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-   -   BDR vibration issue finally fixed (http://www.clubcobra.com/forums/backdraft-racing/142926-bdr-vibration-issue-finally-fixed.html)

spdbrake 11-04-2019 11:14 AM

BDR vibration issue finally fixed
 
Since I bought this car back Dec 2015 I chased a lateral vibration (shuffle) above 60 mph. Steering wheel shake + rear end L-R L-R (axial).

The car sat for approx 12 years (2003 - 2015) and had 892 miles on it.

My first thought get the tires and wheels balanced. Which was a no-go since they were 13 years old no one would touch them.
Changed tires from Goodyear F1 to M-T street comp 245/45R17 & 315/35R17. No change = N/C
Had them road force balanced. N/C

So started to change parts out and many were needed. Blown shocks etc..
In no particular order

Front end:
New Control arms
Ball joints
Poly bushings
Shocks
Repacked steering rack
Camber plates
Tie rod ends
Rotors
Calipers
Hubs / Bearings
Steering shaft bearings
Steering linkage, universals, support bearing, vibration reducer
Experimented with a shock style steering damper

Rear end:
Upper and lower spring perches
Springs
Full poly bushing set
Lower adjustable camber control arms
Shocks
Axles
Driveshaft
Rotors
Emer cables and shoes
Hubs and bearings
Diff attaching hardware
Sway bar bushings

Suspension alignment, experiments with corner weights and tire pressures.

During all this I had the wheels balanced two more times.
The last one I asked for the Oldest tire guy in the shop and to break the tires down and rotate them on the rim for the lowest weight requirement. N/C

I had already done Radial and axial run-out measurements on the rims and Pin drive hubs. Hub had less than 005" radial run-out. the max axial I could get on any rim was .030" at the bead seat which is pretty good.

I knew:
If I ran the car up on jack stands the vibration was present.
If I ran the car up on jack stand with front wheels installed on the back the vibration was present.
If I ran it up With Out wheels it was smooth. (No real rotating mass)

Then I started looking into replacing the wheels. Bolt-on this time. I spoke at Length with Bob @ Vintage Wheels and Scott @ ET Wheels.
Settled on the ET Classic V (Original Torq-thrust Look in 17X8 and 17X11) on the offsets I needed. I was almost ready to pull the trigger but thought "Maybe I could borrow a neighbor's BMW wheels to troubleshoot with". That fell flat as everyone politely declined.

I went ahead and ordered new Gorilla wheel studs in 12mmX1.5 then ordered a New set of Pin drive nuts from Trigo thinking if I sold the wheels they should at least come with a decent set of Nuts.
Installed those on the car. Of course N/C.

Then it hit me. Remembering my old helicopter days. A lateral rotor vibration (radial on wheel) manifests itself as a Vertical vibration (axial on wheel) in-flight.

I bought 20 12mm X1.5 -20mm long bolts from Mcmaster.
Removed the pin drive hubs from the car and attached the drive drive nuts to the hub using the short bolts. Then attached the hubs to the wheel using the Knockoff spinner.
Had the whole assembly road force balanced as a unit. Once done match marked the Hubs to the Wheel clock angle. (I even noted where each pin drive nut was located)

The car is like Glass now at ALL speeds.

There are some variables I don't have hard answers for.
Were the hubs really the problem?
Was it the large diameter inner wheel bore not getting the wheel centered on the machine?
The experience level of the Tire shop personnel?

I used House of Hot Rods in Mansfield TX for this this last balance. I must say their folks have their $hit together.

krausewich 11-04-2019 09:47 PM

So the drive nuts were the issue?!?
What a hassle!
... and what a way to stick with it !!!

spdbrake 11-05-2019 05:34 AM

Quote:

Originally Posted by krausewich (Post 1468242)
So the drive nuts were the issue?!?
What a hassle!
... and what a way to stick with it !!!

No it was the hubs I think. Before assembling the wheels + hub this last attempt. I removed all the previous weights, outlined the location position and wgt in Oz using a Sharpie pen.

Post balancing + hubs the new weights and amounts and even locations were totally different on every wheel.

I got a little OCD on the new Trigo pin nuts as I had to cut the heads down .090". Although I Mic'd and weighed them all I get carried away on removing variables.

nathanmargolis 11-07-2019 08:31 AM

Never knew your BD was #53, sat for so long, and so few miles. Shows one that a car must be driven.
It was a balancing issue in the hub. Have not seen it done in over 35 plus years but remember the "good shops" would do a spin balance with wheel & tire on the car vs. old bubble balance. The spin balance machines like you see now were not around where tire/wheel are spun on a machine and then placed back on the car when completed. Guess if you found a place that did the early spin balancing method earlier in the trouble shooting, it would have been saved you lots of time.
Enjoy the Cobra on the highway.
Good job.
Nathan
Houston, Texas

spdbrake 11-07-2019 02:01 PM

Thanks Nathan. On the On-car spin balancer I did do quite a bit of calling Mom and Pop tire shops the last couple of years. Perused Craigslist and Ebay thinking I'd find a spin balancer. I did speak with a couple 18 wheeler shops but the machines they use are way too large.

I'm not upset on the outcome or my outlay $. I don't turn wrenches for a living anymore so working on the car actually is more fulfilling than actually driving it for me. Plus it did need a lot of replacement parts and my standards are pretty high.

The car will never be "Done".

Mattsvtcobra 06-06-2020 06:21 AM

Sorry to ask, but how did you have the assembly balanced? If you have the wheel/tire attached to the knock off assembly, how does it attach to the machine? Chasing down a vibration too.

spdbrake 06-06-2020 08:37 AM

From above:
"I bought 20 12mm X1.5 -20mm long bolts from Mcmaster.
Removed the pin drive hubs from the car and attached the drive drive nuts to the hub using the short bolts. Then attached the hubs to the wheel using the Knockoff spinner.
Had the whole assembly road force balanced as a unit. Once done match marked the Hubs to the Wheel clock angle. (I even noted where each pin drive nut was located)"

The Wheel, Pin drive hub, spinner fits on the balancer actually better as the Pin Drive hub ID is smaller and easier to fit a centering cone in it. The outer retaining "Wingnut" (for lack of a better description) usually has a rubberized face to prevent marring of wheel finishes is tightened again the Spinner.

The pin drive hub caps (if you have them) will need to be removed so it will slide fully on the balancer.

Those short 20mm long bolts mentioned above are assembled with the drive nuts you have to remove to get the pin drive hubs off the car.

The most important item is to match mark the hub to the wheel (Sharpie pen) so when you reinstall the wheel on the hub on the car the clocking is the same as the balance.

Quentin Z 06-06-2020 11:44 AM

1 Attachment(s)
Hey spdbrake,

On my Vintage Wheel setup the pins are the "lug bolts" (like the attached pic, but 5ea), so I'm guessing that I would have to buy nuts to hold them to the hub. Right?

spdbrake 06-06-2020 12:45 PM

Yup that'll work

Mattsvtcobra 06-06-2020 02:25 PM

spdbreak, thanks for breaking it down a little for me. Made it easier for me to understand how the shop is to make this happen... or maybe I just need to find a shop than can tell me the process of doing it (meaning they know what they are doing!)

hauss 06-27-2020 08:39 AM

Great article! I will be performing the same surgery soon.

ErikinSC 04-17-2021 06:46 PM

Wow, thanks @Spdbrake - glad that I searched “shake 50 mph” this evening. I have BDR 962, and have a noticeable vibration between 45 and 55. Car was built in 2011, has mostly sat and only has 1,800 miles on it. I’m wondering if this is my issue, also. I just dropped the car off with for them to check the individual wheel’s balance.... I will contact them Monday and review your procedure for an initial path to correct.

primetime1267 07-06-2021 07:28 AM

Quote:

Originally Posted by ErikinSC (Post 1491920)
Wow, thanks @Spdbrake - glad that I searched “shake 50 mph” this evening. I have BDR 962, and have a noticeable vibration between 45 and 55. Car was built in 2011, has mostly sat and only has 1,800 miles on it. I’m wondering if this is my issue, also. I just dropped the car off with for them to check the individual wheel’s balance.... I will contact them Monday and review your procedure for an initial path to correct.

How was the outcome ?

ErikinSC 07-07-2021 07:28 PM

The drivers side front tire was 1/4” out of round. Also found that both front tires were 16 and 13 years old… (rear were replaced more recently, and the tires must have been new old stock when they were installed). I got the car back after a 5 week wait - tech schedule, tire shipping, tire shop, etc - and the vibration is mostly gone…..like 80-85% reduced. I need to make a return visit to the shop, and see if they can balance the hubs attached to the wheels.


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