Hydraulic Transmission?

[300SDude]

I heard or read something recently about Mercedes having a hydraulic transmission. Is the transmission in my '79 300SD hydraulic? and if it is, do I use hydraulic fluid in it instead of ATF?

I am wondering because recently the tranny seems to have lost power. I have to have it floored and in "S" (what the hell does that mean anyway?) selection of the selector and it still only tops-out about 35mph.

Any thoughts on why it's doing this?

Thanks,
300SDude

[BWalker82]

All transmissions are hydraulic (except CVT's), and all transmission fluid is, effectively, hydraulic fluid.

I believe our 300SD's use standard ATF Fluid.

[TJ 450]

BWalker82's post is correct, however I'm sure he means all standard automatic transmissions on cars are hydraulic in basic operation.

ATF is absolutely required, nothing else will suffice.

"S" if for slope, and it forces the tranny to use first, then second speeds only. Not to be so much of an alarmist, but if you have to resort to these sorts of measures, then you need to determine the cause as soon as possible. Engine/transmission damage may have, or will occur otherwise.

First thing to check is the fluid level, with the engine running, at 80 degrees C or equivalent in Fahrenheight, it must be within the two marks on the dipstick, preferably half way between.

I hope you do indeed find the cause of the problem soon.

Tim

[BWalker82]

Yes, forgive my ambiguity.  Manual's use hydraulic fluid (gear oil) for cooling/lubrication purposes, like differentials.  It's why manual gearboxes (especially older) are sometimes harder to engage in cold weather... until the fluid has warmed up at least.

Fundamentally the idea is the same for auto 'slushboxes' except the fluid goes a step further to act as a coupling in the torque converter.  If memory serves it also reacts to different solenoids inputs, as to which channel it flows through inside the gearbox, to aid the spooling of gears during shifts.

Do get that checked out though.  You don't wanna ruin the powertrain.

[1980sdga]

Well, the torque converter is basically your clutch with the pump right behind it. The pump pressurizes fluid which travels through a maze-like valve body which channels the fluid around engaging/disengaging different packs of clutch discs which engage/disengage different gear sets. Mostly planetary gear sets on the autos I've rebuilt. (GM TH350/400's) 

I've rebuilt several and there are still a BUNCH of things about them I don't understand 

[Arockz1]

When was the last time the (2) Fuel Filters were changed? Just a thought...

[300SDude]

Thanks everyone for the input! It is greatly appreciated.

This is my first Mercedes (I have wanted one forever), so it does have a few little oddities that I don't find in out American cars, lol.

Actually, I have only really driven the car about 600 miles since we got it in August.

It spent the winter at our mechanics who installed a greasecar kit in it and then it went to the upholsterer's and now it is in the paint shop. Hopefully I will get to pick it up within this next week. 

I'll check the tranny fluid once it is warmed up. If I remember correctly, the old man that I bought it from said he had just put some fluid in it, but he hadn't driven it for a while before I bought it.

For all the money we have put into this car since August, I would hate to have to have the tranny replaced or something like that.

Thanks Again!

300SDude

[BWalker82]

I found this link online.  I think we have the 722.1 or 722.2 version, but this should be some direction.

Link

[peterq]

I think the original question may arise from Mercedes' use of a hydraulic coupling in their earlier automatics, rather than a torque convertor. I don't think the hydraulioc coupling made it into any V8 W116, not sure about the six and the diesel.

[koan]

Transmission fluid has to lubricate the gears but not to lubricate too well which would prevent bands and clutches doing their job, it also needs to work has a coolant and as a coupling fluid.

I think hydraulic coupling refers to the device used before torque converters came along, a fluid coupling with out the third component that multiplies torque.

koan

[300SDude]

I think the original question may arise from Mercedes' use of a hydraulic coupling in their earlier automatics, rather than a torque convertor. I don't think the hydraulioc coupling made it into any V8 W116, not sure about the six and the diesel.

It is 5 cyl. diesel. That was one of the reasons we bought it.

[jbrasile]

The last car to use a fluid coupling was the very early 350SL  with the 4 speed auto, from then on all MB's use a torque converter on their 3 and 4 speed boxes. There is one exception which is the W100 (600) that stayed with its original 6.3 engine and 4 speed fluid coupling transmission till the end of production in 1981.

Tks,

Joe