Yesterday my 300D speedo suddenly started reading about 10mph high. The odometer was fine (as accurate as ever). The speedo needle was a tad jumpy, but nothing too unusual. A little history, this is a 125mph (83/84 300D) unit that I put in about 8K ago to replace the silly 85mph unit. Anyway, I pulled it apart last night to see if the spring was broken or lose. Everthing looked intact. Based on some info from this web site:

http://members.ispwest.com/jkcaplan/Speedofaq/speedo.htm

I removed the needle and "preloaded" the spring by setting it's "neutral" poition about 10mph below the pin. I then CAREFULLY lifted it over the pin and reassembled. I gave it a try (using mile markers and a stop watch) and it was still about 5mph high. I repeated the process with more "preloaded" and got within about 2mph at 80mph. At that point I called it a day. I will try to check it a various speeds next time I'm on the highway for a while.

I realise this is not the proper way to calibrate the speedo, and I will get it done correctly at some point and/or keep an eye out for another used speedo. I was just wondering if anyone else has seen this behavior, and wanted to pass along my half ass fix. I'll let you know if/when it fails again, but at the moment it seems to be working OK.

the cable. is it jumping around too?

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I think the cable's OK. The speedo was only a little jump at low speeds than it smoothed out. The speedo was not spiking like the cable was hanging up then releasing. Also the cruise control was smooth. About a month ago I drove it with the cluster removed (just the oil pressure connected) while I was working on it and I could watch the cable spin.

Also, when I moved the speedo pointer to increase the spring pressure the jumpyness seemed to go away. It was acting like the speedo spring somehow got out of adjustment and lossened up, but I couldn't see anything wrong, strange.

like you know more about the subject than i do.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Hi Craig,

Is the speedo cable attached to the cluster in a particular way? I haven't really taken off the entire cluster (messy oil line) so I squeezed my hand in to check the innards.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

The cable is just screwed into the back of the speedo. Hopefully, you have enough room to reach it. If not, there are other threads here that address releasing the cable at the lower end to get more slack.

intimidated by the oil line. it wont leak enough to do anything, as long as you remember to reattach it before starting the car.

ask how i know!

and that car had the parchment mats too. what a mess.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Hi Craig, I was able to remove the speedo and plug it back in--tight. Still reads 10mph off. I'm now beginning to think it's the speedometer itself that needs calibration.

Tom, thanks, I always have a rag handy "just in case" (knock on wood). I do try to keep my car clean, just did a carpet-cleaning day not too long ago. Now I have those plastic covers over them.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

I still don't know why mine was reading high, but I've used it for about a month (2000+ miles) since I "calibrated" it by moving the needle and it's still accurate. We'll see how long it keeps working correctly.

Mine's been like this since I got it, a year and a half ago!

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

If you decide to get it calibrated, please let me know the cost and results. It's probably just a matter of time until I have to have mine done too. The other option is to replace the speedo from eBay, salvage yard, etc.