serious thudding sound when putting truck in gear
10-15-2010, 08:11 PM
#1
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Thread Starter
serious thudding sound when putting truck in gear
question for all of you...
you stop/park on a incline/decline and put the truck in "park". release the brake. the truck rolls just a smidge (an inch or two) due to the slack in the drivetrain than stops.
now pull the transmission out of "park" and put it in "drive"... "reverse"... "neutral"... makes no difference - there is a serious thud when the tranny "releases" the tension in the drivetrain when in "park"
i thought that i can prevent the truck from rolling in park by applying the emergency brake, but it seems that the ebrake has enough slack in its own to still load up the drivetrain... so it makes no difference. and yes- my ebrake works well otherwise.
does your gl do that too?
you stop/park on a incline/decline and put the truck in "park". release the brake. the truck rolls just a smidge (an inch or two) due to the slack in the drivetrain than stops.
now pull the transmission out of "park" and put it in "drive"... "reverse"... "neutral"... makes no difference - there is a serious thud when the tranny "releases" the tension in the drivetrain when in "park"
i thought that i can prevent the truck from rolling in park by applying the emergency brake, but it seems that the ebrake has enough slack in its own to still load up the drivetrain... so it makes no difference. and yes- my ebrake works well otherwise.
does your gl do that too?
Last edited by alx; 10-15-2010 at 08:16 PM.
10-16-2010, 10:54 AM
#2
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09' Gl450
Try putting the ebrake on, release regular brake (so the ebrake takes the full weight of the vehicle) THEN put in park. When leaving; engage regular brake, release ebrake, THEN engage transmission. Never let transmission hold vehicle on incline/decline before ebrake/brake. My aology if this is what you do already not clear from your post. My 09' GL450 does not make any different transmission noise when I engage transmission on incline/decline using this method.
Last edited by Madcmm; 10-16-2010 at 11:35 AM.
10-16-2010, 05:01 PM
#3
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2007 GL450 2005 C55 2002 C32 sold 2001 ML320 sold
same as Madcmm - makes the same noise going into or out of gear no matter what the incline.
Strangely the E350 loaner i have with the same tranny makes almost no sound going into/out of gear. I thought it was the electronic vs mechanical engagement that was the difference before, but both now have the electronic engagement - weird.
Strangely the E350 loaner i have with the same tranny makes almost no sound going into/out of gear. I thought it was the electronic vs mechanical engagement that was the difference before, but both now have the electronic engagement - weird.
10-16-2010, 08:23 PM
#4
MBWorld Fanatic!
If you do park it on an incline without using the e brake, the transmission is holding the whole load of the car's weight on the parking pawl. This is straight from Wikipedia:
A parking pawl is a device fitted to a motor vehicle's automatic transmission on order for it to lock up the transmission. It is engaged when the transmission shift lever selector is placed in the Park position, which is always the first position (topmost on a column shift, frontmost on a floor shift) in all cars sold in the United States since 1965 (when the order was standardised by the Society of Automotive Engineers (SAE)), and in most other vehicles worldwide.
The parking pawl locks the transmission's output shaft to the transmission casing by engaging a pawl (a pin) that engages in a notched wheel on the shaft, stopping it (and thus the driven wheels) from rotating.
Most vehicle manufacturers and auto mechanics do not recommend using the transmission's parking pawl as the sole means of securing a parked vehicle, instead recommending it should only be engaged after first applying the vehicle's parking brake. Constant use of only the parking pawl, especially when parking on a steep incline, means that driveline components, and transmission internals, are kept constantly under stress, and can cause wear and eventual failure of the parking pawl or transmission linkage. The pawl might also fail or break if the vehicle is pushed with sufficient force, if the parking brake is not firmly engaged. Replacement can be an expensive operation since it generally requires removing the transmission from the car.
It is highly inadvisable to use the parking pawl to stop a vehicle in motion. The pawl mechanism is not strong enough to stop a vehicle in motion or may not engage at all. Under that much stress, the pawl may break off in the transmission, leading to costly repairs.
That clunk you're hearing is the parking pawl unlocking the output shaft while under the load of the vehicle's weight. Do it enough times and it may break. $$$.
A parking pawl is a device fitted to a motor vehicle's automatic transmission on order for it to lock up the transmission. It is engaged when the transmission shift lever selector is placed in the Park position, which is always the first position (topmost on a column shift, frontmost on a floor shift) in all cars sold in the United States since 1965 (when the order was standardised by the Society of Automotive Engineers (SAE)), and in most other vehicles worldwide.
The parking pawl locks the transmission's output shaft to the transmission casing by engaging a pawl (a pin) that engages in a notched wheel on the shaft, stopping it (and thus the driven wheels) from rotating.
Most vehicle manufacturers and auto mechanics do not recommend using the transmission's parking pawl as the sole means of securing a parked vehicle, instead recommending it should only be engaged after first applying the vehicle's parking brake. Constant use of only the parking pawl, especially when parking on a steep incline, means that driveline components, and transmission internals, are kept constantly under stress, and can cause wear and eventual failure of the parking pawl or transmission linkage. The pawl might also fail or break if the vehicle is pushed with sufficient force, if the parking brake is not firmly engaged. Replacement can be an expensive operation since it generally requires removing the transmission from the car.
It is highly inadvisable to use the parking pawl to stop a vehicle in motion. The pawl mechanism is not strong enough to stop a vehicle in motion or may not engage at all. Under that much stress, the pawl may break off in the transmission, leading to costly repairs.
That clunk you're hearing is the parking pawl unlocking the output shaft while under the load of the vehicle's weight. Do it enough times and it may break. $$$.
10-18-2010, 06:27 PM
#5
Super Member
Not too sure of the accuracy of the Wikipedia article on PARK position. On my 2007 and 2008 GLs the PARK mode is engaged by a button on the end of the shift lever and only when the lever is in neither the 'up' (reverse) position or the 'down' (drive) position, ie. the lever is centered. This clearly doesn't meet the Wikipedia description of topmost or first position for column shift. Maybe in 1965, but not now!
10-19-2010, 12:02 AM
#6
MBWorld Fanatic!
How MB engineers designed the controls of what happens inside the tranny may differ from the good people at Ford circa 1965, but the way it works remains the same. A pawl engages the shaft so it doesn't rotate and the vehicle remains stationary (hopefully).
