Page 22 (Updated 22-Oct-08)
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Instrument Cluster:
- Structural Explanation; Electronic Speedometer
- Maxima Electronic Gauge assy
- Calibration
- Older Mechanical Speedo's
- Precision Gauges
Free Service Manual, Free Download.....see FAVORITE LINKS -page 26- FAVORITE LINKS
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Structural Explanation; Electronic Speedo
Nissan Maxima has electromechanical speedometer and rpm gauges. Following text explains the electromechanigal gauge structure and DIY repair (not the instrument assembly)
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Nissan Instrument Panel
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The whole gauge assy is very simple to take out, steering wheel is not taken off. The panel around first, then open the 4 assy screws, disconnect 3 connectors behind the assy. The panel disassembly startup is from the panel around the stick, lift it up first, then few screws for the panel around radio and so on (see page7).
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Basic electhromechanical gauge composition, part A:
Electromech gauges are about all the 'same', been like that last 80 years. Coil around a magnet, spring pulling back to zero. Typically plus/minus is conducted via two screws (inside the gauge assy). The structure is similar in rpm, voltage, amp - whatever mechanical gauge on the market. Stuructures still have variations depending on utilization.
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Needle, bezel, permanent magnet & axel
- a needle pressed onto an axle (red).
- on the axle there is a std polarized permanent magnet (green).
- also there is a spring; one end attached to axle, other end to base structure.
- base stucture contains bearings on both ends of the axle.
Troubleshooting the mechanism:
- needle has been aligned with permanent magnet, this zero position setting is critical. See previous picture. Before taking needle off, lock permanent magnet assembly in place and mark needle position for installation exactly on the same angle. (Another possibility is to lift the needle 'behind' zero pin, and mark down the spot where it settles.) Symptom of wrong installation is linear low/high reading: always erroneus.
- The bearings supporting the needle axle may wear down, can be corrected. Symptom is that needle jams to some position, may get loose from vibration.
- spring breaks or gets loose, dirt on the spring causes non linear needle movement throughout scale. Spring may be replaced; lenght and strenght are critically balanced with the gauge input source. The spring presses against the magnetic force created by the sender unit current and returns the assembly to zero position.
- axle wears out so that magnet starts to drag on the base structure. Symptom is that needle jams to some position, may get loose from vibration.
- permanent magnet loses magnetism (highly unlikely). Symptom is linear low reading. Magnet may be recharged with special pulsing direct current magnetizer; any changes in the magnet forces have to be balanced with the spring and/or limiting sender unit current.
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Basic electhromechanical gauge composition, part B :
Base assembly where electromagnet has been installed.
- Base assembly supporting a electromagnet which surrounds the needle assembly A
- To the base top is attached the gauge bezel, zero position pin for the needle (yel), attachement for the spring (yel, right), wiring attachements to assembly screws (bottom).
Troubleshooting the 'electronics':
- Windings may break, correction next to impossible. Scratch the wire bare near the magnet and measure resistance to figure out the location. Wires from winding may be broken to the screw terminals, here it is possible to resolder a new wire. Symptoms are intermittent jumpy behaviour, or sudden drop to zero. May start working if dash is hit with a fist.
- Typical problem is screw terminal oxidation between the gauge assembly and the screws. Clean.
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A+B , Whole gauge assembled.
Whole assembly A+B.
Sender unit current is directed to the electromagnet. The current creates a magnetic field which starts to counter the permanent magnet in the needle assy A. Axle starts to rotate against the spring induced force; needle moves. The greater the sender unit signal, the farther the needle moves. When current stops, spring will pull the needle assy back to the neelde zero position pin (yel).
Troubleshooting, misc:
- Dirt between moving mechanism, clean.
- Metal bits shorting the screw terminals.
- Wrong reading after bezel change; see A
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Maxima Electronic Gauge assy
Note: Maxima may have this std type electronic gauge assembly -or- DIGITAL gauge assembly. The latter one is NOT discussed here...
Instrument Panel; front-rear
The rear view: red arrows point to odometer motor and its connector which has been disconnected from speedo (goes through the adjacent hole). Speedometer electrical connection and mechaniocal attachement holes, 4pcs, red... Three (yel marked) connectors from harness to the assembly. At top left is the annoying melody maker.
Take the assy off on a table, take 'glass' off. The gauge is attached to the assy with 4 screws, take them off. For detail info get the FSM; see Favorite Links on p.26.
The Speedo from various angles (Odo connector redlined)
The Odometer is powered by a small motor; its control is routed via Speedo module. Here Speedo has been taken off, see the four attachment holes (redlined):
Odometer dissassembled from cluster; motor screw gear redlined at left:
Trip mech: Either spray (careful) or spray to a small cup corner and insert with a toothpick lubricant to the button mech and to all 'bearings'. This will not hurt... If smtg is already broken (possibly) then its gonna take determination to fashion the plastics with a soldering iron tip (only electronics solder, radio shack small one. (Later the solder tip is easily cleaned to papertowel.)
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Calibration:
I figure u took needle off from speedo, right? If u did not lock the gauge axel in place, u lost zero position. That means the needle is now more forward compared to the gauge axle.
Speedo Calibration, DIY:
1. Measure your actual speed: Use the speed u think is most important for u to be accurate. The only way is to use a CHECKED distance, steady speed and stop watch and calculate your speed. Its easy, but u have to be accurate. Recheck, recalculate.
2. Write down your measurement speed and what is the actual speed u just calculated
3. Take gauge off.
4. Find a way to lock the needle axle in the position where u measured the speed.
5. Pull the needle off, push it down to the position that the actual speed was.
Note: -Most often the gauge is not linear, meaning error in 30mph is different form error say 70mph. This is why (*1) its good to select the most important speed for your calibration process.
- Wheel size change (front) also causes errors to the speedo, odo, may be corrected like this.
- When odometer error is known, it can be used as distance 'yardstick' in this speedo calibration.
- The longer your distance is, the easier it is to be accurate in your measurement. If there is an exact 5mile level strip where u can keep steady pace, good. Half a mile is ok, but needs accuracy in timing.
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Note: 60kmh / 37.5mph / 637rpm
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Older Mechanical Speedo's
Old mechanical speedometer structure for comparison, Bluebird speedo at right:
Needle position on the axle, zero postion stopper and spring mechanism is same as described above. Instead of magnet on the axle, there is a steel cup (blu) attached in the axle end. Inside the cup is a permanent magnet (blk/grn); being rotated via a mechanical wire (red) attachement to the trasmission. As the permanent magnet rotates, created magnetic field rotates the cup and needle moves. The needle assembly is separate from the magnet. Bearings (b.) attached to base, keep both assemblys aligned and out of touch each other.
Troubleshooting:
- The bearings supporting the needle or magnet axle may wear down, can be corrected. Typical problem of the wear is that magnet starts to touch the cup, needle wobbles.
- Dirt between moving mechanisms, clean.
- Wire to tranny needs lubrication, indication is wobbling needle.
- Spring breaks or gets loose, dirt on the spring causes non linear needle movement.
- Permanent magnet loses magnetism (highly unlikely).
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Precision Gauges
How Precision Gauges are built?
Here is shown a expensive precision gauge in contrast to the mass produced cheap automotive gauges...
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Precision Voltmeter front; View from rear, supply terminals as in any typical gauge.
Zero position adjustment is provided from outside at the front panel screw.
Internal view as top has been taken off.
This precision gauge has permanent magnet outside, the electromagnet coil is on the needle axle. Current is guided via wires to springs and to coil: two springs sit in both magnet ends on the axle. Two springs also facilitate balanced load on the axle. Axle bearing top end has adjustment screw; also multiple other adjustment screws are available to finetune this precision instrument.
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"Give, and it shall be given unto you; good measure, pressed down, and shaken together, and running over, shall men give into your bosom. For with the same measure that ye mete withal it shall be measured to you again." ; Luke.
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