What is the best speed (in Km/h) for changing into the 2nd, 3rd and 4th gear on a 4 speed manual gearbox Mercedes W123 with a 3005cmc diesel engine (617.912)?

I'm asking because I find the speedometer markings totally unhelpful (I rarely drive past 70Km/h in the 3rd gear for example). Does anyone have any recommandations based on his experience about this issue?

Just sound it out. You can tell when the engine is getting near its limit because it goes like "WWWWAAAAAAAAAAAAAAHHHHHHH"

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1982 240D.
My name is Michael, and I am an 18 year old binge-drinkin', cigar-smokin', novel-writin', all around unsavory and unnattractive guy. I tell long-winded stories, and I only shave once a week, although I've had to do it every day since I was 16.

Puttering around town, shouldnt be to hard to sound it out... if you feel your winding it up real tight, shift... I dont know theres ever a "perfect" speed to shift in ANYthing

Yeah, sound it out

~Nate

Speaking of "WWAAAAHHH," my 240 sounds like a freight train when it's travelling at speeds above 70 miles per hour.

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1982 240D.
My name is Michael, and I am an 18 year old binge-drinkin', cigar-smokin', novel-writin', all around unsavory and unnattractive guy. I tell long-winded stories, and I only shave once a week, although I've had to do it every day since I was 16.

I have a 220d 615.912, which also has the "I" "II" "III" "IV" on the speedometer as it doesn't have a tach either. I believe they're just indicators of red-line or near red-line rpm's in each respective gear and are not indicators of when you should shift. Generally, you don't want to shift until you know you have some torque available in the next higher gear; when entering a freeway where you need some acceleration, you'd wind the engine a little tighter. Neither do you want to shift at too low an rpm and lug the engine, that's bad for building carbon up. It's mostly an experience sort of thing and you get the feel of it after a while.

The problem is that I don't want to "whaaa" my engine too much - I got it into mint condition and this is how I want to keep it so I really need to put some "method" into my gearshifting strategy.

Now I'm ending up either overdoing it or getting into the lag area and this rear axle transmission is not as forgiving as my VW Golf front trasmission was. Any suggestions on how I can keep this engine working at it's best?

You do realize that by not winding it up occasionally, your being hard on it... It causes carbon deposits, and if you never rev the engine, your not gonna find problems untill the part fails... Verses when you know what it should do, and can tell when theres a part failing (funny noises)

Have you ever heard of an italian tune up? It's been helping me pull mine out of storge, combined with diesel purge (EXELENT STUFF!!!)

Read this http://dieselgiant.com/injectorcleaning.htm to understand how to do a diesel purge, because if you contine to "baby" your car, youll be needing to do this (and its really not hard)

Can I have your transmission? I'll trade you transmissions, so you wont have to shift

If your really intune with your car, you should eventually figure out where it WANTS to shift, and you should shift at that special range unless conditions are adverse or whatever... Also PLEASE dont ride the clutch, I get aggravated when I jump in a car and its got a burnt clutch... makes driving stick even more fun when you cant use the clutch between gears...
And one clutch saved is worth what I've said

So what kind of car do you have? its a 123 chassis, but you didnt specify year or model

thanks alot
~Nate

My W123 is a '79 300TD Estate with a 3005cmc 617.912 Diesel Engine.

I've heard about italiantunning but I'm not such a big fun of it - I guess it works better for a gas powered Ferrari than a Mercedes-Benz Diesel. Until now the best bet was good diesel fuel and, once in a while, some ATF dropped in 10-15l of fuel.

I need to know the best speeds to shift up or down because sometimes it's easier to look at my speedometer than hear the engine, especially during citydriving

You don't want to hear the engine vibrate ("buzz") when you step on the fuel -- that is lugging. On level ground, in leisurely mode, shifting just after "10s" will work --- 10, 20, 30 --- and downshift if you slow too much to be above those speeds. In other words, only drive in 4th over 30, in 3rd only over 20, in 2nd only over 10. These are minimums, feel free to exceed by 10, especially in 2nd & 3rd ---- and, obviously, 4th.

Want your clutch to last? Learn to slip it as little as possible: use minimum fuel for the situation when starting from rest; hit the pedal AFTER the clutch is fully engaged (the stump puller Mercedes first gear makes this easy to learn). In all gears except first, engage the clutch fully before pressing the fuel pedal at all. This eliminates most of the wear from the clutch discs -- it's how smart truckers drive -- and can be done smoothly, with practice. Hit the fuel pedal immediately after engaging the clutch ... Do not use the tranny to slow down -- brakes are much cheaper & easier to replace than clutches.

I drive just like you do. 10, 20, 30mph shifts and that works just fine on level ground. There are some steep hills around here so the shift points are more or less determined by engine vibration and pitch.

I do downshift sometimes but you do have to give the engine a good stab at the throttle to match the revs. The downshifts are about as seamless as it gets for an engine with such tall gearing and all that driveline slack

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1974 240D 3.0L 4(M) - 250K -OM617.910 + 300D FW + Rajay turbo power!
1977 6.9 3(A) - 84k

Never did figure out why they didn't put a tach on all the manually shifted cars....... and then they put a tach in my automatic 300D. Go figure.

Without a tach, I would tend to run it up to about what sounds comfortable and then shift. If you think it might be lugging in the new gear, run it a little higher next time. Most all of these MB engines, gas or diesel, are intended to wind up pretty well. (My wife's 280SL sounds as if it is wound tight at 75 in top gear, but it still has a lot of rpms left.) You stand a better chance of hurting the engine lugging it than by winding it up too tight (within reason, of course).

just my $.02,
Wes

The markings on the speedometer "I", "II", "III", etc., represent the maximum vehicle speeds in the specified gears, i.e., at which speeds the engine will be at redline. If you do not have a tachometer, then those help you figure out where you are relative to the redline, in that gear.

Those markings serve another purpose however, even if you have a tachometer. They represent the vehicle speeds below which it is safe to DOWNSHIFT to that gear. So if you are coming into an offramp from a higher gear and braking, when the needle passes the "III", it means it is safe to downshift to 3rd gear, as you are sure it will be below redline. You might need to "double-clutch" and blip the throttle however, to rev-match the engine to vehicle speed, for a smooth downshift.

On my 5spd manual 190e2.6, I use both the tachometer and engine sound as guides for upshifting and downshifting. I really get some satisfaction out of pulling out smooth upshifts and downshifts in my car, since the clutch in my car is not easily modulated, and the shift action is notchy. This is getting to be a lost art ...

Now to heel-and-toe downshifting ...

Thank you for all your helpful replies. I think we got this sorted out. Now's time to get some more practice Thank you again for the clutch tip, I think really needed that one.

The only problem left is downshifting speeds but, most of the time, I let the car "glide" to the next stop rather than downshifting all the way to the 2nd. By the way, do you know what can happen to a lugged engine beside carbon buildup (regarding injectors, compression, valves and such)?

According the people in the know around hear, an Italian tune up is a good think for our Diesels

__________________
Jason Green
1977 240D AUTOMATIC the Beast
1974 Super Beetle



Suppose you were an idiot. And suppose you were a member of Congress. But I repeat myself.
- Mark Twain, a Biography

By the way, how is it best to do an italian tuning: on the highway or with the car stopped (in neutral), engine warm?