Tach Info To Copy , Again

[crossy]

IF YOU DON'T SAVE THIS IT IS NOT MY FAULT. DAVE
all4trux@snip.net

,PLEASE READ ON FOR PROPER
APPLICATION. This is one of those items that is commonly mis-advertised as
73-87 when in fact there are several differences in each unit The first
thing to keep in mind is that GM did offer a Tach as an option after
1981 in light trucks,but they are rare as Hens teeth .I have found Canadian units that were supposedly from Mid 80's
trucks/blazers but the speedo is in KmH .there are even guys on Ebay trying to advertise them as” 140 speedos” but don’t tell you that they are KMH not MPH. It would be easy to install a U.S. MPH
speedo to it.There were 6 cyl. and 8 cyl. models available and a 6 cyl. one
is going to read high in a V-8 application. 95% are probably V-8's. Try to
know it works before you buy it. I have been TOLD that the 73-75 units are
NOT serviceable[I verified this now] and if they are bad, and keep in mind that ANY service will
probably set you back $125+. I see very few advertising that that “I saw this unit work” so you are on your own if you buy one not knowing it works. As a note * 30-40 % of the ones I buy are BAD either they don’t work at all or they read WAY off . The tachs are very easy to wire and check so there is no excuse in my book for a guy to say he never checked it ,yet try to get $100 or more for one . I also found out Most of the tach repair places do'nt carry parts for these year tachs. The Light trucks were only offered with a
5,000 RPM tach but I have seen 4,000 RPM ones also. probably big diesel.

{when i say BIG ,I mean like a C-60/C-6000 series truck. The tach is easy to wire, but getting at least a short piece of the factory pigtail to the back of it is nice to have, But not a
necessity. If you look close at the back of the tach it will tell you where
the wires go. many people don't know that there was a 'filter', that looks like a condenser, installed in many years of the factory wiring for radio interference reasons.It was mounted on the firewall behind the distributor. this is not a necessity .Speaking of distributors it does not matter if you have and old point ignition or HEI the tach still works.I am not familiar with aftermarket ignitions ,but most have web sites with tech help that could answer your question.

MOST Tach dashes WITH a VOLT gauge are the common ones and will work in 78-84 for sure as pretty much a
"plug in and go" unit. It is possible to work on 1985 and 1986 models
depending on what you have still have in the way of the factory computer
[I.E.= if you have removed the factory feedback carb And ESC distributor,
Etc. and DON'T need feedback then it will be fine]. As far as pickups go it
will not work on an 87 and will not work on Blazers and Burbs from 1987 to
1991 because of feedback needed for the factory EFI computer(ECM). Again it can be made,and at least one will be made by me to sell. This is not a job for amateurs and you are going to need 2 units just to make one! ( THIS ONLY APPLIES TO THE MODELS REQUIRING A REAL ECM). The 1973
to 1975 models used an AMP gauge instead of the VOLT gauge and this can
cause major wiring problems (meltdown) if installed in later trucks equipped
for VOLT gauge or vice-versa. The 1976-77 used the volt gauge but had a
mechanical oil pressure gauge and creates a two year only dilemma of sorts.
If you find a 1976 or 77 unit with the VOLT gauge and the MECH. Oil pressure
then it can be used in 78-up models by converting yours to mechanical, and
actually better, oil pressure gauge. The only thing to keep in mind here is
to get at least a little piece of the factory oil line and fitting that was
on the back of the gauge. I say this because the factory gauge has a unique
type of ferrule and fitting on the back of the gauge that is good to save
and reuse. I have made aftermarket lines/fittings work but have also had
them blow off the back and make one heck of a mess. The factory used a
steel oil pressure line and I prefer that to plastic or you can buy 1/8" copper.now THE OTHER BIG PROBLEM WITH THE MODELS THAT HAVE THE mechanical oil pressure gauge instead of the of the Elect. One is that the whole cluster is wired differently because of that .I rewired one to work and it takes awhile and some ‘know how’ . I am by no means a ‘TECH’ but I do understand wiring. SO it is better to leave the 77-78 units alone also.

Keep in mind that there were also several variations of needle colors and the type of
lettering/numbers on the gauges. Mixing and matching gauges can create a
weird looking unit. The big trucks ,like C-60's are easily identified by a
tiny fuel gauge UNDER the tach and anything from a clock, air pressure
gauge ,or vacuum gauge, to a blank CAN be where the small ,round ,lower left clock option goes in a pickup dash. Some big trucks only had 4,000
RPM tachs also[and you thought a 5,000 was too low]. LOL.. Big truck tach dashes can be made to work in a pickup ,but offer there own unique problems and the years of options mentioned above DO NOT directly apply to them.

big things to get from all of this is , AMP or VOLT gauge could = FIRE. KNOW it works! or BIG $$ to fix, 6Cyl. or 8 Cyl., Elect. Or Mech. Oil pressure gauge?75% of sellers on Ebay Don't care about your concerns because i Email them all the time hoping they will correct their ad and they Don't. 25% are very grateful. ONLY 25%.!! YOUR WELCOME,DAVE






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