[racerboy]

I was thinking of possibly swapping the points out of my '70 RA III distributor and use the M&H Breakerless SE system. Is the one that Ames sells the same unit? THey look identical, but Ames does not refer to it as an 'M&H' unit, only as AP (Aftermarket Product). In the long run, I think I will send my distributor to Dave's small-body HEIs, but figured the M&H conversion could happen much more quickly.

thanks

[Peter Serio]

Be forewarned that if you have a factory tach in your dash & it is working now off of your points distributor; and you change that to something modern, such as pertronix or GM-HEI your tach will no longer function. The original tach for all 1970 GM cars had a one wire plug-in on the back. That circuit board is designed for a points signal (a pure square wave). If you change your points out for something new you will have to replace the circuit board inside of your tachometer so that it has an accommodation for a 2 wire plug-in on the back. The HEI compatible board is more complex in that it has a transistor in the circuit. Therefore it requires a separate power supply (12 volt "+") and another wire that looks for the RPM signal from the coil.

The power wire is a 12 volt + signal (key on) from the fuse block, run thru a 1 or 1 & 1/2 amp in-line glass fuse. The other wire is the same one you have now, it's the wire from the "-" side of the coil to the back of the tach. That wire carries the RPM waveform information from the ignition system to the tach.

[racerboy]

Thanks Pete. I did not realize that. Is that true of any conversion? If I want to eliminate the points, I have to modify my in-dash tach as well? I am not interested in running an aftermarket tachometer

[racerboy]

If I do have to modify the in-dash tach, is that very complex (other than getting it out in the first place)

[428goat]

Used Dave’s small body and a MSD 6al and my hood tach works fine plugged into the MSD box. The MSD box is hidden up under the dash so everything looks stock.

[Peter Serio]

If the car you are working on is the red car in your tiny photo then yes. Those 2nd Gen Firebird Trans Am style tachometers are very fragile. The main tach-speedo cluster has to come out first then the tach-clock assembly comes out from the back. The clock is in there which you have to be VERY careful. The second hand on that clock is made from aluminum, and it is easily bent or broken. NOTHING comes out from the front as far as getting into the tachometer circuit board!!! You do need to remove the clock set-knob as well as the front lens but after that it all is accessed from the backside. The printed circuit; that has to be about 1/2 way removed and very gently folded over out of the way. I take those all the way off anyway, most often they are old & brittle & need replaced. The meter movement to that tachometer is easily damaged by lint, dust or dirt getting in around the magnet. There is an inspection sticker on the back of that tach right behind the magnet. Often that inspection sticker is missing or torn. Road dirt will find it's way inside of there and stick to the magnet. A tiny piece of dust or dirt is all it takes to hang up the moving coil. That coil is attached to the white pointer via a long formed (bent) aluminum tube. DO NOT mess around with that little tube or the pointer. If that gets bent the meter could be ruined!!!!

[racerboy]

Hi Pete. My car is a 1970 GTO Judge. It has Rally Gauges (no clock), but it sounds like the info you provided is the same. I will have to remove it to get to the tach if I want to go with one of these breakerless ignitions.

[Bill Hanlon]

Peter:
I won't argue that using a GM tach designed for points on a later electronic ignition system could/would destroy the tach, but I will take exception to your statement "a pure square wave".

Back EMF from the coil in combination with the condenser will cause oscillations on the coil - terminal that can be as high as 200 volts positive or negative FOR A VERY SHORT PERIOD OF TIME, maybe a millisecond or two, after the points open. Need proof? Either put an oscilloscope on the coil - terminal or just grab the terminal with your fingers while the engine is running. Most people can't feel 12VDC, but I'll bet one could get a decent jolt from the coil -.

[racerboy]

Instead of swapping in a conversion to my original RA III distributor, I am going to have Dave do one of his small-body HEI conversions on a ‘70 455 distributor that’s been on my shelf for years. Will keep the group updated on that progress.

On a related note, I am likely to change the cam this winter. Would you do both at same time, or would you get engine running with new cam and old distributor first? I remember reading something somewhere that when firing up a new engine for the first time it was always good to use a known carb and distributor so it started right away.


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[98 SNAKE EATER]

Originally Posted by Peter Serio

Be forewarned that if you have a factory tach in your dash & it is working now off of your points distributor; and you change that to something modern, such as pertronix or GM-HEI your tach will no longer function. The original tach for all 1970 GM cars had a one wire plug-in on the back. That circuit board is designed for a points signal (a pure square wave). If you change your points out for something new you will have to replace the circuit board inside of your tachometer so that it has an accommodation for a 2 wire plug-in on the back. The HEI compatible board is more complex in that it has a transistor in the circuit. Therefore it requires a separate power supply (12 volt "+") and another wire that looks for the RPM signal from the coil.

The power wire is a 12 volt + signal (key on) from the fuse block, run thru a 1 or 1 & 1/2 amp in-line glass fuse. The other wire is the same one you have now, it's the wire from the "-" side of the coil to the back of the tach. That wire carries the RPM waveform information from the ignition system to the tach.

I've been told that the Breakerless SE setup does not effect the factory tach like the Pertronix or HEI setups

Can anyone here confirm this for sure?

[padgett]

Gee whillickers Sandy, Is much easier today than in the last century. I used to replace 68-72 hood and dash tachs (with the little white round ceramic circuit board ) with a transistor one from a Vega (plentiful then). Change the capacitor, do a little calibration and hey presto.

However today a replacement circuit board is available and the picture shows a transistor. (Q1).

Appears to adjust via a pot with a screw rather than having to scrape plated on carbon tracks.

Just ordered one and will see how it works with a Pertronix in my 400.

[98 SNAKE EATER]

I've been trying to contact Breakerless direct, but they have yet to respond to any of my emails

Their website says it works fine with the factory tach, but I still want to confirm before a fry anything.

Furthermore, I plan on running a hidden shift light using an RPM switch like I have in my Road Runner, but I wanna use the parking brake light instead of LED's

https://www.youtube.com/watch?v=nLTr1Wyk7uM

Just curious if this will pose a problem with the factory tach and the Breakerless setup

[padgett]

Originally Posted by 98 SNAKE EATER

I wanna use the parking brake light instead of LED's

Do not know what year car you have but for 1968 and later the BRAKE light also illuminates if the proportioning valve detects a problem.

[98 SNAKE EATER]

Originally Posted by padgett

Do not know what year car you have but for 1968 and later the BRAKE light also illuminates if the proportioning valve detects a problem.

I plan on using a diode between the output relay and the parking brake switch.

System should still function as normal.

I'm more concerned with the factory tach working together with the Breakerless setup and the RPM switch at the same time.

In all my previous hidden shiftlight setups, I've either had MSD or HEI units with aftermarket tachs.

[tom s]

I read that Dave is not doing conversions right now because of health reasons.Tom

[Jerry H.]

Originally Posted by Peter Serio

If the car you are working on is the red car in your tiny photo then yes. Those 2nd Gen Firebird Trans Am style tachometers are very fragile. The main tach-speedo cluster has to come out first then the tach-clock assembly comes out from the back. The clock is in there which you have to be VERY careful. The second hand on that clock is made from aluminum, and it is easily bent or broken. NOTHING comes out from the front as far as getting into the tachometer circuit board!!! You do need to remove the clock set-knob as well as the front lens but after that it all is accessed from the backside. The printed circuit; that has to be about 1/2 way removed and very gently folded over out of the way. I take those all the way off anyway, most often they are old & brittle & need replaced. The meter movement to that tachometer is easily damaged by lint, dust or dirt getting in around the magnet. There is an inspection sticker on the back of that tach right behind the magnet. Often that inspection sticker is missing or torn. Road dirt will find it's way inside of there and stick to the magnet. A tiny piece of dust or dirt is all it takes to hang up the moving coil. That coil is attached to the white pointer via a long formed (bent) aluminum tube. DO NOT mess around with that little tube or the pointer. If that gets bent the meter could be ruined!!!!

Peter is 100 times more knowledgeable about this subject than I, HOWEVER, I've installed the M&H conversion (same as what Ames sells) in 2 65 GTO's with factory tachs and a 65 Catalina with the factory tach and all worked just fine. Maybe I was just lucky.