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post #1 of 12 Old 30th June 2019, 01:46 AM Thread Starter
trane294
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Driving downhill issue

Hello everyone. I recently purchased 2008 m5 with 100k km on it. It is running great however I had a weird car acting going downhill on 1st gear. I was going to underground parking with quite large angle and car started kinda punching felt like smth wrong with transmission. I had checked in again and it only happens on certain downhill angle. If angle small car doesn't do it.

Did anyone else had that issue? Can't really find anything similar on this forum. Thank you
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post #2 of 12 Old 30th June 2019, 03:49 AM
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post #3 of 12 Old 30th June 2019, 03:53 AM
HM506
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Assuming SMG? Could be a a lot of things...like clutch, cylinder, pump fluid, etc...

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post #4 of 12 Old 30th June 2019, 02:13 PM
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my drive way is a ski slope, and no issues going down hill, what exactly are you feeling.

SMG is confused as hell though going up it though.

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post #5 of 12 Old 30th June 2019, 08:48 PM Thread Starter
trane294
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Is happens not just on cold start. Its twitching movements. Like short jerking. Maybe clutch trying to slip?
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post #6 of 12 Old 30th June 2019, 09:03 PM
HM506
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Quote:
Originally Posted by trane294 View Post
Is happens not just on cold start. Its twitching movements. Like short jerking. Maybe clutch trying to slip?
Most likely from what you are saying...searched these forums or Google and maybe you will get a better answer...or take it to an indy shop and maybe just bite the bullet and replace it?

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post #7 of 12 Old 3rd July 2019, 12:54 AM
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This caught my eye and I've experienced a similar issue in my downhill driveway.

This is my interpretation:

In my rig (SMG) there is a "magic" speed where the computer isn't sure if it should engage or disengage the clutch when coasting downhill. Too slow and it's disengaged to prevent stall, fast enough and clutch is engaged. Depending on the grade, first gear will engine brake you enough that the car will slow down to the point of disengaging the clutch to prevent a stall. You pick up speed, until clutch re-engages, and then you find yourself in a herky jerky cycle.

I just drop it in Neutral and coast down to the end of my driveway, but YMMV in a parking garage. I don't have to worry about traffic so much in my driveway.

Cheers


Afterthought: In my mind the computer does a damn good job 90% of the time. I find it fascinating! But, in cases like this, there are some nuances to a manual transmission that the computer isn't necessarily privy too. That's why I opt for a Neutral coast in this specific case, primarily to reduce cycles on the components. ^_^ OK shutting up! Thanks!

Last edited by Gothamitic; 3rd July 2019 at 01:05 AM. Reason: Afterthought!
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post #8 of 12 Old 3rd July 2019, 08:23 PM
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Get your SMG flashed to the Euro spec.

Buttery smooth downshifts forever after.
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post #9 of 12 Old 5th July 2019, 09:14 PM
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Quote:
Originally Posted by Gothamitic View Post
In my rig (SMG) there is a "magic" speed where the computer isn't sure if it should engage or disengage the clutch when coasting downhill. Too slow and it's disengaged to prevent stall, fast enough and clutch is engaged.
Agreed. For me it tends to show up at the worst possible moments - when I'm trying to manoeuvre really carefully, but the extra acceleration from the slope throws the system off. I'd control it fine if I had a manual clutch! ...but the computer just seems to get confused in that specific situation.
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post #10 of 12 Old 5th July 2019, 10:38 PM
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