Recalibration

[RAY]

My speedo needs to be recalibrated due to a rear axil change making it about 13mph out when doing 70mph.
A friend mentioned he believed there is a 'gadget' that can be added to the speedo cable drive that will achieve the same thing.
Anybody seen or heard  or used such a gadget ?

[Nicolas Aristodemou]

You can find on eBay speedometer gear reducer adaptors that will multiply or reduce the speedometer cable rotational speed. But is is very hard - if not impossible- to find the correct ratio that will give you the correct reading. Plus you would need adaptors to connect your cable to the gear reducer making the whole exercise very difficult.

A speedo recalibration would be easier to read the correct speed, the odometer however would still show the wrong distance travelled since a recalibration does not correct this issue.

Maybe you could use the speedometer from the car that the rear axle was sourced from, if it fits, and if the car had the same tyre size as the ones on your car?

[Desertpagoda]

and, I learned the hard way that NH or Palo Alto cannot adjust the odometer, only the speedo. They forgot that detail until AFTER they had spent $400

[Pawel66]

Just thinking: maybe, given time and patience, these little plastic gears are topic for 3D design and printing?

[RAY]

Now considering purchasing another, not necessarily new speedo and the question is ;

When anyone buys a speedo is there any way of knowing what that speedo is calibrated for axil wise. Are there any marking anywhere on them. Seems to me that anyone who does buy a speedo should have some way of knowing if it will be accurate for there car.

Anyone have a speedo for a 3.46 diff ?

[WRe]

Hi,
the corresponding "Wegstreckenzahl" W is printed on the back.
- 4,08  rear axle : 945 revs or W=0,945
- 3,92  rear axle : 908 revs or W=0,908
- 3,75  rear axle : 869 revs or W=0,869
- 3,69  rear axle : 855 revs or W=0,855
- 3,46  rear axle : 801 revs or W=0,801
...WRe

[RAY]

Fantastic, Thanks Wre.

[RAY]

Is there any difference between a 280 speedo, which i need, or the 250/230 in either appearance, the speedo cable attachment or the fitting/clamp ?

[WRe]

Hi,
afaik there are only different cable for LHD and RHD and reading for km/h and mph.
...WRe

[450sl]

The odometer-zeroing knob is different.....

[Garry]

Also remember when buying a speedo that it is either LHD or RHD speedo with the input on the rear angled left or right handed.

[WRe]

The odometer-zeroing knob is different.....

Indeed! ...WRe

[RAY]

Thanks Guys.

Of course the other 'difficulty' will be getting the mileometer to read the same as my original.

Any idea's how this can be achieved ?

[lurtch]

Hello All,

At the PUB in 2009 there was a presentation by one of our members about speedometer  calibration.

I seem to remember the presenter saying something about an adjustment that could be made to something called a "drag clutch" which regulated the speed of the spinning magnet core by increasing the amount of friction on the shaft. Cannot remember the exact details but it required a jewelers screwdriver to increase or decrease this friction with minute 1/4 turn adjustments. This then required a series of trial-and-error test drives (using a GPS iPhone app as the standard for real time road speed) to dial in the correct setting.

Larry in CA

[RAY]

This is interesting, can anybody remember who made the presentation or remember any more details ?

[Peter van Es]

https://www.sl113.org/wiki/PUB/Dash

[FGN59]

Hello Peter,

I for one have been looking all over for something like these presentations, and would be fascinated to read them. But there's nothing I can do except stare at the first page of each. There is no download, no link, nothing?

Thanks

[DavidAPease]

Hello, François,

I was thrown by this for a minute, too.  However, I just scrolled down the page, and all of the presentation was there.

             -David

[Pawel66]

I also do not see where... having scrolled down the page.

[FGN59]

Indeed, there are now many pages, where until this morning there were only 4

[Peter van Es]

It used to be a presentation in the old .swf format (Shockwave Flash) until the Denizens of the Internet decided that was insecure. So many moons ago I converted it into a series of screen shots. Because of the shadow, they are rather large, and take a while to download. Visit the site when it is less busy and if need be, refresh your browser (typically F5)

If you have slow internet connection, be patient.

[FGN59]

Thank you Peter, it is clear now.

[FGN59]

Assuming I saw all of the presentation, it was really helpful in identifying most components and some electrical fixes.

I would still be interested in information on the inner workings of the speedometer and tachometer and possible adjustments that can be made.
Larry in CA alluded to something I have been wondering about : how does one translate the spinning motion and revolution speed of both cables into displayable information on a dial with a needle? My guess is through a spinning coil in a fixed magnetic field generating an electric current that moves the needle in another coil/magnet setup, and the question that comes next is: how does one calibrate the needle movement? Through a variable resistor? I haven't been able to find anything on the web about his.

[AGT]

Ray

When Colin Ferns fitted a Getrag gearbox to my car we couldn't get the correct speedometer drive cable at the time.  Instead Colin fitted a "box" which is calibrated to read the road speed from turns of (I think) a magnet on the propshaft.  The speedometer needle can flutter a bit at slow speeds but is remarkably accurate against GPS from about 20kph upwards.  The odometer also works.  The "box" has been in my car trouble free for six years.

It would be a very non-intrusive fix for your issue.  Have a word with Colin for a more enlightening explanation.

Regards
Andrew

[RAY]

Many thanks for your post Andrew, sounds like and interesting fix.

Colin does most of the work on my Pagoda anyway , i'l have a word.