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
#2 ·
Somebody please tell me,(I am getting desperate):
1. at least if there is any other way than something wrong with kickdown(for example b1 piston or band) for this transmission to start in 1st gear?
2. Can kickdown solenoid be stuck acting that ist always on even if the cable is unplugged?
:bowdown:
thank you
 
#4 ·
Hahaha....

:p:p

Yea, every transmission has a solenoid..Bnze good guess..Not this tranny...

My Slovakian friend,

It is hard to say as it can be an adjustment issue in the linkage. Vacuum Modulator, K1, K2, B2 piston, B2 seal...

Look at the links from this thread in post 2 and 13...

http://www.benzworld.org/forums/w14...6-s280-australia-transmission-no-reverse.html

I assume your fluid/filter is recent? Upto the proper level?

Martin
 
#5 ·
Hi,
thank you guys for help :), I will try to explain you my situation as far as my knowledge and skills are, as well as what I've already tried. Well, I studied this transmission countless hours already throu servise manuals and internet(pretty much all english and german speaking sources) and I found very little of my kind of problem discussed(probably 5-7 topics mostly on german forums). These kind of topics usually dont have an answer solved. In those german cases there was always kickdown switch under the shifter the problem. But I still have questions very importat to me to understand how this transmission works to know what to do next time i get to use a lift because I dont own myself a lift, so I have limited access.
In manual there is this complaint related B1 where is something like "shifts from 1st to 3rd or slips in 2nd" which is not really informative because there are 2 kinds of 722.3 transmission (1st start and 2nd gear start). How can I know whether they mean every 722.3 would act the same or whether the 2nd gear start one would slip in 2nd and the FGS would skip the 2nd? Would there be functional 1st and 3rd gear with NO slipping if B2 piston was the culprit?

Also I've already tried to unplug the cable from kickdown solenoid and nothing changed. I will try it again because I didnt get much of a test drive then and I also messed with the bowden so I could have messed wrong so my observation could've been wrong. + I disconnected the b switch under shifter and nothing happened.
Yesterday I also messed with bowden cable to the point where there could not be more slack and the trannsmission shifted with VERY light throttle at about 2000-2500 RPM from 1st to 3rd I guess. It was defintalety 1st gear.

Next I am about to check the solenoid with my bare hands(I have an overhaul kit) and try to analyze if its stuck any help on this would be so much appreciated.

Edit: The transmission was opened 2500 km before because of dreadful reverse (not by me) and I must say the B1 clutch was not gone at all it looked pretty much 3/4 new so maybe the guy put it back in wrong, but I guess it wouldn't last 2500km in that case...

I must confess I have very little practical skills with these kind of things so its all new to me, but I am trying to make it up with knowledge.

Thanks :thumbsup:
 
#6 ·
Anticore,

First, You have done your research well !! I did the same thing, and I was no genius at it either? I spent two-years researching before I fixed mine...

Since you reside in the northern part of the hemisphere, I would think the reverse issue would not be an issue, but now that the reverse was fixed. All bets are off, this transmission has experienced being overheated, so...

My thoughts(from the comfort of my chair), the seals/o-rings around the parameter of the transmission are hard, brittle, and cracked. Consequently, this includes B1 and B2 pistons. You could have internal leakage as one of your problems..

The dog bone that mates from the B1 piston to the B1 band could have been disturbed, and is now miss-aligned(not in the socket), but with a transmission this old the plastic frame that aligns B1 could have broke, and the B1 is just floating...

Have you removed the oil pan from the transmission? Looked at the debris if any?

Now, a transmission 20+ years, and reverse seal was replaced 2500kM ago. To me you are spinning you wheels too much to figure this out. Seriously, I would buy a $200(USD) rebuild kit, and rebuild the whole thing. You will need a few other parts, but you will come out wining instead of patching this or that...You have a rare V12 car. I would do it.

The link from the post above. Has enough information to do the whole service job.

Those are my thoughts,

MArtin
 
#7 ·
Hello MAVA,
So you are assuming that faulty inner parts would cause this kind of 1st gear start? This one I just dont understand for example if B2 went out than you couldnt move, it doesnt just put you in 3rd or 4th gear and tries to move like that right? This is supposed to be kind of "dumb" transmission with no electronics to force 1st gear right? That is one thing that I just cant get sorted in my head. I want to avoid taking the tranny out of the car as its time and space consuming.

I would be thinking exactly as you pointed but still cant figure this out,
I can add some pictures of the trasmission half taken apart
here's a link with pictures of the actual transmission 2500km when it was taken apart you can see b1 clutch to me looking almost as new all the seals were replaced around that area(the guy who did it was ex-employee of a tranny rebuild shop):
anticore | 722.362 ? rajce.net

actually the car has 270k km on the clock so I dont know maybe its just blown, I hope not. Other than this the transmission reacts as new little time to any gear and smooth as silk.

Thanks a lot I appreciate that :)
 
#9 ·
Ok it has not been fully rebuilt, the pics just show the pump removed to get access to the reverse problem. No pics of dogbones or brake band guides or the pistons.

Both of my band guides were damaged and needed new ones, and one of my pistons had a very worn teflon seal, but it still actually shifted and drove fine in forward gears.
 
#10 ·
Yes you are right just to get to the B3, but there is the B1 band in the first picture I guess which isnt all that gone. It could be the piston though(its the self leveling one B1). I am almost sure it cant be B2 band nor piston related cause my 1st and 3rd gears are fine.

Can be B1 piston somehow be removed with transmission in car? I know its springs are very strong but I guess it could be done somehow...

thanks
 
#11 ·
Did he have B1 piston apart? Any more pics available?

It would be a tough job to remove B1 piston in the car but I think it would be possible. Might have to loosen the rear gearbox mount to push the gearbox over to one side or pull the box down a bit for a bit more room. The springs can be squashed in a fair bit by hand, but need a clamp to remove and put them back the last couple of inches depending on how strong you are. Maybe someone who has actually tried will respond here.

Thinking about it I might pull my B1 piston out to double check it again before I put the gearbox back in the car!
 
#12 ·
Nope I dont have anymore pics just those that the guy sent me. I doubt he would put it together when there was any major damage. The tranny shifted like a DREAM literally until some random point I didnt even notice when. I gues after I was kickdowning for like 3 times It first happened. I guess it then worked for a little while (ride home frome a friend where I tried to adjust vacuum modulator I thought it was the culprit)and then from the next day I's been like this. I dont really remember exactly its just all blurry somehow I didnt pay much attention back then I was late to drive somewhere or something.

I guess nobody checked the b1 piston. Do they ever go bad? I mean what the hell of a bad luck this would be :crybaby2:
 
#13 ·
If you don't want to do a full rebuild then B1 piston and related parts might be a good place to start. As you know 2nd gear is the only gear to use B1, and B1 has been disturbed when getting reverse fixed, even if it is just from the removal of the brake band itself.

On the 722.4 box the plastic B3 shim is locked into place by the B1 band guide. In your 3rd pic the shim is in the foreground but the band guide is still in the gearbox. Maybe the 722.3 is different and this is not a problem, but on the 722.4 putting the shim in place with the band guide already in would be very difficult.

Again, maybe the 722.3 is different. If you can find out off the guy if he removed and inspected B1 it might help. In that 3rd pic the pin that B1 piston pushes B1 and the guide are all just sitting there.

Also your B1 is black. My B1 was orange similar color to new. Find a pic of a new B1 for your box and see what it looks like, maybe your B1 is black from slipping and burning as MAVA suggested.

Just some ideas from someone who only has a little experience with the 772.4 box. Last pic shows my B1 on left to B2 on right. B2 comes black new.





722.4 gearbox at 220,000kms. B1 on left, B2 on right.
 
  • Like
Reactions: MAVA
#14 ·
I remember him telling me that the gearbox might have been out before and some parts changed which according to the mileage could be about right also it could have aftermarket B1 band (i remember some of those being pure black or very dark) also here is a topic where some guy has also black b1 band: 722.358 - PeachParts Mercedes ShopForum
Also i have this, i guess, its front pump gasket that was there before the reverse repair that is branded "reinz afm 32"
Aslo he told me it looked very clean and Ok not heavily used.
I think if you look closely you can see the actual band b1 from my transmission not severly deformed on the surface it looks evenly used up I would say and also quite thick to be seriosly slipping like it maybe is.

edit: actually found a link with black B1 band: Europeantransmissions and...

thank you my enthusiastic benz friends I really apreaciate you help :rolleyes:
 
#18 ·
Anticore I was under my car today installing the gearbox. Access to B1 piston is easy with the exhaust removed, huge amount of space for clamps etc. B1 piston has a lipseal the same design as the clutch packs and reverse piston. B2 piston has the teflon seal that was worn on mine.
 
#19 ·
So do you think the piston seal can go easily bad? Today i messed with the kickdown solenoid and also tried to push the b1 piston in with a prybar which wasn all that bad. I could push it to see the "C". I put the prybar resting against the exhaust I have probably defferent than most of the W140 being it V12. But I don't know how long it actually is I had like 10cm maybe more if I could pull it(the piston) sideways (up direction).

Also I probably should chceck the pan and the B1 control valve which should be accessible (manual refers to it as a possible culprit) maybe another B1 valves...

I test drove the car and used tempomat at 60 km/h then put it manually in B-2 when I noticed it was trying to find grip while it was supposed to be in 2nd gear it then found SOME grip at probably 4000-4500 RPM (but VERY light grip felt very fragile)

Do you think that the B1 without a dogbone would get any grip?
To me it kind of reminds me of a B2 piston behavior but relating the B1

thanks
 
#20 ·
If you look in the rebuild guide it has clearance values for the bands. The dogbone is much much longer than the clearance value.

I only have experience with one gearbox. I can not make comments about the reliability of different components.

If you don't want to do a full rebuild all you can do is check B1 and related parts. If you look at the manual and at parts diagrams you will see there are shims to adjust B1 piston.

But you have to ask yourself what has changed in such a short time that caused this problem? Adding shims may not fix the problem.
 
#21 ·
Hello, so I opened up the B1 piston and changed the seals but nothing changed.
EDIT:But one thing I dont understand is how to adjust the self adjusting piston? You were talking about shims, there were "no" shims but I am not sure if I have any shims that fit in the overhaul kit. And the mechanic told me there was not a possibility to add a shim of that kind.

Is it the correct way to adjust the "self adjusting" B1 piston by adding a shim?


thanks
 
#22 · (Edited)
B1 has small washers that act as shims to space out the pin or dogbone that compresses the band. Mine had two installed at the factory.

B2 has different length dogbones. Mine had the smallest size installed at factory but I went a size up when I put it back together.

Different thickness shims/washers for B1 or different length dogbones for B2 do not come in the overhaul kit.
 
#23 ·
I read somwhere that there are 3 designs of b1 piston... what year is your car/transmission?

I have i guess this kind: B1 self adjusting piston - PeachParts Mercedes ShopForum

I dont really understand the discription provided in that thread so please can you help me with it?
Also I guess there isnt really a chance of getting shims there my mechanic keeps telling me it must be different design maybe the 3rd and the last one.

Also i found this thread that points maybe to the same problem: replacing B1 piston - PeachParts Mercedes ShopForum

it really drives me crazy because this is not really an ordinary issue assuming from all the sources around the internet It's rather rare.

thanks
 
#24 · (Edited)
Mine is a 1996 722.4 it does not have the self adjusting piston. The shims are just very very nice washers.

Find out your transmission number and we can try to work out what exactly is in your gearbox. Did you take any photos when you disassembled your B1?
 
#25 ·
Sorry for delay, my transmission is 722.362 and my car is made in february 1993. I dont know the part number but I have the latest self adjusting piston which my mechanic took apart and he told me: "It's going to adjust itself through the pressure inside." It looks exactly like the one in the first link I providied in my previous reply.

It is possible that the piston was rebuild as well as the entire transmission before I dont know when so it might not be the original part(assuming I have this red modulator instead of light green and the mentioned stuff I posted before

I kind of feel it might be something in the valve body. Has anyone rebuilt the valve body? Is it pain to do so? I have seen some diy with photos it doesnt look impossible. Sort of reminds me LEGO :grin

I hope this wont happen ever egain even to the worst enemy... such a shady issue

thanks
 
#26 ·
OK sorry for thinking you had the manually adjustable type. If your B1 piston is operating correctly as per the rebuild guide it is either the valvebody or the brake band at fault, you are running out of options! As MAVA suggested a full gearbox rebuild really is the best way to ensure many years of reliable service.
 
#27 ·
Actually I have never read over the internet about 2nd gear slipping before and only 2nd gear due to worn b1 band not to mention in my case it was not a matter of consequence it happened without warning probably matter of second.

I personally think even if the band was badly/totally worn it would still move the car "in gear" but it would slip in steep hill and such.

I forgot to mention I checked the pan for debris and nothing was found literally nothing. Nice sweet smell of ATF, no burnt.

Must be the valve body I guess.

Imagine the frustrated feeling after rebuilding the tranny and putting it together and bang! nothing same old blues.

this car is cursed!:devil

:crying
 
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