Auto Tranny Question

[robs-mbz]

Why is it that my 1997 E300TD rolls back on an incline when the gearbox is switched to S with the engine running, but holds stationary when in W? Is this normal or is there a possible fault?

 

[OmniCognateNeutronRangler]

Why is it that my 1997 E300TD rolls back on an incline when the gearbox is switched to S with the engine running, but holds stationary when in W? Is this normal or is there a possible fault?

I'd guess it's because when it's in W it's in a higher gear. I'm sure someone will correct me if that's wrong. I haven't tried it myself but I will do now you've mentioned it

 

[robs-mbz]

Let me know what happens!

 

[cyps]

My 1997 e320 v6 holds in either s or w so would find a fault could be possible


Trannys they are so much hardwork if they dressed in mens clothes there would be no more

 

[Ultymate]

When in "W" the car always starts off in second gear therefore less likely to hold station on an incline, no fault completely normal

 

[OmniCognateNeutronRangler]

My 1997 e320 v6 holds in either s or w so would find a fault could be possible


Trannys they are so much hardwork if they dressed in mens clothes there would be no more

oddly a colleague of mine says her E240 holds on the steepest of hills, but my C240 never has. It rolls back on even slight inclines.

 

[cyps]

wonderwhat it is that holds the car cause on mine on v steep incline it works like a pedal back brake on a pushbike

 

[OmniCognateNeutronRangler]

Malcolm, a little technical assistance if you are around. Ta

 

[Parrot of Doom]

It holds because you're in second gear, more torque from the gearbox.

I think. :-|

 

[eric242340]

It holds because you're in second gear, more torque from the gearbox.

I think. :-|

Correct

 

[Hibbo]

My w123 and w124 will both roll back on steep inclines, whereas the w201 (190) wouldn't at all, even on REALLY steep inclines.

It is the torque converter that stops the car rolling back as it is providing just enough torque to the box to oppose gravity pulling the car back.

In W the box is in 2nd when stationary, in S it is in 1st.

 

[premmington]

Correct

Would agree, it holds because its in second gear...



E300D W124 owner

http://www.remmington.plus.com

 

[Andrew Rolland]

robs-mbz

There is nothing wrong with your tranny. Autoboxes 'hold' on inclines due to the torque being generated (from the torque converter) being multiplyed by the gear ratios in the tranny and again by the gear ratio in the diff.

2nd gear has a lower ratio (approx 2.5:1) than 1st gear (approx. 3.5:1) so the torque multiplication will be biggest in 1st gear than 2nd gear. However this does not explain why the car holds in 2nd and not 1st.

The torque multiplication that takes place in the torque converter varies with engine speed. Engines produce less torque at idle than they do higher up the rev range. When you switch the tranny into W, the ecu may increase the engine rpm to compensate for the extra effort that will be required to move the car off from stationary becasue you will be pulling off in 2nd gear. This extra rpm will mean there is more torque being 'fed' into the torque converter so there will be more torque from the output of the torque converter. This may over compensate for the difference between the torque required to move the car due to the different gear ratios between 1st and 2nd.

Does the engine rpm vary when changing between S and W?

I had an auto Vauxhall Senator 3.0i 24v beast which would not hold on inclines in D, but my mums auto Vauxhall Carlton 2.0i would hold on inclines in D even with a caravan hooked on the back! My Sennie used to idle very low, about 600 rpm so there was not much torque being generated by the engine for the torque converter and gearbox to multiply to hold the car stationary on inclines. O.k. so the Sennie was about 300kg heaveir than the Carlton, but the lower engine rpms of the Sennie was not sufficient to 'hold' the car on inclines.

When stopped at lights when driving an auto, you sit with your foot on the footbrake. The brake components are now having to resist the torque from the engine being multiplied by all the components of the transmission. If car manufacturers let engines idle faster on auto cars, you would very quickly wear out the brakes trying to stop them and while sitting at lights etc.

If you are worried about your tranny, get it serviced by an Automatic Transmission Specialist. I believe Merc trannys are like BMW, 'sealed for life' which I personally don't believe, I would get your tranny serviced every 30,000 to 50,000 miles.

Andrew

 

[television]

When in "W" the car always starts off in second gear therefore less likely to hold station on an incline, no fault completely normal

We have had this question before, and as said above, normal, Some do,some dont

My last SL did,my new one does not, am I going to look for a fault = no

Malcolm

 

[eric242340]

We have had this question before, and as said above, normal, Some do,some dont

My last SL did,my new one does not, am I going to look for a fault = no

Malcolm

It is, indeed perfectly normal, it all depends on the EGS programme. EGS/EGAS is the control unit for the transmission. It controls the transmission and not the transmission control it. These programmes are, from time to time, modified by Benz depending on what feedback Benz are getting on a particular transmission build number and date. Incidentaly I notice people keep saying ECU, this is the Engine Contol Unit and not to be mixed up with the Transmission control unit. They are two different units, although they are interlinked on the CAN - Control Area Network.

 

[television]

It is, indeed perfectly normal, it all depends on the EGS programme. EGS/EGAS is the control unit for the transmission. It controls the transmission and not the transmission control it. These programmes are, from time to time, modified by Benz depending on what feedback Benz are getting on a particular transmission build number and date. Incidentaly I notice people keep saying ECU, this is the Engine Contol Unit and not to be mixed up with the Transmission control unit. They are two different units, although they are interlinked on the CAN - Control Area Network.

I do not think that anyone here gets the ECU's mixed up as we only ever refer to a gearbox ECU or engine ECU.

Re the CAN bus, these ECU's are linked to every other part of the car and the CAN bus has nothing to do with the control of these units.

The engine and gearbox ECU's do talk to each other,but not via the CAN bus.

How can you make post like it eric. Malcolm

 

[eric242340]

I do not think that anyone here gets the ECU's mixed up as we only ever refer to a gearbox ECU or engine ECU.

Re the CAN bus, these ECU's are linked to every other part of the car and the CAN bus has nothing to do with the control of these units.

The engine and gearbox ECU's do talk to each other,but not via the CAN bus.

How can you make post like it eric. Malcolm

MALCOLM, how can you make a statement like this. The CAN (Control Area Network) is the wiring loom, and through this all the signals are sent. The CAN bus has everything to do with all these modules/relays/sensors/control units. If you have no CAN bus you have no connections. You are supposed to be an expert (how can people trust you, when you quote from manuals and dont understand the CAN bus?)

 

[television]

MALCOLM, how can you make a statement like this. The CAN (Control Area Network) is the wiring loom, and through this all the signals are sent. The CAN bus has everything to do with all these modules/relays/sensors/control units. If you have no CAN bus you have no connections. You are supposed to be an expert (how can people trust you, when you quote from manuals and dont understand the CAN bus?)

Eric do us a favour and go away and learn what type signals are used in the CAN bus before you make yourself look even more stupid.

The guy at the start of this thread did not have a problem, you are the only problem in the thread.

I am not an expert and I have never pretended to be one, I just do my best in helping some people here with their problems in the most simple way that I can.

Re quotes from manuals like on the 202 fan, as there are 12 different 202s I would rather use a manual to get the exact fault, then no one complains.

You claim to be a big MB service outlet yet you have only had WIS for a few weeks, you never use info from STAR as you do not have that either

When forum members tell me to go away I will so, go and read up a little on the CAN bus.

Malcolm

 

[OmniCognateNeutronRangler]

I just tried the W/S thing on my drive and with the box set to W it was like having the handbrake on, no roll at all (even though you would normally need crampons to get up my drive). As I said way back at the begining of the thread, with it on S it would roll backwards even on the flattest piece of land.

 

[television]

I just tried the W/S thing on my drive and with the box set to W it was like having the handbrake on, no roll at all (even though you would normally need crampons to get up my drive). As I said way back at the begining of the thread, with it on S it would roll backwards even on the flattest piece of land.

My SL is doing the same,just tried it, thats handy to know.

Malcolm