The 2 leather boots are wired (and laced) to the shaft at the rear-end and at the end of transmission and ensures the grease stays in the joint as well as protecting the joint from dirt and debris. They can be easily removed for checking play in joint and replaced. I had a NOS kit a friend gave me for my '31 CD8, which by the way also had this same joint system despite master parts book suggesting it should have had the Spicer type joints.

[EThomas]

Thank you all for the answers and feedback. I'm glad I didn't fiddle with the covers. I'm learning to step back and try to look at things from a more simplified point of view. It's been interesting to have to modify the knowledge I have from modern cars to this car. Humps and bumps along the road, but well worth it. It's absolutely fascinating to learn a mechanical and analog point of view.

 

I did attempt to move the driveshaft yesterday. It will not move side to side; however, it will move front to back a slight bit. I assumed that was ok as the car has freewheeling and it does work (which is a very odd sensation to experience, I must say). Is it fair to assume the front and back movement is a concern or is that intrinsic to having a working freewheeling system?

 

I will also do the turn it off and shift into neutral trick. Pretty slick idea!

 

I had not considered an issue with the wheels. I think a round of tightening the spokes and balancing is in my future. I'll also check for flat spots (which I feel like an idiot for not even considering!).

 

Looks like I have a busy upcoming weekend with a myriad of things to try. Thank you so much and I'll let y'all know what the ultimate issue is, when I find it.

 

 

[JACK M]

You need to make sure there is no pressure on that driveline when trying the wiggle test.

In neutral with one rear wheel off the ground might be best.

[Tim Wolfe]

Check out balance beads that go inside the tires, I have them in my 550-18 tires and at 55 MPH they feel great,  ( they are small ceramic beads )

[EThomas]

Thank you for the additional information. I really appreciate folks chiming in to help out and sharing knowledge with me!

 

That's a good tip to test the driveline! I hadn't considered there would be pressure on it.

 

I didn't know balancing beads even existed! I'll give that a try as well. That's pretty slick and takes some of the pressure off of having a shop perfectly balance the wheels.

 

 

[hchris]

If  its wheel / tyre related it's probably going to feel relatively slow and rhythmic in  intensity; as opposed to higher frequency for a mechanical/drive train issue. 

Also (may have already been asked) does it go away whilst rolling along in neutral  ?

[pre1939chrysler]

I'm not sure but does the 31 have a vibration damper between the motor and the firewall? 

What weight oil does the trans and rear call for, If 600 wt. Then use it. Check your engine mounts

they might to be redone.