Gearbox clonking This topic has 5 replies, 3 voices, and was last updated 4 years, 11 months ago by Gerben Haringsma. Viewing 3 reply threads Author Posts 26th October 2018 at 20:42 #14533 Geoff Pedlar @geoffpedlar I get a load clonk when engaging reverse, both from park and neutral; and it also jerks the car. A quiet clonk with drive and no jerking. Advice so far is to re-new the rear gearbox mounting. I’ve done that, with no difference. Any thoughts gratefully received. 29th November 2018 at 21:05 #14796 Paul @paulf42 How high are your revs at idle? It sounds more like the car is trying to drive rather than the gearbox clunking against the transmission tunnel. 6th January 2019 at 15:05 #15004 Geoff Pedlar @geoffpedlar Hello Paul, Thanks for your thoughts. When cold the revs are a bit high, about 1100, probably the auxiliary air valve. when hot revs are correct at aroung 600. Sure the clonking is louder at higher revs, although still very much there when hot. Would that solution apply bearing in mind its only when putting it in to reverse ? I’d better get that air valve changed ! Thanks 3rd December 2018 at 08:57 #14819 Gerben Haringsma @gerbenharingsma have you ever flushed (cleaned) the gearbox ? it can lead to spectacular improvement. I had the same with my mercedes automatic after 120.000 km. after a quality flush, it was back to new. 6th January 2019 at 15:11 #15006 Geoff Pedlar @geoffpedlar Hello Gerben Well that’s an interesting thought. I’ve never changed the gearbox “oil” as it always looks so clean, and rarely have to top it up. Do Mercedes use the GM box at all, or are their boxes always their own manufacture ? Worth a try anyway. Thanks 11th January 2019 at 20:14 #15023 Gerben Haringsma @gerbenharingsma it is not about changing the oil,but a flush,to get all debris out of the very small canals and valves ! changing the oil will not help at all. so my advise:flush/change filter/new oil. best regards Author Posts Viewing 3 reply threads You must be logged in to reply to this topic.