Main.TrailIndexPage | Electrical Systems | Dashboard Instruments | Speedometer

Speedometer

This component is part of Dashboard Instruments.

Definition

Define the component. Include, if known, the german language word for the component, as well as the English or American equivalent. Show a picture, a diagram.

  • Its technical name & common name(s)
  • part # - start year & end year
  • which area it belongs to - engine, transmission, body, injection etc, link back to the relevant section

Function

Describe, in general terms the function of this component. Meaning what is it there for and what role it plays. Describe how it works, the inside mechanism. Use diagrams to explain.

Maintenance

Describe common maintenance procedures, and common faults that may occur. Describe how these may be diagnosed and resolved. Again, include diagrams, photographs and explanations. Where possible, include measures, tolerances, weights etc.

Link to related components where appropriate.

Some simple speedometer calculations.

  • For cars with 3.92, 3.96. 4.07 rear end ratios, and manual transmission (auto transmission figures can vary slightly.)
  • If the speedometer is not working or not working correctly: the pointers of the tachometer and the speedometer will be roughly parallel when in 4th gear (1:1 ratio). When going at say 3,000 rpm, the speed pointer should be at about 60 mph (96 kph). This will vary slightly depending on the rear end ratio and the diameter of the rear tires.

For easy conversion of Kilometers and Miles while driving, 6 can be used as the conversion factor. The actual conversion is not 6 but 6.2. The calculation using 6 is for convenience not precision.

To convert from Miles per hour to Kilometers per hour:

  • Multiply the first digit of the mph speed by 6 then add the result to the mph speed to get the speed in kph. Example at 50 miles per hour: 5 x 6 = 30, 50 + 30 = 80 which is the speed in kph.
  • At speeds over 100 mph, multiply the first TWO digits of the mph speed as above. At higher speeds, there will be a larger error in the result when using 6 as the rough conversion factor. At 115 mph, as an example, the result will be about 5 mph below the actual speed.

To convert from Kilometers per hour to Miles per hour to:

  • Multiply the first digit of the kph speed by 6. The result is a slightly understated speed in mph. Example at 50 kilometers per hour: 5 x 6 = 30, which is the approximate speed in mph. (50 kph is actually 31 mph.)
  • At speeds over 100 kph, multiply the first TWO digits of the kph speed as above. As noted above, at higher speeds, there will be a larger error in the result when using 6 as the rough conversion factor. At 120 kph, as an example, the result will be about 2 mph below the actual speed.

To estimate speed in miles per hour by using the Tachometer alone:

  • When in 4th gear (1:1), the rpms in hundreds times 2 is the approximate speed in miles per hour. Example at 4000 rpm: 40 x 2 = 80 which is the approximate speed at 4000 rpm in 4th gear.

Note: The estimation calculations here are for the rear end ratios noted above, manual transmission, and only when in 4th gear.



Back of speedometer with bracket

Note the orientation of bracket for the installation procedure. The photo shows the speedometer from a LHD drive 280SL, however, since the part numbers for speedometers are the same for LHD and RHD W113 cars this view applies to both LHD and RHD vehicles. {It may not apply to other Mercedes models!}

The tan cover is rubber.


Speedometer and Tachometer bulb holder

The bulb is a 2 Watt / 12 Volt / Ba9s / MB# N072601 012800 / Bayonet type / Osram Equivalent 3796


Repair of Trip Indicator (small odometer)

Two methods for repairing a non-working trip indicator are described here.

  • The trip counter may show failure when the dials do not move at all or alternate between moving and stopping. This is a common failure on many VDO speedometers.
  • The numbered wheels are on a shaft that rotates one turn per mile (km on metric speedos). At the right end of the shaft is a pot metal gear of the same diameter as the digit wheels. A system of cogs on another shaft allow the "ones" wheel to advance one mile each time the shaft and gear make one revolution. The "tenths" wheel advances one number each revolution of the "ones" wheel; then the hundreds, thousands, etc.
  • The pot metal drive gear is pressed fit on to the shaft and after a while can work itself loose and start to slip on the shaft.
  • The fix is to take the speedo completely apart. Using a small, very sharp chisel (or similar tool), cut several parallel shallow marks (parallel to the axis) on the shaft. The marks should be exactly where the gear wheel mates to the shaft.
  • Getting all the wheels and cogs back into place is a tedious job. One wheel out of alignment will make all the number wheels ahead of it drop half way between the numeral markings.
  • The mileage needs to be written down before dis-assembly so that correct mileage dialed in before it is all reassembled.

Alternative method for trip indicator repair:

  • The odometer drive has a spiral gear that drives a cog on one end of a shaft that runs through the number wheel set. The pot metal drive gear is pressed on to one end of the shaft and engages the first number wheel. Every revolution of the drive wheel moves the first number wheel up one number (1/10th of a revolution).
  • The cog rarely loosens on the shaft but the pot metal drive gear often looses its grip and begins to slip on the shaft. Eventually it moves along the shaft so that the shaft backs out so far that the cog on the other end looses its engagement with the spiral drive gear. The shaft may even have backed out of its locating hole in the odometer housing at the pot metal gear end.
  • Here is a fix: Drive the shaft out the rest of the way using a long leather-working needle of slightly smaller diameter than the shaft itself. A drill bit will also do the trick.
  • Push the needle through the locating hole in the odometer housing, through the set of number wheels, and through the locating hole in the odometer housing on the other side. This will free the drive shaft from the assembly.
  • When the shaft is completely free of the instrument, the needle takes the place of the shaft and acts as a temporary substitute shaft. All the number wheels should have retained their relative positions.
  • To keep the pot metal drive gear from spinning on the shaft, some shallow splines need to be cut into the shaft where the pressed gear sits. A pair of model working (small) vise grips with jaws that have small parallel teeth can be used to introduce a splined surface by clamping the area near the end of the shaft for a brief time. (Model working vise grips have jaws that are barely 3/16" wide.)
  • The surface irregularity required is very slight. The marks should be parallel to the length of the shaft and confined to the area where the gear sits when pressed on the shaft. Do not create any surface irregularity in the section of the shaft on which the number wheels ride or on the tip of the shaft that rides in the locating hole of the odometer housing.
  • After the parallel ridges have been pressed into the surface, push the shaft back through the number wheel set, displacing the temporary needle or drill bit shaft, until the actual shaft is ready to be pressed into the pot metal drive gear.
  • Be sure to support the odometer housing with a small socket so that you do not damage the housing when gently tapping the newly splined portion of the shaft into the pot metal drive gear and tapping the end of the shaft through to the locating hole in the odometer housing.
  • Do not press in too far. There s/hould be some "end float" so that the shaft does not bind and the number wheels can move freely on the shaft.

This is a fairly permanent fix. The pot metal drive gear should not spin on the shaft again.

Speedometer Lights

What is the best way to gain access to the speedometer light for replacement? Initial inspections indicate removal of the dash may be in order...

The lights on the tachometer and speedometer are accessable only from the back. They are simple bulbs with a bayonet-type mounting. If your light is not working it could be because of a short at the bulb. This can easily happen because the wires and bulbs are exposed and if touched by something else metal then you don't have any light. The bulb could be slightly touching the bracket that holds the speedometer into the dash from the back. It is very tight but get some mirrors and a good light and force your body under the dash. Most of it you will have to do by feel.

Fixing a speedo cable squeak

Symptom: a speed related squeek which appears to be coming from the speedo cable (the squeek is not continuous - just a chirp but it gets faster as the car speeds up and vice versa). The speedo is working fine and not jumping.

Question: Is it possible to remove the cable inner from the outer cable from the gear box end, trying to avoid the terrors of getting into the back of the instrument cluster.

On an automatic transmission we have observed an M-B technician uncouple the speedo cable from the tranny, shoot some lube up the speedo cable housing and reconnect it.

Have a pair of long needle nose pliers handy to use when working with the cable end because the average three year old doesn't have the strength and motor skills to deal with its removal and reinstallation and hands much larger than a three year old's just won't fit!

Steps needed:

  1. Get the car on a ramp, chocks, etc.
  2. pry the shift linkage off of the selector lever on the side of the auto box. The end of the linkage has a nylon clip pressed into it that will snap onto and off of the fitting on the end of the auto box selector lever. (He also recommends keeping a spare of this inexpensive nylon clip in the glove box for emergencies because its failure is notorious for stranding folks without notice!)
  3. On my car, a 65 230SL manual, the outer cable is secured to the housing on the side of the gearbox by a 10mm bolt. You can get at this without taking off the plate below the gearbox, although having double jointed wrists and two elbows each arm would make it slightly easier. I used a short ring spanner (one from an old Sears Ingnition set) which was only about 100mm long. Once the bolt is out, the cable comes free and all is needed is to twist the cable inner and pull at the same time.
  4. The pinch bolt that secures the drive end of the cable is a 10 mm metric allen headed bolt and needs an allen socket with at least a six inch long shaft to reach in tight quarters.
  5. The allen bolt must be removed completely to allow the cable end to be withdrawn, and there should be a rubber boot on the cable end to prevent debris from entering the connection.
  6. Withdraw the cable end, pull it up into the engine compartment so that you can shoot some engine oil into the cable sheath and patiently allow it to penetrate down the length of the cable. Multi-purpose grease can be used for this.
  7. Then lower the cable back down the same path to the tranny where it formerly ran, and patiently allow excess fluid to drain out of the cable. You are not trying to drown the cable, just lube it up a bit!
  8. Be prepared to jiggle the cable initially to get it to seat into the back of the speedo, and then to play round a little to get the gearbox end to seat into the slot in the housing.
  9. Then carefully re-insert the cable end into its socket on the side of the tranny, being careful to seat the rubber boot and carefully hand-thread the allen bolt back into place. You can't thread the bolt if the cable end is not inserted fully or pushed in too far, but you can thread it in if the cable is not inserted far enough into the socket for the square drive tip of the cable to engage the drive gear in the transmission, so you need to check to see that you can't pull the cable end out if its socket after you have the bolt fully threaded but not tightened down. Don't use the socket drive handle until you are ready to snug up the threaded bolt.

Time taken; 30 mins inc putting the car up on the ramps.

Erratic Speedo

At the Blacklick tech session in July 2007 we correctly diagnosed and identified a problem with a members Pagoda. Here is a copy of the documentation sent to his mechanic.

If your speedometer has become erratic, and your transmission is not shifting smoothly, the slotted spanner nut on the output flange of the tranmission may have come loose. This slotted nut holds the entire third fourth gear cluster tight. In addition the drive gear for the speedometer is NOT keyed to the shaft but depends on the tightness of the cluster and slotted nut before it can operate correctly.

Consider inspecting and replacing the rear tranmission mount, the drive shaft rubber flex disc, and the rear transmission seal if needed during the transmission work.

Start by removing the multi-bolt tunnel plate and transmission mounting plate. Remove the rear transmission mount and bracket. Remove the 19mm driveshaft bolts. Pay close attention to the configuration. There are three long bolts and three shorter bolts. Refer to the information and diagrams for re-assembly. This must be installed exactly or the rubber disc will not last or will come apart.

The drive shaft has a slip joint half way back. Loosen the 44mm and 46mm slip joint and slide the drive shaft rearward. This will allow you to split the drive shaft at the drive shaft flange/centering bushing connection and enable you to remove the flex disc, and move the drive shaft out of the way.


Home made spanner for spanner nut

Check the slotted spanner nut for tightness. If it is loose it must be re-tightened. A special four prong socket is still available from Mercedes for these nuts. Some mechanics make their own with a die grinder and a 1/2" drive 1 1/8" deep well socket. In a pinch the nut can be driven tight using a drift and hammer (not recomended). The sheet metal lock ring must be "staked" outward and inward to prevent the slotted nut from coming loose again.


Speedometer drive gear

This is a picture of the speedometer drive gear. Notice it has no keys or teeth on the inside to keep it from spinning on the shaft. The pressure from the tight spanner nut keeps it from spinning. If the spanner nut comes loose the gear can no longer function correctly.



The gear on the shaft



Flex disc position

Before re-installing the flex disc, check it for condition. Also note that the three tabs on the flex disc MUST be postitioned on the three flanges of the transmission out-put shaft (see diagram).

Notice locations of the long and short diveshaft bolts and the washers. Review the diagrams, this is critical. Notice that three of the washers are positioned under the bolt heads and the other three under the nuts of the other three bolts. In every case the washers are positioned next to the rubber flex disc. The nylock nuts can be reused if the condition is ok and everything is re-assembled correctly. The driveshaft bolts should be quite tight and you may feel the nuts bottom out against the bolt shoulder as you tighten them down.

This is an excellent photo with text by Bob Possel
Pump a bit of grease into the driveshaft end at the Zerk to lubricate the centering bushing assembly.

Install the transmission mount paying attention to the spacer washer between the mount and the mounting plate. Tighten the drive shaft slip joint last after the tranmission is secured.

Replacing a speedo cable

The picture below shows what can happen if the speedo cable end where it connects to the automatic transmission is forced out without first completely removing the 5mm allen bolt. The drive gear housing can break. It is simple pot metal...

To disconnect the end of the speedo cable that connects to the automatic transmission, you must completely remove the 5mm allen. With the 5mm allen bolt removed, you can slide the cable out of the trans end.

Old Yahoo content

The following is the content from the old Yahoo documents on the site. It needs to be structured and edited in the correct sections of the entire document. After moving particular content to its correct place in the manual, please delete it here.


I own a '69 280 SL, 4-speed manual transmission. I have to repair the gear at the transmission which drives the speedometer cable. The question is: do I need to drop the transmission to do this, or can I just pull the drive shaft out of the way and have enough room to do this job with the car up on 4 jackstands?

Frank Mallory says: are you sure that the gear itself is bad? Usually what happens is that the slotted nut on the rear-end of the mainshaft gets loose, and it is only necessary to disconnect the driveshaft and tighten it up, in order to get the speedo working again.

I don't know yet, but I tried to be ready for the worst with some spare parts and the correct tools. I've never been into that part of the car before and I'm trying to gather as much information as I can before going ahead. The Service Manual is helpful but still leaves several questions in my mind, for example:

  1. Can I move the driveshaft out of the way just by disconnecting it from the rear of the transmission, or do I have to disconnect it somewhere further back as well.
  2. From what I can tell, the driveshaft attaches to the three-legged output flange. Upon removing the driveshaft from the flange, I will see the slotted circular nut.
  3. If I understand correctly, all I might have to do is use a slotted nut spanner (I was able to borrow the correct one) and tighten that slotted nut.
  4. According to the Service Manual, there's a special "holding spanner" used to hold the three-legged flange while you loosen or tighten the slotted nut. I don't have this tool but can I use something else (i.e. just grab it with a vice-grip)?
  5. Is there a way to check while the car is still up on jack stands to see if tightening that slotted nut fixes the problem? (probably not, right, and I have to take the car back down and drive it to see).
  6. If tightening the slotted nut doesn't fix the problem, do you know if I can do the job on jack stands without dropping the transmission.

Frank Mallory sends answers:

  1. You will need to disconnect the center bearing also. Be sure to mark its position first.
  2. You will need to remove the rubber "donut" also. Replace it with a new one if it shows signs of deterioration, being sure to connect the "ears" on the donut to the transmission flange.
  3. It would be best to use the correct wrench and torque the slotted nut to the specified value. But I suspect that most owners just use a drift and hammer to tighten it. New slotted nuts are very expensive (~$50), so it would be best to use the proper tool to avoid damaging the old one. Apply some Loctite to the threads first, and afterwards bend the lock plate into position.
  4. I don't know if vise-grips will work. Generally, if you just put the transmission in high gear, you will be able to get enough torque on it.
  5. Not in advance; but if you find the nut is loose, you can be pretty confident that tightening it will cause the gear to work again. After tightening the nut, you can put the transmission in neutral and turn the flange to verify that the gear is turning.
  6. Should be able to. The rear of the transmission will come down when you remove the rear mount. Also, thereís a plate on top of the trans tunnel that can be removed to give you more access to the rear trans cover screws. Of course, it's best to avoid this job if possible, because you have shims, seals, and the gasket that tend to turn a small job into a big one.

More questions, if you don't mind:

  1. What is the "lock plate" that has to be bent into position?
  2. Looking through the parts catalog as well as the Service Manual, I cannot identify the rubber "donut" with "ears". Please tell me precisely where on the car this is located.
  3. What do you mean "the rear of the trans will come down when you remove the rear mount". Does this mean that I should support the engine first before removing the mount? Does it also mean that I will have a hard time replacing the mount unless I raise the engine back up?

Frank Mallory responds: Well, we were discussing the trans flange and driveshaft. The "donut" is the large rubber ring that goes between the two. The more I think about it, the more difficult I realize this job is. I assumed that you knew how to get at the rear transmission cover, but that does not seem to be the case. It requires removal of the large metal apron that forms the front of the driveshaft tunnel and carries the rear engine/transmission.

This apron is held on by about 22 bolts; for some of these you may need to drop the exhaust system in order to get a wrench on them. The rear mount can also be difficult to remove from the apron. The last one I did was so deteriorated that the bolt just spun around; luckily, an impact wrench gave it the necessary impetus to back out. The bracket that holds the motor mount to the transmission rear can also be difficult to remove.

Your rear mount will need to be adjusted when reinstalling it to the apron. The apron can be tricky to get in place. No doubt you will encounter other problems, some due to the fact that you are working on a 30-year old car and others due to "the nature of the beast". And doing it with the car on jackstands makes it even more difficult.

Everything considered, I recommend you postpone this job until you have some reason in addition to the speedometer gear fix to perform it. Hopefully in the meantime you will gain experience by taking on less difficult jobs on your 113.

I have a 4-speed manual transmission. Speedometer is accurate in 1st, 2nd, or 3rd at speeds below 35mph. It's occasionally flaky in 3rd above 35mph and always flaky in 4th. Flaky means that it seems to maintain a pretty constant reading that can be anywhere from 50% too low to the correct speed.

Often when I take my foot off the pedal when the speedo is reading 40 and I'm going 70, the speedo reading will increase to approx. correct while the car slows down. Needle does not oscillate wildly at any time. Any suggestions on what might be wrong? I suspect that the problem is not in the speedo head but at the other end of the speedo cable.

Frank: Bingo! This was discussed at length here some months ago. Bottom line: it's easy to fix, but getting access to the part that needs to be fixed is not easy.

Will: you might hope it is the speedo. It is the easiest to fix. Or the cable is getting ready to break. But if it is at the transmission, the problem is the 3 eared yoke that comes out of the rear of the trans. This is what the flex disc bolts to.

The yoke is held in place by a special nut and a lock ring. When the nut loosens, it allows the yoke to loosen. The yoke is pressing on a bronze gear that drives the speedo. The bronze gear is a slip fit on the shaft and the only thing that holds it in place is the pressure of the yoke. The special nut takes a special tool. It is easy to make the special tool by using a socket and grinding away part of it to make the 4 pins that insert into the special nut.

Regarding the Odometer, mine sticks when it's very hot outside, but it hasn't bothered me enough yet to get behind the dash... In my case, both odometers (trip as well as regular) just stop. Probably wear on those little gears.

My carís speedo makes a noise at low speed. Probably the cable needs lube. Suggestions? I have lots to do in the dash like radio replacement, heater lever replacement. If there are maintenance lubrication tasks to be done in the dash, it would be nice to do them at once.

Will says: the noise in the speedo is usually inside the speedo, not in the cable. It is especially noisy in cooler temps. The fix is to have the speedo serviced. Also, do not reset the trip meter when the car is moving.

Will is correct. I have the same problem with my tach. No choice but to have it serviced. If you need to know a good place to have it done let me know.

I had my speedometer and tachometer rebuilt but, the rebuilding shop did not provide new seals which sit between the instrument bezel and the dash. I had to order the seals separately I also ordered a new seal for the center instrument cluster.

I am refurbishing the interior of my 280SL and while the instruments work fine and look OK, I would like to clean the haze from the inside of the glass. Can anyone advise how to safely remove the glass from the tach, speedo and central instrument cluster?

Cees: I removed the glass from my tach which was very hazy, in a manner that is definitely not the recommended procedure: being impatient by nature, I decided to have a go myself and carefully pried the chrome ring loose from behind with a small screwdriver as much as necessary, until the ring could come off.

I cleaned the glass, re-fit the ring by tightening the spots where I had bent it open previously, and put the instrument back in the dash. Of course I slightly damaged the chrome ring in the back, but this is invisible when the tach is fitted (i.e. always). Procedure took 15 minutes. It is pretty easy to remove the tach.

If I recall correctly, it took removing the lower dash cover panel(s). There's a curled nut that holds a bracket in place that keeps the tach tight against the dash. Loosen the nut (don't drop it, and you should not use large fingers for the whole procedure) and the tach comes right out. A good time to also replace the cable, if the needle bounces or the tach screeches (sometimes). I put in an aftermarket cable, not original MB, two years ago, still works perfectly. There's one light that you need to unplug, and you have the tach loose.

'71 280 SL...while happily humming up the valley of the Hudson River to see the Fall leaves, the speedo cable (I think) began to make a whining noise, fairly loud. I touched the speedo glass, it was vibrating...the speed needle began to gyrate from 30 to 50 mph...after a few minutes, back to normal, then repeated whines every few minutes... Is this a loose or dried out cable? What's the fix (details if possible for someone who has never been into the instruments)... Also, the shaking caused the small silver cover in the center of the dial to fall to the bottom of the gauge...do I use glue??? to put it back...

This happened to me on my way to the Classic Center in Stuttgart (how fitting), albeit to the tachometer. I simply replaced the cable with a new (aftermarket) one and this corrected the issue. I would think the speedometer could work the same way. The tach needle also became rock-steady, was jittery before. You may want to see whether the cable is loose, but my guess is that it's just worn. I have no experience on the center cover.

It is either the cable or the speedometer will need to be removed. The cable is cheaper, approximately $30. There ia a shop which specializes in rebuildig our instruments in Mamaroncek, NY. They rebuilt my speedometer for $100. Getting the instruments out is difficult. In order to get the speedometer out I first had to remove the tach and loosen the center instrument panel. Once the speedometer is out the chrome bezel can be removed by slowly prying it off. Once it is off the The "button" can be glued back on. I hope this helps. If you want we can discuss this off line.


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