# AFX Wobble



## Grandcheapskate (Jan 5, 2006)

Hi Guys,
Once you know the wheels and tires on your car are straight and the bare chassis will roll straight, what else would cause your car to:

1) Pull to one side down the straight
2) Wobble on the back end upon acceleration down a straight

I have a couple original AFX which seem to have both of these problems.

In fact, I have a small section of straight which has the plastic guard rail along the side. Sometimes when I accelerate down this straight, the back end of the car will keep bouncing off the guard rail - that's how bad the wobble can get.

Bear in mind on Tyco track, the guard rail is a little closer to the slot than on Aurora/Tomy track. But the car still shouldn't hit it.

My guess is that there is enough play in the rear axle holes for the axle to twist slightly upon acceleration and cause the car to pull right or left. I'm also guessing part of the problem may be that the crown gear, by design, is more toward one side of the axle than the other, causing the rear axle to always "torque" in one direction. Or could the armature/magnet combination cause the car to "pull" to one side?

Thanks...Joe


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## slotking (May 27, 2008)

torque
some setups can over power the rear
or
front wheels sticking on the chassis or body
or
just not enough grip

if you slowly provide power does it still swing?


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## Hornet (Dec 1, 2005)

Are the rear tires identical,it'll always pull to the short tire,that's an inherant problem with solid axles .
Check the guide-pin length and breadth for the wobble,sounds like the pin's not sliding properly through the slot.
Wouldn't hurt to push the car by hand through the parts of the track it's got problems on,just to make sure the car is sliding freely through those sections.
Don't forget Tyco's guide-pin slot is shorter then Aurora's was


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## JVerb (Oct 6, 2006)

On the top plate, look at the rivet that holds the last gear in place. A little slop here will cause your problem. The gear can twist up and disconnect from the rest of the gear train. 

Verb


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## Grandcheapskate (Jan 5, 2006)

slotking said:


> torque
> some setups can over power the rear
> or
> front wheels sticking on the chassis or body
> ...


Front wheels are completely free. If I power up slowly, the rear does not wobble, but the car does pull to one side. You can notice this on Tyco/Mattel track because of the flare at the slot joint. When the car constantly rides against one side of the slot, the car will follow the flare and you will see the car "jerk" at each track joint.

Let me mention I see this happen a lot with Porsche 917 body, which is always (by design) loose on the chassis because the mounting clip on the body does not have a top half. Maybe that is why it is more noticeable with this body.

I also tried this car on a small test routed oval (using braid) and as far as I can tell, the pin always rides one side of the slot. 

Thanks...Joe


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## Grandcheapskate (Jan 5, 2006)

Hornet said:


> Are the rear tires identical,it'll always pull to the short tire,that's an inherant problem with solid axles .
> Check the guide-pin length and breadth for the wobble,sounds like the pin's not sliding properly through the slot.
> Wouldn't hurt to push the car by hand through the parts of the track it's got problems on,just to make sure the car is sliding freely through those sections.
> Don't forget Tyco's guide-pin slot is shorter then Aurora's was


Hi Rick,
See my previous post. I do not believe any of the things you mention are causing my problem, but thanks for the suggestions.

Joe


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## dlw (Aug 17, 1999)

Not sure if this was intended in slotking's explaination, but with the front wheels/axle, does the free-spinning wheel spin freely, or does it hang up on the head of the axle-pin? That can make a car wobble, jump and/or sway to one side as if it's trying to brake.


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## Grandcheapskate (Jan 5, 2006)

JVerb said:


> On the top plate, look at the rivet that holds the last gear in place. A little slop here will cause your problem. The gear can twist up and disconnect from the rest of the gear train.
> 
> Verb


I checked out the rear gear and tightened the rivet. The rear gear did have a little play in it, but was not overly loose. No change.

The front wheels do spin freely and are not getting hung up on the front axle.

I'm still thinking this is caused by either:

1) an unbalanced armature and/or unmatched magnets
2) loose rear axle holes which allow the rear axle to pull to one side

I guess I can swap out the gear train and check (or swap out) the magnets to check theory #1. To check theory #2 I'll have to swap out to another chassis (which I think I already tried).

Joe


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## jobobvideo (Jan 8, 2010)

one axle hole lower than the other? a loose rear wheel or tire under torque? just throw stuff agsainst the wall:freak:


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## Grandcheapskate (Jan 5, 2006)

I did a little more fooling around with this car today.

I tested the magnets and they are close in strength.

I stripped it down to a bare chassis and rolled it down an incline (using a piece of steel). The car does tend to drift to the drivers side - not too bad, but consistant. I replaced the rear tires with O-Rings and reversed the front axle - same thing.

I then tried it with another chassis and it rolled fairly straight (nothing is perfect). So I moved all the components into this other chassis. I tried it with the same gear plate and then another gear plate (and armature). No real differance, it still tends to ride one side of the slot (and therefore, it must be drifting).

I noticed the brushes were worn to different heights, so I replaced them with a matching pair. Put everything back into the original chassis and tested again. Still pulling to one side (maybe not as bad), but now the car seems faster than before as I cannot get it to go slow - one touch of the controller and it's at about 60% full speed.

This isn't the only AFX or AFX MT which exhibits this behavior. There's quite a few that seem to ride one slot wall or the other (nearly all these cars were purchased used). These cars will make the most noise at each track joint. Some AFX ride smooth as can be, others see every track joint.

That's what makes the hobby fun, right? grrrrrrrrrrrrrrrrr

Joe


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## alpink (Aug 22, 2010)

sounds like the guide flag/pin is too long. or have we covered that and I forgot to read it?


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## Grandcheapskate (Jan 5, 2006)

alpink said:


> sounds like the guide flag/pin is too long. or have we covered that and I forgot to read it?


 I'm using the pin side of the guide, so length shouldn't be an issue. I did file down the blade side to see if that would help and I think it's a little smoother with the blade as opposed to the pin, but you can still see the car wants to pull to one side.

When a car wants to ride the slot wall on Tyco/Mattel track, it is very noticeable at the track joints where the flares make it wobble a lot. Just for those who don't know Tyco/Mattel track, even though the slot is 1/16" in the middle of a track piece, at the widest part of the flare it is at least 1/8" - twice as wide.

Joe


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## Bill Hall (Jan 6, 2007)

Well Joe, you bein' a cheapskate and all....LOL....did ya change the back wheels side to side; or heaven forbid, change the axle, and BOTH wheels. Did you mention what kind of rear tires and the body your running? Sloppy rear tires will expand under throttle and rub the wells. Make yer car run like a dog pooping razor blades. 

....are you running those dang A-dub guides with the big hanging radius from the bottom flange to the guide shoulder?

They suck....did I mention they suck even worse as the nose goes lower. Makes the chassis plow and the tail skate out. Guide button not scraping crickets?

Got all four tires touching? Are the pick up shoes properly toe-rolled so they skim and not plow? Pick ups riding in the middle of the hanger window? Meaning is there enough travel to prevent shoe bind against the chassis....sledding the rail because the spring is fully compressed. Got a little front axle in a big hole chassis further aggravating handling issues?

Good luck!


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## AfxToo (Aug 29, 2003)

Pancake motors have lot of torque and this torque can cause a lateral force on the chassis. Some things to try:

If you have some jumpers with alligator clips and a variable power source try clipping the jumpers to the car (without body) and let the car hang free. Then apply power and run up the motor speed. Does the car want to move to one side?

Reverse the magnets and run the car around the track the opposite direction. Does this change which side of the slot the car wants to hug?

Put taller tires on the rear and see if this makes a difference. The thing I'm looking for here is something rubbing on the rails, like the bottom rivets.

Put stickier tires on the rear and see if this makes a difference. The thing I'm looking for here is the back end breaking loose and causing the car to skate and be more likely to succumb to the motor torque. 

On the A/FX chassis, replace the domed brushes with flat brushes. My preference is JBs or Wizzard copper brushes, but original TJet brushes will work if they are clean. I tend to setup 'runner' cars with lighter brush tension so they are not so punchy. A good indicator that you've overdone the brush tension is the car wanting to slide sideways under braking if you've setup your track and controller for dynamic braking. Like I mentioned, pancakes make torque. Taking some tension off the brushes will detune the car. Whenever making tension adjustments always clean the comm and check it after running the car for a couple of minutes. A slight film of gray is okay. A black ring or a shiny ring is not so good. Again, this is for runners. Racers don't mind reducing longevity or maximizing torque to gain an edge.


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## slotcarman12078 (Oct 3, 2008)

This may have been covered and I missed it, but worth a mention. Check if the shoe travel is straight. I've run across a few chassis where the shoes would twist when the chassis is on the track causing a rub with a front tire.


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## 88T-BIRD (Jan 14, 2000)

I stripped it down to a bare chassis and rolled it down an incline (using a piece of steel). The car does tend to drift to the drivers side - not too bad, but consistant. I replaced the rear tires with O-Rings and reversed the front axle - same thing.

It sounds like the chassis, you need to measure front axle to rear axle, both side and compare. If one side is longer than the other the chassis will run down the track to one side.


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## Grandcheapskate (Jan 5, 2006)

Well, it seems I have corrected the "wobble" to a point where it is no more noticeable on this car than on any other. How I did it remains a bit of a mystery.

I changed only two things.

First, I swapped sides for front wheels. This seemed to have no effect.

Then, as I mentioned in a previous post, I replaced the brushes with another pair. The brushes that were in the car had different heights. I replaced them with two (probably) used brushes which were the same height, but less than the taller one I was removing. This seemed to have the effect of loosing up the drivetrain (just a tad) and the car is a bit faster than before.

The car does not seem to "pull" nearly as much as before but now that the car is faster, it is also more sensitive to drive. Just a touch on the (60 ohm) controller and the car takes off, so it's impossible to go slow and see what happens at the track joints.

So, my only theory is that the different brush heights put uneven pressure on the armature so it would be at an angle as it spun, causing the car to pull. I also would not discount the fact that the rear axle holes are a little loose, allowing the rear axle to move. I'm sure the axle torques to one side once power is applied to the crown gear. At least, that's what I'm putting on the repair slip.

To answer some of the questions from the three previous posts...

Bill...
I did not change the rear wheels or axle, although I did swap chassis and that had no effect. I tried it with three types of tires; soft silicon, harder silicon and hard rubber O-Rings. All acted the same.

I was using a two sided AW guide, pin side down. I also tried it with the blade side shaved down. I am using o-rings for front tires with a slightly larger OD than originals - these are on all my cars.

Pickup shoes look good. At rest, they are about mid hanger window. All four tires touch.

A dog pooping razor blades???? ouch....

AFXTOO...
I like the idea of testing with the alligator clips. I have to try that.

Very hard to tell which side the pin is riding against. The bare chassis pulls a little to the left when run down an incline, but when I stop the car on the track, it looks like the pin is on the right side of the slot - but that may occur as the car is stopping.

More than enough clearance on the bottom of the chassis. I can clearly see there is nothing rubbing.

I tried with some very soft silicon tires and saw no real difference.

This is am MT chassis, so it doesn't have the domed brushes. Nor do I have brakes. But the changing of the brushes does seem to have been the answer.

Slotman...
The shoes are no where near the wheel on this chassis.

Thanks...Joe


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## slotking (May 27, 2008)

AFX is correct, all cars will push to 1 side because of the torque applied to the crown gear.

but how much depends on getting the car balanced

The front brush is the power side and will wear faster than the rear normally. The left shoe is the power shoe, I like the tension here to be normal or a little less. with the passenger side having less tension than the driver side. this can help with reducing over torque at start up, and allow for smoother driving. (but you have to play with it to find the balance between speed and handling.

the rolling you do with the metal
hold it lightly and roll it with you hands, and feel for any out of roundness (or listen to it as it goes around the track)


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## Hornet (Dec 1, 2005)

Wonder if you could paint the pin Joe,and see any wear marks in the paint,don't know if it'll work,but it might give you a clue to which side of the slot it's predominately riding on.
Just a thought.


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## slotking (May 27, 2008)

> Wonder if you could paint the pin Joe


what color:tongue::wave:


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## Grandcheapskate (Jan 5, 2006)

Hornet said:


> Wonder if you could paint the pin Joe,and see any wear marks in the paint,don't know if it'll work,but it might give you a clue to which side of the slot it's predominately riding on.
> Just a thought.


Hey Rick,
I thought of that. The problem is when you go into a turn, the car is always going to get thrown to the outside slot wall. Until it fishtails, then it's going to try to go back to the inside slot wall.

Now, if the paint (or whatever) rubs off onto the slot wall in the straight, it might show something. But I'm guessing it's a low probability of this working. But maybe I'll give it a try.

Thanks...Joe


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## Hornet (Dec 1, 2005)

LOL,i gotta admit,i didn't think it was much of an idea either Joe,but i figured i'd toss it out there.
It's a pretty small entity when you're looking for wear marks in paint
Rick


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## Grandcheapskate (Jan 5, 2006)

I got a chance to show someone the car I have been tring to fix. When I pointed out the play in the rear axle, he immediatly knew it was too loose and would cause the problem I have been trying to address.

So although I have the car running better than ever, the only way to completely correct the "wobble" would seem to be either (a) install a larger diameter rear axle or (b) install some kind of bushing. Or (c) just leave it alone.

This is one of the pitfalls of buying used cars, which is why my offer price for a used car lots is a max of $5 per car. You get cars which require a lot of work and which need extra parts just to bring to life, along with some which are plain junk. For $3-$5 it may be worth it, but nothing more.

Thanks..Joe


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