Other: Vibration at Highway Speed

[wdills]

I had my Hawk out on the interstate today for the first time. Previous driving has all been 2 lane roads. At 60 mph it is nice and smooth. At 70 mph it starts to pick up a little vibration and it gets worse quickly above that. All of the wheels and tires were recently balanced and the front end aligned. I know Jack balanced the engine when he built it. Odd thing is, the vibration is not transmitting through the steering wheel. In fact the steering wheel feels nice and steady in my hand. The rest of the car including the seat on my butt is vibrating.

I am looking for input on the most likely to least likely cause. The first thing that comes to my mind is drive shaft. All input is appreciated.

Wayne

[JoeHall]

I am guessing the problem was not as much of an issue in the 1960s, when speed limits were lower. To address your problem: The tires have a bit of radial runout and could benefit from shaving. Once shaved, spin balancing while mounted on the car would insure the tire, wheel, and drum/disc are balanced as an assembly. Unfortunately, I am not aware of any tire store that provides this service anymore.

I have experienced the same vibration you describe, on every Hawk I ever drove. Except it usually has a speed range that it is at its worst, i.e. around 70 MPH. A little higher or a little lower is usually less vibration. As you say, up to 60-65, it is fairly smooth. Put another way, I have never driven a Hawk that did not have the vibration you describe.

Here's another recent thread on the same subject: http://forum.studebakerdriversclub.c...-MPH-vibration

[BILT4ME]

I would say a rear tire out of balance for that speed. Could also be out of round or a slightly bent wheel rim.

My Lark does fine with no vibration until I exceed 80 MPH.

Balance tires
Check wheels for run-out/bent
Check tires for out-of round, flat spots, slipped belt
Worn/bad shock on one corner (rear most-likely)
Front wheel bearing adjustment
On-car wheel balancing like a big truck (this balances the entire rotating assembly including the brake drum, but must be re-done whenever the tires are rotated)
Alignment
Weak or broken rear leaf spring
U-Joints
Driveshaft alignment/balance

That's the list I would hit, in that order.

[E. Davis]

Sure sounds wheel related to me. Neither of my two Hawks (1959 and 1961) ever exhibited any vibration like you have described. In fact the faster they go the smoother they get has been my experience.

[jclary]

I agree with you that it sure seems like center drive line issues in the absence of no vibrations felt through the steering wheel. It has been my experience, even for rear wheels, some vibration will be transmitted along the frame rails. Since the engine was removed for overhaul, how 'bout the bellhousing alignment? We have had numerous discussions regarding "dial-in" issues. Additionally, check the U-joints. You can check them for play, or even "clock" them by changing their orientation. Perhaps, jack the car up, and use a dial indicator to check "run-out." Let us know what you find.

[Hawkowner]

Welcome to the club
To up my fighting this problem I found I have an out of round brake drum and a rear bent hub or axle. Discovered this when putting car on jack stands.Headed north will follow up in Sept.
Some thought on this subject.
The highways are smoother and do not have the expansion joints to brake up the frequency.
Begining to believe the road surface may be washboarded
I drove my 15 Impala 500 miles in 90 degree weather yesterday This morning upon starting out on smooth asphalt I had the dreaded 70 Mph bounce. Not as severe as my Stude but same frequency.Crossing bridges with joints vibe stops.
After about an hour driving the vibe is gone.
Did the tires flat spot over night an need to warm up to round out ?


Hawkowner

[wdills]

To address some of the suggestions. The wheels are new Dayton Knock-Off style. The tires are new Diamond Back Michelen Defenders. The tire and wheels were computer balanced with no abnormal amount of weights required. All 4 shocks are new. U-joints are new and tight. New flanged rear axles from Fairborn, so no hub anymore. (Axles were replaced because I had a bent hub / axle). The bell housing was dialed to the block and was within 0.002" all the way around. The rear brake drums were turned but not balanced. The front has Turner disks. Alignment was just done about 200 miles ago.

The car's only interstate outing was going to work one day. My commute takes me down about 30 miles of 2 lane at 60mph where everything was fine. The last 10 miles is interstate which is where I noticed the problem. Seems the tires would have been nice and warm before I got to the interstate.

The rear springs are not broken but they are weak. Lets the car squat a little in the back but I liked the stance so I didn't get new springs.

Thanks

[az64stude]

I would try rotating tires, maybe if the problem is showing up in the rear move both of those tires to the front. At least you could put the tire & rim questions to rest then. Now are your rims all the same dimensions? Do you you have a twin trac?

[wdills]

All tires and rims are the same size. Not a TT it has an open Dana 44 (4.09). Rotating front to back sounds like a nice easy step to eliminate tire and wheel questions.

[JoeHall]

All tires and rims are the same size. Not a TT it has an open Dana 44 (4.09). Rotating front to back sounds like a nice easy step to eliminate tire and wheel questions.

What kind of transmission is mated with the 4.09 Dana? If its a 4-speed, or FOM your motor is probably turning around 3500 RPM at 70 MPH. So that vibration may be the motor about to blow. LOL

OTOH, if its an OD the car is probably pleasant to drive at 70, since it would only be turning 2600-2700 RPM then.

[wdills]

It is a 3 spd OD. At 70 it runs a nice pleasant 2500 or so.

[Ron Dame]

Have you checked teh U joints and driveshaft to be sure they aren't bent? Have you checked yu braked drums to be sure they are balanced?

[Dan Timberlake]

I'd use this to get an idea what the rpm/frequency of the vibration is. Knowing the frequency/rpm would identify what component(s) are likely the problem.

https://www.jackssmallengines.com/jacks-parts-lookup/part/briggs-stratton/19200?gclid=cm_67emrgdqcfdslswodkqgdka

In 3rd gear (direct) the driveshaft rpm is the engine rpm.
At 70 mph driveshaft vibration would be about 3500 rpm. That is about 40 Hz, which would likely also be audible as a low frequency "boom" in the car.
At 70 rpm the wheel/tire/brake drum rpm would be about 800 rpm. That frequency is low enough numerically to be silent/inaudible, but can be visible when the seat back is vibrating and you can almost count the individual pulses.