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Discussion Starter #1
I own a 1972 220d, with the w115 chassis and stock diesel engine.
As far as I can tell, everything in the car is stock (the guy I picked it up from prided himself on that bit). The only thing I don't absolutely love about this car is that it's a little on the slow side. I know it's old, and a diesel, and (i'm sure) really quite heavy, but it has a top speed right now of about 76, without pushing the engine too hard.

My questions are thus:
1. Is it possible to change out the stock 4-speed transmission for a 5-speed one, and keep the first four gears the same? Essentially, would adding a fifth gear to the transmission mean I would be able to reach higher speeds?
2. The acceleration is slow. Would turbocharging or supercharging the motor make any difference with the acceleration and top speed? Also, is this a feasible modification?

I'm not trying to turn it into some of racing car or anything like that, it's just that I live just outside a large city and spend a lot of time either on the highway, or in the center of the city. I'm having trouble keeping up with a lot of the traffic on the freeways around where I live, and am worried about not having the acceleration speed I would need if I ever needed to quickly execute a left turn onto a busy road.
 

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1965 220S, 1999 Volvo V70 (wagon), 2006 Ford Crown Vic Police Interceptor, 72 350SL 4 Speed
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That's right, slow is it's middle name. You can always swap in a 5 cyl turbo diesel engine if you want.
 

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Discussion Starter #3
That's right, slow is it's middle name. You can always swap in a 5 cyl turbo diesel engine if you want.
That'd be ideal, but I'm strapped for cash.
Would either changing the transmission or turbocharging it work?
 

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2001 Volvo V40
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With some difficulty you can put in a five-speed transmission of the W123. Those transmissions are rare, even more so in the USA. The fifth gear is an overdrive, but reaching higher speeds is unlikely or will take a long time because of the low power of the 220D (60 hp according to DIN).

It should be able to do 85 mph if it is a manual. See if the throttle plate reaches its stop when you press the accelerator. Check if the engine reaches the maximum speeds in the gears (indicated by marks on the speedometer). If not, adjust the stop of the throttle.

Do basic maintenance: fuel filter change and valve adjustment.

Turbocharging is no option, the engine cannot take significant turbocharging.
 

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Discussion Starter #5
With some difficulty you can put in a five-speed transmission of the W123. Those transmissions are rare, even more so in the USA. The fifth gear is an overdrive, but reaching higher speeds is unlikely or will take a long time because of the low power of the 220D (60 hp according to DIN).

It should be able to do 85 mph if it is a manual. See if the throttle plate reaches its stop when you press the accelerator. Check if the engine reaches the maximum speeds in the gears (indicated by marks on the speedometer). If not, adjust the stop of the throttle.

Do basic maintenance: fuel filter change and valve adjustment.

Turbocharging is no option, the engine cannot take significant turbocharging.
Part of it is that I'm not sure how far I can push the motor. It doesn't have a tachometer, just tics on the speedometer that tell you when to shift. So I have no gauge of how high it'll rev.
Any suggestions on how to figure this out?
The speedometer was mis-calibrated and is off by seven mph, and i'm not sure if the same goes for the tic marks, or if I should go by how they are now. I can go a bit past the marks without shifting, but I don't know if this will damage the motor.
 

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Part of it is that I'm not sure how far I can push the motor. It doesn't have a tachometer, just tics on the speedometer that tell you when to shift. So I have no gauge of how high it'll rev.
Any suggestions on how to figure this out?
The speedometer was mis-calibrated and is off by seven mph, and i'm not sure if the same goes for the tic marks, or if I should go by how they are now. I can go a bit past the marks without shifting, but I don't know if this will damage the motor.
First check if the throttle in the intake manifold reaches the full stop when you press the accelerator pedal fully. Use an (charming) assistant or put something heavy on the pedal. Do this with the engine off and don't forget to take the heavy object away before starting the engine.

If the throttle doesn't reach full stop, check if there is something under the pedal (like the carpet), otherwise you will need to adjust the pedal. There is a adjustment possibility on the firewall (difficult to see or loosen the bolt. Adjustment is done by loosening the bolt, pulling pedal up and tightening the bolt whilst the pedal is held in the up position, you'll need an assistant).

If the throttle does reach full stop, have a drive until the engine is nice and warm (15 miles or so), so that the engine oil has its full lubricating quality. Make sure that the oil is not old. Then test the full load speed. This is done in second gear and third gear, so when in second or third gear, fully press the accelerator pedal and see where the car stops accelerating. It must be around the second or third gear mark (two or three ticks) on the speedometer. (the marks are not shifting points, but maximum speeds for every gear, one tick for first gear, two ticks for second gear and so on) In your case around 7 miles above the mark, because the speedometer is not correct. The engine will make a lot of noise, it will rev at around 4300-4400 rpm at that point. If the engine cannot reach that speed, adjust the full stop on the throttle (it has an adjusting screw with a locking nut) until it does reach that speed. The engine can handle this, as long as it is warm (not only the coolant, but also the engine oil)

The marks on the speedometer only work if the tires are stock size and the differential is original. Is the speedometer mis-calibration always 7 mph? or does it increase with increasing speed?

Again: proper maintenance is vital, for performance: checking/adjusting valve clearance, fuel filters and oil change in the air filter and injection pump.
 

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Discussion Starter #7
First check if the throttle in the intake manifold reaches the full stop when you press the accelerator pedal fully. Use an (charming) assistant or put something heavy on the pedal. Do this with the engine off and don't forget to take the heavy object away before starting the engine.

If the throttle doesn't reach full stop, check if there is something under the pedal (like the carpet), otherwise you will need to adjust the pedal. There is a adjustment possibility on the firewall (difficult to see or loosen the bolt. Adjustment is done by loosening the bolt, pulling pedal up and tightening the bolt whilst the pedal is held in the up position, you'll need an assistant).

If the throttle does reach full stop, have a drive until the engine is nice and warm (15 miles or so), so that the engine oil has its full lubricating quality. Make sure that the oil is not old. Then test the full load speed. This is done in second gear and third gear, so when in second or third gear, fully press the accelerator pedal and see where the car stops accelerating. It must be around the second or third gear mark (two or three ticks) on the speedometer. (the marks are not shifting points, but maximum speeds for every gear, one tick for first gear, two ticks for second gear and so on) In your case around 7 miles above the mark, because the speedometer is not correct. The engine will make a lot of noise, it will rev at around 4300-4400 rpm at that point. If the engine cannot reach that speed, adjust the full stop on the throttle (it has an adjusting screw with a locking nut) until it does reach that speed. The engine can handle this, as long as it is warm (not only the coolant, but also the engine oil)

The marks on the speedometer only work if the tires are stock size and the differential is original. Is the speedometer mis-calibration always 7 mph? or does it increase with increasing speed?

Again: proper maintenance is vital, for performance: checking/adjusting valve clearance, fuel filters and oil change in the air filter and injection pump.
I didn't know those were speed ranges... that system makes a bit more sense now.
As far as I know, the differential and wheels are stock, with standard size Michelin tires.
And the speedometer is always off by seven: If I'm going 20, it reads 27, and if i'm going 70, it reads 77. That's part of why I've been stopping at 75; The top gear's tic mark is around 83, so that's where the needle is when i'm going 75.
Because the gauge is off by a consistent amount, is is easily fixable? or should I just mentally shift the tic marks, like what I've been doing with the speed?
also, would it be an easy task to install a tachometer? it might be nice to be able to keep an eye on my RPM.
 

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I didn't know those were speed ranges... that system makes a bit more sense now.
As far as I know, the differential and wheels are stock, with standard size Michelin tires.
And the speedometer is always off by seven: If I'm going 20, it reads 27, and if i'm going 70, it reads 77. That's part of why I've been stopping at 75; The top gear's tic mark is around 83, so that's where the needle is when i'm going 75.
Because the gauge is off by a consistent amount, is is easily fixable? or should I just mentally shift the tic marks, like what I've been doing with the speed?
also, would it be an easy task to install a tachometer? it might be nice to be able to keep an eye on my RPM.
I've read somewhere that there is an adjusting screw on the speedometer, but I cannot help you with the details. If you do some searching on the internet, you may find the article I've read.

For the test you should mentally shift the tic marks.

The W115 was never fitted with a tachometer, Mercedes-Benz deemed it not necessary because of the tic marks on the speedometer and because the governor of the pump prevented overspeeding. Also the engine will make so much noise at the highest shift marks, most people tend to shift earlier.

There are tachometers (of other models) which fit into the clock spot, but the signal might be a problem. If the tachometer is mechanical, you must make a connection to the top of the oil pump. If the tachometer was originally made for connection to the ignition system, you must make a connection to the W terminal of the alternator and use a converter to convert the signal.

Aftermarket tachometers might be easier to install and find. They can take the signal from the pressure waves/ticks in the injection lines or the W terminal of the alternator. If your alternator doesn't have a W terminal, you can make one, but the alternator has to come off and has to be opened.
 

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Discussion Starter #9
I've read somewhere that there is an adjusting screw on the speedometer, but I cannot help you with the details. If you do some searching on the internet, you may find the article I've read.

For the test you should mentally shift the tic marks.

The W115 was never fitted with a tachometer, Mercedes-Benz deemed it not necessary because of the tic marks on the speedometer and because the governor of the pump prevented overspeeding. Also the engine will make so much noise at the highest shift marks, most people tend to shift earlier.

There are tachometers (of other models) which fit into the clock spot, but the signal might be a problem. If the tachometer is mechanical, you must make a connection to the top of the oil pump. If the tachometer was originally made for connection to the ignition system, you must make a connection to the W terminal of the alternator and use a converter to convert the signal.

Aftermarket tachometers might be easier to install and find. They can take the signal from the pressure waves/ticks in the injection lines or the W terminal of the alternator. If your alternator doesn't have a W terminal, you can make one, but the alternator has to come off and has to be opened.
I'll look around for that article.
Mentally shifting the marks is no problem. I'm just worried about over-revving the engine and damaging something. I don't know what a pump governor is... Does that keep the rpm from going too high, or is that something else?
 

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An engine needs a device to start it, keep it idling, prevent it from overspeeding and turn it off. On gasoline engines this is done by the throttle valve in the intake manifold. The position of the throttle is determined by the accelerator pedal and the position of the throttle determines the amount of fuel added (so that the amount of fuel is exactly enough for the amount of air). Add some cold-start device (extra fuel injected) and a by-pass for the idle and you can control the engine speed.

On diesel engines it works slightly different. Only air is sucked in the cylinders and when the air is compressed (and hot), diesel is injected. The amount of diesel determines engine speed. In order to prevent a runaway engine and to keep it idling, a governor is connected to the injection pump. It is called a governor, because it governs the engine speed. The governor determines the amount of diesel injected. Several types of governor have been invented over the years, Mercedes-Benz used so-called pneumatic governors from the 1930s to the late 1970s on their passenger diesel cars. It also has a throttle in the intake manifold, with a venturi on the bottom, so that a vacuum is created. You operate the throttle with the accelerator pedal. Vacuum is highest at idle when you don't press the pedal. If you press the pedal, vacuum is reduced. A vacuum line runs from the throttle to the injection pump governor. The variable vacuum created by the position of the throttle is used to control the amount of diesel injected.

Here you see a diagram of the throttle in the intake manifold:



You can see the venturi tube at the top (on your engine it is probably on the bottom). The second valve is to prevent the engine from running backward.

Here you see a diagram of the governor:



The tube is connected to nr. 12. The vacuum will pull on the membrane (nr. 10, the thick black line). The membrane is connected to the control rod (nr. 8) of the injection pump, thereby controlling the amount of diesel injected. If the vacuum is reduced, the spring (nr. 13) will push the membrane to the left, increasing the amount of diesel. At full load (wide open throttle) the control rod will come to a stop on the full load bolt (nr. 20). When the speed of the engine increases, the vacuum will increase again because of the venturi effect (a lot of air will be sucked into the engine at 4000 rpm, much more than at 1000 rpm). That vacuum will pull the membrane back from the full load bolt and at a certain point an equilibrium will be reached between the vacuum and the force of the spring, keeping the control rod in a certain position so that you cannot accelerate further. That speed must correspond with the tic marks on your speedometer. If not, the maximum opening of the throttle must be adjusted (more closed to reduce speed and more open to increase speed).

So the governor prevents the engine from overspeeding. Just make sure the engine is fully warm before testing it.
 

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Discussion Starter #11
okay that makes a lot more sense now. thank you.
if that system keeps the engine from turning too fast, could i put the car in neutral and slowly depress the accelerator until the engine note stops rising? that seems like it would give me a good guess as to where i need to shift...
 

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No, if you fully press the accelerator pedal with the transmission in neutral, the engine will rev to the highest speed unloaded, it wouldn't give you any indication on when to shift.

The tests I described are to determine whether the accelerator pedal fully opens the throttle and whether the throttle opens wide enough, because if not, the car will be slower than it should be.

I drive a similarly powered car (the 1980 200D, has the same horsepower but slightly lower torque) and in city driving I shift at around 2000-2500 rpm. That corresponds with the following shift points:

1 > 2 at 10 mph
2 > 3 at 20 mph
3 > 4 at 32 mph

When I'm accelerating to get onto the highway, I may shift at 50 mph from 3 > 4
 

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1981 240D, 1981 280e, 1982 240D, 1982 280SL, 1990 300SEL
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I know this post died along time ago but I was wondering how you would be able to tell if the throttle was opening enough? I have a 1981 five speed 240D but the odometer has been disconnected for a very long time. I'm having problems getting my car up to speed sometimes. I've checked all the obvious like the linkages and the fuel filters so I'm not sure those would be the problem. I've checked a lot of other things that might be causing the car to accelerate slower than usual but I haven't run across anything obvious...
 

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I know this post died along time ago but I was wondering how you would be able to tell if the throttle was opening enough? I have a 1981 five speed 240D but the odometer has been disconnected for a very long time. I'm having problems getting my car up to speed sometimes. I've checked all the obvious like the linkages and the fuel filters so I'm not sure those would be the problem. I've checked a lot of other things that might be causing the car to accelerate slower than usual but I haven't run across anything obvious...
The 1981 240D doesn't have a pneumatic governor, so there is no throttle. The 1982 240D does have a throttle for the EGR, but I don't think there is one on the 1981 model. If that is stuck, it can have an effect on performance. It is easily checked, there must be linkage from the valve cover to the intake manifold and the throttle is visible if you remove the air filter housing.

Have you checked the tank fuel filter? Checked all the fuel supply lines for possible air leaks?

The 1981 240D is a W123, that model has a specialised forum:
W123 E,CE,D,CD,TD,TE Class - Benzworld.org - Mercedes-Benz Discussion Forum
 
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