A Class Auto Reverse

[paoloh]

My A class drives perfectly forwards but when you put it in reverse, it starts to go, stops, starts to go.....

Bad explanation but I think you get what I mean.

Any ideas?

[paoloh]

To try and explain better, it feels like the engine is "hunting" between say 900 and 1500 revs but only in reverse.

Come on guys, please help.