So I recently bought a 1984 300SD. The speedometer does not work, and the previous owner told me that he had replaced the transmission with the W123 version which has the mechanical speedometer output, not an electronic speedometer sender. I was thinking about a universal sender to hook up to the mechanical output, but I can't seem to find anything that is advertised to work with a Mercedes. (I see plenty of options for Ford, Chrysler, GM stuff) I've also thought about getting a GPS sender, but I'm not sure that the W126 speedo uses the same type of signal. Does anyone have any ideas for getting my speedometer working without changing the transmission?

I once had a different differential put in a truck and the speed was off on the speedometer due to a changed ratio... So I went to a "speedometer repair shop" (large cities have these) and they made me a "custom" reduction box (connected between cables) and that made the speedometer accurate.

I got the impression they could do anything speedometer related, even a bit of magic! So may want to see if your city has a speedometer shop or maybe in a larger city near you.

I'll look into that for sure. At worst, maybe they could adapt a GM TH350 sender to mating to the speedo output on the transmission. Does anyone know why hooking up a GPS sender wouldn't work. This looks simple and reasonable:

https://m.summitracing.com/parts/izl-s9020?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-intellitronix-corp&gclid=CMOLk9Sg-NICFRBEfgod18IPhA

Will my speedometer be compatible with the signal this thing puts out?

I am confused as to why the 126 inst cluster can't work... Was the differential swapped out too? At least on my 300SE the electronic speed sensor is mounted on top of the differential.

__________________
-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

Any particular reason that the original W126 electronic style sender couldn't be installed in the transmission? The W123 is mechanical, the W126 is electronic.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

As far as I can recall the W126 sender unit is built into the W126's transmission harness. It bolts into the tail shaft housing on the transmission. There is a special gear in there that is read by the sender. So you would have to swap tail shaft housings reverting back to the W126 unit and then plug in the sender unit that (hopefully) is still on your transmission harness.

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Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Please disregard my previous post where I said the sensor is on the differential. Turns out I was thinking of the ABS sensor not the speed sensor. I went through all of that several years back in this thread here:

My Differential FELL OUT WHILE DRIVING!! W126

At any rate, that's what I was remembering not the speedo sensor. Sorry for the bad info.

__________________
-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition