1975 tach switch

[rgtrough]

Hey, guys, has anyone swapped the tach out of a '74 and installed a '75? I am wanting to install a HEI dist. and not pay the high dollars that go with one that has a mechanical drive. Is there a modem or such on the tach that receives the signal from the dist. or is it all enclosed. Thanks for any information you can share.:cool peace Bud

 

[Jack]

Hey, guys, has anyone swapped the tach out of a '74 and installed a '75? I am wanting to install a HEI dist. and not pay the high dollars that go with one that has a mechanical drive. Is there a modem or such on the tach that receives the signal from the dist. or is it all enclosed. Thanks for any information you can share.:cool peace Bud

I did same thing to my 71 ... retrofitted a 75-77 tach and HEI dist. I can't remember which terminal is which on tach ... but on back of elec tach there are three (3) terminals ... a negative ground, a positive power from a switched source, and a trigger from the HEI's "tach" terminal atop HEI dist cap. If I recall, I used simple push on female connectors ... I think the tach had male terminals.

 

[Robin7TFour]

HELLO, i also have the same set-up on my 74. it's easy to change over.the tach will have the correct wiring listed where each wire goes.+ ,-, dist.
good luck


robin

 

[rgtrough]

Hey guys, thanks for the feedback. Now I need to decide which way to go. '75 tach, original tach with msd6al box or HEI with mechanical tach drive. Decisions decisions. peace Bud

 

[Jack]

Hey guys, thanks for the feedback. Now I need to decide which way to go. '75 tach, original tach with msd6al box or HEI with mechanical tach drive. Decisions decisions. peace Bud

Bud:
If you're not concerned about originality ... I suggest following for your 74:
Install an HEI distributor in excellent condition and retrofit a 75 thru 77 vette tach. Later on ... if you must ... you can add the MSD box by removing the ignition module from HEI distributor and simply using the HEI's pickup to trigger the MSD. BTW ... the HEI mag pickup wires are polarized thus: White HEI pickup wire is Positive and connects to the MSD's small Violet wire ... Green HEI pickup wire is Negative and connects to the MSD's small Green wire. The MSD probably has a small Brown wire that will connect to 75-77 vette (or other electronic) tach; serves as the "trigger" wire. This is exactly as I have wired up our circle track car ... works great! IMHO, for a street car the MSD box is overkill and probably a waste of resources on anything but one having both very high compression and a very rich fuel mixture. The "stand-alone" HEI is extremely reliable, easily repairable and parts are readily available. On the other hand, MSD boxes are not as reliable... and they are not readily repairable ... MSD much more likely to strand you than a good stand-alone HEI.
JACK:gap

 

[rgtrough]

msd boxes

Hey Jack, thanks for the info. I had heard about the reliability concerns of the msd boxes. If I go with the '75 tach I probably will forgo the box. An old hot rodder in town suggested using one with my original dist. as a good upgrade for the '74s ignition. Any suggestions on a high quality performance HEI. The split tails primary usage is 90% street 10% strip. With the addition of the World Sportsman II heads, roller rockers, and larger 280H Comp cam, I am estimating 400+ hp. Thanks again for the help. :cool peace Bud

 

[Jack]

Hey Jack, thanks for the info. I had heard about the reliability concerns of the msd boxes. If I go with the '75 tach I probably will forgo the box. An old hot rodder in town suggested using one with my original dist. as a good upgrade for the '74s ignition. Any suggestions on a high quality performance HEI. The split tails primary usage is 90% street 10% strip. With the addition of the World Sportsman II heads, roller rockers, and larger 280H Comp cam, I am estimating 400+ hp. Thanks again for the help. :cool peace Bud

Bud:
What's your budget for distributor alone? With that, I can better advise ... I do have a spare new performance HEI for sale but your budget might warrant something more exotic. BTW ... if both your mech tach & points dist are working OK ... I'd suggest only to ensure the current dist-coil-sp wires are tip-top ... a good points dist is very reliable and can easily make all the juice needed for your 90/10 motor. Email me if you'd like.
JACK:gap