jkowtko

I couldn't find anything specific about this symptom from the other transmission troubleshooting threads --

I've recently done a transmission fluid filter/flush using the new 236.14 spec oil, Sheel ATF 134. The transmission sounds quiet and feels very smooth, good shift patterns, etc.

The only thing I noticed now (and this has been going on for a few years, well before my tranny flush) is that, when the engine is stone cold, as in driving it for the first time in the morning, when I stop at the first few stop signs, if I accelerate quickly from the stop without hesitation, the tranny slips a bit before engaging in gear.

It seems as though when it drops out of gear coming to the stop, it has a delay setting itself in 1st gear again, and I get a slip. It's only for a half second or so, but enough to notice.

I can get around this by sitting at the stop for a second or two ... it seems like that gives the tranny enough time to get itself into gear and ready for acceleration.

I have also tried this in comfort mode (I usually drive in S) ... haven't done this too much but it seems like the symptoms are still there, even though I would be starting out in 2nd gear.

Looking through the diagrams and troubleshooting on valve bodies, and the Sonnex repair kits, it seems like just about every valve listed in the diagram can resolve a "delayed engagement" issue.

Any suggestion on what this might be, or how to further isolate the problem for easier diagnosis?

By the way, no CEL codes ... everything seems completely normal except for this behavior. The car is otherwise peppy, downshifts well on the freeway, etc.

Thanks. John

SunnyRayToronto

Make sure you have proper level of transmission oil in there,... measure it at 80 degree Celsius.

Do ECU reset,... it`ll reset your throttle & transmission adaptations.

Glyn M Ruck

+1^ on level. An ECU reset does not reset the TCU.

Transmission adaptions can only be reset with Star (I'm not talking about learning)

The fact that it does it in both C & S makes it unlikely that a clutch pack is slipping. More likely a slight valve leak in the valve body. Did you break open your old transmission filter & look for wear material?

What happens when you select Drive from Park or Neutral? There is some delay on these cars but then it should lock up.

There is only one way to check this properly & that is to check that all lock up pressures are in spec with a Star.

You might have a broken solenoid spring. It can also be a torque converter problem.

Get it on to a Star.

Carsy

My 5 speed has always had a definite lag when asked to accellerate quickly from a stop. It was annoying at first but now with anticipation it is not as noticeable. My 33 year old Borg Warner 35 is more responsive !!

It would be interesting if you drove a similar 5 speed ATM to see whether it reacts differently to yours.

jkowtko

Right after I did the flush I checked the fluid level twice after driving for a while (temp on the pan never seemed to be able to exceed 65) ... both times the fluid was dead center of the 80C range. My measurement could only err on the low side ... the fluid should be in the upper half of the range.

I didn't break open the filter ... the pan bottom and magnet had only a light film of very fine residue, barely enough to color the cleaning cloth, and no sign of metal shavings. So to me all looked pretty good and I didn't think to break open that (messy) filter.

I haven't paid much attention, however every morning I back out of the driveway, turn the wheel, move from R to D, and drive off. No issues at that point (btw the PS shudder is gone now) and the engine has been running for maybe 10-20 seconds. I don't make a habit of gunning it just as I shift into D ... I usually wait a sec until it starts pulling forward before giving it the gas. It does sometimes linger a bit in first before deciding to shift to 2nd. But have never noticed the R->D hesitation here. It's only when coming to a stop from 35mph, and accelerating from the stop.

Question -- what is the progression of gears in this situation? e.g. ... 4->3->2->1->unlock->lock? Or 4->unlock->1->lock?

How much time does a STAR reset take and what should I expect to pay for it at a local dealership or Indy?

I assume pressure measurements are involved, and low pressure under any set of scenarios will point to specific solenoids, valves and/or springs?

Would it matter that by the time I drive to the nearest dealership the problem will not be reproducable?

Thanks. John

Glyn M Ruck

On the 5 speed it runs down the gears from 5 to one or 2 depending on C or S setting under almost complete TC lockup/minor slip & then the TC clutch releases as you come to a halt.

I"m out of touch with US pricing. You need local knowledge. The Star is capable of of checking every pressure range etc in the transmission for each clutchpack, solenoid, speed sensor, shift etc.

Just to clarify. When you talk about slip. Is it lag or is it slight rev flare before she locks up & takes off?

jkowtko

I would say it's a slight rev flare, then I can feel the TC lock in. This is consistent with your description of how the transmission changes modes as you decelerate to a stop (i.e. ends up in 1st gear unlocked)

So once the TC clutch is released as you come to a halt, when you step on the gas again is it supposed to re-lock instantly before it opens the throttle body?

And how is this different with shifting from Reverse or Neutral into Drive? When I do that is the TC also unlocked and waiting for me to step on the gas?

Thanks. John

LILBENZ230

John, I had the same car as you and through 146,000 miles mine never behaved that way. At one point, due to a misunderstanding between myself and my indy mechanic, my 722.6 was way overfilled and even then no such behavior. I also used the Shell 134 in the last change I did on my car at 120,000 miles.

STAR charges and dealer capabilities vary widely. There is an indy mechanic in my town with a STAR computer who hooked mine up for free without blinking. Then there are dealers who charge $120 and then tell you they can't do hardly anything with it.

Glyn M Ruck

jkowtko

The diagram above states "Transmission output speed". Is that the speed of the driveshaft? If so, it seems like the transmision will be slipping until I reach a reasonable speed (15-20 mph?).

What exactly is "open" vs "slipping"? I thought TCs were always slipping or locked. Is "open" the same as not engaged in gear?

So am I feeling TC slipping vs locked? Or am I feeling TC open?

Thanks. John

grane

Ii's been very cold around freezing here - I have a similar issue with the AMG when it is clear and cold out, esp. if I haven't driven it in the bad weather snow for a week or so.

When it is cold I drive very gently the first 10 miles or so. Otherwise I get the slight slip or interval to engage you speak of. Factor in a bit of a cold surface too where the tires are also trying to get grip?

Transmission drain was completely OEM serviced last summer.

Glyn M Ruck

Oops ~ my reply disappeared.

The above table is indicative only. Benz has modified the software frequently for optimised performance.

~ Transmission output speed = propshaft speed
~ Open = no clutch lockup. TC operating as a fluid flywheel.
~ Slipping = TC lockup clutches allowing controlled slip.
~ Closed = TC locked up solid for maximum efficiency. TC losses no longer in the equation.

jkowtko

Is "slipping" variable, as in with a manual clutch?

If so, then I'd say the issue I have when cold is that the clutch doesn't start to engage soon enough, or engages too gradually before tightening up, allowing the engine to rev a bit more than it should.

And by rev I mean between 1500-2000 rpm, not higher. When the TC is engaging properly I would say I don't go much above 1000 rpm before the clutch is heavily engaged.

Glyn M Ruck

Yes the slipping is a little variable. Obviously not in the manual clutch manner a TC becomes more "solid" as input revs increase.

jkowtko

So any idea why is this happening?

* It's only when the transmission fluid is cold and the car has been sitting overnight.

* It only happens after I decelerate from, say, 4th gear to a full stop and not when shifting into Drive from reverse or neutral.

... and if there is anything I can do about it?

I am thinking not worn clutch plates, as the transmission doesn't have that many miles on it and I didn't see much residue when I did the recent service.

If it's a suspect solenoid, valve or valve spring, I can always plan to inspect and/or replace parts in the valve body when I do the next service.

If topping off the tranny fluid level might help this, I still have half a quart sitting in the garage that I was saving for a rainy day.

Or if, like my power steering shudder, the problem will go away over time as I let the fresh 236.14 fluid slowly work its magic through the system, then I'm fine with the wait-and-see approach.

...

Carsy

To help diagnose the problem ,you could ask an expert what component /system in the ATM is most likely to be susceptible to oil viscosity changes.ie oil cold vs oil hot.

In the meantime drive it sensitively when cold so it does not occur .

You could always top it up to the max on the stick( when at operating temp, 80'C) but no more as they are sensitive to incorrect levels.

Please post the outcome .

John

Glyn M Ruck

It seems that the pressure rise in one of the circuits (probably the TC or TC clutch circuit) is delayed. This being aggravated by cold fluid.

Drive it & see what happens. Otherwise get it onto a Star for diagnosis. It can't be terrible or it would trigger limp mode to protect itself.

jkowtko

** Update **

I've been trying to capture a video showing the behavior, but the past few mornings haven't seen it clearly. There seems to be a slight bit of mucking around when I pull out of the stop quickly, but not a consistent slippage that I could get on video.

I've also noticed that when the engine is fully warm, occasionally when I come to a stop the transmission seems to drag the engine down a bit below idle speed before fully disengaging, and I get the momentary rough idle. At least that's how it feels ... I don't think it's the torque-acceleration effect because if it was it should happen every time. But I also don't know if its the throttle body being a bit slow to respond to ECU instructions. (I've already cleaned the TB throughly, front and back.)

What's your take on that? Do I have a TC clutch that's a bit sticky, hesitates on engaging when cold, and late to disengage when hot? Or are these two unrelated problems?

Thanks. John

Glyn M Ruck

Yes ~ it could well be a problem with the TC clutch circuit. Slow to engage & slow to release.

jkowtko

** Update from this morning ** -- I felt it again.

Coming quickly off the stop, the RPM pulled up to about 1500 as I started accelerating, and then a "thunk" as I continued to accelerate. I was probably doing only 5-10 mph when the thunk occured, so it was delayed maybe a half second off the start. The thunk did not pull the engine revs down -- instead it pulled the car forward.

It felt like the clutch was engaging (since I was accelerating at a reasonable rate) and the thunk would be it locking before the clutch had tightened up enough.

In comparison when the engine is warm I can't sense anything that feels like a TC lockup.

jkowtko

** Update **

This morning I was able to reproduce it a few times, counting gear shifts as I accelerated. It was definitely in first gear when it happens. The feeling is that, accelerating from a standstill, the TC clutch starts to engage but is still slipping, then around 1500 engine RPM the ECU backs off the throttle until the TC can lock up, "thunk", then the engine surges ahead and the tranny goes through the normal gear changes.

I am still unsure of what the normal behavior should be for these transmissions (and what I experience when the tranny is warmed up) --

- Should the TC be locking up in 1st gear right off the start, and lower than 1500 engine rpm?

- Should the TC be slipping longer and lock up at higher engine rpm?

- Is the lockup timing fine but the clutch should be tightening up at a faster rate so the lockup is not felt?

For reference, and to make sure I'm identifying the gears correctly, these are the approximate speeds I am going in each gear when the engine is running at 2000 rpm:

* 1st - 10mph
* 2nd - 17mph
* 3rd - 28mph
* 4th - 40mph
* 5th - 50mph

Thanks. John

Glyn M Ruck

The car should be retarding the timing at the moment of gear change to smooth the shift. Sounds like the ECU is doing what it should but the TC clutch lock up is delayed OR the first to second clutch pack is slipping & locking up late.

Carsy

Do you have access to a car with the same GB ?

Could save you a lot of heart ache to drive it & compare with yours .

Alternatively take all your info to your local service manager for advice.

John

jkowtko

Glyn, let me clarify -- I do not believe this is a gear change ... it's still in 1st gear during and after the thunk.

After the thunk I'll accelerate up to 3000 or so rpm and then shift into second. The 1st->2nd shift is identifiable and has no problems. So this noise is all happening during the first gear acceleration from the stop. I'm pretty sure at one of the stops I used manual shifting to confirm this.

Does this change your diagnosis? I assume the oil is cold and therefore more viscous, which means a potentially sticky valve? I wish there was an animation somewhere that explained the fluid flows ...

Thanks. John

Glyn M Ruck

I have diagrams of all the fluid lows somewhere. If it takes place before the first to second change then the ECU should not be retarding timing and the issue would seem the TC lockup clutch.

If you put the transmission in comfort mode so it pulls off in second you still have the problem then ~ Yes?