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Re: Question for all M50 owners (archive)

[ Follow Ups ] [ 5-series (E34) Message Board ] [ Msg. Board FAQ ]

Posted by Andy T on April 12, 1999 at 15:25:06:

In Reply to: Question for all M50 owners posted by Antony on April 11, 1999 at 23:24:37:

The lock-up clutch that bypasses the torque convertor can often betray its engagement by a drop in engine revs. It happens while you are accelerating hard because above a certain engine speed (4,500 rpm? Something like that) the 'box reduces slippage. Reason for *this* is that the torque convertor seeks to multiply torque at low speeds. At higher speeds the engine is into its stride (and non-VANOS M50s produce peak torque at something like 4,700 rpm). So the 'box locks up even when you are accelerating. And as slip is reduced, engine speed is reduced for a given road speed. So you may, indeed, see a slight drop in engine revs evn as the car is accelerating (think of it as a change in gear ratio from variable to a fixed, higher hear).

I should be surprised if the car actually *decelerates* while it's doing this. If you can take your eyes off the road for long enough, watch the speedo when the tacho needle does its little shuffle - I would wager that the speedo needle will continue to rise as the lock-up clutch engages and the car continues to accelerate, without slip, into the 5000's (where no slip is necessary).

If the 'box acts normally otherwise, with no racing between gears driving normally, no jerking, no excessive slip when accelerating from rest, you may just have an aggressive lock-up clutch, that's all. As I said unless the car decelerates when you notice this phenomenon, I wouldn't worry about it.

Hope this helps.

Andy T

: Hey 325 and 525 drivers!

: I've got a peculiar problem with my car (non-vanos M50 mated to a 4-speed automatic). The dealer (a very good one) was baffeled for a while and finally tried out three other M50 engined cars, and concluded: 'All M50's do that'! I find it hard to believe but trust him as he's been rather helpful in the past, so please try this out and see if you can or cannot duplicate the problem.

: Here it is:

: Drive about 65-70 and kick down into 3rd gear for hard acceleration. Watch the tach pass 4000 and klimb towards 5000 (should be up to about 80-85 now). Somewhere between 4 and 5k you should see (and feel) a 200 RPM correction/dropout. You will actually see the needle go backwards. I can make thi shappen every time in 'E' mode and I think most of the time in 'S' (maybe every time, I don't use 'S' that often).

: My dealer said he couldn't find anything from the BMW tech database either. I it hard to belive that these three things could happen at the same time:

: - All M50s do that
: - BMW has no tech info on this
: - Nobody on this list has ever complained about it before

: I hope you guys can assist me here, I still have warrenty coverage for 1000 miles! I would guess if this is a transmission or engine problem that that is a rather expensive repair.

: So hopefully somebody with a stick can try this to see if maybe it's a transmission problem, and maybe we've got some 325 owners too for variety.

: Thanks a bunch ...
: ______
: Antony Pohl o/______\o
: 92 525iTA "Sharked" (Oo=00=oO)
: BMW CCA, Houston Chapter []=****=[]

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