factory tach
 

i have a couple of factory tachs and they're not reading right. seem to be in hundreds instead of thousands. is there a converter that i'm missing? i remember the old sun tach needed a transmitter box that you mounted on the firewall. and i've gotten aftermarket tachs for these trucks but they don't seem to have that problem.

any help would be appreciated. maybe there a small converter that could be hidden under the dash. don't know...

Re: factory tach
 

63-66 tachs don't need a transmitter, but the 60-62 versions do. They also made both a 6 and 8 cylinder tach, getting them switched up would cause it to read wrong but probably not that far off.

Re: factory tach
 

For reference, 63 was the first year for no transmitter required.
Available on light duty with V8's only.
Medium and heavy duty could option Inline 6 or V8.
Totally irrelevant as to your original question, sorry.

Re: factory tach
 

do you guys know a part number or some way to tell if its a 6 or V8 tach?
i put a dwell to the engine coil and its pulsing ok, reads right. I've got a tach in a 65 cluster and one in a 63 and they both read very low rpm's.

Re: factory tach
 

The decal on the back side of the tach will tell if its 6 or 8, at least on the 63-66 tachs. You might have to take the tach off of the backing plate to see all of the decal.

Re: factory tach
 

http://www.gmpartswiki.com/getpage?pageid=62578

In another parts book
Group 9.750 HEAD, TACHOMETER
3852111@ 1966/ALL CHEV W/250 or 292
3839947@ 1966/ALL CHEV W/V-8
@ NEW PARTS MASTER CATALOG

3828689* 1963 w/V-8
* NEW PARTS INITIAL CATALOG

In another parts book
3771216 1961-62 W/V-8

TRANSMITTER/ TACHOMETER
2339638 1961-62 W/V-8

Re: factory tach
 

thanks for the input guys.
i sprung for a repro tach. might as well install it while the cluster is out and then try to figure whats up with these original ones.

Re: factory tach
 

Might just need calibration

Re: factory tach
 

yeah i thought that might be it but what are the chances that two different tachs are giving the same slow reading and both need calibration.

the transmitter for the older tachs have a set screw for adjustment but i haven't tried messing with one of those. also it seems that most factory tachs came in the bigger trucks and most of them ran a six cylinder for the torgue. so, theastronaut may be right that these are both 6 cylinder tachs.

i love a mystery and will eventually get to the bottom...

thanks for the input...

Re: factory tach
 

I'll see if I have any pics of the one I have. I took pics of the back prior to reinstall. I believe its an EB-8 that I have, dated 1964 and has an "8" stamped on the back in yellow. I've always thought the 6cyl tachs were much harder to find

Re: factory tach
 

If they do end up being 6 cylinder tachs I would be interested in buying one for my blue '66.

Re: factory tach
 

ok… got it figured out. the original tach is a V8 tach with the signal coming from the negative side of the coil. there is a hot lead that was wired to the brake lights at the fuse block and the ground was weak that passed through the cluster. changed the hot lead to the ignition and ran a screw through the tach in the back that contacted the cluster. just messing around with it and it worked.

i will check the 63 tach that i have and if its for a 6 'the astronaut' i will let you know...