speedo markings.

[craigb]

Being a poverty pack, I have no tacho, but have bought a set of instruments with a tacho. I am interested that my speedo (replaced a couple of years ago according to the receipt) has a 'I' marking at about 95km/h and 'II' at 155km/h. The new speedo has 'I' at 50, 'II' at 90 and 'III' at 145. I have a feeling if my 4spd manual car was somehow in 1st at 95km/h there would probably be dents in the bonnet from the valve springs!! I am guessing this comes out of a higher geared car - a 6.9? None of it really bothers me because once I have a tacho I will change at the indicated 6500 (!!) and the speed will be the speed. Just interested.

(And in my intro I forgot to mention that my daily drivers in the past have found there way on to the track for supersprints and hillclimbs with MSCA - so I do really need a tacho. With a bit of luck there could be a team of 116's running next year!)

Also does someone know about wiring the tacho? I think one wire comes off a joining block across from the distributor. Does the other wire from the back of the tacho go to earth?

[Andrew280SEL]

Hey again Craig,

If I had to say, I'd wager that your old speedo is one from the 450 models. However, luckily for you it sounds like your new speedo is the proper 280 one. 'I' at 50 Kms sounds correct to me.

I have no idea about how to go with wiring a tacho, but I'm sure there's an old thread here...if I find it I'll post it.


EDIT: Here Craig, hopefully this helps you; if not there's sure to be people here who still can:

http://forum.w116.org/mechanicals/installing-tachometer/0/

[WGB]

There is definitely a thread on wiring up a tacho - just do a search and you should find it.

The markings on the speedo will probably be for a 280 4 speed automatic as all V8's were 3 speed automatics and that is why your old speedo only had two maximum shift points.
I assume the gearing is the same on the manual as the automatic but wouldn't be definite about that.

I know I sat down and did the arithmetic on all the models from ratios gleaned from Road test reports and posted it some time last year - try a search on Diff ratios and see what comes up.

Not sure that I included the manual 280S though.

Bill

[Andrew280SEL]

I assume the gearing is the same on the manual as the automatic but wouldn't be definite about that.

There's an ever so slight difference, in that the manual is slighty higher I think.

For instance, the manual 1st gear maxes out at 50kms, whilst the auto 1st gear maxes out about 40-45...or something like that. It allows the manual about an extra 5kms to the factory rated top speed.

[craigb]

Thank you very much for that. My new speedo will look close enough and as I was saying, with a tacho you really don't need the marks. Great link for the wiring too.

[oscar]

Hi Craig, apart from Andrew's link there's another shortened version when a similar Q was asked recently.  The main diff is that it has some of the pics that were lost in the first thread.

http://forum.w116.org/interiors-and-exteriors/help-with-instrument-cluster-tacho/0/

But there's good info in Andrew's link about the various markings on a speedo and tacho.  There's always a few discrepancies and there is another thread regarding speedo and tacho markings specifically but be buggered if I can find it at the moment.  The most important thing is to have a matched tacho for your engine.  Mix a V8 tacho on an I6 and you get wrong readings.  Cheers

[craigb]

Thanks Oscar, yes reading the thread sounds like a 450 speedo as someone suggested. The change points sounded so high I thought it must be a 6.9....... but that is even higher!

The guages I have are from a 280se so should be no probs.

Many years ago I was in the Alfa club in SA and had a lot of fun in sprints, hillclimbs etc organised by the Marque Sports Car Association. Having seen a lot of younger guys come and go from the Merc club for lack of stuff that they find interesting, I thought it would be good for the club to affiliate with them. This has now occurred but I have moved to Keith, but I am pretty sure we will move back again in March so I intend to compete next year. There are a number of members that have shown interest but to my knowledge none have competed yet. I am thinking if I get out there it may encourage others more. I am keen to take my 113 out initially, mainly because on the track is the best place to find the limits of your car but partly to show others that it really is safe if I am going to risk a toy worth so much. Before we moved here I actually bought a 108 3.5 for the task but that needs a bit of work, so in the back of my mind the 116 I thought would be good for the task also. Having now driven it I am absolutely sure it will do nicely!......... but then this is a bit off topic but a reply to your other comment.

[CraigS]

Change points ? Never looked at them. I drive by sound and the tacho. The more noise - the faster I must be going.

[koan]

I'll just throw in the reminder that a speedo for 280 is different from a 450 is different from a 6.9 is different ....

It's not just that the change points are different, the odometer is geared differently.

Unlike common Fords or Holdens where the speedos are much the same and the calibration for various diff ratios and tyre sizes is determined by the choice of the driven gear at the gearbox takeoff point, Mercedes-Benz adjust for diff and tyre size by changing the gearing in the speedo head.

Anyway, why don't you just remove the speedo from the current instrument panel and put it in the panel with the tacho? it's only 3 or 4 self tappers that hold it in.

Some time ago I posted about the "W" calibration number stamped on the back of the speedo head and what it means.

koan

[Ferdinand]

Hey guys,

I own a 280S 4-speed auto and have noticed these "|" markings (mines at 50km/h, which indicates its the right instrument however by the time the niddle reaches the first "|" the automatic is already in gear 4. What i'm thinking is, is that these markings are to let the automatic drivers know what there rev limit is for for the differernt gears, i.e. 1st gear goes to 50, etc etc. seeing as the automatic versions of the instrument cluster does not generally come with a tacho (mines converted). However i have tried keeping my 1st gear in till it hits about 5000rpm (don't dare more, seeing as the water pump is about to fall out), and i will only reach about  20kmh, . the indications i.e."|" markings may indicate the rev limit if you keep the car in "D" and floor it cause then as most of you know the changing revs for the gears are extended when your foot is welded to the floor of the accelerator pedal, this would make sense as the 2nd gear does stay in till about 50kmh (safely). (Looks like i keep conuterly myself here) But it is also possible to acceralte from the start in first while still in "d" ( you pretty much hit the accelerator pedal with your foot. anyways thats my findins

[CraigS]

I don't think they changed the speedo depending on whether it was manual or auto. Most of the original drivers would probably not have come close to these marks - in an auto or manual, so I don't really know why they put them there. Without a rev counter, it does make it easier through the gears, but if you can't hear what the engine is doing, I don't think speedo markings are going to help you much.

[Andrew280SEL]

However i have tried keeping my 1st gear in till it hits about 5000rpm [...] and i will only reach about  20kmh.

Really?

My auto 280SEL will reach the 'I' marking in 1st....

Wonder what the difference is...?

[koan]

My auto 280SEL will reach the 'I' marking in 1st....

Wonder what the difference is...?

Adjustment of the throttle position linkage?

koan

[Ferdinand]

yeah that's very true koan, the throttle linkage position does play a role in it, but what i mean by the first gear is placing the automatic gear into "L" which will place the automatic into the first gear, otherwise the car will start off in 2nd gear int in drive. the thing that concerns me is that you can get to first gear 50kmh with your 1st gear seeing as i will only get to 20 and the gear ratio is very small very high torque i get which makes sense. I have to say i am confused as to wat is correct now, oscar if you know something about this could you please explain?

[oscar]

yeah that's very true koan, the throttle linkage position does play a role in it, but what i mean by the first gear is placing the automatic gear into "L" which will place the automatic into the first gear, otherwise the car will start off in 2nd gear int in drive. the thing that concerns me is that you can get to first gear 50kmh with your 1st gear seeing as i will only get to 20 and the gear ratio is very small very high torque i get which makes sense. I have to say i am confused as to wat is correct now, oscar if you know something about this could you please explain?

I can't add anything really, except to say your kickdown linkage may need adjustment.    I've always assumed the markings were to indicate a recommended change point or limit in each gear.  But I'm confused now why for the 3spd autos (except 6.9), there is a "III" mark around the 140-150km/hr mark.  Top speed is supposed to be 205 for the 350.  Anyone got an owners manual handy? I bet there's some description in there.