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  #1  
Old 06-12-2019, 01:31 AM
igru25 igru25 is offline
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Mein Auto:
Rear axle behavior

How is the following rear axle behavior to explain (rear wheel drive and automatic transmission):

1) Start the car
2) Push break pedal
3) Shift stick to Drive
4) Free the break pedal and drive...


The first question:

After I switch to "D" and if the foot is still on the break pedal - the rear part of the car sinks/descends a little bit. The rear part of the chassis "sinks" about 2...3 cm I suppose. Really noticeable for driver.

This effect isn't noticeable if I remove the foot from break pedal immediately after switching to "D".

Why does it happen?



The second question (by the way).
Something squeaks during the descending. I suppose it is ball joint in lower steering stub / wheel carrier. Any ideas?
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  #2  
Old 06-12-2019, 01:57 AM
igru25 igru25 is offline
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Here is this effect from outside (20s).



But I have 316d 85kw usual car. No extras. No power...
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  #3  
Old 06-12-2019, 06:09 AM
southcoastguy southcoastguy is offline
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Physics; reaction of suspension to torque applied by engine.
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Old 06-12-2019, 07:07 AM
Michael Schott Michael Schott is offline
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Quote:
Originally Posted by southcoastguy View Post
Physics; reaction of suspension to torque applied by engine.
Except the car is not yet moving. Itís more likely the suspension compressing under the load of the transmission engaging the rest of the drivetrain. Or maybe heís feeling the driveshaft putting force on the rear differential.
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Old 06-12-2019, 07:53 AM
John MS John MS is offline
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It's torque that can't turn the wheels so it pushes the rear end down and compresses suspension springs. Nothing new.
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Old 06-12-2019, 01:02 PM
southcoastguy southcoastguy is offline
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Quote:
Originally Posted by Michael Schott View Post
Except the car is not yet moving. Itís more likely the suspension compressing under the load of the transmission engaging the rest of the drivetrain. Or maybe heís feeling the driveshaft putting force on the rear differential.
Exactly.
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  #7  
Old 06-12-2019, 10:46 PM
igru25 igru25 is offline
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Mein Auto:
Many thanks!

Also.
After switching to D (and still pushing the brakes) the drive shaft and differential are engaged... but without real rotation of the shaft (due to no real connection between shaft and gear --> hydraulic torque converter).
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