W202 5 spd auto gearbox 1st gear problem?

[philnewmerc]

good point buggerlugs

Thanks for pointing all that out buggerlugs, there is a lot more to it than meets the eye. I completely take your point about all that wear debris and the torq conv shear is an interesting one - not sure myself. I still suggest that its a much less harsh environ than the engine.

I'm still puzzled why this problem of cold (too thick?) fluid only seems to cause trouble on my car.

Rovinghawk- I was just being facetious becasue you took a dislike to my questioning style. I didn't mean to be offensive, just silly, apologies to you.

I know myself that after having spent x pounds on anything it MUST be phychologically more likely that you think the car runs better - my car always goes faster when its polished - lower drag coef I think!

 

[Rovinghawk]

I'm still puzzled why this problem of cold (too thick?) fluid only seems to cause trouble on my car.

Temperatures slightly below zero & possible water contamination in your ATF? ie Tiny amounts of ice- just enough to cause problems?

RH

 

[Buggerlugs]

and the torq conv shear is an interesting one - not sure myself. I still suggest that its a much less harsh environ than the engine.

It'd be interesting to find out........Although on balance I'd agree that the engine probaly "wins" in terms of general oil abuse.

If you want to look further, consider this, the torque converter basically relies on fluid shearing to transmit crank power to the gearbox input shaft in a smooth and progressive fashion, especially during initial take off, consequently there is substantial localised heat build up in the TC due to the shearing effect, especially under heavy load conditions, for this reason the TC fluid is exhausted directly into the trans cooling circuit BEFORE it returns to the main gearbox, basically the cooling circuit exists to dissipate TC generated heat.

I know it's not something to try at home boys and girls, but try joining the cooler pipes together, put the car in D or R, wedge the wheels, leave the engine idling and walk away, return in about 40 mins and marvel at the glowing converter and the billowing plumes of boiling oil smoke from the gearbox breather........Oooh errrr missus

 

[Dieselman]

basically the cooling circuit exists to dissipate TC generated heat.

Isn't it more that the radiator heat exchanger is also there to quickly warm the ATF before it enters the gearbox then keep it at that level.
Obviously the TC doesn't benefit from warm fluid so it passes through there first.

Do you think fitting an auxillary heat exchanger before the rad is a good idea given that heat is what kills ATF and boxes.?

 

[philnewmerc]

torque converter basically relies on fluid shearing to transmit crank power to the gearbox input shaft
[/quote]

Let me say I'm no expert before anyone shoots me... but are you sure this is the case? Isn't it more likely that the fluid from one impeller is thrown at the other and the simple act of impact produces a thrust on the second impeller (or whatever they're called). Shearing is consequential but not the actual drive mechanism. OK now shoot me.

Today with warmer weather I could detect perhaps v slight slip/drag in 1st then all is well after 2 min driving. As I understand it, autos change gear by applying brakes on planetary gear sets, so if the fluid was v thick when v cold this could affect the act of braking and therefore produce this slip phenomenon???

 

[Smiley]

I have changed the fluid on a number of mercs over the years. If it is changed every 36k miles like my w124 then it never loses its clear pink red colour and I notice no difference in the shifts when it is changed - the car has now done 200k miles and the box shifts the same as when it was new. Mind you it has had 5 fluid changes in the meantime.
Other mercs that I have bought second hand have benefitted from a fluid change - I noticed the difference when the fluid on the dip stick had lost its clear red colour and had changed to look like engine oil - obviously had not been changed for a while.
SO my advice would be check the dipstick and if it is not a clear red then get the fluid and filter changed. If it is clear red may still be worth doing as a preventative but up to you.

 

[Smiley]

Were you bullied at school? eg For name-calling?

With lots of folks saying don't change the fluid?

So why start this topic if everything's ok?

Ever heard of anyone changing hydraulic fluid? I've never heard of 'filled for life' brakes.

Who should presumably have a clue.........

Why not ring up that auto box place again and have a pop at them for telling you porkies?

RH

Whats the point of this post? It does not seem very helpful. I think the OP had a genuine concern / question unless I have missed something.

 

[sweeper]

Going back to the original query, a small amount of "slip" is normal, these five speed electronic boxes have a two stage torque conversion, at most other times whilst driving the box will be in the partially locked state making changes more positive and with less slip, the ecu decides at what point and which gear to give more or less torque conversion. I would recommend a fluid change, possibly the fluid has been topped up or replaced previously with the wrong type of fluid? or it may just be contaminated (moisture from condensation from short journeys for example) also you may experience an increase in slip if driving in W mode, where the car starts off in second gear. I changed the fluid in mine at 130k, just for the peace of mind, i have to say the oil looked perfect, also note this oil comes out slightly yellowish colour and this is normal, it is a job for experienced diy mechanics, greatly eased by having ramps of some sort, no drain plug on torque converter means draining down and refilling several times, if you change filter as well there is a likely hood of seized bolts holding the pan, this can make the removal of the clamps difficult as the bolt will seize in these and the haed will break off, having a new set of bolts and clamps at hand will help (coper grease trhe shanks on replacement to prevent happening again, a small drop of low strength thread loc on the bolts will stop them coming loose) Only use Mercedes fluid (alteratives are available, but rare and more expensive. One thing i did notice was a deteriation in change quality after the oil change, this i put down to having battery disconnected and adaptation figures being lost from the ecu, this took some time to correct itself, but changes have been fine since and now has 173k on the clock.

 

[Shaun's C280]

Definatly CHANGE THE ATF!

If your car has a ATF dipstick take it out and check the level

Where is the dipstick located on W202 4 speed?

 

[philnewmerc]

Hi Sweeper, Thanks for that info. Are you saying my 1999 c class doesn't have a drain plug on the TC? If so then can a garage be trusted to go to the trouble of running fluid through it i wonder? When this 1st gear problem occurs it def feels like driving with the brakes on - so maybe one or other of the brake bands (clutches I think they call them) that act on the planetary gears is slipping?

Many thanks for all your replies. Merry xmas.

 

[sweeper]

Hi Sweeper, Thanks for that info. Are you saying my 1999 c class doesn't have a drain plug on the TC? If so then can a garage be trusted to go to the trouble of running fluid through it i wonder? When this 1st gear problem occurs it def feels like driving with the brakes on - so maybe one or other of the brake bands (clutches I think they call them) that act on the planetary gears is slipping?

Many thanks for all your replies. Merry xmas.

It may not have a drain plug, i believe some did and some didn't, can a garage be trusted? depends on the garage!
I'm not an expert, but brake bands and planetary gears i think are a thing of the past and multi plate clutches are in, are your brakes binding? How bad is the slip? I would definately get the fluid changed and see if there is an improvement, if not you may have to way up the cost of a gearbox repair or replacement or just living with it.