Wiggles.........

I have experianced similar issues and I'll share what i know and what i think i know.
- A fast wiggle or "shimmy" is a result of rear end alignment being off or opposing each other. One or both rear wheels are not settling in one position on the axle. I found that tweaking rear alignment and/or tightening the wheel gaps will take care of this.

- A car that drifts off the rail (slow wiggle) is either not enough steer or not enough weight on the DFW or a combination of both. Keep in mind that the rear alignment can also cause the front to veer off the rail. Checking rear alignment with machiniest 1-2-3 blocks I found to be the best method. I also measure the height of front and rear of the car. I aim for even height so I don't have to worry about inducing toe-in or out issues on the rear axles.

Adding/moving weight on front of car can illiminate drifting off rail but leaves untapped speed locked up. Increasing steer can also illiminate a slow wiggle but again, locks up untapped speed.

Optimal weight on the DFW depends on class of car. I can get away with 9g on razor wheel cars but need about 12g to 15g on fender cars. I don't do well in the BASX class but I've been running about 11g to 13g with about 2 inches of steer over a 40" distance. I think a few of the fastest builders run far less steer but don't know how much weight is on the front.
My thinking for an ultimate set up is to strive for minimum steer with minimum weight on the front and have the car run smooth. Assuming alignment is optimal, all that is left is perfecting wheel and axle prep, easier said than done of course.

Fujimo here are my 2 cents:

I agree with DWS regarding check your rear wheel alignment (FIRST and foremost!) following Lightninboy's 123 blocks test. A good rear drill is an essential prerequisite (solid foundation) for a fast car.

B_Regal is a great guy contact him and he'll get you up to speed!

Here are my answers to the issues:
>Wiggle at the start on the ramp?

• Rear drill alignment is dramatically off; check and if off, fill-in holes with toothpick and re-drill, or start fresh
• Difference between the weight on rear wheels is very high (>10g)

>Really fast side to side wiggle – almost banging back and forth?

• Rear drill alignment is dramatically off (see corrective measures above)
• Car is very aggressively weighted and has an alignment issue that is magnified by very little steer (<2" over 4') and or large rear wheel gaps

>Slow wandering back and forth wiggle in the flat?

• If the front wheel is wandering, DFW might need a little more weight to hold the rail, try moving a cube towards the DFW side in the rear weight pocket and see if it helps. Use the three identical weight scales (centered under the running wheels on a level surface like granite plate) method to record your results.
  
• If the rear is wandering slowly, try tightening the rear gaps and see if it solves the problem

>Straight run with a slow wiggle developing toward the finish line?

• Less steer - living on the edge, try adding just a tad more 1/4" to 1/2" until it stabilizes

Good luck and welcome Fujimo to the Pro racing family! The more cars you'll build the better your skills are gonna get and before you know it you'll be running at par with the big dogs I'm chasing for the last 3 years! 

MAGLEV

If you're not drilling on the The Block, it doesn't really make sense to test alignment with one. Use BRACKETRACER 's method to verify your alignment with the 1-2-3 blocks.

Also, have you possibly tried micro 's method of inserting a pin gauge into the first drilled hole on the jig before drilling the other side? Might be worth a shot.

Finally, make sure your #43 bits are a tight fit in the jig.

Edit: Oh, one more thing. Put two pin gauges into your jig and make sure that they meet in the middle when pushed in! If they don't, your jig could be off.

Interesting! Didn't Cramjet Racing suggest something similar in regard to toe-in a while back?

Mojo, I remember that post by Cramjet but I can’t remember why he suggested offsetting the rear axle holes.

Lots of good info posted above. I am probably wrong here but I think most of my BASX speed problems are wheel/axle prep and oil quantity related. I should get my cars back tomorrow so this weekend I can start the re-prep process.

Thanks again for the input gentlemen.

VK do you have links to Brackets 1,2,3 alignment test I searched but didn't find anything on it. I have been using a 1,2,3 block on the side and push it up to check that the drill is perpendicular to the body.

Admin - thank you for the kind words and suggestions. I had been running a pretty severe angle (9-10 degrees) until a destroyed a hub in my first and only set of $50 wheels. Learned a few lessons from that fiasco. Since then I have been running somewhere around 4-5 degrees and polishing the heck out of the bending groove.

Thanks Skywalker! Maglev gave me a head's up that Fujimo was looking for that video and I was just sitting down to look for it when I saw your post. The granite surface plate in the video is available from Woodcraft for about $28 or so when it's on sale, the 1-2-3 blocks came from Amazon, and I bought a selection of pin gages from Mcmaster. I bought several sizes from .088" through .092" in .0005" increments to cover all the different axle tip sizes. If you only run one brand of axle you could buy just a couple pairs of pins to fit what you use. The fit of the pins in the body is important, you can't use ones that are too loose and too tight might enlarge the holes. They should just slide in with light pressure. I'm a big fan of Lightninboy's method but at the time of the video I didn't own The Block so I improvised with what I had. I machined up a fixture not long after and I now use that in addition to the method in the video.