Wobble?

jmattox
Posts: 131
Joined: September 24th, 2006, 9:40 pm

Wobble?

Post by jmattox »

OK, after the trip to tech to have my suspension "looked at." I am willing to put up with the suggestions that will be offered here. Daytona, May 7/8 other than the "other" problems we had, tires, carb linkage, shifter linkage, REALLY bad tires and, oh yeah, brakes. The tech inspectors could not find anything to write in my log book, so I am good to race in June at Sebring. We have a Vista Bushwacker with zero roll rear suspension and to the best of my knowledge everything is hooked up correctly (probably not adjusted correctly) and tight with no broken, bent suspension parts. The "wobble" seems to start at slow speeds right after hard braking (3 and 5 at Daytona) appears to go away and ride quite smoothly through high banks (yes, I stay right above the yellow line because I don't like what the other cars leave on the apron). The "wobble" seems to be quite harmonic and all I could see was the front end "dancing." As I got slower the "wobble" would go away and as long as I didn't step on the brakes (my son says he doesn't use them anyway) the "wobble" did NOT reappear until I braked for 3 and 5. Oh yeah and the rear cowl now needs attention after the "scrape" with the armco. I will obtain better tires before June. Now, I will shut up and let the "fun" begin. Thanks

John
FV42
brian
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Re: Wobble?

Post by brian »

we used to get a lot of slow speed wobble, we called it the grocery cart syndrom, caused by excessive caster. If a large amount of effort is needed to steer the car, the caster may be too high. A pair of shims behind the upper tube of the h-beam will reduce camber. Redo the toe if you shim the front end. If braking, rather than slower speeds, really triggering the wobble, it could be out of round drums or tramping. Try to apply the pdeal very gently and if the pedal pulsates, the drums may have to be turned. Tramping is a condition caused by the car rocking back and forth on the rear rockers. The driver will get a sense of the car flopping back and forth if it''s tramping. A quick fix is to tighten the bolts where the rockers attach to the frame to provide a friction dampening to the roll axis. Some have gone to a steering dampner from a rocker to the frame and this will dampen side to side movement as well. Last, an out of balance wheel can cause a zone or harmonic vibration. Mount a tire on the front spindle and if it wants to seek the same position after rotation it may be out of balance. hope this helps.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
Veefan
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Joined: August 14th, 2007, 9:22 pm

Re: Wobble?

Post by Veefan »

If everything is tight, no slop in the steering or linkage, shocks are smooth with no dead spots and the wheel bearing are adjusted correctly, it might be your rims and tires. Did the wobble start and end at the same speed? Did you try swapping out the tires?
smsazzy
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Joined: June 24th, 2006, 5:56 pm

Re: Wobble?

Post by smsazzy »

This might be very elementary; do you have a front sway bar or two spring packs in the beam?
Stephen Saslow
FV 09 NWR
Matt Clark
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Joined: August 31st, 2009, 9:34 pm

Re: Wobble?

Post by Matt Clark »

Sounds like the exact same problem I am having.

Initially it started when the toe was set straight from the massive toe out I started with. Hard braking induces it to the point of almost taking the wheel out of my hands. Also had a talking to from officials for "scaring the workers". Should've been in the car for it! Swapped drums and wheels out, still did it. Seems to go away once I get the car turned & a sideload on things. I've swapped front end bits out, but have not had a chance to try them yet.

I have a full needle bearing beam with sort of a pair of these needle bearing spacers in the top on the sway bar. Think I'm gonna try a set on the lower beam/spring pack next to try to eliminate any sideways movement there. The SR site says they're for the sway bar beam, but I've seen pics in both.
http://www.sracing.com/Store/FV_Stuff/S ... EARING.jpg

Let me know how you make out with yours!


~Matt
~Matt Clark
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hardingfv32-1
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Re: Wobble?

Post by hardingfv32-1 »

1) Why would go to tech with your car problem? What expertise do you think they have? Are you saying that you showed the car to Fred Clark?

2) Did you rebuild the front end before using this car? Did you buy, mount and balance these tires?

You are working with a car built from mostly used parts. Unless you inspect EVERY suspension and steering part on the car before using the car, you have no idea where you stand.

Brian
hardingfv32-1
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Re: Wobble?

Post by hardingfv32-1 »

Matt

WHY would there be any sideways movement with the spring pack? Is it not anchored in the center of the beam or ride height adjuster?

Again, have you had the front suspension completely apart? This means removing and inspecting the inner control arm bushings for wear.

You guys are scary!

Brian
brian
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Re: Wobble?

Post by brian »

Assuming all the front end parts have been checked and the drums have been either checked or swapped out, there is one other circumstance that will trigger a violent wobble. As the VW suspension compresses, the front end looses caster as the turkey legs travel upwards and the car's nose dives relative to the rear. If the caster travels through 0 and goes into a negative caster angle, it will often trigger a violent wobble. Take a look at the spindle and see if the top is angled backwards relative to the bottom of the king pin. Then, while watching the king pin, push down on the front end and watch the top of the spindle travel forward. As the king pin rotates, caster is reduced. If the king pin travels beyond verticle and becomes the least bit angled forward, relative to the bottom, the caster has gone through zero and ventured into the negative zone. Bad stuff! By shimming the lower tube of the h beam you will increase the initial caster and reduce the possibility of hitting zero.

While checking parts for integrity, make sure the rod ends, steering box and king pin bushings are tight as well. Checking the bump steer, toe change as a result in change in ride height, as well.

Anyone may call me a 916-712-5742 to discuss this or any vee issue. Hope this helps.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
Matt Clark
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Joined: August 31st, 2009, 9:34 pm

Re: Wobble?

Post by Matt Clark »

@ Brian (Harding):
Yes, it is pinned at the ride height adjustor. And I didn't say there was any sideways movement, I just wanted to absolutely eliminate any possibility of some under loading. I stripped to a bare beam. And Ray Carmody had that corner apart as well. Neither of us found any glaring issues. I am trying all different corner parts to see if it is in fact one of those bits. This isn't my first time working on a race car, I'm just still new at the Vee stuff, so I'm just going down a list of possibilities.

@ Brian (BRM):
That was actually something I was thinking too. We don't have a nice level floor to really check exactly how far the castor rotates, but the front of my car is pinned down hard by my shocks. Too far, actually. The setup sheet that came with my car list around 3" of front ride height. My front shocks (black Penskes I bought later) are internally limited & only allow about 1.75". Definitely something I need to take care of. Shimming the bottom of the beam was the next thing to try if the different parts didn't help.

@ John (jmattox):
Sorry, not trying to hijack this thread for myself. Hopefully we both get this sorted. Really adds a level of frustration.
~Matt Clark
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Re: Wobble?

Post by FV80 »

The simple answer (generally ) is to add a *Steering Damper* (the stock VW Beetle had one for a reason) from the pitman arm (near the tie rod end) to someplace on the chassis. I've had this problem off and on for YEARS and NEVER found an explanation or cure - other than adding the damper. I have swapped the entire front end in the past and had the problem go away (same caster/camber) - and then had to change it again later (crash) and the problem came back. My new car is 'marginal' - MOST of the time, it's OK, but occasionally it would just take off. In my early years, I got meatballed a couple of times, so just added the damper right away on Bullet - problem solved... (regardless of what actually causes it).

Steve, FV80
The Racer's Wedge and now a Vortech, FV80
problemchild
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Re: Wobble?

Post by problemchild »

Matt,
The torsion bar changes length as it twists .... so you will either have spacers loose and doing nothing or spacers binding when suspension compressed (perhaps a clever tuning tool but generally undesirable). Also, Matt, if that car has the inverted steering box behind the dash, as expect it does, I would make sure that all the fab and components were in perfect condition with no binding. There is alot of load that goes through the strg box mount. That config should be less prone to wobble than most FVs ..... perhaps consult with Mr Womer.
Greg Rice
"Happy 50th Birthday"
hardingfv32-1
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Re: Wobble?

Post by hardingfv32-1 »

The last time I saw this issue the inner bushing had moved out of position. That is just one of many possibilities that everyone has stated.

Steve is right. Sometimes a certain set of loose (maybe not noticeable to you) tolerances between the front end parts sets up chassis harmonics that must be controlled with a dampener. The issue could even be in the rear suspension manifesting itself at the front. The steering damper would be a good fall back plan to have so as to limit lost track time.

The shocks are acting as a droop limiter. As a general question: Anyone, Is this type of setup know to cause brake trap?

Brian
brian
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Re: Wobble?

Post by brian »

I don't think limited shocks cause this problem. If anything the limited travel will reduce caster change. Tramping is caused by the geometry of the rockers relative to the centerline of the chassis. Mysterians are well known for this issue and tightened rockers or dampners help. VW beetles have dampners for two reasons. The caster change I mentioned before and steering box wear. If the steering gear is loose the steering wheel will wooble. The super beetle, 1971 type 1 with the macpherson strut front end was terrible, and even the factory couldn''t really fix it. Not only would it wobble it would consume steering boxes like they were candy.

If memory serves me factory caster on a Type 1 is about 3.5 degrees. The lynx had so much angle in the h beam mounting area that the preset was well above 7 degrees. One of the reasons for so much preset was that most folks lowered the z bar car and that reduced the final caster Turkey legs that are parallel to the ground reproduce the factory settting and provided the softest ride. As the car is lowered, turkey legs angled up reducing caster and increasing the spring rate. My old Lynx B just loved 45 mph cause the front end would wobble so much I'd have to drag the brakes on the pace lap. Reduced the caster, raised the car back up and everything went away.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
jmattox
Posts: 131
Joined: September 24th, 2006, 9:40 pm

Re: Wobble?

Post by jmattox »

Keep the suggestions coming! I will be addressing the front end before I go out June 4/5 at Sebring. We will also be looking at the brakes. $$$$ says stock VW shoes and a regrind on existing brake drums with a look at the cylinder(s). Thanks to everybody. In defense of the group of "tech" people, thet did suggest a call to Fred Clark. And, the SOC who "sent" me to tech said it was for MY safety and the safety of my fellow competitors. I guess they didn't like my Publix grocery cart fake em out move.

John
FV42
cendiv37
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Re: Wobble?

Post by cendiv37 »

John,

I'm not sure I understand when the "wobble" occurs. You describe it as occurring "after braking". So it's happening at turn-in or in the corner? Some of the rest of your description sounds like it is "during" braking. Also, describe the "wobble" as best you can.

Always go back to the basics, especially if the car is new to you. As everyone has said, check everything in the front end for looseness and fix what isn't right. Then do the alignment, front and rear. As Greg says, you shouldn't need spacers on the trailing arms attached to the spring, just the rubber seals to keep the grease in and dirt out. Set up the spacers on the trailing arms attached to the sway bar so that they move freely, but with minimal free play (a few thou is enough). Usually one of the trailing arms is movable relative to the sway bar with a stud and not at the end of the sway bar and a flat pinch bolt against the sway bar.

Over the years, I've had a few different types of front end problems.

If your car still has the "horns" on the beam between the trailing arms, the front suspension can bottom on these under hard braking: not nice. You can test for this by wrapping the lower trailing arm with some contrasting color vinyl tape and checking it after a session. Fix it by either raise the ride height or move or cut off the horns. If you cut of the horns, you need to make sure the suspension doesn't drop too low when you jack it up or it can bend the tie rods. Droop limiters in the shocks is a nice fix unless you don't want them. I suppose that very hard travel limiters on the shock could do the same as the arms hitting the droop stop horn.

I once had a loose pitman arm bort. It caused some weird stuff to happen, but not a wobble. Torque the pinch bolt to 70 - 72 ft. lb.

Make sure your tie rods are straight. Since our cars are "rear steer", the tie rods are under compression during braking. If they are not stiff enough or are slightly bent, they will experience a type of "column failure" and the car can lurch from side to side as first one side and then the other toes out as the tie rod gives under compression. I found out about this the hard way :oops: Too much toe out can do something similar, but I doubt it would be as severe.

As Steve said, adding a steering damper to the front is a good idea. It can cover up a number of possible resonance type problems that can be hard to diagnose and fix otherwise. If you can find nothing wrong and it still has a wobble, add a damper. I use a Type 2 damper on my car and have for years. I've also run just fine without it ... sometimes. Like Steve says, some beam set-ups just seem to need it.

Last but not least is a "second" of something Brian M. said. (Matt this may be what you are dealing with.) If it is a pretty violent shaking happening under hard braking and lighter braking doesn't cause it, it might be a resonance problem that is due to a lack of roll damping in the REAR suspension. It is known to some as the "Mysterian Shakes" because Mysterians seem more prone to it than other cars. I think it is a combination of the relatively short steering arms in the front (for quicker steering) and the nearly true zero roll resistance of the rear suspension. I've had it on mine off and on over the years and have fixed it every time by adding some kind of rear roll damping. I've added a steering damper between chassis and one rocker (fixed it). I've tightened up the lower rocker pivot bolts (which pinches the surfaces of the flanged bushings together providing some frictional damping). This is a pretty easy fix if you have that type of rear rocker pivot (note that it doesn't take that much). After I changed to rod ends as the rocker pivots, I could no longer do this, and initially, I had to resort to tightening up the axle tubes by removing a gasket or two. This is a nasty kluge, but it works. I finally fixed this semi-permanently by running the shock as long as possible and moving the lower rocker pivots inwards as far as I could. This subtle geometry change seems to add some "natural" damping to roll at the rear and solved the problem to where I no longer need a steering damper or added friction somewhere in the system.

Lastly, have you cracked tested your front spindles? If the car is new to you, this is something you just must do and then redo at regular intervals unless you add the bearing spacers that stiffen and strengthen the spindle. Even then you need to crack test the spindles first before you add the spacers. This is unlikely to be your problem, but I have heard people say that their car didn't "feel right" for a few sessions before they later broke a spindle. And having seen some of the broken spindles, they were clearly driven many laps in a cracked but not yet broken condition.

Good luck!
Bruce
cendiv37
halifax
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Re: Wobble?

Post by halifax »

Now I know why my Lynx/B sits higher than most Vees. Thanks Brian/BRM for that one.
Matt Clark
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Joined: August 31st, 2009, 9:34 pm

Re: Wobble?

Post by Matt Clark »

Hmm. I definitely will dig into the castor stuff deeper, but the steering dampener sounds like a worthy solution too. My first school at the Glen, the front became uncontrollable on the pace lap. Started as a rumble in the front, then grew into a violent shake. Without the gyroscopics of spinning at speed, I literally had to pull over and stop quick. It didn't do it that bad again because we ripped it apart after that. Harmonics were my description back then. Could some of you guys post pics on how all that is mounted in your car? As Greg mentioned, my steering box is right behind the dash, and I'm kinda cloudy on how exactly the damper would install.

The front shocks tie the front down just so the arms are level to the ground, so it's not like its tied down in a nose dive. Either way, I will look at all the movement up there. One thing that crossed my mind was if the internally limited shocks and the ride height adjustor fighting each other somehow. Not knowing how everything works yet, I could almost envision something there because the ride height adjustor isn't the controlling part. When I take the shocks off, I have an offroad racer.

My rear rockers are bolted pivots, so I will try snugging them up slightly too. I have/had them set with a tiny amount of play for free moving suspension. Same with the front torsion bar bolt. Just enough I can barely move things by hand. The horns on the beam do not stop the down travel, either. The car bottom well before hitting those. I have not crack tested spindles yet, either. The car normally uses standard VW spindles, but I have my dads quicksteer spindles on right now. My quick test drive looks like that makes the steering odd due to the inverted steering box & long length of Pitman arm. I am ordering new spindles since I have no spares anyway, but what do you guys recommend as the best DIY crack test method? I assume it doesn't involve sending them somewhere all the time.

Thanks again for any responses. Learning a lot about the cars on this one.
~Matt Clark
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FV80
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Re: Wobble?

Post by FV80 »

Matt,
First step I would recommend would be to reset the adjustable droop so that the arms are level WITHOUT the shocks attached. HOLDING the shocks down that far (you indicated 2+ inches IIRC) sounds like ... well, it's does NOT sound like a good idea to me. A shock limiter is supposed to limit upward front end travel - I've never heard of anyone tying the front end down by 2+ inches before.

I don't have a current pic handy but this [ external image ] is a pic of my car during construction before I had the frame powder coated. I attached a simple 'u' bracket just behind the pitman arm mounts for the tie rods - and ran it to a custom fabricated aluminum channel bracket attached to the 'passenger side' box end of the steering box tube. Depending on the actual damper that you use, you'll need to make sure that the damper doesn't reach the end of its travel during any possible steering angle. In my case, the pitman bracket is offset to the driver's side of the pitman arm to prevent that. It runs at a moderately high angle, but still provides adequate damping action to control the shimmy.

Steve, FV80
The Racer's Wedge and now a Vortech, FV80
Campbell Motorsport
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Re: Wobble?

Post by Campbell Motorsport »

This sounds a lot like what happened to me at my first drivers school in my old Lynx- slow speed wobble and shake, high speed all was fine. Lybarger and Beaumia told me to go faster and check my spindle/carrier assemblies for looseness. I had set up the spindles too loose on the king pins. For the drivers school I went faster and then reshimed the assemblies to make it a tighter fit and all was fine.

Larry Campbell
hardingfv32-1
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Re: Wobble?

Post by hardingfv32-1 »

Steve

That is an impressive steering arm. Anyone have something longer?

Brian
billinstuart
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Re: Wobble?

Post by billinstuart »

Vista? Isn't that what Courtney/O'Neill ran? If so, they gotta TON of caster. It's called "caster shimmy". However, it makes a slick front end. Us old farts remember them at old Daytona without the busstop on the back straight.
FV80
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Re: Wobble?

Post by FV80 »

hardingfv32-1 wrote:Steve

That is an impressive steering arm. Anyone have something longer?

Brian
Mine is actually longer than shown in the picture, but I made it TOO long and couldn't steer the car initially. I had to go back and modify the spindle end to make it all work (since I couldn't move the steering box without ruining my powder coating job <g>).
Steve, FV80
The Racer's Wedge and now a Vortech, FV80
Matt Clark
Posts: 31
Joined: August 31st, 2009, 9:34 pm

Re: Wobble?

Post by Matt Clark »

Thanks for that guys.

Looks like I'm going to get new spindle assemblies for the time being, and really go over my current parts. I have no spares of those, so buying some doesn't hurt my feelings. When you grab the front wheels and shake the car, nothing clunked or rattled, so maybe there is a hidden problem in something. I will also reset ride height without the shocks while I have it torn apart. I'm not sure I could get a VW damper in my car, but I am looking at one.
~Matt Clark
RTJ-02 #81
jmattox
Posts: 131
Joined: September 24th, 2006, 9:40 pm

Re: Wobble?

Post by jmattox »

Thanks to everybody. It worked. Front end had dead Fox shocks, replaced with stock VW. Tighten up kingpins, a little too much (will be better next race). The wobble started this time from REAR end. Adjusted the toe in more the first time, less the second time and a little for the half hour race short course Sebring. Now I have to learn to trust my tires and "drive the line." Daytona will be better in August. Maybe I won't get a trip to the stewards and tech.

John
fv42
Matt Clark
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Re: Wobble?

Post by Matt Clark »

As an update for my issue in this, I think I have finally figured out the problem.

After rebuilding everything & trying different parts without any success, I ended up softening the front spring way up this past weekend at Watkins Glen (trying to reduce an nasty oversteer from changing spring packs), and the wobble during racing all but went away. It is back during caution, but I think I can address that yet too through dampening as mentioned earlier in the thread.

Here is the story of how I arrived at this; My spring pack used to be in the bottom beam, so I moved it to the top for better camber under braking/cornering as recommended by several people. As I was doing all this teardown, I noticed the springpack had 2 narrower leafs on the outside of the pack, so I wanted to try a pack of solid leaves I had on the shelf. Once I got on track, all this greatly increased the spring rate in the front, and oversteered like crazy in addition to having no grip on harder tires in very cool weather. Between races, I took it apart & changed the spring preload (I have a straight-knurled "rumble strip" style adjuster) and did a quick re-align as best I could alone. I was really worried as soon as I went back out on the pace lap since it was back to shaking like crazy under caution, but went away when we went green. I have to tune the shocks now to balance the car out, but overall, I am heading in the right direction. I ran very competitve laps as I worked through the weekend and ended up with 3rd fastest lap (finished 5th in a nice battle) out of about a dozen cars, behind Arnie Carbaugh & Gary Kittell.

I am guessing due to the fact I was so much heavier than the previous drivers (they had lead bolted in the rear), my body added weight to the front wheels & went over the threshold of what the car likes. I put new spindle assemblies, new tie rods, rebuilt shocks, different brake drums and new wheels/tires on before finding all this. There are some other things I want to do yet to see if they help even more (new steering box, take the limiters completely out of the shocks, damper, etc). Being new to the FV stuff, I just assumed that was where the springs needed to be. I never guessed that change would have done that.

Anyway, I just wanted to update my status finally in case someone else ever has a similiar issue & might benefit. Thank you to everyone in here that posted, the guys at the track that helped, as well Ray Carmody & Steve Pastore for talking me through so much of this. That's what I love about this class. :P
~Matt Clark
RTJ-02 #81
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