Transmission Question - Mercedes-Benz Forum
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post #1 of 19 (permalink) Old 03-23-2019, 03:43 PM Thread Starter
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Transmission Question

I have an issue with my transmission. It drives and shifts fine. I just replaced the filter and drain both the converter/pan. I put Valvoline Dextron III in it as that's what I've seen these cars need.

My issue is that often, when I pull up to a stop light, the transmission goes into a free spinning mode for a few seconds, (like I put it into neutral or the fluid was low), and then catches again and is ready to go. I don't know much about transmissions and was hoping the filter/fluid change would fix that, but it didn't change a thing.

Any suggestions? I am thinking the hydraulic pressure is not keeping up or low at idle or something. Wondering if I should drain out some fluid and add an additive such as Lucas Stop Slip or some other snake oil type stuff that seems to work. Wondering if seals are not keeping the pressure....

Appreciate suggestions.
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post #2 of 19 (permalink) Old 03-23-2019, 07:53 PM
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Recheck your fluid level and make sure everything is level. These cars are really sensitive to that leveo being between the two notches.

Drive it so it's hot and then check it. Add small amounts of fluid and then recheck until it's between the notches on the dip stick.
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post #3 of 19 (permalink) Old 03-23-2019, 08:06 PM
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Check your shift linkage bushings.
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post #4 of 19 (permalink) Old 03-24-2019, 05:04 AM Thread Starter
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While under the car, I noticed the bushing was gone/missing at the selector rod end and trans mounted shift lever so there's quite a bit of slop. Sure those names are wrong but will get the bushing. I sure hope that installing the bushing and ensuring the level is correct will fix this....otherwise not sure what I'll do
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post #5 of 19 (permalink) Old 04-02-2019, 10:33 AM Thread Starter
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So bushing are replace, fluid level is fine. I also added a product called 'LubeGuard - Red' as my local Mercedes guy suggested I add that to see if it'd free up something. Transmission works great for about the first 10 miles, in reality probably when the fluid is cold. Once warm, the issue starts. Ideas? Wondering I could take out the valve control body on the tranny and clean it or; my Mercedes guy has a spare one I can try to see it that's the issue.
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post #6 of 19 (permalink) Old 04-02-2019, 11:01 AM
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I hate to tell you this, but most likely the problem is not the control body. Very likely there is an internal leak. You can check the control pressure to verify. It is measured at the plug beside the vacuum modulator. Your shop should be able to put a gauge on this. They should see in the vicinity of 54lbs at idle and while running and should stay fairly constant. If low, try turning up the pressure with the adjuster on the vacuum modulator. If it goes up, that’s good, If turning up the pressure has no affect, that strongly suggests an internal leak.

Your mechanic is going to want to check the pressure in gear and out of gear and while driving the car to duplicate when the problem occures. You might find in one position the pressure is good, but when in another position, the pressure drops out. That way you can check the pressure when the problem shows itself. A longer hose will bring that gauge into the car to observe while driving.

The threads for the check port are 8x1.0 mm, which is not a common size. Conveniently enough, the $25 harbor freight pressure check set comes with this size adapter. http://www.harborfreight.com/engine-...kit-98949.html

There is also some possibility of the modulator itself being an issue. I have not found this to really be the case in most I have seen. There is an updated modulator as well as the actuator rod to match, which is available.

Rick

Last edited by rick; 04-02-2019 at 11:18 AM.
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post #7 of 19 (permalink) Old 04-26-2019, 03:20 PM Thread Starter
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Thanks Rick - great info for me to check up on. Will see if my buddy has the right tools to check this.....

On another note, been out driving the last few days. Runs and drives nice but still has the issue. I added a quart of Lucas Stop Slip as my shop buddy suggested I do that as well. It may swell up some seals....Probably drove around 200 miles so far. Tranny shifts fine but when in drive it still at times goes into free spinning for a few seconds then catches back in gear, when pull up to a stop. Also does it when I do a quick 90 degree turn in the neighborhood. Fluid level is fine, and I checked with another owner to make sure I had the right dip stick.

Curious thing. If I am 3 gear (not in Drive), it doesn't act up at all. No symptom of this free spinning issue ever. Could that indicate a sticking valve in the valve body?

I still plan to do at Rick suggests in his thread in check the pressure.....

thanks for ideas.
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post #8 of 19 (permalink) Old 04-26-2019, 08:39 PM
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Transmission Question

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Originally Posted by orbit398 View Post
So bushing are replace, fluid level is fine. I also added a product called 'LubeGuard - Red' as my local Mercedes guy suggested I add that to see if it'd free up something. Transmission works great for about the first 10 miles, in reality probably when the fluid is cold. Once warm, the issue starts. Ideas? Wondering I could take out the valve control body on the tranny and clean it or; my Mercedes guy has a spare one I can try to see it that's the issue.
I posted a reply about a week ago but it has disappeared. I repeat-
Add a can of SeaFoam Transmission Fluid and run the car. It Might take two or three days for it to work.
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post #9 of 19 (permalink) Old 04-27-2019, 10:40 AM Thread Starter
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well - just added seafoam to the mix. will see what that does; can't hurt. assume a rebuild in my near future but what the heck, one last try. quit a mix I have in the tranny fluid...
lubeguard, lucas, seafoam.....
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post #10 of 19 (permalink) Old 04-27-2019, 01:12 PM
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im going to ask the dumb question....are you checking the fluid running?

also if you want to pump fluid without going for a drive just sit with the brakes on and cycle it thru the gears and give it a little throttle

what kind of milage are we looking at?

turning the line presure up would be my last resort on something like this before a rebuild

another thought, have you tryed manualy shifting the trans to see if you can replicate it?..if you can replicate it in reveres then you have a fluid issue most likely the converter , if you can only get it in drive at a stop then its the 1st gear band, if its all forward gears then could be bands could be pump could be fluid

sadly what your descibing generaly means its time for a rebuild, but sometimes you can buy yourself time....in some cases many many years
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