Body Vibration

[ScottS]

This is the latest,

Took tires off the front and went back to the original CC manual. I did not have all the attachments that were suggested. So, out came the power drives and self taping screws. After that, test drive. No luck, so I had a beer (well maybe 2). I then thought back at what I had done when I put the new tires on and at that time I was adjusting the rear spring tensioners that raise and lower the back end height. So, I got my trusty 3/4 inch socket and wrench and adjusted both sides all the way "up". In other words the back end was at it's most lowered point. I believe it was probably at most a half inch lower in the back. BIG DIFFERENCE! Almost all oscillation is gone.

So, is this an aerodynamic or a (spring/shock) problem?

As always all comments welcome,
Thanks to all,
Scott

[Ronbo]

Raising / lowering the rear alters the caster angle of the front end. The shorter the wheelbase is the bigger the effect becomes.

[Double Venom]

It ALSO CHANGES PINION ANGLE! Measure the degree of your driveshaft!!!!!!!!! At ANY setting (of the rear end height) plus or minus 3 degrees negative is pretty critical. You do not want it perfectly flat/horizontal/level. Underload the pinion on the rear end will want to raise, you never want it to go or close to a plus/positive degree!

Sounds like you are winning ???
DV

[ScottS]

Thanks Again,

This pinion angle thing is very interesting. When I installed the new drive shaft I tried to measure the angle that was suggested (plus or minus 3 degrees). It was very difficult because I was using jacks at the time to get under the car. But, from my initial measurements I determined the tranny had to be raised about 2 inches to get me in alignment. I fabricated a 2" aluminum spacer that sits on the crossmember and attaches to the trannly mount. That put the angle of the drive shaft more in line (perpendcular) with the pinion. That in turn raised the engine more perpendicluar to the frame.

Now for the interesting part. When I do get up to 60MPH I have a vibration sound coming from the rear drive train (drive shaft back to rear end). When I push in the clutch at 60-70MPH the vibration sound is still there. At lower speeds no drive shaft sound.

So, maybe the two are related??

So, at this point maybe I should go back to the drive shaft shop and get some professional help...

Thanks,
ScottS

[Double Venom]

Scott,
Easy to check ( if your a skinny guy!), but the car has to be on its own paws, full weight. I actually set the car on all fours, push on each corner a few times to set the springs then put a degree gauge on the drive shaft close to the pinion. ( You can buy small magnetic level gauges with a degree back ground with a floating needle from any tool truck, most equipped hardware stores)

Keep in mind that your air cleaner should be as close to '0' as possible. In other words the motor should be horiZontal to the frame. If not this can cause a multitude of problems from floodiing carbs (especially Holley) to almost undiagnosable vibrations through out the car!

If you haven't, start following the thread about Cpteddies build, I will be posting pictures soon of seting his rear suspension and driveshaft up along with where I reset his engine because it was off over a 1/2" from left to right. (Very rare problem and the first one I have ever seen. The CR's motor mount was measured,cut and welded wrong!)

DV

[ScottS]

Thanks Again,

Things to do this weekend! One of the reasons I up-spaced the tranny was to get the engine more to the horizontal. I will check that I am close to zero and then check the pinion angle.

Scott

[ScottS]

The latest on the vibration.....
I finally got things set up to check the pinion angle. As suspected it was way off. Or what I should say is pinion to transmission angle is way off. Pinion agle is sitting 1 degree positive (pointing slightly up). Tranny output shaft is pointing 6 degrees positive (pointing down). So I have a 7 degree problem! Plus the engine angle is bad at 4-5 degrees (pointing same way as tranny. So, I am fabricating a new tranny crossmember. I believe if I level the engine I will straighten out the tranny angle. I tried this when I was measuring the angle using a jack and I can get the angle of the tranny out shaft within 2-3 degrees positive (pointing down) without causing any reengineering of the motor mounts or drive line cowling.

However, I would like to get the pinion angle 2-3 degrees negative (pointing down) and I don't see any way of doing it with the rear suspension setup. The upper and lower control arms and sway bar looks like they lock the angle in. It seems like I would have to do some "major" suspension changes to get a negative pinion angle. I have read that the negative pinion angle is not as much of a problem with my suspension setup. It does matter a bunch when you are running leaf springs but then a few spacers and you problem is solved.

Any ideas on this one greatly appreciated.

ScottS

[capteddie]

Scott,

You would only need to swap out your upper rear control arms with a pair that is adjustable. That would give you the ability to change the rear pinion angle.

This would be one option http://www.hotchkis.net/p-747-dbl-ad...iling-arm.aspx

HAPPY THANKSGIVING EVERYBODY!!!

Ed

[ScottS]

I think that's a GREAT Christmas present. I better get started writing Santa!

Thanks The-Other-Ed,

Scott

[Double Venom]

Scott,
Very uimpressive. You have tackeled this problem in the absolute correct way! "The other ED" has hit it dead on. There are other ways but a lot of work and possibly welding would be involved. Adjutable control arms, especially the uppers sounds like your answer to the "pinion angle" solution. "JEGS amd Summitt" both sell the adjustable upper arms too. Just some more choices-Engine level, tranny almost level, at the tail, and the pinion angle negative (down 3 to 3.5 degrees depending on HP, traction and how hard you get on it! ( The more it hooks up, the harder you drive, the amount of time you stay in it, all equals to the 3.5 degrees!)
DV

[tcrist]

Thanks capteddie, I just ordered the adjustable upper trailing arms. I think that when/if CR gets going again, they should include adjustable upper trailing arms in their kits. That would make things alot better for all.

Terry

[capteddie]

Originally Posted by tcrist

Thanks capteddie, I just ordered the adjustable upper trailing arms. I think that when/if CR gets going again, they should include adjustable upper trailing arms in their kits. That would make things alot better for all.

Terry

Glad to help!

if/when CR gets going again. I think it would be a good idea for the new owner to solicit feedback/suggestions/ideas from as many CR owners as possible. I built (well DV built it) my car without any donor parts and have a pretty good list of what worked and what didn't. Granted, most of the stuff that didn't work was from my own pure ignorance

[ratsnst1]

I was wondering, do all your body mounts have rubber isolaters, and where your exhaust mounts to the body as well, they all should have, just a thought.

[tcrist]

ratsnst1,

The body has no rubber isolaters at all. It has foam tape between the body and frame and the body bolts directly to the frame.

Terry

[Double Venom]

The Foam tape Terry is referriing to (1/2"), seperates the body from the frame and the Sidepipes are supposed to have a rubber Isolator between the end of the exhaust and the bolt holding it on!
DV

[tcrist]

Ok, trying to get to the root of it all. This is what I understand so far.
1) get everything on the ground with the body on with the tires that you are going to run.
2) set your ride height.
3) make sure that your motor is level or a little tilted nose down to the horizon. How much 1-2 deg?
4) set your pinion angle so the nose of the rearend (where the driveline bolts up to) is about 3 deg down.

Please correct me where I am wrong.
I just received my double adjustable upper trailing arms and trying to get it correct in my mind before I tear into it.


Terry

[Double Venom]

Terry,
If all this doesn't elimiinate your vibration then I am ready to......well you want to bring the car to Pentwater?
#!- forget about the horizon! Sorry for any confusion there.
#2- When the car is as you indicate
#3- assuming your floor is reasonably level- lay a level on the flattest/straightest top part of the door. Pay very close attention to the lay of the bubble. A degree wheel would be great..
#-4 Set your motor as close as you can to the level measurement you just got from taking the level of the body, I.E.; say the body is all set and it is sitting level.
#5- the motor should be level, if necessary a degree or two with the back pointing down is ok.
#6 Install the driveshaft, it should lay in a straight line, NOT necessarily level and probably wont be. Now measure the angle of the driveshaft with a short level or a degree wheel.
#7 It is from this point you can check you pinion angle, it should AT THE MOST be level or now straight from the drive shaft. Never UP. Trying to explain this is hard on the internet.....Lets say your engine is pointing down a degree or two, transmission of course will be the same with the drivehaft following the same line. Here comes the pinion... lets say you have a pretty hot motor and typically good rear tires all resulting in decent torque and HP. This is where you will want the pinion to go below the tranny tailshaft from DOWN 1-1/2 degrees to a max. of DOWN 3-1/2 degrees. From what I am reading about your driveline I think you would get by with a NEG. 2.

If you end up with wheel hop, which I doubt very much, drop the pinion DOWN a half degree unitl the wheel hop is gone.

This make sense to you?

Whish I wasn't on dial-up, I am only a couple of days of setting Cpteddies. I certainly will now take a full set of photo's on what I do. I already posted getting his motor in left and right as well as front to back with a down angle of .01. I need to get his driveshaft set up and photographed, and then adjusting the pinion angle.
DV

[tcrist]

Thanks DV,
I think I got it. I am going to draw up something and e-mail it to you. I'll try and make it clean enough to use as an instruction page for the manual.

Terry

[ScottS]

Latest Saga on Body Vibration.

I received the new Hotchkis uppper control arms and fabricate my new tranny cross member with an additional 2" lift. It took my approx. 3 hours a peice to get the old cross member out. The F$%#*ng upper rubber bushings are glued into the can. I'm sure glad the curse police weren't around or I would out big money

But, I did get them installed and I got the cross member in and started the pinion alignment. The control arms give me "plenty" of adjustment so that was great. After experimenting with several different settings (-1, -2, -3 degrees pinion angle) I settled on -2 and there is relatively "zero" noise in the drive train. So, that problem is solved!

However, the vibration is still just as prevalent at 65-70 as before. I am leaning now toward tires rotation, front end alignment. Has anyone tried the "Tire Beads" I hear some good things about them but I don't know if that is all hype (http://www.innovativebalancing.com/). Also, I am running modified corvette brakes and rotors (don't ask) and the rotors had to be drilled to fit the wheels (2.5" bolt pattern). So, I am wondering if a professional alignment is in order.

As Always, Any Help Greatly Appreciated.
ScottS

[Double Venom]

Scott,
I don't know what more a guy could do? Did it all and it sounds like you did it right! The only thing left is rotating parts! Wheel, rotors, drive shaft, alignment, bad shock?

I know full well about the theory on the internal full time balancing of tires. Did you know that early paddy-wagons ( ) and ambulances ('50's-60's) used "mercury" in the wheels to do the same thing? Then it of course was ruled illegal. Not only was it used to balance the tires but it also allowed emergency vehicles to make faster turns without flipping over! Now there is a trivia question for ya! .

DV