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Odometer - failed today

4K views 32 replies 10 participants last post by  MBGraham 
#1 · (Edited)
Issue:
The odometer on my 72 350SL failed today.

I was going on a longish day trip and wanted to check mpg. So last night when I filled up, I noted the mileage. I also pushed the trip reset button. Aftr driving about 100 miles, I noticed that the trp and odometer only showed about 30 miles. And it was not advancing. I pushed the reset and then both advanced a little - maybe 1/2 a turn. So it seems the gears are broken or slipping. Might have been caused by pushing the reset button?


Problem:
What to do if speedo is un-repairable (by me)??

It is a 1-160mph. Very expensive new, if even available!
Nothing used showing up on eBay
Some complete cluster show, but most have clock while mine has separate clock. (my cluster says 1075420801)

Question:
If I get cluster out and need a repair, who repairs these old mechanical speedos? Ideally in Canada, but USA shops OK too.

Sorry - I am probably jumping the gun. Need to get the cluster out and have a look. But also have appointment for new tires Monday, so this will have to wait. Did find this among my 300D stuff. https://www.ifixit.com/Guide/Repairing+Mercedes+W123+Odometer/25421
 
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#3 ·
Thanks for encouragement. The 72 has a mechanical speedo. I hope it is similar to the W123 one I posted above or the Diesel Giant one here
How to Repair Your Broken Odometer

I just did a search and found this source of gears, apparently for the early mechanical speedos.Odometer Gears - Mercedes-Benz - SL (107) 72-80

We will see later in week after I get the new tires if I have the strength to get the wheel off (on W123 it doesn't have to come off)
 
#4 ·
Of all the concerns or lack of concern I've had removing steering wheels, I can honestly say the only time I screwed up on was removing the emblem from the horn pad. I've accidentally scratched more than one if them. The flathead on a keychain Swiss Army knife seems to work best for me but there are probably far better tools to use.

Then on the early cars, the nut on the small spline can be removed with a socket on an extension.

The trick here is to get a 2x4 or similar to use as a post between a left spoke and the floor to hold the wheel from turning while you crank on the nut. I like to protect the floor/carpet with a piece of plywood and the steering wheel with a rag.

Of course don't forget to put the key in the ignition in the on position to assure you don't break your steering lock.

That's all a lot of description for something that is very simple once you do it the first time.

And the odometer gears are easy once you have your cluster at your desk or workbench.

Oh... And as you have probably read before, do NOT start the early cars with the oil line for the oil pressure gauge with the cluster out. You will get an oil bath... So I've heard.
 
#6 ·
True, but the odometer gears are a soft material that turns to mush after years and are a common time to fail. There's no reason to "blame yourself" for the odometer failure. This should be one of the "routine maintenance" items for anything older that 30 years old IMO. Even my 1992 r129 odometer has failed, maybe from hitting the reset while driving. I don't know.
 
#9 ·
Probably too distant from you but there is a speedometer shop in San Francisco that repairs Mercedes instruments. There are probably others much closer. Try Googling it.

The secret to getting the steering wheel off, is to give the extension a hard and sudden jerk, rather than apply constant pressure. You don't even need an extension. I broke an extension with the steady pressure and now don't even use extension with a normal breaker handle.
 
#10 ·
#13 ·
Gears

This speedo problem is well known in the older cars .If you have ever repaired one, then you will see how it can get damaged .I was lucky after removing my head [speedo] i could see what had gone wrong .The pot gear had come loose on its shaft .The small shaft had moved out of its location ,and the small gear on the end , was not making contact with the drive gear . So a small drill was pushed through to hold all the number drums in place ,then i put tape across the numbers to stop them turning..Removed the shaft ,roughed it up with a small dianond file. Apply dab of super glue to the shaft ,Not to much, or it will glue everything together .Then push the shaft back in to place .Tip the speedo up so any glue runs away from the other drums . But to start with allways take pictures with camera ,so you know how to replace it all .All numbers must be right and not move as you work on it .If they do , then the oddometer wont be working right .
 
#16 ·
On my trip to get tires installed, odometer and trip both worked for about 10 miles, then stopped again.

Time to have a look. Checked the steering wheel nut. It has green paint on it that shows it has never been off. Looks like a 22mm socket from my 1/2" impact set should work.

Anyone used an impact wrench on that nut? Bit worried about using my el-cheapo little butane torch to do it manually- don't want to burn the leather!
 
#20 ·
MB if you take off the speed pointer .First lift it anticlockwise , over the resting stop .Then mark the face in the area that it rests. If you dont do this the speed will be out after refiting the pointer .So realy your taking pressure off the spring ,lifting it over the end stop.Refit on to the mark you put on the face then all will be fine in that area.
 
#27 · (Edited)
I was able to get the odometer back together and it seems to work fine on bench.
What I did, was:
- Mark the shaft so I knew where the pot gear fitted.
- Grip shaft in vice at that end.
- Using center punch, punch a series of small indentations at 90 deg intervals.
- trial fitted, but would not go through casing hole.
- Using miniature file, smoothed off the punch holes until shaft would just go through casing
- with drill still in and casing supported on far side, tapped the shaft in
- Tapped a bit harder when it reached and just entered the pot gear (it went in tight)
- using a thin wire, ran a little blue Loctite into the pot gear hole (which was now blocked by shaft)
- tapped shaft all way in while making sure shaft was centered in second casing hole

Reassembled speedo and bench tested using electric drill with a Robertson square head bit. (My drill runs at 50 mph!) Numbers advanced as they should.

Haven't put cluster back in yet - Looks like the dimmer switch is kaput. Dash lights were working - It was probably in bright position. I think I will just bypass it (I did that on my 300D)
 

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#32 ·
Took steering wheel off. No reason not to. As posted earlier, it takes just a minute or so. May be easier on older cars like mine with hex nut instead of Allen type screw.

I doubt that anything useful could be done on cluster with it in place or even pulled as far as it will come with wheel in place. Shop manual says to remove wheel.
 
#33 · (Edited)
Did a final test using drill after re-assembling cluster. Speedo, odometer and trip all seemed to work normally. Went to reset trip and wouldn't reset :(

Decided to take everything apart again. At first could not figure out what problem was. Had a beer, then dinner. Came back a few minutes ago and had another look. Shoot, there is a shaft that the little gears on the trip run on - It had moved toward trip lever and was preventing it from moving properly. I pushed the shaft back in and tried again - resets normally. Failing better ideas, I will need to put a drop of Loctite on that end to try and keep the shaft in place. Otherwise it could vibrate out again. Perhaps a small spring clip washer could be used?

Just thought I should document this in case others have same problem.

This is the trip section shaft with small gears



Lever end of the shaft had been sticking out and catching on the lever



Other end of shaft

 
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