So you think you want to replace your Digital Cluster
Last Updated April 12, 2001
If your Digital Cluster is acting up, you're probably thinking about this as an alternative. I must have answered the question "What would it take to replace the cluster?" a hundred times. So I decided to post a page to answer this question for me.
Personally, I'd never think of replacing my digital cluster. Mainly because I've devoted so much time to learning to repair them and helping others repair them that it would seem like a waste of time. And I like it. It's as much a part of the Corvette as that passenger side factory dash pad and the cheesy sounding horns. And I'm worried that the damage to the factory wiring harness that this would require would be irreparable. And I worry that if I ever sell it, the conversion will significantly devalue the car.
Note: George Grouse has been kind enough to provide me with the following information that now takes the place of the document I prepared:
Ok so sue me- I never appreciated the silly video game dash Chevrolet put in early 4th generation Corvettes. I didn’t like the tach which can’t go over 6000rpm; I didn’t like the speedo which only reads digital above 85mph; and I really hated having to flip a switch to see Coolant Temp vs. Volts or Oil Press vs. Temp; and on top of that having to read and comprehend numbers. This is not what I want to be doing on the front straight at Firebird Raceway at 130mph. I want to quickly glance down and see everything is OK. Besides, a performance car of this caliber deserves real gauges, and needs them readable at all times.
A 3-1/2” speedo and tach are just the right fit for the Corvette dash, and very readable. Oil press, oil temp, coolant temp, volts, and fuel are 2”. I also wanted boost/vacuum and fuel pressure gauges since I’m supercharged, yielding a total of 7 small gauges to fit in the dash while keeping it uncluttered and readable. After playing a while with a full-size cardboard template, the best layout was the speedo and tach in the center with two small ones on each side. More than that was too many dials to comprehend at a glance.
Hmmm… 3 to go. Since I wouldn’t be needing the silly switch panel to select English/Metric, coolant vs. volts, etc; I mounted the two least critical (volts and fuel level) gauges in it’s vacated space in the center console. The right side warning lights stay as is.
Back to the main dash: oil press and temp on the left, coolant temp and boost on the right. I finally figured out I need a digital fuel pressure gauge (see below). I added it to the lower right; the digits set it off from the others and didn’t distract my eyes like three analog dials would have. I added a couple lighted switches to the left to sort of balance it out. Indicators for turn signal and high beam fit along the top.
With the cluster out, it was easy to fasten steel angle brackets to the dash structure to mount a 1/8” aluminum dash plate. I cut out the center plastic bezel of the instrument panel so my new plate would sit flush against the back. A handy circle cutter attachment for the drill press almost made making the new panel fun! The existing corner screws go thru the plastic and aluminum into the mounts; some extra screws hold the plastic trim to the plate at the midpoints. After final fitting, I mocked up all the wiring before disassembling it for final priming and painting with this black metal-flake epoxy stuff.
Since the tube on the mechanical coolant temp is permanently attached, I assembled everything else onto the panel on the workbench, then installed this last gauge after the panel was in the car. This tubing and that of the boost gauge were routed behind the dash and thru the firewall at the ECM electrical connector to the engine compartment.
Putting the two gauges in the center console was similar. Make an aluminum panel and shim it so it fits against the back of the metal retainer. Screws go thru the retainer and the new panel; the console plastic trim installs over top just like before.
This whole project took 4 days over X-mas vacation, except for finding the correct adapter to fit the coolant probe into the cylinder head.
VDO is an old German company that’s been making gauges for European sports cars forever. Their Cockpit Series looks great, has a small 160mph elec speedo, and a complete complement of gauges for everything else (except high fuel pressure.)
VDO 437-053 Cockpit 3-3/8” Programmable Speedo, 160mph
VDO 333-055 Cockpit 3-3/8” Elec Tach, 7000rpm
VDO 180-040 Cockpit 2” Mech Water Temp, 265°
VDO 150-061 Cockpit 2” Mech Turbo, 30” vac / 15 psi boost
VDO 350-063 Cockpit 2” Elec Oil Press, 80psi, GM 0-90 W
VDO 310-012 Cockpit 2” Elec Oil Temp, 265°
VDO 301-104 Vision 2” Fuel Level
VDO 332-103 Vision 2” Voltmeter
Intellitronix M8434 2” Digital Fuel Pressure, 15-100psi
VDO 323-058 Oil Temp Sender, 300°, ¼-18 NPT
VDO 150-081 6ft pressure tubing kit
Intellitronix TH8034 Stewart-Warner fuel-safe sender, 0-100psi
The speedometer is driven by an inductive Vehicle Speed Sensor (VSS) mounted in the tail shaft of the transmission. It produces approximately 4000 sine wave pulses per mile. The higher the speed, the higher the pulse frequency. The speedo knows how many pulses per mile, then counts them and compares to its internal time base to get miles per hour. Example: 67 pulses in 1 sec => 4000 pulses / minute => 1 mile in 1 minute => 60mph. The odometer merely counts total pulses to track mileage. Some aftermarket electronic speedos will auto calibrate by driving exactly 1 mile (using mile posts or pacing another car); other require setting this pulse/mile figure with DIP switches.
· Mileage: Usually can’t program the odometer with your existing mileage, so you’re starting over at Zero. What a great feeling!
· ECM: The digital dash cluster halves the frequency and outputs a 2000 pulse / mile 12V square wave to the factory ECM. This controls EGR, evap canister purge, and torque convertor lockup. If you have an aftermarket computer like I do, it may not support these functions and probably doesn’t even have a speed input. If you need to keep this compatibility the easiest way is a buffered speedo ratio converter, used to recalibrate after rear axle / tire changes without changing your speed sensor gearing. Ecklers and most speedo shops sell these. If you’re electronically inclined: think about an edge triggered flip-flop with input hysteresis, wired in toggle mode.
· Cruise Control: Since the digital cluster contained the cruise control “brain” you’ll need to replace it with a standalone unit. Easiest one is from a 86-90 GM full size, i.e. Caprice or something. All the wires are there in the harness (even the same colors). Your existing turn signal lever is fine; it's just providing the switches for on/off, set/accel, resume.
· FX3: The speed sensor also goes to the FX3 module if your car is so equipped. My speedo didn’t like the fact that the FX3 computer grounded one side of the output. I don’t have FX3 shocks anymore so I just unplugged the computer. You may need to look at the above mentioned speedo ratio converter to buffer the signal for the FX3 controller.
· ABS: Uses wheel sensors only, measured relative to each other. Doesn’t use the VSS.
The tachometer is triggered off the negative side of the coil primary; there’s an extra output from the ignition module (inside the distributor) for this purpose. It pulses 8 times (as each plug is fired) every 2 revolutions. A filter removes high frequency interference and give reasonably square pulses. An electronic tach uses switches/jumpers to set the number of cylinders so it can divide and find actual crank revolutions; V8 => divide by 4. An internal time base provides the per minute reference.
· Multiple spark ignitions (MSD, etc) provide their own tach output because the coil is being fired multiple times per cylinder. They may require bypassing the original tach filter and/or using a tach adapter. If you hooked it up correctly and your cluster tach works, you’re new one will be fine also.
The stock GM sender is in the side of one of the heads (depending on year). You might find a gauge that works with it (1060 ohms = 110F, 75 ohms = 261F); but it is easy to swap in the matching aftermarket sender for your gauge. This is the easiest way if 90 degree sweep is ok. Again use the coolant temp wire from the cluster harness.
I wanted a full 270 degree sweep for better temperature resolution. Mechanical gauges have a sealed copper tube containing something like Freon. The tube connects to a probe tip which is inserted into the water passage. As it’s heated, the Freon expands; so we’re basically translating temperature to pressure, which moves the gauge. This is the last gauge to put in, as the copper tube is permanently attached and must be behind the dash, thru the firewall to the engine. I went thru the electrical bulkhead connector in the passenger foot well which comes out behind the pass side of the engine. Used the stock sender location in the right cylinder head.
· Included probe tip was 2” long and bumped into the canted valve guides on my AFR heads. Needed a longer adapter to back it out a bit.
Usually need a new sender matched to the gauge you’re using. Easy to change out; the oil temp sender is found on the lower rear driver's side of the block. Use the existing oil temp wire from the cluster harness.
In addition to measuring oil pressure: 0 ohms (0 psi) to 90 ohms (80 psi); the oil pressure sender also contains a switch which supplies +12V power to the fuel pump any time oil pressure is above 5 psi. This is what keeps the fuel pump running after startup (not the ECM.) Aftermarket senders with a switch or “warning contact” only switch to ground so they won’t work. Fortunately, most manufacturers make a gauge compatible with the factory GM 0-90ohm oil pressure sender (unless you want to rewire the fuel pump relay.) Use the oil pressure wire from the cluster harness.
The GM fuel senders use 0 ohms (empty) to 90 ohms (full). All aftermarket gauge manufacturers make a fuel gauge compatible with this; so no need to change the sender. Just connect the fuel level wire to the new gauge.
Connection is easiest of all- connect between switched +12V and ground.
So you’re asking why the switch to Vision series gauges? These two are mounted separate from the others and I liked the styling better- the voltmeter doesn’t have the dopey colored scale, and the fuel gauge has normal “E” and “F”, instead of the Euro style “0” and “1/1” like their Cockpit counterparts.
It’s good to monitor boost levels with a supercharger or turbocharger. Various gauges are available to measure 15, 25, 30 psi of boost. Since my boost levels are 10psi max, I used a combination gauge which reads 30 in vacuum to 15 psi boost. These gauges are usually mechanical, so you’re running a hard plastic vacuum line thru the firewall to the intake manifold. I teed off one of the vacuum fittings at the pass side rear of the plenum. At least this gauge connects to the line with a compression fitting; it’s not permanently attached.
Needed to preserve a bit of the digital dash nostalgia; actually it was the best solution given the choices:
1) Short sweep elec: try differentiating 45psi from 47psi when the gauges reads 0-100psi in 90°
2) Full sweep elec: way expensive; easier to read but the critical 40-55psi range is still small
3) Full sweep mech: needs high pressure isolator to keep gas out of the passenger compartment
4) Digital: accurate to 1psi increments, have to read the numbers
I used an Intellitronix (now Nordskog Performance) 2” gauge with red LED (to match my lighting) and a Stewart Warner pressure sender made for fuel use. Sender mounts directly to the fuel rail pressure test point using a 90° adapter. It requires power/ground plus a signal wire which goes from the engine compartment to near the dash. I used my coolant temp wire (since mine was now mechanical). The gauge itself has basic power/ground and signal connections; and when connected to the dimmer will even dim the LED to ½ brightness when you turn on the lights.
You'll need left/right turn signals and high beam indicator. Radio Shack and auto parts stores have nice looking blue, amber, red, and green 12V lamps that are perfect. Just hook them between the existing wires and ground.
You can also get creative and add useful switches. I have one for manual fan control, and a second for the invisibility screen . How about a push button starter?
Wire all power in parallel to +12V ignition power; the existing cluster power is fine for this and is protected by the cluster fuse. Wire all grounds in parallel and use heavy wire to a good chassis ground- not the one in the cluster connector. Electric gauges which measure resistance to ground depend on this for accuracy! Since my dash pad was off, I put a bolt into the frame below the windshield.
Many gauges have “bulb condoms” which change the lighting color from white to red or green. Wire all gauge bulbs in parallel to the Dimmer control and ground.
Many thanks to George Crouse for the info provided.
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