Hi all,

Im hoping there are some suspension gurus here that can help me out on a front end vibration ive been chasing for a very looooong time.

Ever since we got our 56 sunliner it had a bad vibration.  At 52 mph, the front end starts to shimmy.  In fact, you can see the right front headlight/fender top going up & down.

Well, i had figured doing a frame off resto would have cured it.  With new floors in, al new suspension bushings, tie rods, shocks, springs, spring seats, sway bar bushings, ball joints, tires, rims and brake drums ..... and it is still there!  It isnt nearly as bad, but still somewhat there.

So last weekend i decided to try to chase it down.  I just replaced all 4 rims with new ones (welded vs. rivited), and had all 4 balanced.  I measured the lateral runout at the mounting face of the brake drum and it was 45 thousandths(!).  I re-indexed the brake drum (roatated it about 180 deg relative to the hub), and got it down to about 8 thousandths.  Thats weird too since I had the new drums cut with the spindle, and had kept them indexed as they were cut... but anyways.

Today i pulled it apart and repacked the wheel bearings, and tapped the inner races to ensure they were fully seated.  Put it all back together and got the lateral runout to 6 thousandths.  HOWEVER, the fore/aft runout (not sure of the term) is at 95 thousandths (although im not sure if that is a precise dimension, and i havent figured out how to measure if the lugs are that far out of whack, if that makes sense)

So the vibration is still there, although much less.  I did notice that when i spin the wheel it feels like it drags or tightens up at one point in the rotation, even after I adjusted the brakes out a bit to ensure they werent dragging.

Im relatively certain that at some point in its life the car was hit in the right front corner.  Im wondering if the front hub got knocked out of whack somehow?  Im not sure what else to look at/adjust/measure, etc.  I dont want to just go swapping parts, but what else to do?

One other thing that may offer a clue is that sometimes its worse than others.  As example, in a long high speed left hand sweeper, sometimes the front will start to shake after not doing it for a while.  Also, how tight is too tight on the front wheel retaining castle nut?  Ive read the shop manual, but everyone has a different interpretation of touch stuff (just start to feel drag...).

Anybody have any thoughts?  What did I miss or screw up?  Any thoughts are REALLY appreciated at this point, since im at my wits end!  Thanks!

Ron Grove

Wauconda, IL

Interesting problem. Be sure to let us know if you find the solution, as I also have vibrations/shimmies that come and go. Though I SHOULD know better, due to a lack of patience I often throw several different remedies at a problem simultaneously, thus I never REALLY know what cured it!



Re: castle nut tightening, I have read at least a dozen shop manual procedures, all a bit different. Currently, I use this one:

Get a "micro-nut" type, two-piece castle set (NAPA). While turning the wheel in a forward direction, torque to 15-20' lbs. to set the bearing. Loosen the nut and then bring "finger tight". Place the stamped nut cover so that it is just BEHIND the nearest cotter key slot position. Using slip-joint pliers, tighten the nut/cover just enough to insert the cotter key (use a new one).



Anxious to hear others' opinions/suggestions.






6 VOLTS/POS. GRD. NW INDIANA

Come on... anyone? 

Here is some more info based on some more poking around today. 

Fore/aft runout on the edge of the front hub is 48 thousandths.  This was measured on the center section of an old but true rim i have.

If I bolt the rim up to the hub without the brake drum, I get 68 thousandths measured at the lip ot the rim. 

Also when i was tightening the castle nut i noticed something unusual.  If i kept a constant pressure on the socket while spinning the wheel, the ratchet would advance further/move easier at the same point every revolution.  Does that make sense?

Ive rebuilt/repacked both front wheel bearings.  there is no movement if i grab eitehr tire from at the top/bottom.  If i grab on the sides, there is a tiny bit of play, although im not sure if that is loose tie rods (having been beaten by the vibration) or play in the steering box, PS control valve, etc?

My current thought now is to find a replacement hub, and at that point probably having to replace the tie rods.  But I also have a bad habit of interpreting information to "tell" me what I want/think the answer is, so im looking for a sanity check as to other stuff im missing?  any thoughts; anyone???????  HELP!

Thanks!

Ron Grove

Wauconda, IL

a few questions I have. Did you have a front end alignment done? Were the tie rod ends replaced? Have you changed the wheel bearings? Are they the correct ones?

John F

Ballwin, MO

Also when i was tightening the castle nut i noticed something unusual.  If i kept a constant pressure on the socket while spinning the wheel, the ratchet would advance further/move easier at the same point every revolution.  Does that make sense?

    No, not to me! Try putting the left hub on that side and see if the same thing happens.

Frank/Rebop

Bristol, In ( by Elkhart) 

yes, had an alignment done.  I replaced the tie rods when we did the body off resto, about 8 years ago.  All new bushings, etc too at the same time.  I also replaced the wheel bearings at that time, and I assume they were the right ones.

The weird thing is that this problem, in varying levels of severity, has been with this car since we bought it.....before the resto and after....

As for the idea of switching sides with it, what would that tell me?  Would i just be looking to see if i have the same issue on tightening the castle nut?

Thanks for all the replies!!!

Ron Grove

Wauconda, IL

It would tell you if the hub was drilled off center, or the problem was a bent spindle AND an off center hub. Beyond that I'm totally at a loss to explain the issue.

      If the hub form the left side does not exhibit the tight / loose condition, you at least know the right hub is the problem. If it acts the same, then the issue is probably with the spindle. You could do your runout checks with the left brake hub (on the right side) as well.

Frank/Rebop

Bristol, In ( by Elkhart) 

This is a long shot, but front end shimmy is often an issue on solid axle cars, even with properly  set up cross steering.  In some cases it can be cured by using slight amounts of toe out rather then toe in, or by modifying the base spec's. Radials to bias plies sometimes seem to aggravate this.  I've never had it happen personally, but if the frame is a bit out of square, who knows how the tolerances stack up.  If you don't fine anything else, maybe a good old fashioned front end guy can help, someone who can still bend a truck front axle.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

I don't remember offhand if the upper A arm shafts are the same frontwards as backwards on a '56, but let me offer a scenario.  If they are not symetric, suppose the PO turned them around, and when you did the frame off, you put them back the way they were.  Then maybe you have negative caster, and if the front end alignment guy didn't suspect that to be the case, didn't recognize that the caster angle was on the wrong side of zero.  Negative caster invites shimmy.  When you were a kid, did you ever try to run while pushing a shopping cart?  The front wheels on carts have negative caster, and will shimmy like crazy.

John - "The Hoosier Hurricane"

Ron:

I looked at my nos upper shaft, it is not symetrical.  If installed backwards, it moves the upper A arm forward or back from its intended position.  The distance from the bolt hole to the shoulder for the bushing is different by 3/8", so installing it backwards moves the arm 3/4".  Unfortunately nothing on the shaft indicates which way is "front".  If you need to know, maybe I can measure it on one of my Birds, they have the same front suspension as passenger cars. 

John - "The Hoosier Hurricane"