I attemped to switch out my tach dash

[rocktriviagod]

Well the weather here in Wisconsin finally warmed up to 25 or so , so I started taking apart the dash on my 78 Chev 1/2 ton in hopes of replacing the cluster with the tach cluster I bought off of ebay last week..... Wrong. For starters, The cluster was out of a 73 Suburban and as Captkaos informed me, there are a LOT of differences, and don't believe all of the hype on ebay about 'fits 73 to 87 Chev and GMC'. Yes, it will physically fit, but mechanically and electrically speaking, its a whole bunch different. I'm sure most of you already know this stuff and some made the same mistakes as I did, but I'm posting this as much for the new guys like me, so they can learn from the mistakes of others.
I want to send out a special thankyou to 'N2TRUX' offering to assist me through these trying times. Needless to say, I'll be selling a tach dash out of a 73 Suburban pretty soon on ebay. (my seller name is 'cpe1') Hopefully, I can recoup some of the (gulp) $180 or so I put into it.
Well, thanks for giving me a place to vent. I guess I'll just put up with my big ol' gas gauge and idiot lights for a little while longer.
Craig

[N2TRUX]

Hey we all learn from burn sometimes. I know I have many times. Don't let it get you down though. I just missed out on a super clean dash myslef. I had to be at my daughters basketball game, and couldn't protect my bid in the end

Oh well I still have a really nice one I can use for back up.....unless you want it...

[MJN]

Hey man, sorry to hear about your dash problems. I see your from Holmen. I live in Ettrick but for now I'm in Michigan going to school. Welcome to the board. Maybe we'll run into each other some time down the road. Good luck with the dash.

[mike reeh]

rtg: that sucks. But you live and you learn. This is not a for-sale post but I have a tach dash out of either a 78 or 79 that Id be willing to sell you (only bringing this up because you're looking for one for a 78).. the thing is the tach doesnt work. it is however complete and in pretty good shape. If you're interested let me know. Swapping the tach electronics w/ another would work so long as they use the same sweep. 7:30 - 4:30 on the clock is 0-5000rpm

mike

[crossy]

OK, here it is again for the 'new year' members. I'll buy the 73 dash for the right price email me at 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 .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 also found out Most of the tach repair places do'nt carry parts for our 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.
As you can see the 78-80 gauges do not 'MATCH' the 81-87 NUMBERING style But this cluster will work in 81-84 as a
"plug in and go" unit But you will not have use of your factory Electronic cruise control that was used from 83-up. (the green box behind speedo). It is possible to work on 1985 and 1986 models also
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 NO LONGER NEED FEEDBACK then it will be fine]. As far as INJECTED 1987 pickups go it
will not work on an 87 and will not work on INJECTED Blazers and Burbs from 1987 to
1991 because of speed sensor feedback needed for the factory EFI computer(ECM).IF YOU DO NOT UNDERSTAND THIS INFO THEN YOU ARE PROBABLY OUT OF YOUR LEAGUE OF CAPABILITIES WITH THIS-will be made by me to sell. if you have a 90-91 with optional ABS brakes then forget it altogether as there is a special crap hooked to your speedo housing that are not tranferable. 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 only be used in 76 and 77 models unless a complete and UNDERSTANDING wiring change is made in the later model wiring connector.It is not just a simple matter of using the mechanical pressure gauge instead of the electric. If you are Brave and think you can rewire it to be compatible and use the mechanical oil pressure gauge then something 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. 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,blank , air pressure
gauge ,or vacuum gauge 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 many of there own unique problems because of optional gauges that were available in them and the years of compatibility and options mentioned above DO NOT directly apply to them. If you try to make a dash of parts & pieces bought you had better t know that you need the CORRECT printed circuit for your year truck/dash also.
The big things to get from all of this is 1.), AMP or VOLT gauge mix ups could= FIRE, 2.)Know it works! or BIG $$ to fix, 3.) 6Cyl. or 8 Cyl., 4.) 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%. this is a common statement I see in one guys ads AFTER i told him that mixing them up can cause wiring meltdown. QUOTE=" The cluster fits all models from 1973-87, but it may require some rewiring for units other than 1984 to 87 " thats BS!!!!!!!. YOUR WELCOME, DAVE

[crossy]

Originally posted by mike reeh
Swapping the tach electronics w/ another would work so long as they use the same sweep. 7:30 - 4:30 on the clock is 0-5000rpm

mike

Mike , IF you or anyone else EVER finds a tach that will swap out with that fits that bill let me know. I never see others that are 5000 limit. and this sweep.

[rocktriviagod]

Thanks for the GREAT info. I'd heard there was a god named Crossy, but from all of the amazing things d about him, I didn't
think he really existed!! I sure hope plenty of people get a chance to read your post. I'll save it and pass it on as needed!!
OK, so now I have a cluster I want to sell on ebay, and YES, I try hard to make my listings as accurate as posssible. (cpe1 has a 118 rating with 100% satisfaction, thank you)
Are there any easy tests to insure customer satisfaction? I guess I'm mainly concerned that the tach works.
Thanks!!! Craig

[crossy]

whew you new guys are really testing my typing skills, Actually I have no typing skills so I saved all this stuff a while back. And just so you know. this is exactly what i send to someone that is elling a tach and over half of them never reply back, prolly because they know the one they are sending is bad.
TACH TESTING ,

Hello, I am interested in the condition of the tach. They are very expensive to repair. They are also commonly bad. If you look closely at the back of the tach you can see the markings as to where each lead needs to go. COIL,GND, 12V. They are very easy to hook up and test on an V-8 engine especially if you have one around with an HEI distributor . ( HEI's have a 'TACH' terminal right on the distributor cap.). if you have anything around with the old points distributor then the terminal marked COIL of the tach goes to the (-) side of the coil. the 12V terminal of the tach and GND terminal are kinda self explanatory. You need any 12V power and a ground .. if you do not have original wiring pigtail then a .250 female spade crimp-on connector on the end of a wire works fine. I would be very likely to bid if I knew that it worked . Since I redo these dashes and hobby at 73-87's I know a bit about them. 60% of the ones I have bought are bad so I know all to well what I am asking for here. when they START to go bad they read high, like 1200 RPM at idle, and get worse as RPM goes higher. Having a known good tach in the vehicle to compare it with is a real plus. I have bought more than one that the person tolds me 'works' only to find out that it is way off on readings. At idle you should see 500-800 RPM and a quick tap of the throttle should see 2500 RPM or so. As some go bad the needle responds very slow to RPM increases or 'stick' as they move forward. when they really get bad they will bury immediately or not register at all., I am more than willing to pay/bid fair money for known working units. lemmeknow, thanx , DAVE

[mike reeh]

Originally posted by crossy

Mike , IF you or anyone else EVER finds a tach that will swap out with that fits that bill let me know. I never see others that are 5000 limit. and this sweep.

crossy good to see you around again. But what I was talking about, was swapping another GM factory tach (of same or similar vintage).. not an aftermarket.. If there was an aftermarket one I would be all over it!

mike

[Blue Beard]

Sorry to hear about the differences.......

Kind of glad to know this possiblity, just purchased a 91 that needs things attented to and wondered about compatability....

[rocktriviagod]

Man, you ARE amazing. I've been emailing back and forth with N2TRUX and asked him if anybody had written a book on the subject of truck dash clusters. Crossy, you gotta do it!!
Thanks again! Craig

[crossy]

Originally posted by mike reeh


crossy good to see you around again. But what I was talking about, was swapping another GM factory tach (of same or similar vintage).. not an aftermarket.. If there was an aftermarket one I would be all over it!

mike

mike , been there too. Even looked at F--D's and mopars. these tachs are LARGE and only having a 5,000 limit means to either find a good one or get yours fixed . I emailed 8 differnt tach repair places and only two were willing and Had appx. $100 Minimum. I know for a fact that original 73-75 style (maybe76 also) cannot be repaired at all.They are totally sealed in some red-ish epoxy.
What makes me sick is that I work with all these RETS electronics guys and Navy Nuke boys that our Nuke plant loves to hire because of their backgrounds. I can only find 2 out of 100 guys that give flip about cars/trucks. I have asked about building a new PC board for them from scratch (prolly $10 worth of parts from radio shack) or buying a Heath kit or something. No luck.
I took apart a tach i had that was bad and unsoldered every little piece and chacked the componets but here are some transistors on there that have no identifiable numbers on them that can't be tested and can't be replaced unless you know how they were programmed. Really ticks me off because i know how simple they must be. I even looked at new tachs figuring to 'gut' them and use the PC board but newer ones are made a lot different around the center area to mount needle. (hard to explain). Hey but damnit I tried.
And I have another idea that May take a while to complete. DAVE

[crossy]

Originally posted by rocktriviagod
Man, you ARE amazing. I've been emailing back and forth with N2TRUX and asked him if anybody had written a book on the subject of truck dash clusters. Crossy, you gotta do it!!
Thanks again! Craig

Yeah, I'm writing a book to sell the bad ones i have on ebay. it starts out like this
Page 1- see page 2
page 2- this fits all 73-87 trucks and 73-91 blazers & burbs,
page 3- don't worry about that smoke- amps & volts are the same.
page 4- I know your 87-91 HAD a VSS on it before for the computer, but thats only for pollution stuff right???
page 5- You'll know for sure when out of fuel now!
page 5- This unit works. My Cousins friends uncle told me.

find it under BOOKS/HUMOR/BUSINESS

[rocktriviagod]

Now I WOULD buy that book!!

[crossy]

I had not looked on ebay in a while , JEEZ! there must be 15 on there. Man, i saw 3 or 4 that the guys swore it fit every chevy made from 73-91.
some had buried tachs( a sure bad sign).
one guy selling the tach & fuel gauge to convert your dash ,WRONG the whole plastic housing and the PC is different.
what a CLUSTER f*** (pun). :-)
watch out.
DAVE

[rocktriviagod]

CLUSTER F**K, Man, that's a good one!

[NeCrOmAnCeR]

This is my first post so please bear with me. Having adapted many GM tachs to other vehicles i may have a solution to those which do not read correctly. When I placed an 86 pontiac tach into the custom dash for my wifes 67 mustang, I found this valuable site containing valuable information on adjusting the electronic components to make a six cylinder tach read correctly on a 8 cyl. for those tachs which progressively get worse with age, the most common fault is most likely the electrolytic capacitor. These devices eventually leak or suffer some other electrical failure so replacing the capacitor will most likely return proper operation. Since i have never recieved an inoperative tach i have not been able to verify this. To adjust the reading, simply follow the modifications shown on this site. effetively removing the calibration resistor and replacing it with a multiturn variable resistor allows you to adjust the accuracy, or the number of cylinders the tach operates on. Although this information is intended for fierros, I have see the same components used on the GM tachs (older) I have used. This same site also has the capacitor values needed if that is all you need.
When replacing the dash of my 74 GMC with the tach dash out of a 78 (I think it was), I traced all the circuits of the new dash to the connector location, and those of the old dash, and moved the contacts of the electrical connector to the proper location. I replaced the temp and oil pressure gauges with aftermarket gauges which fit into the stock location and gives me more confidence in the readings.
If you are creative with image editing software you could also generate a new tach face reading up to any desired RPM (8 grand) and place it over the stock tach face and then use the beforementioned modification to adjust the reading of the tack to match. If anyone would like to try this, I am interested because if done correctly, it would maintain the stock look and be very unique. With my research work I don't have much time to do this myself, but it is an idea i've had for a few years.

http://www.thefieroclub.com/osg/tachmod.html
Capacitor values

http://home.t-online.de/home/O_Scholz/tach.html
Modification

Hope this information helps those of you with ailing tachs, and gives valuable information.

[Paul_S]

Well, you guys have the history down pretty good thanks to Dave. I was going through this stuff and research about 10 years ago. To make the clusters work outside of their application years (plug & play years) you have to research the wiring and components of both and modify accordingly. You may end up swapping parts between the tach and non-tach clusters to give you a plug-n-play unit or atleast closer to one. It also usually comes down to the style and condition of the plastic tach cluster housing and the gauge faces/style to determine if it's do-able. Most of this was said above, but I thought I would touch on it.

The main thing I wanted to say is that if you find a tach cluster in a truck Do Not Cut the Tach Harness, I repeat Do Not Cut the Tach Harness. The tach harness is only a three wire 4 ft. to 5 ft. long stand alone harness. Follow the tach harness back and disconnect the ground, the positive wire at the fuse box and the tach wire off the distributor. The harness goes through the firewall with a grommet between the fuse box and the steering column. Pop the grommet (it stays with the harness) and pull the harness into the interior. Now you'll have a correct and probably complete harness to use.

Paul

[crossy]

necromancer & paul, welcome to the forums. To Nec. i had read that a long time ago about correcting the tach in a V-8 vega installation(yeah, I'm feeling old now). i was never able to come up with part numbers though. i might be able to save two high reading tachs I have here, but trust me when i tell you the other 5 or 6 I still have laying here are JUNK, but if I can save any it is a Big $$ relief to me. I will definitely look into it.
AS FAR AS the rewiring of the connector. you are right, it CAN be done and I have done it , but I have also had problems with people I send that info to. we never know the mechanical/elect. capabilities of the peole we are talking to by email. even though they say they 'understand'.There are differences that can't be overcome with wiring though when you are talking about AMPS gauges vs. VOLTS. I even had a guy that overcame that with some special jumper wires but then again he is a college TECH teacher. My original point was that these EBAY guys are telling you that it works in all applications and it does not . I have done a lot of digging to find out what years are different from each other and although I won't tell anyone how torewire one I will send them the info above to tell you what to look for and be aware(or BEWARE) of. thats it I'm typed out.

paul ,that tach harness is not that big of deal though . you can use insulated .250 female spade crimp connectors on the ends of the wires. The grommet is nice to have but a suitable is available nearly anywhere. If you look close the tach is clerly marked where each wire goes. Thanx for the input though. DAVE