Upgrading the tachometer, to remove that bounce Options

[timothy_nd28]

First I would like to give thanks to Terry, my uncle, for his time on this and my other RGB backlighting project. He has spent more time working on this than he cares to admit. He's more of a Corvette guy, but his vast knowledge and willingness to help, transcends which benefits our community.

Okay, so I have been told that our tachometer has a problem with bouncing. I personally have never seen this problem and I have to admit that I've never really paid much attention to the tach while driving, so I decided to put the signal generator on the tach and see how it performs. This signal generator bypasses the ignition system and provides a clean signal. This also serves as a control because a bad condenser on the dizzy can cause problems as well.

This video shows the untouched tach in its original state running on a function generator. As you will see, it does bounce and over shoot during the sweeps.

https://www.youtube.com/watch?v=rbC37l1z_oA


This next video shows our tach but with a cheap modern 30 dollar tach stuffed inside. The bounce seems to have disappeared, and there is no more overshoot during the sweeps.

https://www.youtube.com/watch?v=cmk1lSop_iE



The VDO tach was designed for mass production and had a very simple but effective design. This modern tach uses an air core massless motor which is controlled by sine/cosine inputs which tends to be a bit more responsive and accurate. The original vdo design is a motor/spring contraption which will always have some bounce. Over time, capacitors and dampening fluid may leak or fatigue which will aggravate the problem.

In this write up, I will show how to incorporate a off the shelf 30 dollar tachometer commonly found at the auto parts store, and make it work with our VDO gauge can.

[Optimusglen]

Taking another approach. Thought I would share.

I was liking the idea of a different color gauge face a'la the Singer Porsches. (er, some of them) I thought that instead of messing around with the resistor, why not change the face to display the lines/numbers in the same orientation and spacing as the aftermarket tach, ya know, since I was changing the face anyway.

I measured out the Bosch tachometer in the two previous posts and created a drawing with the lines at the same angles and spacings. The only difference is the face is sized to fit within the VDO tach, and I used VDO style text and lines.

I placed my redline where I wanted, from what I could tell this is the proper redline for the engine I'm putting in, from a 1971 911T. Obviously this can be changed easily to match the engine/car.

Black
(IMG:http://www.914world.com/bbs2/uploads_offsite/c1.staticflickr.com-19709-1521140463.1.jpg)

Blue
(IMG:http://www.914world.com/bbs2/uploads_offsite/c1.staticflickr.com-19709-1521140463.2.jpg)

The workflow here would follow the same steps for removing the selector switch on the rear and routing the wires. It would skip the resistor change. You would still follow the mounting bracket instructions. And you would add the new face.

I have a really high quality printer at home, so I'll try printing my gauge face on high quality luster paper first. If that doesn't turn out I'll probably look into having the image printed on aluminum.

If anyone else is interested, I can send you the SVG file I made. This is a vector file that you can open using Adobe Illustrator ($$$) or Inkscape (free) With this file you can change your redline, gauge color, line/number color, or even add other graphics. Just shoot me a PM with your email address.