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Buggy darts while driving
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cudabear
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PostPosted: Sat Oct 21, 2017 2:33 pm    Post subject: Buggy darts while driving Reply with quote

While driving my 2 seat buggy it wants to dart left or right . It has a ball joint front end with drop spindles and beam adjusters. I have aligned the front and rear end with specs according to Air Cooled . Net . I have raised the front end by the adjusters and reset front toe to 1/8th total toe to no avail. It has KYB gas shocks frt & rear , soon to be changed out with oil filled shocks from ACN. A friend suggested the drop spindles may be the problem throwing off the factory geometry. My first 2 seater had no problem at any speeds, & my 4 seater with front end at factory height steers true. Any advice or experiences ?
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jspbtown
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PostPosted: Sat Oct 21, 2017 2:40 pm    Post subject: Re: Buggy darts while driving Reply with quote

Tire pressure? Steering stabilizer?
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PostPosted: Sat Oct 21, 2017 2:47 pm    Post subject: Re: Buggy darts while driving Reply with quote

Do you have caster shims?
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cudabear
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PostPosted: Sat Oct 21, 2017 3:49 pm    Post subject: Re: Buggy darts while driving Reply with quote

It has a new good quality stabilizer. The original had a binding during the stroke. And yes it has caster shims with caster at around 4 to 5 degrees that I recall. I also disconnected the 2 tie rods and checked ball joints and tie rod ends for binding. Backed off on ball joint lock nuts to ease the effort to turn the spindles. All turns freely.
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cudabear
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PostPosted: Sat Oct 21, 2017 3:50 pm    Post subject: Re: Buggy darts while driving Reply with quote

It has a new good quality stabilizer. The original had a binding during the stroke. And yes it has caster shims with caster at around 4 to 5 degrees that I recall. I also disconnected the 2 tie rods and checked ball joints and tie rod ends for binding. Backed off on ball joint lock nuts to ease the effort to turn the spindles. All turns freely.
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Dale M.
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PostPosted: Sat Oct 21, 2017 5:14 pm    Post subject: Re: Buggy darts while driving Reply with quote

Usually caster shims under lower beam stops this ...... Seem to remember caster should be around 7

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PostPosted: Sat Oct 21, 2017 7:39 pm    Post subject: Re: Buggy darts while driving Reply with quote

Look for simple things first. What is your tire pressure? Shouldn't be more than 10-15 psi.

What wheels are you running with what offset and backspace? Did you make a change in rims and tires during your build? Rims with a neutral or positive offset will rather dramatically add to a car's tendency to wander unless you correct with more toe in. This in turn has its own effects on steering and handling, not all good.

Find a friend with stock VW wheels and tires, borrow them, put em on your car and take a spin. If your problems vanish or diminish you know where to start looking.
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slalombuggy
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PostPosted: Sat Oct 21, 2017 9:28 pm    Post subject: Re: Buggy darts while driving Reply with quote

What size of tires are you running in the front?

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cudabear
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PostPosted: Sun Oct 22, 2017 5:28 am    Post subject: Re: Buggy darts while driving Reply with quote

Tire size is 145/65-15 on Douglas aluminum rims about 3 1/2 inch to 4 inch wide. Tire pressure @ 22lbs One thing I did change before I started having this problem was the rear tires. It had 295/50-15 street tires. But under hard acceleration the tires would spin 1/2 way thru 1st all the way thru top of 3rd. So I put on a pair of M&H cheater slicks. From what I can tell they aren't radials, the fronts are. This can cause over steer from what used to happen when radials first out over bias tires. I'm going to put 295's back on too try it out. Will report back. Dale the castor setting at 7* is for and good for high speed handling. The factory ran 2 * for easy turning with no power steering. For what it's worth I also had to replace tranny and I installed a berg poor mans posi trac kit. Wouldn't think this would cause a problem. .???
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PostPosted: Sun Oct 22, 2017 8:00 am    Post subject: Re: Buggy darts while driving Reply with quote

cudabear wrote:
Backed off on ball joint lock nuts to ease the effort to turn the spindles. All turns freely.

Red flag here. If you have to back off the nuts on the ball joints to get the spindle to turn freely then you need new ball joints...
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PostPosted: Sun Oct 22, 2017 9:26 am    Post subject: Re: Buggy darts while driving Reply with quote

cudabear wrote:
For what it's worth I also had to replace tranny....

Swingaxle or IRS? Swingaxle replacement can affect rear wheel alignment. That could cause all kinds of evil handling problems. I would also try dropping front tire pressures a bit more. Cool
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Dale M.
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PostPosted: Sun Oct 22, 2017 9:38 am    Post subject: Re: Buggy darts while driving Reply with quote

cudabear wrote:
Tire size is 145/65-15 on Douglas aluminum rims about 3 1/2 inch to 4 inch wide. Tire pressure @ 22lbs One thing I did change before I started having this problem was the rear tires. It had 295/50-15 street tires. But under hard acceleration the tires would spin 1/2 way thru 1st all the way thru top of 3rd. So I put on a pair of M&H cheater slicks. From what I can tell they aren't radials, the fronts are. This can cause over steer from what used to happen when radials first out over bias tires. I'm going to put 295's back on too try it out. Will report back. Dale the castor setting at 7* is for and good for high speed handling. The factory ran 2 * for easy turning with no power steering. For what it's worth I also had to replace tranny and I installed a berg poor mans posi trac kit. Wouldn't think this would cause a problem. .???


But a shorten, lowered pan and small tires up front and large tires on rear throws out all the factory settings out even change the Ackerman steering geometry for original length pan....... I can let go of steering wheel at any speed and have no fear of darting.... My buggy tracks true up to about 90MPH (never pushed it beyond that)... And alignment front /rear is basic garage setup Yes ts a link pin with one set of caster shims.... BUT I also had a later chassis with full IRS set up so low it would not go over speed bumps at entrance to racecourse parking lot ..... Car was setup for autocross and uses basically all the wrong front caster and camber and it handled well....

Some people have resorted to two sets of shims to correct problems...

Dale
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oprn
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PostPosted: Sun Oct 22, 2017 7:12 pm    Post subject: Re: Buggy darts while driving Reply with quote

Ok, confession time, I am not familiar with castor shims.

What?

Where?

Why?

When?

I had my buggy in for an alignment just a few weeks back. They told me the castor was wrong but said it was not adjustable. They didn't say what it was or what it should be.

The Buggy steers ok.
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Dale M.
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PostPosted: Sun Oct 22, 2017 8:14 pm    Post subject: Re: Buggy darts while driving Reply with quote

Caster shims are 1/4 moon shaped (end view) piece of aluminum that goes between lower beam and frame head... It kicks the lower beam a 1/4 inch (maybe 3/16 inch) or so further forward and in effect moves the top trailing arm pivot (either ball joint or link pin) further to the rear (or bring lower joint forward - its interpretation of movement), thus increasing the caster angle also know as king pin inclination.... Increasing positive caster...

http://vwparts.aircooled.net/Caster-Right-Shim-Kit-Caster-Shims-Pair-p/caster-shim-kit.htm

Caster angle is what help car return to center when you let go of steering wheel... It also minimises death wobble when front wheels shimmy back and forth like the bunged up "caster" on shopping cart....

Image may have been reduced in size. Click image to view fullscreen.


Get a set of shims.... Loosen upper beam bolts about 3 turns, and lower bolts about 8-9 turns, pry lower beam forward and slide shims in between frame head and beam... Tighten everything to proper torque.... Drive it like you stole it...

Dale
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PostPosted: Sun Oct 22, 2017 11:30 pm    Post subject: Re: Buggy darts while driving Reply with quote

My buggy was super twitchy and finally had it professionally aligned, front and rear helped out a lot.

I have caster shims in the lower beam, with dropped spindles and adjusters so it tracks well, it still had a bit of oversteer (oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver.) when going into corners so I added a front sway bar (didn't have on for off road) which helped more.

It still has a tendency to oversteer at speeds between 30-70 mph, so I have to pay attention and have a good grip on the wheel. The shortened pan, 8" rear wheels, lowered front, sagging rear ('56 torsion bars)have a lot to do with it.
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PostPosted: Mon Oct 23, 2017 4:37 am    Post subject: Re: Buggy darts while driving Reply with quote

Yes I am familiar with what castor is and does.

So the need for shims comes with a lowered front end. Is that a result of the trailing arms being at a different angle regardless of rear height or is it due to the car sitting at a rake, ie: front down but back end at the stock height?

My Buggy presently sits somewhat front high due to the body being lighter than the stock one. I plan to change that.

I will give my wheel alignment guy a call and see what the actual numbers are.
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PostPosted: Mon Oct 23, 2017 5:29 am    Post subject: Re: Buggy darts while driving Reply with quote

Yes the rake angle is the reason for the shims, so if your front sits higher you may need them on the top beam.

As Dale M. stated there's a lot going on with a buggy. Stock settings and numbers are good to have and start with but it will take trial and error to get it safe and drive-able.
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PostPosted: Mon Oct 23, 2017 6:44 am    Post subject: Re: Buggy darts while driving Reply with quote

Don't bother dropping the tire pressure in the front, those tires are so stiff, they won't change at all if you drop the pressures 5 or 6 psi, all they'll do is roll around on the rim.

I think you might be on to something with the mismatched radial/bias ply tires. I tried to drive a car with that mismatch once. I gave up after a mile, it was horrible.

7* caster is lots, that's what I had in my buggy when I ran 121mph and I could let go of the wheel. I only run 1/16" toe IN on the front and "0" toes in the rear.

brad
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Dale M.
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PostPosted: Mon Oct 23, 2017 6:54 am    Post subject: Re: Buggy darts while driving Reply with quote

The beam sits roughly 90 to the pan... If pan is dead level (to road surface) beam is at true vertical... IF front of pan is lower than rear, the 90 angle does not change how the beam connects to pan but changes the angle of the beam to the road surface tilting the top of beam forward... With top of beam pulled forward it pulls the top pivot of trailing arm forward and changes caster angle to a more negative angle there for reducing caster...

The book "Chassis Engineering" by Herb Adams (HP Books) goes to great length to explain how caster, camber, center of gravity and roll center effects car handling and adding front and rear anti sway bars effect handling.... Even goes so far to comment on how terrible trailing arm suspension is not best design for handling and specifically mentions VW ...

Lots of things at play here, lot of things alignment shop dont understand about VW suspension...

Dale
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goodsofar
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PostPosted: Mon Oct 23, 2017 8:04 am    Post subject: Re: Buggy darts while driving Reply with quote

I just recently got a Manx style buggy and you guys are scaring the begeezus out of me talking about going over 100mph! 65 is the maximum I'm comfortable at in mine, with white knuckles.

I've read a lot about changes to the vw front end to help with darting; mine appears to be stock, the front trailing arms just about rest on the snubbers, so I don't think the front leafs have been cut to soften it up.

It sits about level as it is.
Do you think adding the shims for more caster would be a problem? Seems like that would also raise the front end up a bit.
I'm guessing it might just be trial and error?

Its also got some wheels that I'm pretty sure have more negative offset than the stock wheels.
Would getting a set of stock wheels on the front be a good step?

I'm sort of on a budget, if I could I'd probably get a whole new front beam with adjusters and go from there.

Thanks!
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