Pagoda SL Group
W113 Pagoda SL Group => Electrical and Instruments => Topic started by: RAY on June 20, 2021, 20:44:06
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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 ?
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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?
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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
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Just thinking: maybe, given time and patience, these little plastic gears are topic for 3D design and printing?
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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 ?
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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
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Fantastic, Thanks Wre.
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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 ?
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Hi,
afaik there are only different cable for LHD and RHD and reading for km/h and mph.
...WRe
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The odometer-zeroing knob is different.....
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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.
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The odometer-zeroing knob is different.....
Indeed! ...WRe
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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 ?
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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
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This is interesting, can anybody remember who made the presentation or remember any more details ?
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https://www.sl113.org/wiki/PUB/Dash
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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
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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
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I also do not see where... having scrolled down the page.
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Indeed, there are now many pages, where until this morning there were only 4
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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.
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Thank you Peter, it is clear now.
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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.
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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
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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.
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Ray
Colin installed the Getrag in my car in 2015. My car is French registered (CH-692-LP) if Colin needs to dig out the paperwork for what was done.
Regards
Andrew
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Hi WRe,
I enquired after a refurbished LHD speedo for sale at Vintage Euro Parts and they checked the numbers on the back and it reads W1520.
So they don't correspond with the 'WEGSTRECKENZAHL' numbers suggested by yourself.
Any ideas ?
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I expect that the W numbers that WRe gave are for a km/hr speedometer; i.e. the number of cable turns per km travelled. The speedometer at VEP is probably in mi/hr; so would be stamped with number of cable turns per mile travelled.
If that assumption is right, then the VEP speedometer would correspond to a 4.08 rear end, according to WRe's numbers, because 1520 X 0.6214 = 945 (where 0.6214 is the number of miles in a km)
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I had two speedo adjusted by a belgium guy one for the pagode and it was calibrated by grindind some magnetic block slowly with trials after measuring the distance after 50 wheel rounds and measuring how many turns on the propshaft….
The other speedo was for a jaguar and the adjustment went by stretching more or less a spiral spring as he said but it seems still dtrange for me 🤔
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Meyer, Good point, well made.
Thanks.
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Don'tcha love that 3.46? My '68/69 car came with a 4.08 and I couldn't get through some large intersections without shifting. There are different tastes, of course -- as in motor oil and pizza -- but that 3.46 is just about right for me.
The "recalibration" needs to be rethunk from another direction, which will eliminate the odometer issue along with any need to mess about in the exotic innards of the speedo head.
Yes, there is a little box thang that does it for you: alters the rotational speed between cable drive output and speedo head input, giving you the appropriate input for distance and rate right at the speedo fitting behind your dashboard. It's done with gear sets in a small gearbox inserted into your drive cable -- buy a nice new one to be so modified and give years of trouble-free service. Have it mounted in the middle area of the cable so that it can benefit from the factory cable retainer there on one of the bellhousing boltsand locating it pretty much out of sight as well.
They used to be much more common but some old-school speedo shops still have the kits of various gears and the small gearcases to contain them. (Joe has some of it somewhere but has a hard time locating it, and the go-to guy for that gizmo in North America passed on some years before my similar quest, leaving his son in the business of selling radioactive headlights and lacking headspace to even consider anything not using solid state electronics: total deadend there.
I got mine from Powl's Speedometer, 2340 Dairy Road, rural Lancaster PA. www.powls-speedometer.com (717) 898-2552, a small business in southeast Pennsylvania.
You ought to be able to connect with someone closer than that, of course, and I did drive my car up to them, but it could easily be done remotely if everyone kept their heads. My relevant diff ratios were 4.08 and 3.46. This is a 15% reduction from the larger to the smaller. The M-B TDM lays all those diff drive #s out so i could see that M-B chose their ratios in 5 and 10% increments -- which is how I arrived at the happy choice of my 3.46 diff in the first place--so as a customer I knew that I wanted the gizmo to give me rotational data input at the speedo exactly 15% less than the cable drive delivers out of the transmission. So the speedo shop folks didn't have to go through all the road-testing and whatever other usual gyrations necessary to discover what needs to go into the little box. And all I had to do was convince them to take my word for it: "15%". And I relied on M-B to've given me an accurate speedo setup in the first place. The resulting setup reads out more accurately than my ability to measure; that is, real-world performance is closer to GPS than I can differentiate with my poor equipment: it is 'spot-on' for our purposes.
I thought this was here in the Forum years ago; odd it doesn't come up in searches. But then I once searched for "oil" in irritation and spite and got......no result. And it is a terrific resource the rest of the time, no argument there.
Possible web searches: mileage settings tachographs (?) Their usual work is accurizing speedos to 0 error for biz & govt.
It is, admittedly, another dying art.
All best all,
Denny
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I thought this was here in the Forum years ago; odd it doesn't come up in searches. But then I once searched for "oil" in irritation and spite and got......no result. And it is a terrific resource the rest of the time, no argument there.
Possible web searches: mileage settings tachographs (?)
Remember where you are searching… if you are in a topic, and then use the Search box at the top of the page, you are only searching in that topic.
To search the whole forum, go to Home on the menu bar, and then use Search on the menu bar.
Peter
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Mine was exactly the same as your's Denny, 4.08 and as we do the most milage cruising rather than town driving the 3.46 is perfect I think ..... but I am looking to see if there is a way to get mine to pull away every time in first gear (automatically) which for some reason randomly it does anyway but with no warning, then I may consider fitting a 3.27.
Thanks for all the info, I did not realise just how 'exotic' the innards of our speedo's are until I started looking into this subject. Certainly would not want to take one apart myself, way above my skill set.
Best
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Ray
Is it worth asking Speedy Cables if they can do anything,
speedycables.com
I know they have done some cables for Pagodas.
Keep safe
Paul
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Hi Paul,
Yes they have done work for me in the past and I will possibly go back to them but at the moment, in reality, they are on a 4 month turnaround at best I believe !
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I have a rear axle stamped 3.25 .... it has been fitted by the PO but i don't find any reference about that ratio, is it a "american" ratio used there?
And of course my speedo is not accurate i read 110 when the GPS indicate 100 !
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Yves,
In my experience the ratio is inscribed on a smooth-faced boss, low and forward on the left side of the differential case. It is not stamped, not at all bold and appears hand-drawn in a rather elegant hand as though scratched by a fine-pointed sharp tool. It can be quite plain once spotted but does not jump out at you from a 50-year old undercarriage.
The M-B Technical Data Manuals I have are in English. They do not list a differential ratio of 3.25 but do show the 3.27 ratio.
Peter,
Thanks. Your apparently ubiquitous overwatch is, well, comforting, and an incalculable contribution to the whole sl113.org effort.
Cheers,
Denny