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1993 300TE, 1995 E320 Wagon
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Discussion Starter · #1 ·
For the past several months, the speedometer in my 560 SEL has been acting wonky. There seems to be no discernable pattern to it, but occasionally the speedo just quits (and the odometer with it). Sometimes it never gets started up, then will jump to speed (usually when the car gets to around 40 mph or so). Then it might (or might not) drop out again. Other times it just drops out, even at 60-70 mph. Usually if it's not working, stepping on the brake (even lightly) will activate it, but it usually drops right out again when I take my foot off the brake. Sometimes only a real stomp on the brakes will activate it (I only do this at low speeds on deserted side streets). Other times, it'll be working, and hitting the gas will cause it to drop out (and then coasting will reactivate it). Sometimes a lateral force will drop it out/reactivate it. I was once doing about 75 on a long righthand curve on the freeway, and it dropped out, only to come back on when the road straightened out. I've been able to activate it at low speed by throwing the steering rapidly left and right (on an empty side street of course). I have noticed that it usually works on the first trip of the day (taking my son to school, for instance), but then won't work when pulling away from the curb after dropping him off. It's just weird-- has anyone else had this sort of behavior?

I've traced through many "speedo" threads here and elsewhere, but haven't been able to find much. I've replaced all the fuses with new coppers, replaced the OVP, cleaned and tweaked all of the sensors on the wheels and tranny(North Hollywood Speedometers said that the speedo reads all three different sensors-- not sure it this is accurate). I've disconnected/reconnected the wire at the back of the speedometer, I've whacked the top of the dash and the face of the cluster while driving (frustration's a bitch, isn't it?), all to no avail.

Needless to say, this makes my cruise control inoperative (not always, though), and my calculated gas mileage surely takes a hit because the odo reads maybe 10-20% low when the speedometer is on the fritz more often (my last tank lasted "only" 160 miles), for a whopping "8.5" mpg. On top of that, it's just frustrating to look down at the "crippled" speedometer needle, just sitting there paralyzed, when it should be telling me how much fun I'm having! On the upside, the car is "younger" that it reads (129k miles).

Does anyone have suggestions? I'll look into anything, short of selling the car!
 

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1990 Mecedes-Benz 420SEL
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1,217 Posts
Red, you may have a problem with the speedo unit itself. I dimly recall some members resoldering something in the unit, but I think I would look for a relacement unit (they're separate) or send it for reconditioning. Palo Alto Speedometer does fine work on speedos from older cars - I've used them twice.

Dave
 

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1991 350 SD, 1984 500 SEC, 1982 280 SE Euro
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48 Posts
check the alternator. The same thing was happening to me and my alternator belt had popped off. Good luck
 

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1993 300TE, 1995 E320 Wagon
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1,895 Posts
Discussion Starter · #4 ·
Thanks for the responses so far! I pulled the cluster today and took off the speedo unit-- didn't see anything obviously out of order. I resoldered some of the connections (there was some discoloration), but haven't had it back together long enough to see if everythings fixed. The way things have been going on my other problem (the classic high idle), I doubt it. I also replaced the oxygen sensor today, and put in new plugs. Little by little, I'll have renewed just about everything that has something to do with ignition....
 

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1993 300TE, 1995 E320 Wagon
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Discussion Starter · #6 ·
Yes, it's true they can repair it-- for a cool $400-500. That and the fact that the info they gave me caused me to doubt their sincerity in trying to rebuild/refurbish mine. That amount of money buys a good deal of labor and parts, so I thought I'd try and do a bit of my own attempts first. It also strikes me that I could get a complete cluster for less than that-- and my cluster is in really good shape w/no fading! The way it's acting sure seems like a loose wire/cracked solder joint, so I hope my resoldering attempt

I'm still wondering if anyone else out there has had a similar experience...?
 

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1990 Mecedes-Benz 420SEL
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1,217 Posts
Yes. Try Palo Alto Speedometer. The highest I paid for a ’68 Cutlass speedo repair was $105. OR... you can try re-soldering the contacts on the speedo circuit board, but I think this is probably futile. You may be lucky, but think about the process: Pull the cluster, remove the speedo, re-solder the board, replace the speedo, reinstall the cluster, test the speedo, either HIGH-FIVE OR: curse, pound on the dash, resolve never to use your soldering iron again, pull the cluster, remove the speedo, send to PAS, get it back knowing it is at least eliminated as a problem, reinstall, hopefully it works, if not, you have to go back to ground zero.

Looks to me from your first post you have tried everything but the speedo repair. I spent a half-hour on the forum search and could not find another suggestion for you, Red. You seem to have done everything to eliminate issues except for the speedo.

If you are unwilling to spend the money, you may be able to find one from the junkyard. I hope you have good luck.

Dave
 

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1993 300TE, 1995 E320 Wagon
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Discussion Starter · #8 ·
Thanks Dave for your input (and especially your time on my behalf on the forum search). After my experience at North Hollywood Speedo (it's about 5 minutes from my house), I'm thinking of trying PAS. Then again, I'm hoping for the "high five" to happen this week!
 

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500SEC (560 Euro-spec) , 190E 2.6, W-124 E320, W-124 300CE(560 Euro-Spec EFI Eng),CLK55 AMG
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163 Posts
Had exactly the same problem on my 500 SEC.
The speed sensor cable between the A.T. & speedo had been crushed @ some stage & hence intermittent speedo reading.
Also check that the speed sensor fixing bolt (10mm) at the A.T. is screwed in all the way.
JR.
 

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1993 300TE, 1995 E320 Wagon
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Discussion Starter · #10 ·
Thanks John-- I'll look into the wire path-- it would make sense that the wire is getting pinched, given the symptoms. Where/how does it lead to the AT from the cluster? Is the sensor easy to get at on the AT, and can I R/R it for inspection/cleaning?

BTW-- do you know whether the speedo reads anything from the front wheel sensors, or are those just for the ABS? North Hollywood speedo said that it reads all three-- but other people I've spoken to said no.
 

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Premium Member
1990 SEC
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4,289 Posts
ElRojo said:
BTW-- do you know whether the speedo reads anything from the front wheel sensors, or are those just for the ABS? North Hollywood speedo said that it reads all three-- but other people I've spoken to said no.
The speedo reads the automatic transmission. The wheel sensors are for the ABS only. Which is why the ABS gets upset when you put 14" wheels up front and 20" wheels in the back, while the speedo is simply 15% slow. :D
 

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500SEC (560 Euro-spec) , 190E 2.6, W-124 E320, W-124 300CE(560 Euro-Spec EFI Eng),CLK55 AMG
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163 Posts
G'day ElRojo.
To answer your questions, yes the sensor is easy to get to.
Firstly, jack-up the front of your car(the higher the better) & loosen the AT rear mount, however make sure you support the AT with a trolly jack.
Once you've removed the rear mount slowly lower the AT a few inches.
The sensor is located @ the left side of the AT housing near the drive-shaft flexible coupling.
Look closely & you'll see the 10mm fixing bolt. It may be covered with a considerable ammount of grease & grime due to its position. Simply remove the bolt & ease the sensor out.

The wire enters the car body & obviously ends-up @ the speedo & my investigations show this to be a direct link.
I'm 99% sure the speedo has nothing to do with ABS operation as the front wheel sensors & ABS diff sensor seem to be directly connected to the main ABS control unit.

Rgards-----------------JR
 

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1993 300TE, 1995 E320 Wagon
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Discussion Starter · #14 ·
Electronic Speedo Issues- Resolved!

I just thought I'd post the results of my repairs for future reference-- in case someone else has the same problems I did.

I ended up doing four things, and the speedo has worked correctly for the last month or so. I think the last two fixes did the trick, but I'm not sure which made the real difference (I suspect #3, though).

1. Removed the cluster, dismantled it to remove the speedometer, and resoldered the connections on the back of the unit, especially the larger ones.

2. Removed the sending unit from the transmission a la John Rose 65's instructions. The unit was pretty clean on the outside, and darned near spotless on the inside. I did not drop the tranny to get at the sender, but this would have made access quite a bit less awkward and cramped.

3. Removed the cluster (again) and resoldered connectors #3, 5, and 7 in the 8-pin module at the back of the unit. #3 is ground, #5 is the sensor, and #7 goes to "terminal 15" (a mystery to me). All of these were mentioned in the manual as points for testing the speedo.

4. Carefully rearranged the wiring harness in the cluster housing (behind the actual instrument cluster) to relieve any strains and/or pinching when replacing the cluster back into the dash.

As I mentioned, there hasn't been a problem for over a month. Hope this helps someone down the line!

Dave
 

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1988 w 126 300sel, 1972 280se 3.5, 1997 r129 sl320
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5 Posts
hello, i realise this is an old post but hope to receive some feedback.

regarding this problem:
- my sensor ohms out a 2.1Mohms (not Kohms)
- i get increasing voltage readings during acceleration but at a really low voltage
,061v AC at 60 kmh

does this mean the IC on the speedo pc board is defective or the capacitors?

thanks for any feedback
 

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1988 w 126 300sel, 1972 280se 3.5, 1997 r129 sl320
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5 Posts
my car is a 1988 w126 300sel
the speedo is not working and i am measuring as the db workshop manual instructs from pin 3 + 5 on the dashboard with all plugs connected. sincere thanks!
 

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Super Moderator
1986/1990 W126
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18,056 Posts
Hi John.

Where are you in the world? If you can add this to your profile it helps people to answer technical questions.

However, this one might just have us stumped I'm afraid.

We do have a member JamesDean who repairs electrical stuff and knows it all inside out. He may see this and be able to help.
@JamesDean
 
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