How do I cure extreme sideways under braking. ** FIXED!**

How do I cure extreme sideways under braking. ** FIXED!** - Printable Version

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How do I cure extreme sideways under braking. ** FIXED!** - Top Down - 3rd-Oct-23

I have seven Pioneer Legends. Looking from behind as they disappear down the straight:

Two are totally neutral under braking, stopping in a straight line.
One steps slightly to the right.
Three step slightly to the left.
One steps forty-five degrees to the left.

As they disappear down the straight the sidewinder gear is on the left.

The only difference I can determine is the gearing on the last car is a bit tighter than the other six - but there is no way to adjust the motor and axle shaft positions to ease the gearing.

Any ideas anyone?

All have totally stock running gear, with all tyres trued as near as possible to the same diameter. I know they're mass produced and there will be variations but I'd really like to dial out that massive step-out on the seventh car if at all possible.

RE: How do I cure extreme sideways under braking. - Kevan - 3rd-Oct-23

Does it do it with the body fitted?

RE: How do I cure extreme sideways under braking. - Top Down - 3rd-Oct-23

All were tested complete with bodies and race-ready.

There was a different body screw in the rear of the culprit. Unlikely to make any difference but to be sure I replaced it with the correct one. Unsurprisingly it still pulls up forty-five degrees left.

RE: How do I cure extreme sideways under braking. - Kevan - 3rd-Oct-23

Try testing with the body off to see if there's any bad tyre to body interference.

Is there backlash in the gearmesh, a tight gearmesh can cause super fast braking and inlines kick sideways under severe braking.

Are both wheels firmly fixed to the rear axle and both tyres firmly on the rear wheels and not slipping round.
Are both rear bearings firmly fixed in the chassis.

If all else fails turn the brakes down.

RE: How do I cure extreme sideways under braking. - Top Down - 3rd-Oct-23

Thanks Kev'.

Body off: Should have thought of this myself - but 'chassis-only' exhibits same 45 degree stop.
Gear mesh: As stated. Tighter than the other six cars but no opportunity to adjust it. (Moulded plastic chassis with fixed motor mount and axle position.)
Running gear: Race ready. Wheels superglued to axle. Double checked and no movement. Tyres glued and trued. Bearings glued in place.
Brakes: There are none. Standard Scalextric two wire controllers. Stop by releasing throttle.

RE: How do I cure extreme sideways under braking. - Kevan - 3rd-Oct-23

It's there any backlash in the gearmesh

Are the wheels up tight against the bearings

RE: How do I cure extreme sideways under braking. - MrFlippant - 3rd-Oct-23

are the front wheels/tires coated, or do they have grip?
if they have grip, could one of them be hitting the track and the other one not?
Are both rear tires of the same diameter?

RE: How do I cure extreme sideways under braking. - Top Down - 3rd-Oct-23

Wheels are up against the nylon? bearings but no tighter than the others. No side to side movement in the back axle.
Backlash? Not sure how to judge or measure that but as mentioned, the gear mesh feels tighter with no way to adjust it.
Front tyres are not coated but are glued and trued, as they are on the other six.
(You might have hit on something here though. Thumbup

It looks like the right hand front wheel/tyre is off the track. Strange as it WAS fine when originally set up!)
Rear tyre dia. 21.00mm and 21.01mm

I'll strip the car down again and check nothing is binding and the chassis is flat. I suspect not, since the rolling chassis exhibited the same behaviour.

Thanks guys.

I'll report back when I've finished investigating, probably tomorrow.

RE: How do I cure extreme sideways under braking. - Kevan - 3rd-Oct-23

Ideally there would be some backlash in the gears, you want to be able to rock the wheels back and forth a fraction without the crown gear moving.

As the wheels are up against the bearings the crown may be pulled tight against the pinion, pulling the wheels out slightly to give some axle side-play will help...another option is shoving the crown gear away from the pinion, the easiest way to do this is with two pairs of long nose pliers, one to hold the axle tight whilst using the other to gently lever the crown gear over a few thou'

RE: How do I cure extreme sideways under braking. ** FIXED!** - Top Down - 3rd-Oct-23

GOT IT!

Thanks both of you.

After getting the 'tweak' out of the chassis, once installed in the body it was back, as bad as ever. Initially I tried to set up 'stagger' on the body posts - a 1mm O-ring on one side between body and chassis

BUT ....

I finally noticed the central metal grill was sticking down below the body line and acting as a pivot point for the chassis which, as I habitually do the screws up in the same order, was pulling the chassis higher into the body on one side of the front than the other.

Ground off the offending protuberance so the body and chassis can sit square to one another and she pulls up in a straight line!

Now I guess I need to check the others, just in case the grill is imparting a twist into the other 'non-straight line' brakers.

P.S. Removing the stress point the grill was creating has also helped the gear alignment so now she's sweet as a nut.
P.P.S. The twist imparted to the chassis stayed with it when tested on it's own earlier - but it's already 'relaxing' into its naturally flat state left to its own devices.