Mystery Tachometer

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

ButchM

ButchM

Junior Member
Joined
Oct 19, 2023
Posts
23
Reaction score
30
Location
Idaho
First Name
Butch
Truck Year
1986
Truck Model
K30
Engine Size
454
frickenbored said:
Hi everyone, after a ridiculous amount of online research and coming up with absolutely nothing I decided to join a forum and hope that someone else has seen this gauge before. So I'm in the process of "restoring" my 1986 Chevy K10 Scottsdale, after 8 long years I've finally found the time to install the engine I rebuilt 5 years ago and the transmission I rebuilt 2 years ago. The truck now runs and drives and to my surprise all of the factory gauges actually work, they just needed to be hooked up to sending units. I've got the voltmeter, temp, oil pressure, clock, and fuel gauge working and I have my eye on the factory tach now.

This tachometer has the fuel gauge built into it, I can't find anything about this gauge anywhere, it's like it doesn't exist. Every gauge cluster I've ever seen either has the large fuel gauge next to the speedometer or they have a single tachometer and a small fuel gauge where the clock is. I haven't actually pulled the cluster yet to see how the tach is wired, for now I'm just super curious as to where this gauge came from.

Also, this truck has the body of a 1986 C10 and the frame/drivetrain of a 1975 K10 but these gauges look like the 1980s style to me.

(sorry for the crappy pictures, it's a pretty sunny day)

You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
Click to expand...
Pete
You have a hybrid/Frankendash. The clock is an option (don't have the option code) for "regular" pickups (C/K10-30). The tach you have is from a C50/C60 series medium duty truck with a 366 or 427 engine with air brakes. On those trucks there was an air pressure gauge where your clock is. The 5000 rpm top end is a clue, those engines had a much lower redline due to the heavier piston weight.
I have one of those tachs I plan to install in my truck.
As a side note: I was told by an old Chevy mechanic that the trucks that came from the factory with an air compressor (all air brake trucks) had forged steel crankshafts. May be a good source for that forged 427 crank at a cheap price.
Butch
 
frickenbored

frickenbored

Junior Member
Joined
Oct 27, 2024
Posts
8
Reaction score
16
Location
Michigan
First Name
Pete
Truck Year
1986
Truck Model
Scottsdale K10
Engine Size
5.7L
ButchM said:
Pete
You have a hybrid/Frankendash. The clock is an option (don't have the option code) for "regular" pickups (C/K10-30). The tach you have is from a C50/C60 series medium duty truck with a 366 or 427 engine with air brakes. On those trucks there was an air pressure gauge where your clock is. The 5000 rpm top end is a clue, those engines had a much lower redline due to the heavier piston weight.
I have one of those tachs I plan to install in my truck.
As a side note: I was told by an old Chevy mechanic that the trucks that came from the factory with an air compressor (all air brake trucks) had forged steel crankshafts. May be a good source for that forged 427 crank at a cheap price.
Butch
Click to expand...

Yeah, this doesn't surprise me. The whole truck is Frankensteind together by the previous owner, now I'm doing my best to un-Frankenstein it. Hopefully I can pull the cluster this weekend and find out how that tach hooks up; however, I'm doubting it will play nice with my MSD 6AL box, but I should at least see it do something. I plan to ditch the MSD ignition soon in favor of a Progression Ignition digitally programmable HEI distributor anyway.
 
Redfish

Redfish

Full Access Member
Joined
Nov 6, 2021
Posts
2,718
Reaction score
14,589
Location
Prairieville, LA
First Name
Andrew
Truck Year
1987
Truck Model
V1500
Engine Size
350/5.7
MPWILSON33 said:
I got mine from LMC with a new pod and printed circuit. All works great. I had to cut a bit of the speedo hole with a unibit.
Click to expand...
This conversion is on The List. I just hate to give up my awesome Quartz Clock! I remember GM advertising being really proud of that Quartz Clock.
 
bucket

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
30,622
Reaction score
28,872
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
frickenbored said:
Yeah, this doesn't surprise me. The whole truck is Frankensteind together by the previous owner, now I'm doing my best to un-Frankenstein it. Hopefully I can pull the cluster this weekend and find out how that tach hooks up; however, I'm doubting it will play nice with my MSD 6AL box, but I should at least see it do something. I plan to ditch the MSD ignition soon in favor of a Progression Ignition digitally programmable HEI distributor anyway.
Click to expand...

If the tach still works, it should work with the 6AL just fine. The tach should have 3 terminals. One ignition 12+, one ground and one tach signal. The 6AL should have a tach output.
 
Keith Seymore

Keith Seymore

Full Access Member
Joined
Jul 13, 2015
Posts
2,971
Reaction score
9,611
Location
Motor City
First Name
Keith Seymore
Truck Year
1987
Truck Model
R10
Engine Size
4.3L
MPWILSON33 said:
I got mine from LMC with a new pod and printed circuit. All works great. I had to cut a bit of the speedo hole with a unibit.
Click to expand...
This is basically what my '87 came with (no trip odo).

Clock was in the radio.

K
You must be registered for see images attach
You must be registered for see images attach
 
nvrenuf

nvrenuf

Full Access Member
Joined
Jul 30, 2010
Posts
1,981
Reaction score
2,522
Location
Mobile, Al.
First Name
John
Truck Year
1991
Truck Model
K5
Engine Size
454
bucket said:
If the tach still works, it should work with the 6AL just fine. The tach should have 3 terminals. One ignition 12+, one ground and one tach signal. The 6AL should have a tach output.
Click to expand...


This ^^

I ran a factory tach with a 6AL in my old K10 for years, worked great.
 
frickenbored

frickenbored

Junior Member
Joined
Oct 27, 2024
Posts
8
Reaction score
16
Location
Michigan
First Name
Pete
Truck Year
1986
Truck Model
Scottsdale K10
Engine Size
5.7L
bucket said:
If the tach still works, it should work with the 6AL just fine. The tach should have 3 terminals. One ignition 12+, one ground and one tach signal. The 6AL should have a tach output.
Click to expand...

This is good to hear. My 6AL does have a tach output. Back in the day I used to have a 1988 K5 blazer with a MSD street fire box and a summit racing brand tach, the tach signal was super lazy and inaccurate, I also tried a sunpro tach but had the same problem. I figured I needed the MSD tach signal adapter box.
 
nvrenuf

nvrenuf

Full Access Member
Joined
Jul 30, 2010
Posts
1,981
Reaction score
2,522
Location
Mobile, Al.
First Name
John
Truck Year
1991
Truck Model
K5
Engine Size
454
Just to say it, while the factory tachs are super cool I remember mine being slower than aftermarket tachs.
 
B

Beercelo

Junior Member
Joined
Feb 28, 2024
Posts
15
Reaction score
32
Location
Tucson
First Name
Raul
Truck Year
1982
Truck Model
1500
Engine Size
305
MPWILSON33 said:
I got mine from LMC with a new pod and printed circuit. All works great. I had to cut a bit of the speedo hole with a unibit.
Click to expand...
MPWILSON33 said:
I got mine from LMC with a new pod and printed circuit. All works great. I had to cut a bit of the speedo hole with a unibit.
Click to expand...
Anyone know which kit from LMC will fit on an 82? They only have kits for 78-80 and 83-87. Talked to 2 people from Lmc on the phone both said none of them fit the 81 or 82, period.

MPWILSON33 said:
I got mine from LMC with a new pod and printed circuit. All works great. I had to cut a bit of the speedo hole with a unibit.
Click to expand...
 
frickenbored

frickenbored

Junior Member
Joined
Oct 27, 2024
Posts
8
Reaction score
16
Location
Michigan
First Name
Pete
Truck Year
1986
Truck Model
Scottsdale K10
Engine Size
5.7L
Got my cluster out tonight, that gauge is definitely a custom job as you can tell by the pictures but it's actually not too bad of a job. I hooked it up to my power supply through the circuit board and the tach snaps to zero. I'm not sure why it didn't work in the truck since the power and ground were hooked up, there must have been a bad connection somewhere but it's working now.

I've got some repairs to do on the circuit board but hopefully I'll soon post a picture of everything actually working. Eventually I'm going to install of of those Autometer GPS speedometers.

You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
xc_hide_links_from_guests_guests_error_hide_media
 
Camar068

Camar068

Supporting Member
Supporting Member
Joined
Feb 5, 2014
Posts
4,341
Reaction score
3,393
Location
Kentucky
First Name
David
Truck Year
1986
Truck Model
K10/LM7 5.3/4L60e/np208/3.73/32"
Engine Size
10 yrs Air Force
Turbo4whl said:
^^^ :waytogo:

On the medium duty truck, the last gauge hole would have an air gauge for the brakes, or a vacuum gauge for the booster on juice brakes.
Click to expand...
Thats one of the gauges I want for a quick look at engine vacuum.
 
Turbo4whl

Turbo4whl

Supporting Member
Supporting Member
Joined
Oct 30, 2019
Posts
3,156
Reaction score
7,325
Location
Downingtown, PA
First Name
Wayne
Truck Year
1974
Truck Model
Jimmy
Engine Size
350
More info, Some C50 etc. trucks have a taller fuel tank. If the medium duty small fuel gauge with the tach does not seem to read your fuel level correctly, replace the resistor on the back with the resistor from the original pickup gauge.

Also a blazer or suburban fuel gauge may also have a different resistor to match that tank. Most resistors are white with a color line. Different color, different value. The resister unbolts, can swap big to little gauge resistors, they are the same size.
 
bucket

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
30,622
Reaction score
28,872
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
Turbo4whl said:
More info, Some C50 etc. trucks have a taller fuel tank. If the medium duty small fuel gauge with the tach does not seem to read your fuel level correctly, replace the resistor on the back with the resistor from the original pickup gauge.

Also a blazer or suburban fuel gauge may also have a different resistor to match that tank. Most resistors are white with a color line. Different color, different value. The resister unbolts, can swap big to little gauge resistors, they are the same size.
Click to expand...

I thought all the GM gauges were 0-90 ohm? Different height tanks used a sender with more or less swing in the float arm.
 
Turbo4whl

Turbo4whl

Supporting Member
Supporting Member
Joined
Oct 30, 2019
Posts
3,156
Reaction score
7,325
Location
Downingtown, PA
First Name
Wayne
Truck Year
1974
Truck Model
Jimmy
Engine Size
350
bucket said:
I thought all the GM gauges were 0-90 ohm? Different height tanks used a sender with more or less swing in the float arm.
Click to expand...


There are different resistors on the back of the fuel gauges. That is why they bolt on. Old school tech. Squares are most all the same. MD trucks can be different.
 
You must log in or register to reply here.

Similar threads

dsteelejr
Fuel gauge troubleshooting
Replies
4
Views
566
Scottgenex
S
D
1985 GMC Sierra factory tach
Replies
4
Views
1K
Turbo4whl
Turbo4whl
R
LTZ Seat Swap
2
Replies
18
Views
990
bucket
bucket
C
1981 C30 cluster issue
Replies
4
Views
523
mano
mano
Stormhawk
Voltage Gauge
Replies
0
Views
142
Stormhawk
Stormhawk

Latest posts

Forum statistics

Threads
44,418
Posts
957,175
Members
36,757
Latest member
1978C10
Top