Mercedes-Benz Forum banner

600 SEC transmission starts in 1st and skips 2nd gear(acts like there is no 2nd gear)

11K views 39 replies 9 participants last post by  plinker17722 
#1 ·
Hello everybody,
I have a 600 SEC with a tranny problem. Out of blue the transmission started to shift weird. At first I thought it slipped in 2nd gear, but after more research I found it really starts in 1st with no slipping and it holds pretty much to high revs (2500-6000) depending whether I take off the gas and then it shifts straight to 3rd and then normally to 4th... If i tried to put it in 2nd gear manually say at 80 km/h it would act like its in neutral almost. It also shift weird when i use kickdown it then stays in 1st gear and i always hit rev limiter.

My suspects are bad kickdown something (b switch, kickdown under pedal, solenoid stuck!?)
or something related to b1 piston or band or valvebody in which case I dont understand the 1st gear start anyway.

would I be able to test kickdown switch by pulling the cable from the solenoid or if the solenoid is broken or stuck would it still be acting like its always on?

fluild and filter are OK...
the transmission is 722.362

thank you for any help
 
See less See more
#28 ·
Have you try'd to adjust how the gears change on the adjustment lever next to the accelerator ? :thumbsup:
 

Attachments

#30 · (Edited)
Hello,
so I've been messing with the transmission and the valvebody, and still cant figure out whats the problem, everything seems all right no debris enywhere even in the filter and the valvebody. We looked again at the B1 piston and it adjusted itself so there is pressure and it works, the band is seated OK thrust body is like new.

...But there is one thing I still didnt check and that is reaction valve under overload protection switch which is on the other side of the B1 band and is supposed to work to hold B1 band compressed. It even has pin that holds the band from the other side oposite the B1 piston.

So my question is how the f*** would this part brake and how would I chcek if it works or not? Or do I have to buy a new one to know for sure? Why wouldnt any manual point to this as a possible culprit when its evidently as imporatnt as B1 piston???!?!?

I never read anywhere that this part broke just overload switch leaked or something there leaked.

EDIT: could the pin get misaligned by any chance resulting in slipping band?

Does anyone have any experience with this?

Thanks
 
#31 ·
I did not mention this before, because it is the most basic of rookie errors, have you checked for proper trans fluid level when car is running?

The pin on the other side isn't going anywhere, unless the B1 brake band guide is broken, or thrust body is broken. Reffering back to the below rebuild manula extract, it's either B1 or valvebody. You are going through to process of elimination, next easiest thing to check is the valvebody itself.

 
#33 · (Edited)
You are right, there must be something in the VB, but I couldnt get to valve 10 because one of the screws got damaged because I was trying to unscrew it and it didnt wanna move a bit so it got damaged being it aluminum and fragile. I am thinking about changing the valvebody for another one from 600, I also know a guy who has one but he doesnt really want to sell it because he wants to keep it just in case of upredictable scenario happens to his mounted transmission. But he said that he would sell it, if I gave him an offer and I really needed it, but I dont really want him to do something he doesnt want unless its really necessery.

Other option is to try to rebuild it completely, but I dont have the space for that. I need to find a place where I can leave the car on the lift and take the VB home and do it on my worktable.

And there is one thing that maybe would work, and that I would drive for a while without vacuum hose connected so it would slam to every gear. The pressure inside would probably be much greater and could move some serious dirt out of VB maybe.

thanks
 
#34 ·
I've removed the vacuum hose while setting up the s280 gearbox after its rebuild. I braced for sledge-hammer-slam-shifts, but it's wasn't that bad at all, nowhere near what I was expecting. Try it, it won't hurt.
 
#36 ·
I could just manage to reach under the car on a flat surface to disconnect it, I was under there adjusting the modulator anyway. Yes it plumbs into the engine bay somewhere, but I'm not sure exactly where.
 
#37 ·
Hey there!
Another 600SEC with the same problem.
I was less deep in the transmission than you, but I've got something interested.

When I got the car it shifted from 1st to 2nd, I though it was okay, until I recently found that the "2nd" was actually 3rd gear. So it skipped 2nd gear, like yours.
However, at the speed of 70 km/h I could run 2nd gear manually with the gear lever, then accelerate or decelerate, it was working properly!

I decided to change my valve body for another 600SEC with "checked serviced good quality super part" that had cost me like $400, not including the labor. Well, okay.

Results:
2nd gear miracly appeared. As well as 2nd gear start appeared.
Now I get a "mishift" in 2-3 upshift, as if 2nd gear is off and 3rd gear is too slow to go in. You may call it 2-3 shift flare, but it's huge. If I release the accelerator, it shifts somewhat quick, if I do not so, the rpm may go +500 or +2000 RPM, so I have to release the pedal a bit to avoid something unpredictable.

The man, who changed the valve body insists I have a bad 3rd clutch, wear, blah-blah, that's bullsht, the transmission had not problems with 3-4 clutches.

I'd like to inspect my original valve body to see what could cause the problem, I suppose it has nothing to do with bands or clutches, as it's a hydraulic logic related.
 
#38 ·
If the other shifts are OK and only one particular shift is soft (i.e., 2-3 upshift) you should try the K1 spring kit mentioned back in post #32. You can measure the existing spring wire diameter and compare to the upgrade kit to see if it's different. If more adjustment is needed, the Superior 722-G kit has even stiffer springs available for K1.

Don't forget to try adjusting the vacuum modulator; but keep in mind this will affect all shifts... try 1/2-turn increments (clockwise) to go firmer. If your trans has the modulator with plastic cap, it's more of a nuisance... the rubber-cap version is easier to work with.

On a related note... what fluid is currently in the transmission? I would not recommend the latest fluids (Dexron-VI or similar, MB spec 210.12/210.14) as they are thinner viscosity and can cause upshift flaring. Usually this can be adjusted out with the modulator, but it's better to stick with the higher-viscosity fluid the trans was designed for (Dexron II or III, MB spec no later than 236.10). Some MB techs even prefer Type F fluid for older, worn 722.3 transmissions. Type F is basically Dexron without friction modifiers, so it's less slippery, and allows the clutches to 'grab' more... resulting in firmer shifts. That's not everyone's cup 'o tea though.

:eek:
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top