adding a tach to a 240D (standard tranny)
 

im about reddy to buy a 83 240D with a stick and i would very much like to put a tach in there im wandering how that may be achieved. it has a leaky oil pressure gauge that need to be replaced so i wouldent be instaling a cluster just for a tach. but i also wanted to find out about an inductive pick-up tack and how thouse work as far as cost and instalation. thanks for you help.

Lets include 1980 240d's in this question... since I am interested also....

No help here on the tach but,
 

search this here forum on "oil, leak, gauge" You'll find out all about leaking oil pressure gauges.

ed by R Leo

Actrually, R Leo, I've never found a thread involving installing a tach in a 240D. I'll stand as third in line wanting to know how an OEM unit can be installed in place of the clock. Being a manual tranny, I like to be able to see where the engine is running,.

"I'll stand as third in line"

Put me down as 4th in line. Actually when I got my 5 spd someone mentioned that I should install the clock/tach but they weren't sure about the pick up. Seems it was mentioned that "it may or may not be there" Where? I will be following this thread;)

Me too. I was on the sf bay bridge this morning pushing about 95 mph ( seems like there is still more room to go on my 83 240d ) . I am just wondering what is the red line on 4th. The speedometer shows 1st dot at 24, 2nd dots at 39 and 3rd dots at 64, but what's 4th. Thanks...

Perhaps it is my being used to driving large diesels (I am a bus driver for the U of Toledo.. the best student job there is).. but wouldn't it just get to a point where it will not rev any more.. and still be safe? I know on the 8.2 Detroits and most of our 6V92s that they will sing along maxed out on their speed limiter, which is coincidentially also their rev limiter.
~D.J.~

Yup, MB diesels have rev limiters in them as well. The idea for the tach is to be able to see how hard the engine is working, and to be able to have a visual aid to keep that little engine in it's powerband. Personally, I still like tachs even in automatic tranny equipped cars. They can give you an early indication of tranny trouble that may not be immediately noticeable to the ear.

I once had an 86 Hyundai Excel. It had the ugly large analog clock in the cluster. I swapped it out for a tach (easy to do thanx to modular design), and it worked immediately. I wanted more guages, so I installed a digital set for oil pressure and battery voltage. It had a temp guage, so I modified one of the lines between the tranny and cooler and used the temp guage to monitor tranny temp. I like having a maximum number of guages in a car. It doesn't matter to me if the guage is necessary or not. More guages mean more info on the car's well being. Since I used to drive trucks, I got used to lots of info on the health of the truck, and inevitably look to get more than the designers thought of during the vehicles design. Being an MB, I won't put funky add-on's like those in, but a factory tach is icing on the cake for a manual tranny.

"MB diesels have rev limiters " ..... to a certain extent.... but of course we have the example of Larry Bible's engine going wild and Kapow.
One thing that helps diesels is the fact that valve overlap in the form which gas engines use to make more power is not possible with a diesel... this limits the speed at which reving can happen and helps top out the power before the top of the rpm limit is reached in most cases...this is the basis of the efficiency of a diesel....

Back to the tach question...I guess the big question here is what sort of signal does the tach on a 300D get? Is it a gear-driven signal generator, or a sensor, and what is the sensor reading (flywheel, injector pump, cam, etc)? Also, how does the signal get from the sensor to the tach?

IIRC, on pre '85 300D's, there's some sort of tach amp or something like that, but I really don't remember...

I'm guessing that a tach system from an OM617 could be adapted to fit the 616, but I'm unsure on what parts would be needed.

Just my thoughts on it :)

My 1983 240D came with the tach pickup, but no tach. I guess all '83's and later 240D's had the pickup. It is above the harmonic balancer and is an inductive pickup. It even has a wire that runs into the car, but I have not traced the wire yet. Theoretically, I think you could get the pickup (if not already equipped) tach, and amp out of a 300D and it would work.

Tach mod? Been there done that (long post)
 

Pre-85 W123 turbodiesels use a small amplifier module, the dreaded $70 VDO "RPM SENSOR" that fails when the contact pins get weak, it is a cylindrical plug-in that lives on the left fenderwell, near the relay box. I installed one when I had a turbo engine put in my '79 300TD. The engine has to provide the pulses to this module thru a shielded cable, easy to get from a wrecking yard, unless it was cut like many I have seen (probably when the engine was being held in by a nusiance black cable!)
A wrecking yard is a good place to find the socket and a good module if you are lucky, then you need to mount it on a bracket, that might be hard to get off the fenderwell as I believe they are welded on so I made my own out of sheet aluminum. (addendum - I understand the bracket can be ordered from Benz! I've no p/n sorry. Ask a dealer to search for it before you make one, it is a PITA to fabricate.)
Oh, yes, you need to find the plug that fits the back of tach meter on the instrument cluster. Lookout because they come in two varieties, a 2-pin connection in some diesels, three pins in others. Maybe the W116 is different I am not sure but I have had both and found that the two pin units work with my module and the three pin did not.
Attaching the sender on the crank vibration damper area in the 240D is going to be a challenge. I have no reference of experience with the 240D to give any guidance. I suggest one look at the 300D turbo first and visualize this and take a picture maybe.

I am not even certain how it works actually, I thought a large "notch" in the damper near the timing marks were the source of the pulses. Another poster said there is a small metal pin that needs to be on the pulley/crank damper. Whichever is the case, the 240D might need this pin before any effort to install a tach is successful. Anyhow, basically the magnetic field that accompanies a piece of iron gets interrupted as it passes by the pick-up coil. It operates similar to modern magnetic ignitions in gas engines, and is called a reluctor. The amplifier integrates the pulses from the pickup (sensor) into an analog current for display on the instument meter.
I replaced the large clock in my instrument cluster with a tach/clock from a later model 300D. It now looks (and works) like a turbo car from the factory. I had to supply 12 volts to the module, I never figured where MB gets that source of current. so I tapped into 12 Volts with a 1 amp fuse and fed the module directly, grounding the other pin on it.
An electrical whiz that has time to spend on this "challenge" will figure it out in no time. Just wire it up and it should work right off the bat!
Dieseldiehard
1971 220 (gas) 4-spd manual 104041
1979 300TD w/ ’85 turbo engine 289560
1983 300D 237490
1985 300TD 206150
1975 300D (looking for an engine)
1987 300D 250K newest addition

As has been mentioned earlier, the stock Benz tachs are driven by an inductive pickup. If this drive is not installed on an engine, however, and if an aftermarket tack is acceptable, one could intall an alternator driven tach. Every alternator is capable of driving a tach, although not all tachs have an easily accessible external terminal. A good alternator shop can make this modification.

Phil

'84 Euro 300D, no tach
'85 300D, working tach, suddenly dead clock

cool sounds like puting a tach in might not be such a hard task after all. but i have seen a inductive pick up digital tach. has any one given one a try? id like to know how those work out. on a diffrent note if all goes to plan i will have the car in front of my house by this thursday...

can i just tag along with this thread as i also want a tach.. but i have a 79 300TD (non-turbo)... i really dont know if it had one before or not.. and i dont know as of now if i have the tach amp needed.... i'll just sit in front of my pc for now. checking up on this thread to see how feasible and (cheap perhaps) this upgrade could be.. .tnx.:D

...and that rev limiter would have worked too if Larry had reassembled the IP shutoff correctlly.

If you use the existing tach pickup for a tachometer, you will have to disconnect it from the cruise control, if you have working cruise control.

Squid - just try driving the car as is for a while. With the dots on the speedometer to remind you where the redline is, a tach really isn't necessary.

I used to be a "tach fanatic", too, until I figured out those dots (the top end should be in the owner's manual). The dots won't lie as long as you keep the tire size original and keep the clutch from slipping - then you've got other issues to deal with. I actually went as far as setting a throttle stop with an adjustable strobe light and then test driving to the dots, and found that the dots work. The only time a tach would be usefull on these engines, in my opinion, is when setting the idle or high rpm limit. But then again you set the idle on these little engines by sound and how the engine pulls from a start, and the high rpm in the shop, where those adjustable strobe lights are nice.

yea i know what you mean about the dots but i still like to know what the engine is doing exactly. not just on acceleration but at cruzing speeds. but thanks for the info

"With the dots on the speedometer"

I have revaluated my desire for a tach after looking at whats involved :eek: in getting one, the dots will work for me in my 240Ds. I have spent lots of time running marine engines where you need a tack but I think I will pass on the tach for my cars.:)

Another observation regarding the dots. They also serve as a very good guide to the lowest engine speed per gear as well. Single dot is lowest speed in 3rd, 2 dots is lowest speed in 4th. Happy shifting!

Dredged up from the deep
 

Hey guys, yeah, this thread is from last year, but I think I'm putting something together that a search did not reveal.

I have an '82 240D, it HAS a sensor of some sort on the front of the engine for the EGR "computer" (not sure if its a computer, but its a black box w/ electronics in it)

Could someone find out if the sensor for the EGR (it is an rpm sesor) and the 'reference sensor' on the 617's (w/ factory tach) have the same part number ? If they are (or are even electrically similar) maybe all us 240D owners ('82 and '83...) could just hook that sensor up to a junkyard tach amp and then place a 300D tach in where the clock is and be set.

Can anyone help here ? I can't find the part numbers myself (I have the factory repair manual CD's, but I'm not seeing the part numbers...)

Angel,

Get the whole kit and kaboodle from a junked 300D turbo and try that. I believe the place to hook up is the same at the front of the block. Never looked into the change but would begin by stealing the parts, including the dash instruments, from a similar vintage 300D. I believe the "sensor" you are referring to is probably a cruise control item. I could be wrong on all accounts, but the tach was a factory option on the German model and it is very unlike MB to have a different instrument for the 300D and the 240D. Jim

Jim's right. If you can find all the parts off of a 300D in a wrecking yard you're home free.

Just an observation - Why did my manual shift 240D NOT have a tach while my automatic 300D has one? Don't make sense to me...

Wes

Ever had the speedo check on that 240D? ;) My 240D is really buzzing at 75 mph, can't imagine it doing 95 mph unless pushed over cliff. :eek: Seems like we had the discussion before. :p :D MB says redline is 85.7 mph approx. for automatic and 88.8 mph approx for 4spd manual trans. :rolleyes:

Old navy: I think those dudes that go 100mph in thier 240s are ***seriously*** exceeding the redline

...and providing a testament to the solidity of the OM616 =) =)


Tach seekers- Thats the thing- the sensor on my 240 (looks exactly like the one on the 300 I owned for 3 months, not sure about the connector) and is mounted properly, same place and everything, but sends an RPM signal to the EGR computer (at certain rpms and engine temperatures the 240D's of this vintage (1982 and 83) have a computer that tells the egr valve when to open..., the black box is in the passenger side footwell IIRC.
The 300D tach signal goes from the pulley, through the sensor, to a wire to the tach amp (the cigarette fix thing), then from the tach amp to the tachometer.

If the sensors are the same part number (which I cant find out, not sure how to save going and looking for a p/n on both, and they are tough to see/get at in the first place on an OM617) then the amp and tachometer should bolt/power right up. Thats why I'm asking if someone can look up those part numbers for me.

This could be another 240D easter egg (appl to '82 and '83 models only =)

-John

Us boy's and our toy's. :cool:

this might be of interest to some
 

I was going to buy or build one of these but found 300SD instead. Some of the guys over at one of the Powerstroke web sites spoke highly of them. The only downside is that the display only updates once per second. But, it is easy and cheep.

www.tinytach.com

Also, I was looking into this option.

http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml#Kits

This one is on a VW and is optical but one could be built (for you engineers and techs out there) one using a hall effect pickup mounted somewhere. Most tachs just measure the RMS voltage. The faster the pulses occur the closer the needle moves to full scale. With the correct design and calibration any of the older tachs should work. But I am not an expert, this is just some of the diggin' I've done.

The dots are even better than the tachometer because they show when you can downshift too -- important in a 240D!

As for rpm in fourth, divide the mph by 2 and you have a very good estimate of rpm; e.g. 80 mph is 4,000 rpm. The goverened maximum engine speed of about 5,000 rpm then works out to a bit more than 100 mph indicated.

So, any success?
 

Was anyone actually able to get a tach amplifier and gauge from a 300D and plug it in to an existing rpm sensor in their 240D? It seems there were several discussions, but no specific success stories.

lol...I was just at the junkyard today....
 

and posted a thread about needing a voltage measured- I didnt put it in this thread b/c I need help from someone w/ a 300D - (whom this thread isnt really aimed at...)

I got the tach amp from the junkyard today (not sure if it works...) and I could just solder everything together, but I'd like to have an idea that things are **close** to working before I do it. If the 240D signal needs amplified, I might be able to make/cajole EE friends enough to make an amp for myself and post it up here.

Edit- the 240D egr sensor and the 300D tach sensor are **not** the same connector.

-John

I will try to get info
 

3 months ago I sold a guy everything to put a tach in his 240d except the gauge I just emailed him asking if it worked and if he would share information on his installation. We shall see if he answers email he is in Germany though may not get a quick reply.
DHS

So I took an Oscope to my 240D the other day...
 

my 1982 240D has the EGR system which includes a crank sensor....

At the sensor, you get anything from a 0.1Vpp to 0.4Vpp signal proportional to engine rpm. (unplugged from the EGR computer)

If you go to pin 4 on the EGR computer (with the sensor plugged in), you get 0.5Vpp to 2.0Vpp riding on 2.3vdc.

Sounds like a capacitive pickup ? The computer gives it some DC bias that makes the signal larger (and easier to see ?) I know some electric theory but Cap./Ind. pickups escape me...

I'm guessing the OM617's have an inductive pickup, as they have two signal wires going to the crank sensor. If this is the case, then all I need to do is ground one OM617 sensor wire, and hook the other up to my cap. crank sender so the tach amp gets a voltage pulse.
I still need am OM617 sender signal to compare it to. I dont think that 0.5v will blow the tach amp, but I'd like to know if I'm in the ballpark.

-John