Chain slips when backpeddling

[Whalensdad]

I just swapped out some grip shifters for thumb shifters on my kids bike. I think I did a fairly good job at doing the shifting adjustments and the gears seem to shift correctly when peddling. However, if I am in High/Low ( 3 on the front and 1 on the rear) and I backpeddle, the chain on the rear cassette either shifts1 or 2 positions (until I start peddling again) or it shifts and then binds. Back peddling in Mid/Low (2 on the front and 1 on the rear) doesn't cause this problem. I looked at the cassette and saw it had a slight wobble, but after reading numerous posts, that seems to be a fairly normal occurance. I could use some suggestions on what to check or do.

[binzer]

If by "High/Low ( 3 on the front and 1 on the rear)" you're referring to the largest chain-ring on the front and the smallest cog in the rear then that's most likely the cause. The chain is being forced sideways. It's not a good idea to use that combo for that very reason. It will cause excessive wear on your drive-train.

[Whalensdad]

Actually I was referring to the largest on the front and the largest on the rear. You're right, the chain is slightly sideways by default. Is this a normal occurance in this configuration?

[binzer]

I got it a bit confused myself there. Yes, the large/large and also the small/small is a combo you shouldn't use. If you have a triple crank-set on the front then with the middle chain ring you can use all the gears on the rear. Depending on the number of cogs on your rear sprocket you can only use 3 or 4 low gears with the smallest chain ring and 3 or 4 high gears with the largest chain ring.