A Knocking Sound

I have a 2009 e4 with 142 miles on it. I’m not a mechanic, so forgive me if I use the wrong terminology. Recently, when I depress accelerator or am going up a hill, I get a knocking sound in the front center area (where the generator and transmission are). The knock starts before the car actually accelerates. It doesn’t do it until the vehicle has ran for a few miles. My owner’s manual is useless; of course. To be honest, I do not know of or have any information on transmission fluids or lubrication service. There’s a rubber piece on the transmission that is made to collapse like an accordion; but I’m not sure of it’s purpose. I did find a service manual on the internet; but they wanted my personal information and a payment. Any help would sure be appreciated.

Could be the gearing in the transaxle/differential taking up slack. My 01 is noisy that way but it’s normal. Mine “clunks” when you engage the throttle and then “clunks” again when you disengage the throttle. It’s worse after it’s been running a few minutes and the lubricant gets hot and thins out. Or it could also indicate you have insufficient or incorrect lubricant in the transaxle/differential. Or could be the ujoints are shot and need replaced. The rubber piece you mentioned covers the drive shafts from the transaxle to the wheels. One way to quickly test the ujoints is to jack up a wheel in the air and then try rotating the tire. There shouldn’t be much play. If there is, the shaft/ujoints need replaced. Though with only 142 miles on the cart (that’s miles and not hours right?) I wouldn’t expect much to be wrong in the cart.

In any event if you have a competent dealer in the area, I think I’d have them service it to ease your concerns.


Thank you very much for the reply. This sounds so embarrassing to ask, but where do you fill and drain the differential? I’ve read some threads on the proper oil, and I think I should probably use 80W90. I so need to get a service manual if I am going to keep this vehicle.

There is no drain hole. Only a fill hole. The oil can be sucked out with a small pump tool sold by boat dealers. 80W90 is what I use. The old oil is usually dirty or at least cloudy. Refill until fluid runs back out the fill hole.


I’m curious about this. I’d love to change my diff oil on my 01 E825 short bed but I’ve looked at my diff from all different angles and the only “access” I can see (short of dismantling the GEM) is a rather small vent hole w/ a 90 degree elbow apparently screwed in on the passenger side and vent tube pointing “up” running somewhere near the upper front battery. Is this the “fill hole” to which you refer?


Be nice if we had a service manual to refer to. I’m curious about this too.

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There is a rubber plug in the axle cover. Oil neerd to be removed with a shipon pump and new oil added until it starts to run out the hole. About 12 ounces.