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Old 07-14-2019, 12:21 AM
Roncallo Roncallo is offline
88Black560SL
 
Join Date: Oct 2004
Location: CT
Posts: 3,510
Quote:
Originally Posted by 97 SL320 View Post
If you put a steel tube over the VR sensors body leaving only the end exposed, that might eliminate the nut interference. I'm thinking the nuts are triggering the side of the coil and not the end.
It would but there is only about 1mm clearance between the side of the VR sensor and the bolt. And the bolt only sticks out about 2mm past the nut.

Quote:
Originally Posted by 97 SL320 View Post
I'm thinking it is less of a slot ( window ) length issue and more of a metal length issue. With a short metal length you are probably running into a hall effect reaction time issue where a VR sensor reacts faster.
Not sure but simulating the hall effect sensor output and running it through my circuit show it to work best with more metal. Actually 60% seems optimum but anywhere from about 30% to 90 metal will run the speedo to full speed. The output of the hall effect goes from zero when the sensor is over the metal to + 14V when the sensor is over air. Its extremely clean.

Quote:
Originally Posted by 97 SL320 View Post
Got it, however you will be losing self locking threads that the nut provides.
Absolutely Loktite is your friend.

Quote:
Originally Posted by 97 SL320 View Post
Will the speedo accept a square wave? I'd be minorly concerned that the rapid on / off could affect charge time of a capacitor / inductor and lead to an inaccurate speedo or even component damage.
I have tried all the waves on my function generator. The speedo loves them all, Sine, square, triangle L and R saw tooth. The sine wave requires the smallest voltage threshold to get it to respond, followed closely by the square wave.

Quote:
Originally Posted by 97 SL320 View Post
As for the 100 V,was that an unloaded or loaded voltage? RE: a current transformer not connected to a meter can reach very high output voltages but when loaded the voltage drops dramatically. Increasing sensor to wheel gap is a way to reduce voltage.
Those were peek to peek voltages. I measured both loaded and unloaded. Loaded drops it about 25%. But those numbers were at very limited speeds. My lathe only goes to about 45 MPH. I also got some data at about 70MPH withe the wheels jacked up from both a stock MB system and mine. But what ever I got the speedo would need to accept twice that. You can increase the gap but you need to watch you minimum voltage threshold at low speed. That's the beauty of the hall effect although the speedo doesn't seem to care. I tried a circuit with zener diodes to keep the voltage to never exceed 12V. The circuit worked great but it didn't change a the way the speedometer worked at all.

Quote:
Originally Posted by 97 SL320 View Post
I'd go for a thin coat of plain black paint in a spray can.

Rather than going to all the effort of another wheel, why not mount a second sensor on the diffs axle flange and use the wheel you already have then use a speedo fooler to generate the needed pulses? Even with your proposed new wheel, will you have the proper pulse ratio to give an accurate speedo reading?
Its all a matter of perception, of what you feel is going to be the shortest effective path to getting the job done. And the path you don't choose may be the path you end up on after all is done.

I didn't want to use my diff wheels because they are too far removed from MB's original design 48, tooth verses 4 teeth. I know those frequency changers can shift a frequency +/- 50% but can they shift it 600%???. And then there is sure I have 48 tooth wheels but I would need to make a mount for the sensor. Both those tasks have about the same level of complexity. And then theirs why didn't MB do it that way. Why would they put both a 36 tooth ABS wheel in the diff and a 4 point wheel in the trans??? Bottom line is rarely is something ever as easy as it seems and the pitfalls to each path will only be uncovered by trying it out.
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