Hot Rods I found the front end vibration!

I was reading in Hot Rod mag recently about chasing a vibration in a modern Mustang with some hop up parts. One of the hop parts was a new driveshaft to accommodate some other change (new trans maybe?). They didn't suspect the driveshaft could be the cause of the problem, but the new hipo shaft was out of balance.

 

This post is most interesting, I had a vibration with Speedway rotors drilled for Ford bolt pattern. I read somewhere wheel run out ( steel) max. .040. It urn the rotors 3 times and indicated it, but never thought of the studs.

 

Here is a vibration measurement I made on my old RWD Volvo's steering wheel running on the highway.
I can "feel" vibration in the steering wheel at that speed. I do not "hear" any deep booming/pulsing in the interior when the vibration is very noticeable.
Because there is a "spike" visible at ~ 900 rpm ( the wheel/tire rotating speed) I will be checking the tires for runout, and if that is OK getting them balanced.
I will not have any work done on the driveshaft since the vibration is not at it's running speed of ~ 3400 rpm.
I am not su****ious of flywheel or clutch imbalance because the vibration is very low at engi rotating rpm.

 

Did you indicate the lugs, edge of the rotor or something else? I would think doing the studs would be hard to get repeatability.

 

I recently got 5 wheels from wrecking yard in Austin. They were 15" inside nub 5 on 5.5. I had them bead blasted and powder coated. I bolted them up just for giggles and guess what one wheel was out by .300. Absolutely no sign of distress this wheel was perfect except that the center was riveted out of square! I don't recall ever seeing a wheel welded or riveted that far out! All the others were .008 to .015 out. Believe me when I bought two nore I checked them BEFORE powder coating!

 

The cost of new (replacement) rotors has decreased considerably over the past few years, which is the result of overseas sourcing. At our shop, it's not unusual for a name brand, supposedly high quality "brand new" part to be defective out of the box, or to fail shortly after installation. Another "sign of tyhe times." Probably would be worthwhile to check out thoroughly ANY new component for dimensions, appearance, etc. Just saying.

 

I fixed my vibration by getting the tires shaved.
My build drug on for about 2 years where the car was sitting on the tires without being moved a lot.
Seems to have developed flat spots on the bias plys but after the shaving it's all good now...
Maybe worth a shot for you?

 

When putting new rotors on a car you've been driving and then it vibrates, an out of true rotor is an obvious thing to look for.
But when it's on a new build or a major change in setup was made, vibrations can be a pain in the ***. So many parts are being imported now that even buying a name brand part can be iffy.
Seems like we need to add checking for lug bolt concentricity to the things to do when installing rotors especially on a new build that may be months, or in my slow *** builds, years before the car is driven. You really can't expect Speedway or any other vendor to exchange or refund for parts that are defective when you bought them a year or so ago. After all, they would have to charge a whole lot more for parts if they unboxed and checked every part they sold.
Thanks for posting this, as it adds one more thing to check after installation of a rotor, especially if the car isn't going to be driven for an extended period of time. Really doesn't take too long to get out the dial indicator and check this before you bolt on the wheel and tire.
Sorta speaks up for not buying parts too far in advance of installation on a build.

 

Good job hanging in there and finding the real problem. Now you double and triple checked everything on the car you should have plenty of SMOOTH trouble free miles.

 

.........Was the shop that shaved then there in Waynesboro? Could you mention the name of the shop?

 

Actually it was in Verona.
The shops name is Central Tire.

Central Tire Corporation
228 Lee Hwy
Verona, VA 24482
United States
centraltireva.com

They did a great job. Was in and out within my lunch break.

 

Thanks.

 

I did some research today on the Speedway website
http://www.speedwaymotors.com/11-Inch-GM-Brake-Rotor-with-Ford-Bolt-Pattern,4311.html
and this is what it said on the Q&A tab...

The GM rotor with Ford bolt pattern is not a redrilled rotor, it is cast with 5 on 4-1/2" bolt pattern.

 

Did you ever check it?
You'd think hub centrics wouldn't care too much? And if they did wouldn't the 0.030 offset leave a witness mark on the hub and wheel at the tight spot?

 

Thanks for posting this thread Montana. Gives us one more thing to help trouble shoot, and probably a real good first step before proceeding with the hierarchy.

 

I love these threads. Locking this one away for future reference...

 

I did some more checking and found these rotors to be '70-'78 Camaro or equivalent with 7/16" x 1" studs @ 4 3/4" bolt circle from the factory.

I looked at mine and they ARE redrilled to fit 1/2" x 1 1/2" studs @ 4 1/2" bolt circle.

There's just barely enough room to redrill the bigger hole, but it might not clean up all the way on the outside, making the drill wobble as it goes through the factory hole.

I don't have a rotary table, but I'm thinking about getting some replacement rotors and have a machine shop do it on a milling machine to see if they can be done more accurately.

 

You talking about the speedway rotors? Mine are not redrilled. Bought them 2 years ago. Maybe something has changed?

 

Oh my.... my 37 is driving me nuts, I'm reading this thread and makes me wonder too... my vibration persists after checking or changing.... tires, shocks, springs, rotors, brakes, calipers, spindles, alignment, balance, tie rods, ball joints.... things left to check... driveshaft, rack and pinion, engine mounts.... the vibrations is between 55mpg and above, comes and goes... it has gotten better after all these changes or checked items

 

Have you ever checked to see if both U-joints run at the same (but opposing) angles?

...and, have you ever sat with car not moving, and rev it, hold it steady at those same RPMs, to see if it is in the motor/trans rotating ***'y?

.

 

One of the weirdest balance problems I ever ran into was trying to on-the-car-balance wheel tire that had an ounce or two of water inside it. It would balance, then the water would move.

 

jaw22w, try and find a repair shop that has one of those old tire balance machines that spins the tire/wheel on the car, might expose the problem

 

3 year old post....Jaw prolly has his problem fixed now.

 

Old thread but still great reading. I wanted to add one more vibration cause that just came to light. My 52 F1 had an intermittent rhythmic thrum that would come and go at highway speeds and would send a shake weirdly all down the left side. The tech at Les Schwab spun the wheel on the balancer then said that sometimes radial tires dont seat exactly right on old steelie rims. He broke bead, re-aired, and its fixed, no charge.

 

After reading this entire older thread got me thinking..... I know that's dangerous. Lately everyone is talking about tire shaving, and how it and balancing fixed their vibration. I wonder if the tire shaving is just masking the rotors being drilled off center? This could be proved by re mounting the wheel on the rotor in a different position. Then see if the vibration comes back. This would only be true for tires that were shaved on car, and not on an off car tire shaver. Comments?