Ok what am I doing wrong?

[transam6870]

hey guys
what am i doing wrong? i built a chassis and the rear axle has the worst vibration i have ever seen. once at full speed its great. .095 axles with brass bushings. it has a little play in it but not near as much as a basic scx car. any ideas?

[LloydL]

A process of elimination I think. My chassis often dont run smooth straight away, so I push the chassis along with the front axle off the track, then repeat for the rear. I often find that the front axle is the probem.

Then, once I know which axle it is, I change it. If the problem goes away I know there is a problem with that axle, gear or wheels and eliminate each component by trial and error.

Usually works. If it's not that, it's back to the drawing board with the chassis!

Regards, Lloyd

[pfuetze]

is it vibrating without the wheels?
did you try a different axle?
which pinion/crown?

[OldDogMotorsports]

check wheels and tires!

[transam6870]

sorry guys guess i left out some details. i have never had this trouble with ANY of my brass chassis so i am kinda at a loss. its a plastic chassis, the axle is straight, the wheels are true and the tires are as well,brass bushings, no wobble at all. motor is bolted in. evrything is solid. i hold it up off the track and give a little juice and its fine, hit mid range and vibrates like crazy, full power and smooth as can be. i have never run tires this wide with a housing so narrow, would that be part of the prob?

[munter]

I have never met a plastic chassis that didn't benefit from bracing of some kind. I only run on wood. The axle bearing to motor is a crucial area to firm up. Then there is the bearing to bearing rigidity.

Pick it up and at eye level, hold the rear hubs with one hand and the chassis with the other and give a gentle twist diagonally and then vertically. Watch for any serious alignment changes.

Maybe this will help.

[Datto]

So only at a certain speed? Unbalanced wheels act that way on 1:1 cars right? It could be those fat meats mean more rotating mass than usual. Are the tires free of bubbles? Are the tires well glued? By any chance are the grub screws on the rims offset by 180º, or are they lined up? Just some thoughts...

[OldDogMotorsports]

[transam6870]

hey guys
yes to all of the above, check check and recheck. put a dial indicator to everything and found the problem. the pinion looked fine but it wasnt and i didnt notice at first. once i removed it i could see the hole was off center. thanks for all the suggestions guys.