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1991 S600 Japanese market
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515 Posts
Discussion Starter #1
I got to take my S600 out for a run on our new expressway today. the trans started slipping going uphill.

Pulled off. Dipstick said a bit over a litre low. So, I added 1 1/2 L. All the way home, the car would not move out of second gear.

It goes onto reverse and park just fine. But no matter where the selector is (D, 3,2, B), it will not move out of second gear.

Trans was rebuilt around 2 years ago. About 500km on it since. vacuum modulator, B1 and 2 pistons replaced. All new clutch packs installed.

Any ideas?

IIRC, B2 controls shifting into second, correct?
 

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1991 S600 Japanese market
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515 Posts
Discussion Starter #2
Actually, as it was pulling 5500 rpm at 50 kph, I think it was stuck in 1st
 

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93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
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8,405 Posts
2nd and first are sometimes hard to distinguish.

For starters:

The vacuum line near the rear of the transmission it must be connected, and the moment I cannot remember if that line attaches to the intake manifold on the sides. Test the vacuum( suck on it) if you suck on it and feel you are sucking something you maybe drawing up transmission fluid indicating the vacuum diaphragm has a internal leak.

The bowden cable at the throttle body with a linkage make sure that is all together. Try disconnecting the ball end at the throttle body, and feel the springy movement if the springy movement is there means it is working and is not jammed-up in the valve body, and no springy movement is bad too.

Disconnect the passing gear switch behind the accelerator as they short-ON, and that would force the transmission to stay in low gear.

Try those first,

Martin
 

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1991 S600 Japanese market
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Discussion Starter #5
Martin,

Thanks for the tips. Yes, external pieces will be checked first. Next I plan on pulling the governor.

The reason I think it’s stuck in first is the 50kph at 5500 rpm. Even my XJs will pull 90mph at 5500

Cheers
 

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93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
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You are welcome, and that is an aggressive maneuver as one needs to drop the tranny to get to that, yet depending on your V12 where the exhaust cross-over bracket is. If it is under the transmission, then the exhaust has to come out too..

Best of luck,

Martin
 

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1991 S600 Japanese market
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515 Posts
Discussion Starter #7
As luck would have it. Kampala is a very small town. Someone saw me limping home along the expressway on Sunday.

Very few “whites’ here. And fewer still with an S600. Like 1. So today, a guy shows up at my gate to talk. Turns out he has opened a shop with the best couple of Mercedes mechanics here.

I visited his shop today. Car goes in Thursday to drop the trans.

Fingers crossed.
 

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1991 S600 Japanese market
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515 Posts
Discussion Starter #8
Well, we got the transmission out. Looked like someone had a BBQ inside. Clutch disks overheated and disintegrating, B1 and B2 bands overheated and scored. Metal clutch disks hot spotted.

And check out the B1 piston.

2678736


And here is my team. Under the mango tree (literally).

2678737
 

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93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
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So everyone will wonder WHY???? Why-First-Gear?

Lets get this out of the way first, heat heat heat....

This is the result after "two year rebuild"? The consequences of even driving 50k miles/year would not even come close to that, yet on the contrary it is being coooled from highway driving one would not see burning.
This 733 spent some time idling/ going up long grade slowly/ "hot dogging it" -what else would one do with a "V12"/ spent a while with a "low fluid condition"/ with local drives and HOT weather there it just needs MORE cooling for a separate transmission radiator.

Why first gear only???

The brake bands are in a proper calibrated tension from the inside from left to right(or right to left), and only move millimeters to maybe close to one-centimeter.

If one reads the second page of the troubleshooting guide, one understands the work-flow of the operation, and looks at the truth table when each gear is engaged-see below:
733 Truth Table.jpg


So, when one puts the car in DRIVE from a dead stop both B1 and B2 are engaged or actuated, and clutch pack drum 1 and 2 are locked from turning one gets the reduction of 2.41 But........

From my take due to the evidence of the heat of this "two-year-old-transmission" two or one thing lead to the failure of B1 actuating/ locking drum 1, so clearly from the truth-table at a dead-stop in DRIVE it is at 3.68 (first gear).
My take is the transmission got so hot that it cooked the parameter seals( all the seals that touch the case). It hardens them, so they do not "seal" any more. This B1 piston assembly receives TWO conditions to activate( see photo below)

A) Normal Drive condition, oil enters(from valve body) the oil gallery holes on the big piston there in-between the two black o-rings, and lock that/actuate the pin on the left.
B) In pressing the accelerator all the way down that activates the electrical switch behind the accelerator that activates electrical fluid switch( the knurled part with the two contacts on the right)stops the flow of fluid in the big piston.
If you cooked the seals, you would not get condition A to work, or B the switch shorts out behind the accelerator. Possibly the knurled switch fails too....


B1_Piston Switch.jpg


On the other end of B1 is the spring assembly with the plastic part we all see on the ground(from the post above), but here is what that assembly looks like( See picture below). The plastic part cradles the B1 brake band from moving up and down(from the two torpedo pins on the far left of the plastic). The pocket opening holds B1 from moving Front to Back(that area is burned on your part). Like I said, B1 band moves several milometers if the plastic cannot contain B1 Band it will engage to start at 2.33 reduction. Again, if the case got very hot that it cooked the parimiter seals the pin in the center of springs in the picture below moves out to the left to actuate the B1 Band also, so one loses that function because of the seal, and it stays in a 3.68 reduction.

B1_Piston Assembly.jpg


Hope it makes sense? this is true for all 722.3-722.5 transmissions

The burned clutches makes no difference if each brake band is engaged as the drum is locked.

Like I said at the very top....heat heat heat, or the other conditions too...

These 722.3s-722.5s run way hotter than any 722.6 due to the brake bands floating/rubbing around the drum. It generates heat... There is a new-age transmissions-The ones that DO NOT USE BRAKE-BANDS. Even today a 2021 some models still have "Brake Bands" in the transmissions. Most of the Chevrolet(GMC) Pick-Up Trucks/SUVs they still make them with brake-bands, and here in America one can drive around the city, and what is one going to see on the car-lift at a transmission shop. Some Pick-up/SUV is on the lift yet the Toyota models have NO brake-bands in the transmissions, and that's why those Toyota's will have a typical transmission life of half-million miles.

If you plan to keep your S600, I would think of adding a few fan-cooled transmission cooled radiators, and maybe that will cool your transmission, or think of adapting a second generation 722.6 from a S500 W220 as the W124/W126 diesel crowd has started to do, yet the diesel crowd can get one-million miles from their engines, but their original transmissions are lasting 1/10 to maybe 1/5th of that. Follow the links below on this thread:


I kinda get a little deep here on the W140 forum on this topic of the conversion:


Best of luck,

Martin
 

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