w123 speedometer options - PeachParts Mercedes-Benz Forum

NCfriend · #1 07-05-2011, 01:30 PM

Hey folks, sorry but I was getting lost on my forum searches
so here is the question:

Can I use a 1984 300D turbo's speedometer on a 1983 240D?

First guess is it will be way off because of engine speeds and gear ratios...
Is there a simple way to adjust or conversion part to include and make this work close to accurate??

Please advise

kerry · #2 07-05-2011, 01:35 PM

Gear ratios will be different I think. Simplest solution is a gps.

panZZer · #3 07-05-2011, 01:37 PM

fulcrum converted his--read his thread.

charmalu · #4 07-05-2011, 03:01 PM

Yes you can use the 84 300d speedometer on your 83 240D. How ever it will not be accurate.

The 84 300D has a 3:07 Differential, and the 240D uses a 3:69 Diff. The MB Spedo is geared to the Diff. so either swap in the 3:07 diff, (which will be geared higher, or about 20%) or find another 240D spedo.

Charlie

NCfriend · #5 07-05-2011, 06:40 PM

Thanks for the explanations so far.
Very different gear ratios from the diff is what I expected, but..

#1) I can't find "Fulcrum's" thread about this conversion

#2) I thought I read a post long ago that referenced some website, where they sold something like a reducer or converter to plug in-line with the speedo cable and correct for speedometer-differential variations?

any directions on these, please

vstech · #6 07-06-2011, 09:59 AM

what's wrong with your original speedo?

martureo · #7 07-06-2011, 04:04 PM

Yes, you can convert it to run accurately. But it takes a bit of work and lots of patience.

There are three main things that must be changed from your original to the "new" one.

This worm gear and the brass spur gear it drives MUST be replaced with the originals from your 240D odo/speedo unit.
http://dieselgiant.com/mbodo21.JPG

You must also replace the speedo face, otherwise it will just display an inaccurate speed.
-Lift speedo needle off of rest and mark where it sits neutrally
-Remove speedo needle (two spoons method works well)
-Remove two screws
Installation is reverse. Just make sure to put the needle back on in a neutral (not sprung) position where you marked it.

(I cannabalized a 240D and a 300D n/a speedo to make a fully functional, zeroed odometer and accurate one for my 1984 300D turbo. And I found all the wrong ways to convert them.)

IVIuzzy · #8 07-06-2011, 11:05 PM

if u need one for a 240 let me know, i have a couple. the gearing is way off, probably more trouble than its worth to eff around with retro fitting a 300d one

charmalu · #9 07-07-2011, 02:01 AM

Quote:

Originally Posted by martureo

Yes, you can convert it to run accurately. But it takes a bit of work and lots of patience.

There are three main things that must be changed from your original to the "new" one.

This worm gear and the brass spur gear it drives MUST be replaced with the originals from your 240D odo/speedo unit.
http://dieselgiant.com/mbodo21.JPG

You must also replace the speedo face, otherwise it will just display an inaccurate speed.
-Lift speedo needle off of rest and mark where it sits neutrally
-Remove speedo needle (two spoons method works well)
-Remove two screws
Installation is reverse. Just make sure to put the needle back on in a neutral (not sprung) position where you marked it.

(I cannabalized a 240D and a 300D n/a speedo to make a fully functional, zeroed odometer and accurate one for my 1984 300D turbo. And I found all the wrong ways to convert them.)

Are pulling the brass gear off it`s shaft? or are you pulling the bushing off the other end and sliding the shaft out, and swaping in the new gear and shaft? Iam sure the Brass gear is on there pretty tight. I have pulled the bushing off, it comes off easy. I have had them tore down to the last nut and bolt when swapping in a different Differential and using the spedo from the doner car. then you need to adjust for the correct milage.

this is also a good time to fix the possible slipping potmetal gear.

Charlie

martureo · #10 07-07-2011, 04:03 PM

Quote:

Originally Posted by charmalu

Are pulling the brass gear off it`s shaft? or are you pulling the bushing off the other end and sliding the shaft out, and swaping in the new gear and shaft? Iam sure the Brass gear is on there pretty tight. I have pulled the bushing off, it comes off easy. I have had them tore down to the last nut and bolt when swapping in a different Differential and using the spedo from the doner car. then you need to adjust for the correct milage.

this is also a good time to fix the possible slipping potmetal gear.

Charlie

Oh yeah, that brass spur gear is on tight. The key is getting it off without bending the shaft. But it can be done. Or you can use the old spur gear on the shaft by removing it from the odo completely.

x2 on the potmetal gear

panZZer · #11 07-07-2011, 04:08 PM

Quote:

Originally Posted by NCfriend

Thanks for the explanations so far.
Very different gear ratios from the diff is what I expected, but..

#1) I can't find "Fulcrum's" thread about this conversion

#2) I thought I read a post long ago that referenced some website, where they sold something like a reducer or converter to plug in-line with the speedo cable and correct for speedometer-differential variations?

any directions on these, please

http://www.peachparts.com/shopforum/members/fulcrum525.html

vstech · #12 07-08-2011, 08:48 AM

Quote:

Originally Posted by vstech

what's wrong with your original speedo?

can we get an answer on this question?