1961 Drone/Vibration 65 mph plus

[lostcause]

Correct. My goal is to get the first working angle to be as close to 0 as possible without it being 0. The normal spec range is 0.1-0.5. Right now I'm at 2.9. My goal with the last 2 working angles will be to be in the 3.0-2.0 range with them being as close to the same as possible. Example: 2.5 and 2.5.

I've sent the drive shaft back to the shop to recheck the balance and possibly replace the center support with a shorter one.

[Dave Shepherd]

Your goal is right on target.  Just finished a drivetrain alignment in my shop on a Restomod 53 Chev. Got right at 3.2 degree working angles at the differential and trans, close as I could get, a little higher than ideal. 2 piece is totally different of course.

[lostcause]

Victory!!!

The drive shaft recheck was ok- no issues.

I started by shimming the trans mount as high as I dare then I pulled the drive shaft and shortened the center support (cut/weld) 3/4 of an inch. If I knew what I know now I would have had the center support replaced with a non stock 3R80-10 which is an inch shorter and shimmed up accordingly. It is necessary to cut a 2" wide, 1" deep notch at the rear of the frame for drive shaft clearance when the car is on the rack with the rear suspension hanging.

So I ended up with the drivetrain down 3.9 and the front shaft down 3.7 with a working angle of 0.2 - perfect. If you remember, before the mods I had a 2.9 working angle.  Checking the other two working angles I now have 2.8 and 2.5, I may add some shims back to the lower arms to get those to match.

Test drive was mixed. I can still feel a tire vibration around 30 but it goes away quickly (it has new tires). The great news is the drone/vibration is gone above 60. I ran it all the way up to 90. Don't beat me up but my 66 Chrysler is smoother from 0 to 100+ than this car will ever be. The fact is this car and every other 61 Cadillac left the factory super smooth so something or somethings go south and they lose the smoothness. There is no way it should have to be modified like I did to get the angles right. The issue with this car was the drivetrain angle and center support height. Modifying those like I did solved the problem.

As I said the test drive was mixed. Now that the original problem is fixed I can now hear a rear wheel bearing noise that was masked by the drone/vibration. And so it continues......... 

[79 Eldorado]

Sounds like great progress. If the remaining issue is tire related there are places which do road force balancing.

I know BFG had some great tech articles about 20+ years ago now. I think that's where I read about what they referred to as match-mounting where the wheel and tire are mounted to counteract the impact of either. I guess 61 was too old for any rules like they mentioned about how rim manufactures indicated the position. Tires are normally marked with a dot. As I recall one or the other is the high and the other the low. So when you match mount you turn the tire on the rim so the marks line-up. I don't know how you could apply it exactly with your 61 but if it turned out to be a rim or tire issue and you could identify the particular tire/rim maybe you could try rotating the tire on the rim. I just searched and the source I found made it sound like it was weight based so checking the balance of the rim without the tire could reveal the position on the wheel. If you have new tires they are likely marked.

If you were close we could try that EVA I mentioned. It's kind-of a 2 man job because you need to pay attention to driving items as well as manage the computer/readings.

Since the most noticeable vibration is now at 30mph can you drive at 30mph in a different gear to see if the vibration follows speed or RPM?

Scott

[lostcause]

Sounds like great progress. If the remaining issue is tire related there are places which do road force balancing.

I know BFG had some great tech articles about 20+ years ago now. I think that's where I read about what they referred to as match-mounting where the wheel and tire are mounted to counteract the impact of either. I guess 61 was too old for any rules like they mentioned about how rim manufactures indicated the position. Tires are normally marked with a dot. As I recall one or the other is the high and the other the low. So when you match mount you turn the tire on the rim so the marks line-up. I don't know how you could apply it exactly with your 61 but if it turned out to be a rim or tire issue and you could identify the particular tire/rim maybe you could try rotating the tire on the rim. I just searched and the source I found made it sound like it was weight based so checking the balance of the rim without the tire could reveal the position on the wheel. If you have new tires they are likely marked.

If you were close we could try that EVA I mentioned. It's kind-of a 2 man job because you need to pay attention to driving items as well as manage the computer/readings.

Since the most noticeable vibration is now at 30mph can you drive at 30mph in a different gear to see if the vibration follows speed or RPM?

Scott

Yes, the plan is to get the tires road force balanced next. Back in the day I used a Hunter road force balancer and it would perform miracles with tire and wheel issues. The tires are new but reproduction vintage style tires and my experience with them is never good. They are all hard to balance. The good news is it is a slight vibration and it comes and goes quickly.

If I can't narrow down the bearing noise the plan is to drive it until it gets worse. This car sat for years in a collection so I won't be surprised if I find bearings with brinelling.