Got a problem with 4 speed gear linkage on mk 2 fiesta. adjusted as per instructions in haynes maual but reverse gear can be selected without having to depress lever. I have tried a second linkage which worked fine on donor vehicle but this is just the same on car. I must be doing something wrong or could there be a fault with gear box. Any suggestions appreciated. Linkages work fine when not on car or connected to gearbox.