Replacement in dash tach issues 68 - 69 RR GTX

[Meep-Meep]

I am doing some work on a buddies 69 GTX so he can get it ready to sell and one of the things on my list is to install the repo factory tach similar what is shown here -

http://firebird1979.com/serverfiles/fbshopmain2.asp?hid=112AR9915

I can't say for sure that the Year One tach pictured here is the exact same as what I was supplied with (hard to believe there are multiple vendors for this unit) but the problem I'm having is it's very sensitive to stray magnetic fields.

The design of the meter movement seems to incorporate about a billion miles of fine copper wire and since the center in dash speaker is in close proximity to the factory tach location it affects the meter movement. The speaker is a Pioneer replacement with a larger than standard magnet and when a copper coil is in the presence of a magnetic field it induces a voltage sufficient enough to wreak havoc with the meter movement. Effects of the magnetic field are seen as much as a foot away. I tested the tach on the fender and it worked fine but as I got close with the speaker it went to 4000 RPM and the reading would change as I moved the speaker. The solution in this case was to remove the speaker, which is no big deal since most people put the speakers in the back driven by the killer 500 megawatt stereo :tongueflap:

Anyway, just an FYI.

 

[Pistol Pete]

I wonder if you could shield the voice coil of the speaker. The pcb's we get in work come in these mylar lined bubble wrap packages, obstensibly to block any stray esd. Might work, might not.

 

[69HEMICORONETR/TCONV]

Great Idea !,......I know exactly what you are talking about it's anti-static material .....I would think it would be worth a try.

 

[Meep-Meep]

Yes, you can shield the tach body or the speaker magnet and this is the only material I know that makes a reliable magnetic shield -

http://en.wikipedia.org/wiki/Mu-metal

Seems crazy and most likely an expensive solution, which is why I didn't bring it up. Would be funny if the bubble wrap stuff works :grin:

 

[Pistol Pete]

Makes a great case for an iPod.

 

[69 Runner]

The link you provided takes me to a page that has instruments for the Ralley gauges, which is not what a 69 GTX has.

Maybe some metal screen type material will work to deflect and drain off the magnetic field

 

[Meep-Meep]

The link you provided takes me to a page that has instruments for the Ralley gauges, which is not what a 69 GTX has.

Maybe some metal screen type material will work to deflect and drain off the magnetic field

Strange. I thought I checked it when I posted it and I saw the non rally dash tach. Go to B body gauges non rally and you will find it.

Part # Description Price
TAC120 1968-1970 B-body models square dash tachometer. $215.0

 

[dodge41969]

Those aftermarket tachs are pretty "crappy" the font/pointers are wrong, if you have an original tach "Redline Gauge Works" can convert it using modern VDO internals and it'll be compatible with all ignitions,they can even fix the "Year One" units, I know I use to work there, I probably converted a couple hundred tachs myself, Ford,GM & Chrysler.

(661)259-8891 ask for Shannon.

 

[69 R/T]

Redline Gauge Works tach

I ordered one of those B-Body non ralley dash tachs from Shannon. It's a beauty.....but one word of advice, If you're a purist like me running an OEM points distributor, tell him that when you order it. The VDO guts don't recognize the signal from points and the reading is very erratic. This is solved with a diode he can wire in, or in my case since I didn't know about it until I called him, it can simply be soldered anywhere on the tach lead from the coil.

Once I did this...wow! Magnificent!

 

[Roscoethug]

For the replica B Body Standard Dash Tachs, I needed to shield the tach from the dash speaker magnets. I did it with a can of Campbell's Chicken Noodle Soup, a Dremel and two sided tape. First, eat the soup, remove the label and clean the can. Second, take a Dremel and cut a 1" strip of metal from the belt, and cut vertically. Do not straighten the strip. Next attach the metal strip to the "barrel" of the tack with the two sided tape. The metal must be ferrous metal, non-ferrous will not work, nor will lead. You'll probably need to remove the radio, ash tray assembly and glove box liner. Pictures below:
Before:

 

[69_A12_6BBL]

Redline Gauge Works tach

I ordered one of those B-Body non ralley dash tachs from Shannon. It's a beauty.....but one word of advice, If you're a purist like me running an OEM points distributor, tell him that when you order it. The VDO guts don't recognize the signal from points and the reading is very erratic. This is solved with a diode he can wire in, or in my case since I didn't know about it until I called him, it can simply be soldered anywhere on the tach lead from the coil.

Once I did this...wow! Magnificent!

NICE!
Thanks!

 

[69_A12_6BBL]

For the replica B Body Standard Dash Tachs, I needed to shield the tach from the dash speaker magnets. I did it with a can of Campbell's Chicken Noodle Soup, a Dremel and two sided tape. First, eat the soup, remove the label and clean the can. Second, take a Dremel and cut a 1" strip of metal from the belt, and cut vertically. Do not straighten the strip. Next attach the metal strip to the "barrel" of the tack with the two sided tape. The metal must be ferrous metal, non-ferrous will not work, nor will lead. You'll probably need to remove the radio, ash tray assembly and glove box liner. Pictures below:
Before:

View attachment 1189454 View attachment 1189458 View attachment 1189460 View attachment 1189461 View attachment 1189462

Looks great! Genious thinking too! Wonder if he still sells those?

 

[69_A12_6BBL]

Those aftermarket tachs are pretty "crappy" the font/pointers are wrong, if you have an original tach "Redline Gauge Works" can convert it using modern VDO internals and it'll be compatible with all ignitions,they can even fix the "Year One" units, I know I use to work there, I probably converted a couple hundred tachs myself, Ford,GM & Chrysler.

(661)259-8891 ask for Shannon.

Do you still repair or sell these Tachometers? I have an OEM one in my 69 RR, but its not working. They look great!
Thanks!!

 

[Gary Gaz]

For the replica B Body Standard Dash Tachs, I needed to shield the tach from the dash speaker magnets. I did it with a can of Campbell's Chicken Noodle Soup, a Dremel and two sided tape. First, eat the soup, remove the label and clean the can. Second, take a Dremel and cut a 1" strip of metal from the belt, and cut vertically. Do not straighten the strip. Next attach the metal strip to the "barrel" of the tack with the two sided tape. The metal must be ferrous metal, non-ferrous will not work, nor will lead. You'll probably need to remove the radio, ash tray assembly and glove box liner. Pictures below:
Before:

View attachment 1189454 View attachment 1189458 View attachment 1189460 View attachment 1189461 View attachment 1189462

I tried this with the can, and the needle went from almost 4k sitting with key off to now almost about were yours was sitting, next I'm going to try and attach a magnet to the speaker to see if this will reduce it further, I had it working under the dash frame and there was no interference. as soon as in dash there was, its the aftermarket dual speaker that fits the factory hole

 

[Roscoethug]

The magnets in your speakers must be pretty strong. I suppose you could double up on the soup can shielding. Does the tach read correctly with the engine on?

 

[Gary Gaz]

I have only taken it out to get gas since the replacement and shielding.
Its idle reading is more like I saw with it out of the dash
I need to see what reads at open road speed to know if different or not
thanks