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  #1  
Old 09-13-2017, 03:53 PM
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W126 300 SDL transmission trouble (another 722)

My 400E transmission quit and now also my 300SDL transmission (also a 722.3) started causing trouble.
It started banging heavily during 2/3 up shift especially when cold.
With a warm engine the shift is much smoother and a big harsh shift only with 'no load'. With load and warm engine the 2/3 up shift is smooth.
What is causing the very harsh up shift when cold? This harsh shift is happening under each load situation.
Any help appreciated.

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  #2  
Old 09-13-2017, 07:40 PM
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I had similar behavior in mine with a broken K1 accumulator spring. When cold it felt like someone was running into the back of the car when it shifted from 2-3. BANG! Once it warmed up, it was acceptable, but still a bit on the firm side for my taste. My K1 accumulator spring was in pieces. Replacing it and fluid/filter change and it's nice and smooth.
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Old 09-14-2017, 09:31 AM
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Hi Diseasel,
that K1 accumulator spring is in the valve body.... correct?
What parts are you suggesting to buy?
Mercedes K1 Accumulator Spring Kit
Part #: 126-270-44-77-MBZ
or Superior (I think they have a kit to cure a harsher 2/3 shift too?

Martin
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Old 09-14-2017, 01:22 PM
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The K1 is in the valve body. Easily accessible with everything still mounted in the car. There are tons of threads on the subject on this forum alone. I used the OEM parts, something like $8 for the kit.

Mine still shifts fairly harsh in all gears when the transmission is cold, but after ~5 mins of runtime, it smooths right out. I attribute it to wear in the transmission and being "grabby" until the fluid heats and thins out.
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  #5  
Old 09-14-2017, 02:55 PM
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Hi Diseasel, the OEM parts are reasonably priced I see. Cool, I'll do that and see what comes out.

Martin
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  #6  
Old 09-16-2017, 01:46 PM
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Funny thing is I found the A 126 270 44 77 "Thrust Pin" Kit in my 300SDL box.
I must have bought it a couple years back not knowing much about it.
The kit has 3 springs and a white and black plastic pins.

Martin
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  #7  
Old 09-20-2017, 01:29 PM
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Who out there knows the reasons why the gear shift 2/3 is so harsh?
I see in diagrams that in 2nd gear B2 and B1 are applied (the 2 band brakes that grab the K1 and K2 drum).
During the shift into 3rd gear B1 is released and K1 is applied while B2 stays engaged.
This means that the transition from B1 (release) to K1 (applied) is not smooth.
Basically the modulation pressure is too high.
Is the hard shift caused by a 'hardware' problem (K1 clutch piston seals for instance?) or is it a 'control' issue in the valve body.

Why the probelm happens mainly when cold I don't know. Can it be that the K1 kit parts are controlling the modulation pressure?


I'll change the K1 Accumulator Spring Kit
Part #: 126-270-44-77 as soon as I can and report back.

Martin
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  #8  
Old 04-08-2018, 10:15 PM
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Hi there,

I have the 300SDL on the lift and will change the K1 valve body part I bought long time ago with the hope to solve that very harsh 2/3 shift with cold engine.
I read the note from Diseasel300 and he had a similar issue finding a broken K1 spring.

Oh before I forget. The main reason I have the car on the lift is: I found that grinding noise of the trans: breaking and before the car comes to a stop the transmission was making a grinding noise..also at higher speeds it started vibrating... The rear transmission ball bearing is shot. It had about 1mm play!
I hope my transmission will be 'silent' again AND have a beautiful 2/3 shift.
Wish me luck.

Best, Martin

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