Gauge swap.

Discussion in 'Tech Discussion' started by 73c20jim, Nov 5, 2018.

  1. 73c20jim

    73c20jim Supporting Member Supporting Member

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    Swap to cluster with mechanical speedo, mech oil pressure and voltmeter from Mech speedo, electric oil pressure and ammeter. Not sure of what year the new (to me) gauge cluster.

    A lot of wires to transfer and some changed position, some added, some not used.

    Results:

    • Speedometer works. No longer bounces, but now reads about 10 MPH fast. Old one bounced and read 15 MPH slow.
    • Voltmeter works.
    • Oil pressure not hooked up yet. I have sender and it is wired ready for sender.
    • Temperature gauge is weird. Reads high. Are there more than one sending unit.
    • Blinker indicator lights work.
    • Hi beam not working
    • Gas gauge accurate when stopped, but bounces while driving. Probably loos connection somewhere. Old one worked fine.
    • Brake warning light not tested. Worked correctly on old cluster.
    • Gauge illumination not tested.
    QUESTIONS:

    1. Why big swing on speedo readings?
    2. Are there different temp sending units?

    Any help appreciated.
     
  2. rpcraft

    rpcraft Full Access Member

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    The big swing is probably due to the fact that the one that was bouncing was not reading correctly because the magnetic pickup had too much drag and was reading slower than it should have been. Just a guess. As far as the new one reading fast. Are you running tires or gearing that is lower than the transmission and truck originally came with?
     
  3. chengny

    chengny Full Access Member

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    QUESTIONS:

    1. Why big swing on speedo readings?
    2. Are there different temp sending units?


    1. On the increase in speed - as indicated by the pointer: It's anybody's guess why that is happening. Maybe the strength of the magnet in the speed cup was increased over the years, maybe your original hairspring was losing tension (letting the pointer move higher than when new) or maybe it is as Robert suggests - that there was some kind of mechanical resistance causing the speed cup to run slow/fast/slow fast. I have to ask, how are you checking discrepancy between indicated speed and actual road speed? Maybe the new speedometer is reading correctly - IDK.


    how-speedometer-works.gif


    2. On coolant temperature senders:

    Yes. There are three different types (see below). Broken up by model year, they are 67-73, 74-78 & 79-91. The difference in ohmic values between the first two groups is not so great - you probably wouldn't even notice if for example a 1970 was used instead of a 1975. On the other hand, the senders used with the 79-91 group have significantly higher ohmic values across the entire span.

    But what is most important isn't the year that the sender was originally manufactured for. The key is that the sender (whatever year) is compatible with the indicator (i.e. the dash gauge). IOW - you can't connect an early version sender to a late version dash indicator.



    COOLANT TEMPERATURE GAUGE PARAMETERS


    For Truck Years: 1967 - 1973

    The Temp Gauge Needle Should Point to:
    Left Line (Cold) when sender resistance = 350 Ω
    Middle Line when sender resistance = 76 Ω
    Right Line (Hot) when sender resistance = 51 Ω

    For Truck Years: 1974 - 1978

    The Temp Gauge Needle Should Point to:
    Left Line (Cold) when sender resistance = 350 Ω
    Middle Line when sender resistance = 68 Ω
    Right Line (Hot) when sender resistance = 46 Ω

    For Truck Years: 1979 - 1991

    The Temp Gauge Needle Should Point to:
    Left Line (Cold) when sender resistance = 1,365 Ω
    Middle Line when sender resistance = 96 Ω
    Right Line (Hot) when sender resistance = 55 Ω
     
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  4. chengny

    chengny Full Access Member

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    • Gas gauge accurate when stopped, but bounces while driving. Probably loos connection somewhere. Old one worked fine.
    There is a pulsation dampener (a resistor actually) that bridges the two opposing coils. It's function is to control the rate of movement of the ray (needle) when the sender is generating large fluctuations in a short period of time - like going around a corner fast or slamming the brakes on. If the coil is open, or the entire ceramic plate - on which the coil is mounted - is missing, the gauge will bounce around violently.

    HPIM2163.jpg HPIM2167.jpg HPIM2165.jpg

    If you still have your original gas gauge, you might want to swap out that dampening resistor.
     
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  5. 73c20jim

    73c20jim Supporting Member Supporting Member

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    WOW!

    Thanks guys. More info than I ever could ask for.

    Love this site.

    Yes I have the old gauges.
     
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  6. 73c20jim

    73c20jim Supporting Member Supporting Member

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    Evidently you cannot screw the gauge sending unit directly into the block. The intake gets in the way. So now I have to get a handful of fittings to work around this. After I fix the flat on the Jeep. With the oil feed open the truck is down.

    Can't adjust carb. Can't test gauges.

    There goes the day. Fifty mile round trip to get parts.

    "It's a beautiful morning."
     
  7. 73c20jim

    73c20jim Supporting Member Supporting Member

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    Got fittings. Tomorrow's another day.
     
  8. idahovette

    idahovette Full Access Member

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    Sorry for all the trouble you have , But it sure is entertaining!!!
     
  9. bucket

    bucket Super Moderator Staff Member

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    It's like a car guy soap opera. It seems like the repairs are right on track, but then there's a twist and the plot thickens.

    As for mounting the sending unit, an angled fitting often works well.
     
  10. 73c20jim

    73c20jim Supporting Member Supporting Member

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    Won't it break off. I think I'll have to make a bracket to hold it. 8200 lb springs plus 2 mile dirt road to house with many gullies and holes might cause it to break off on first trip out.

    By the way, I'm glad my entertainment is enjoyed by someone.
     
  11. 73c20jim

    73c20jim Supporting Member Supporting Member

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    My floor panels arrived yesterday. Gonna have to take the seat out to test fit them. Seat is jammed to the rear, can't get to back bolts.

    Seat also has to come out to install OEM rear speakers and install center seat belt. But that's another day.

    Today is oil pressure gauge and carb day.
    After I put some perches up in the wife's chicken coup.
     
  12. 73c20jim

    73c20jim Supporting Member Supporting Member

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    I have to ask, how are you checking discrepancy between indicated speed and actual road speed?

    Wife runs alongside truck counting paces. lol

    Smart phone GPS.
     
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  13. 73c20jim

    73c20jim Supporting Member Supporting Member

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    Maybe I should write a car guy soap opera for TV. Velocity channel might be all over this.
     
  14. CSFJ

    CSFJ ----------------- Supporting Member

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    "As the Wheel Turns"
     
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  15. Blue Ox

    Blue Ox Turning Diesel Fuel Into Fun

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    Usually the factory uses a 45° fitting, often extended length. Let's say an inch or so. Try to get a steel one. Although the senders aren't that heavy so breaking the fitting is a minimal risk.
     

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