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  #1  
Old 05-21-2008, 08:55 AM
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Twin Speedo Transplant

Well, now that I own 3 diesels, I need to fix speedometer problems in two of them. Both problems are the result of previous owners replacing the speedometers with incorrect ones. With 'Beirut Taxi', my '81 240D, the seller replaced the failed original 85 mph speedometer with a 100 mph unit. While the seller insisted it was the correct replacement, when I took the car to Virginia Beach, I verified with the highway mile markers that it reads about 15% low.
As luck would have it, 'Wonder Wagon', my '84 non-turbo Euro 300TD apparently had it's original kmph speedometer replaced with a 100 mph unit that reads about 12% high - verified by comparing the distance reading from College Park, MD to Fort Belvoir, VA on my '98 Nissan Altima (31 miles) with the 300TD (35 miles). I suspect a unit for a US '84 3.07 axle ratio 300TD turbo was installed in my wagon.

I've collected several used speedometers, including an original 240D speedometer that should work with the 3.69 axle ratio in Beirut Taxi, but how to tell which of the others might be compatible with Wonder Wagon's 3.46 axle ratio. (One of those came out of an '83 300D turbo so I'm sure that one won't work)

Is there a sticker, decal or some other marking on these VDO speedometers that indicates what vehicles or axle ratios they're designed for?
If not, I suppose I could swap the low-reading unit from Beirut Taxi into Wonder Wagon and see what happens.

Happy Motoring, Mark

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Last edited by Mark DiSilvestro; 05-21-2008 at 09:02 AM.
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Old 05-21-2008, 09:07 AM
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That's interesting, just about every other car I've seen in the world simply uses a different gear where the speedometer cable attaches to the transmission. As much "original" engineering as I've seen on MB's, I would not be surprised if this was not the case for these cars though...
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Benz Fleet:
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1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250
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  #3  
Old 05-21-2008, 09:17 AM
ForcedInduction
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Quote:
Originally Posted by KarTek View Post
That's interesting, just about every other car I've seen in the world simply uses a different gear where the speedometer cable attaches to the transmission. As much "original" engineering as I've seen on MB's, I would not be surprised if this was not the case for these cars though...
I like it. Its far easier and cleaner (unless you forget to reconnect the oil pressure line! ) change a speedo than it is to remove the driveshaft, partially disassemble the tranny and swap gears.

It also saves MB from having to stock different transmissions or transmission parts for different rear end ratios.
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  #4  
Old 05-21-2008, 09:29 AM
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IIWY, I would start perusing the parts places... Pick N pull etc... the 240's are all over the place. I have 4 NA vehicles, and 6 Turbo's one of which is an 85 with it's rare 2.88 gears... So I know where you are coming from on the cars...
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #5  
Old 05-21-2008, 09:32 AM
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On the T5 tranny, it's just one bolt that holds the speedo cable gear assy. in the tailstock. Out in 30 sec. the 50 cent plastic gear is held on by a spring clip and simply snaps on the end of the assy. Total time to replace is about 5 min. if you take your time...

Mark, are there any colored gears or anything that distinguishes the speedo assemblys from one another?
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Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Last edited by KarTek; 05-21-2008 at 09:40 AM.
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  #6  
Old 05-21-2008, 09:49 AM
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there are different part #'s on the speedometers... color wise they are identical...
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #7  
Old 05-21-2008, 10:05 AM
Craig
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FWIW, the 100 mph speedo in my '83 240D is "123 542 25 57" and it agrees with my GPS within 0.5%.
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  #8  
Old 05-21-2008, 10:10 AM
ForcedInduction
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What GPS do you use? I still need to verify mine. The speed/rpm chart says my top speed should be 93mph and I should be doing 5200rpm at my "real" 107mph top speed.
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  #9  
Old 05-21-2008, 11:33 AM
Craig
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Originally Posted by ForcedInduction View Post
What GPS do you use? I still need to verify mine. The speed/rpm chart says my top speed should be 93mph and I should be doing 5200rpm at my "real" 107mph top speed.
I have a Magellan Maestro 4250:

http://www.magellangps.com/products/product.asp?segID=408&prodID=1959

Probably a little overkill (about $500 with voice, bluetooth, traffic, etc.), but my wife bought it for x-mass and seems to work well.
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  #10  
Old 05-21-2008, 12:20 PM
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Quote:
Originally Posted by KarTek View Post
On the T5 tranny, it's just one bolt that holds the speedo cable gear assy. in the tailstock. Out in 30 sec. the 50 cent plastic gear is held on by a spring clip and simply snaps on the end of the assy. Total time to replace is about 5 min. if you take your time...

Mark, are there any colored gears or anything that distinguishes the speedo assemblys from one another?
On older American cars, the speedometer drive assembly was usually a 1.5 or 2 inch cylinder clamped into a matching bore in the tailshaft. The cable/gear bearing was mounted off-center in the cylinder so that different gears could be used to compensate for the various axle ratios, and the cylinder could be rotated in the tailshaft bore to set the clearance for each specific gear.

I've read on the forums that these Mercedes match the speedometer to the axle ratio.

I DO have a correct 240D speedometer from my local Pick-N-Pull, but I haven't found a non-turbo W123 300D speedometer yet, unless I can identify one of the 'mystery' W123 speedometers I bought from someone on the diesel forum back when I was only trying to fix the 240D.
The seller couldn't recall what model it came from.

I don't have all my various spare speedometers here so I can't say if any have different color gears.

Happy Motoring, Mark
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  #11  
Old 05-28-2008, 05:24 PM
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Well, I transplanted the 85 mph speedometer from the 4-speed Pick-N-Pull '82 240D and the result is (drum roll please!) - Same error as before with the PO installed 100 mph speedometer. Though I'm certain the diff-case was marked 3.69 when I checked last year, I suppose a PO could have changed the ring & pinion. Unless someone else here knows how a speedometer/rear-end ratio discrepancy could be induced in a 240D. (And yes, I did repair the odometer drive gear before installing that used 240D unit)
Anyway, I now have 5 extra used W123 speedometers to play with, but I know two of the are from Turbo 300Ds, so they aren't compatible with my 240D, or Euro non-turbo 300TD.
Is there a part number or other ID on these VDO units that I can use to tell what version W123 they belong with?
2 of the speedometers had a decal that stated K-1425. This decal was missing from the other 3. There are also part numbers on the speedometer dials, but I'm not sure if these part numbers are for the speedometers or just the dials. Thanks in advance.

Happy Motoring, Mark
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Last edited by Mark DiSilvestro; 05-28-2008 at 05:31 PM.
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  #12  
Old 05-28-2008, 06:38 PM
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... I was just reading your original post, and I noticed that you said the mile markers indicated you were reading low compared to actual travel.
it sounds to me like somebody put in a 3.46 from a N/A 300D how is your poor 240 off the line? kinda sluggish? you might even have a 3.07. only way to know for sure is to read the indicator, but it may have the original cover with the original indicator... not sure where they put the ratio on the diffs. pulling the cover and counting the teeth on the diff is a sure way to get the ratio. you could mathmatically figure it out based on odo readings and get the exact % off then find a matching speedo for it.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #13  
Old 05-28-2008, 08:36 PM
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Quote:
Originally Posted by vstech View Post
... I was just reading your original post, and I noticed that you said the mile markers indicated you were reading low compared to actual travel.
it sounds to me like somebody put in a 3.46 from a N/A 300D how is your poor 240 off the line? kinda sluggish? you might even have a 3.07. only way to know for sure is to read the indicator, but it may have the original cover with the original indicator... not sure where they put the ratio on the diffs. pulling the cover and counting the teeth on the diff is a sure way to get the ratio. you could mathmatically figure it out based on odo readings and get the exact % off then find a matching speedo for it.
With the manual, acceleration is fine, and where I use this car in Virginia Beach, there are no hills to deal with. I used to think my automatic 240D was so much noisier because of inherent slippage in the auto-box (no locking converter), and the missing hood pad, but now I'm thinking there's something fishy with the rear-end ratio on this car. I'll recheck the diff markings tommorrow.
I'll also make a list of all the different speedometer dial part numbers, and any other important details.

Ironically, last year I was thinking about getting a 3.46 diff and speedometer for my automatic 240D to try and reduce the engine racket on the freeway. A neighbor offered to give me an '80 300D with a bad tranny.

Meanwhile, I'm almost certain my non-turbo Euro '84 300TD has had it's original Km speedometer replaced with a USA turbo 3.07 300D/TD Mph speedometer, and I'm going to need to install a 3.46 speedometer for a non-turbo 300D/TD.
If I'm lucky, one of my spares will do the trick, and if I'm even luckier, someone here might be able to identify which one of my spares should work from the part numbers.

Happy Motoring, Mark
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Last edited by Mark DiSilvestro; 05-28-2008 at 08:45 PM.
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  #14  
Old 05-29-2008, 11:36 AM
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Well, I crawled under my MT '81 240D and the cast-iron diff-housing is definitely stamped 3.69. However, I noticed the half-shafts are rebuilt replacements.
If this has the type of diff-unit that requires pulling the cover to release the inner axle joints, perhaps a PO went ahead and changed out the gears too. The son of the guy I bought this car from, did work at a Mercedes dealer.
As promised, here is the info on the 5 W123 speedometers I have here in Virginia Beach -

123 542 89 01, 80+ mph, from '82 MT 240D, Decal K=1425
Now installed in my '81 MT 240D.

123 542 62 01, 85 mph, Believed from 240D, Decal K=1425

123 542 63 01, 85 mph, Origin unknown, Decal illegible
(I'm hoping this one is for a non-tubo 300D/TD, so I can try it in my Euro 300TD)

123 542 25 57, 100 mph, Was in my MT 240D, Decal K=1425

123 542 28 57, 120 mph, '84 turbo 300D, Decal K=1200

My other two diesels are up in Alexandria, so I don't have their speedometer numbers handy. Thanks again.


Happy Motoring, Mark

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