Hey everyone,

I'm the proud owner of a 1975 240D with a manual 4spd, I just have a question about shift points. On the speedometer (khr) there are three marking (I don't have the exact location by memory) I, II, III. What do these markings mean? Shift point for I seems very high, the engine sounds and feels like its about done pulling by 15kmh in first. Do the engines like being reved up like that?

What are people's experiences with the manual trans 240s? Should I be double clutching on downshifts?

The dots are the maximum speed that is safe to downshift without over-revving the engine, not when to upshift. You should upshift when the engine will have enough power/rpm to prevent lugging in the higher gear.

You should be using the brakes to slow down, not downshifting. It's far easier to replace a set of brake pads than to replace a clutch. For regular downshifting double clutching is unnecessary, that's why the transmission has synchros.

Double clutching won't hurt anything. Is your car crunching when you downshift? If it is in all gears you may be low on lube in the tranny.

If it is crunching only in second that is pretty normal as second wears more since it is used the most.

I usually don't downshift til the car is slowed down and the speed already matches the gears pretty well. Being an old timer I am conscience of wearing things out. If you let the rpms fall and only shift when you are ready to accelerate out of a turn or from a stop sign you will minimize wear on everything, including brakes clutch etc.

Ina 240 with a stick the brakes will last pretty much forever if you just let off the gas and allow the motor to slow the car down, mostly.

Tom W

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

From what I know or understand, double clutching is only needed for double diaphram clutch systems. I think Alpha Romero and Lamborginni use this type of clutch, at least in th '80s. With this type of clutch, when you have the clutch depressed, the clutch material is wearing. So it helps to double clutch, or let the clutch out between disengage and (re)engaging the clutch. So basically not needed in a MB 240D.
Tom

Double clutching was needed with cars or trucks that lack synchromesh. Worn synchromesh might warrent use of it from time to time too.

I don't have any knowledge of any dual disc clutch systems which if operating do not fully disengage when the pedal is depressed.

Tom W

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The PO of my car double-clutched to go from 1-2 due to a worn synchro.

I tried it, but I never could master it. (May have something to do with learning to drive after WWII )

Instead, I pause slightly in neutral then I can kind of 'feel' when she's ready for second gear. I do the same thing on the downshift and rarely grind (anymore )

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

True, double clutching is not required on a synchronized manual but I can tell you from experience that it will extend the life of your synchros. When you shift without double clutching, the little "thump" you may feel as it goes into gear is the synchro working. The synchro is like a little clutch and the harder it works, the quicker it will wear out.

If I dug around, I could probably find the synchro tabs from a T5 I rebuilt and post pics of them to show what happens when they wear out. I probably threw them out though...

It's also possible to double clutch on both the up and down shift but there's a slightly different technique for each.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Yep, its slow shifting trans by nature. Think of it as walking through the gears. And you lose alot of rpm's on every upshift, so topping the gears up around speedo shift points aint bad idea. You will never find narrower power band engine that keeps you busier paddling through gears than 240D. Rarely have time enough to light a cigarette between shifting gears. And personally i was downshifting all the time when approaching red lights and stop signs. Nevermind highway exit ramps in ice'n snow. I just aint somebody who glides up to red lights in 4th, never worried about wearing out the clutch. Would sometimes skip 3rd and drop direct from 4th into 2nd when slowing down fast from 60mph to about 30. Helacious little hot-rods these cars are.

Double clutch downshift is for straight cut gears on trucks where you can also float em without touching the clutch going into next higher gear.

True. I usually upshift at the dots until I get up to the speed I want to go-unless I'm in traffic.

As far as cars go, I'd say you're right. OTOH, I spent a good bit of time hauling rock with an old International with a 350 Cummins and an 8 speed. That thing kept me shifting A LOT. Peak power was at 2100 and I tried to keep the rpms over 1200 to keep from lugging.

Very true. On said International I only used the clutch when downshifting or starting from a stop. It's possible, but not reccommended, to float gears on a synchronized tranny. I used to do this sometimes on my Suzuki Samurai, but the 240 is too tight for that.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.

This is one thing I disagree with the dog on.....the torque curve on a 240 is wide and imho revving them to the redline does not really result in much additional acceleration but a lot more noise.

Tom W

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Here's a pretty good web site with some video and animation of how a transmission works. It has a few errors which may cause confusion but it's generally correct. Pretty cool to see the animation with all the gears in motion.

http://auto.howstuffworks.com/transmission.htm

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250