The transmission in my 99 ML420 failed at 85,000 miles as I pulled up to a red light in downtown Toronto. I was 2,000 miles from home so this was an expensive event. It limped along for 6 blocks or so before there was no connection whatsoever between the engine and the wheels.

When the pan was pulled, there were large chunks of broken gears in it. Apparently this "sprag failure" is not entirely uncommon on 98 and 99 MLs.

Fluid had been changed at 45,000.

I just want to make sure I read that right. $300 to unsrew a drain plug and pour in some ATF. maybe swap a filter.

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Steve Danville
what i did myself.
CPS
rear shocks
MAS x 3.
SparkPlugs (twice)
Fuel pump & Filter
Window switch
replaced both failed horns with Honda horns.
Cleaned ERG Tube
Oil changes
Oil consumption Fix
Brake Pads
A/C Recharge
Anti-Freeze change X 2.
Front Shocks. Monroe. $90
Mercedes Warrenty Work:
Harmonic balancer,power steering clamp. Cat converters.Drive Shaft Bearing.s
Replaced Outer Lower Tie Rods and front lower ball joints at 156,000 miles

Does anyone know if changing the trans control unit will required a fluid change?

Only if the version of the control unit is updated and it requires valve body change. Then you'll need to pop the pan and might as well change the fluid.

Gilly

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I was going to try to change the AT fluid and filter myself. However, I was told that 1/2 of the old fluid will remain in the torque converter unless I drain it too. How should I handle this? Is it difficult to drain fluid from torque converter. Or, should I change the fluid a few times to get it clean? What do the service techs at the shops do? Thanks for any advice!

By the way, I've got 99 ML320 with 95k miles and fluid hasn't been changed. This will be the first if I can find out how to do it.

Very easy to drain, at least on my 1999 ML 320. There is an allen head bolt that you remove from the torque converter, it's small maybe 5 or 6mm. You just turn crankshaft from front with I think it was a 27 or 32 mm socket until you see the allen bolt.

Regarding the torque converter draining, try this link, it is a posting of an article in the Star Magazine with clear directions and pictures on draining the trans fluid:

http://www.benzworld.org/forums/forums/thread-view.asp?tid=1182558&posts=7&hl=

The picture is upside down but the information is clear enough.