Drivetrain Speedo Issues

Discussion in 'Fox 5.0 Mustang Tech' started by cdurbin, Oct 30, 2012.


  1. cdurbin

    cdurbin Active Member

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    I'm having some speedo issues I'm hoping someone can shed some light on.
    My speedo needle was bouncing around when I was running from 0-40 mph and then would level out and be smooth. I replaced the gear in the transmission to tray and resolve the issue with no luck but now I have another problem. I've noticed that after the car has sat overnight or it's cold the speedo needle sticks. It's rises really slow and sometimes will stick at 20 or 40mph. Once the car has been driven for a while and everything warms up the needle works like it should and everything is smooth. Is it a lubrication issue? I will note that the transmission gear I replaced was the wrong one. When the PO did the 5-lug conversion he didn't replace the speedo gear. I ordered the right one and tested the speedo using my GPS. The speedo is within 1-3mph.

    Thanks
  2. ratio411

    ratio411 Founding Member

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    The cable is worn out and sticking inside the sheath.
    You can try to lube it, but it is probably too late now.
    The cables should be lubed periodically with a DRY graphite powder.

    Also, make sure that sometime in the past someone didn't accidentally route the cable wrong.
    Make sure there are no tight bends/radiuses in the cable. All bends should be long and smooth.
    If there is a tight/short bend in the cable now, it might help your problem to get it out and lubricate, but it might be too far gone.


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  3. ratio411

    ratio411 Founding Member

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    4 or 5 lugs has nothing to do with speedo gear.
    The speedo gear needs the tooth count changed if changing rear gears or tire heights.
    The speedo gear design/style needs changed most of the time when changing from one tranny to a totally different tranny style/family.
    Example: Swapping between AOD and T5, or C4 and T&C. The gears won't interchange, regardless of tooth count.
    88LX5.Oh likes this.
  4. cdurbin

    cdurbin Active Member

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    I'll take a look at it but it didn't start until I changed the gear out.
  5. cdurbin

    cdurbin Active Member

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    Understood.
    The 98 GT rear end has a different gear ratio than the stock 91 rear end. The car still has the original T5 transmission.
    After pulling the code off the rear end tag I was able to research that the gearing is 3:27. Based on that I ordered the correct 21 tooth "red" gear from LMR.
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  6. ratio411

    ratio411 Founding Member

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    I read the post as it was acting up before the gear swap, and you had "no luck" with the gear swap.

    Hopefully it just needs the cable lubricated.
  7. cdurbin

    cdurbin Active Member

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    You're partially correct. The needle was bouncing around at speeds between 0-40mph before the gear swap.
    Now the needle is sticking when the car is cool or the outside temp is cool. Once I've driven the car a bit and its warmed up (from turning I assume) the needle starts working correctly.:shrug:
  8. cdurbin

    cdurbin Active Member

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    I've never lubricated one before. How difficult is that to accomplish?
  9. 88LX5.Oh

    88LX5.Oh Advanced Member

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    I was initially going to run a 3.27 ring and pinion in my new rear end and ordered a new speedo gear as well. I ordered a 19 tooth one and it was pinkish. One of us has been informed wrong lmfao. I hope it was me and not you to be honest. Because I've already switched gears again and wouldn't matter if I was correct in the first place :p
  10. cdurbin

    cdurbin Active Member

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    I ordered by based on these charts from LMR.
    Seems to be the correct one based on using my GPS to verify accuracy.

    gear-1.jpg

    gear-2.jpg
  11. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Speedometer cable replacement for 87-93 Mustangs

    Revised 1-Apr-2012 to clarify steps 11, 12, and 13, cable replacement inside the car.

    How the speedometer works:
    The indicator pointer has no direct connection to the speedo cable. It uses a drum with magnets on it to couple to the pointer. The drum turns and tries to twist the circular steel disk that is mounted on the pointer spindle. The magnetic force is all that connects the drum to the circular disk. There is very little clearance between the disk and drum, only a few thousands of an inch.

    Lubrication warning
    Use a graphite based lubricant for the speedo cable. It is available at most auto parts stores in a very small tube. Lubricate only the lower half of the cable. The reason for this is that if you use too much lubricant, it works its way up into the speedo head and gets between the rotating magnet and the disk. This causes the speedo to seize up and wring the indicator needle off the indicator spindle. You may be able to fix things up with non-flammable brake parts cleaner to clean the disk and magnet assembly. Plan on replacing the current cable and housing with a new cable and housing to prevent the excess lubricant from doing it all over again.


    Speedometer cable replacement.

    Note: All 89-93 cars have a VSS sensor even if they do not have cruse control. The 87-88 only have a VSS sensor if the have cruse control.

    Speedo cable housing assembly without cruse control:
    [​IMG]

    The VSS equipped cars have a speedo cable with a different fitting on the transmission end of the cable. It is the fitting on the LH side of the following picture.

    Speedo cable housing assembly with cruse control
    [​IMG]

    Preparation: if you are only going to replace the inner part of the speedo cable, get lots of newspaper or a painter’s drop cloth to cover the inside front of the car. About the time you have the dirty, oily speedo cable core all over your lap and the inside of the car, you will thank me for this suggestion.

    Replacing only the inner cable: see steps 1- 6, 12, 13, 17-21

    Replacing the housing and inner cable as an assembly: see steps 1-11, 13-21

    Inside the car:
    1.) Remove the shield around the steering column that covers the ignition switch & turn indicator switch.
    2.) You now have access to the two screws that hold the lower part of the cluster housing in place. Remove them and place them in a zip bag.
    3.) Use a stubby or an offset Philips screwdriver to remove the two screws on the top of the cluster housing. The screws are up close to the windshield, so they can be hard to get at.
    4.) The cluster housing will now slide forward: depending on your particular car, you may or may not have to disconnect the wiring for the headlights, hazard lights, or cluster wiring. All of the wiring uses plastic connectors with plastic spring clips on them. To release the connectors, lift the plastic clips and pull straight back.
    5.) The speedo cable is secured in the speedo head by a white plastic clip. Depress the clip or squeeze it and pull the cable out of the speedo head. This can be tricky, but it will come out if you have the white clip depressed enough.

    Speedo head cable clip

    Photos courtesy of Almost Stock


    [​IMG]
    [​IMG]

    6.) With speedo cable removed from the speedo head, try twisting the cable end with your fingers. If it turns more than 1/4 turn, the cable may either be broken or you have damage at the other end where the cable mates to the VSS sensor or speedo pickup gear in the transmission.

    Outside the car, replacing the cable housing assembly.
    The following steps are necessary only if you plan on replacing the cable & cable housing assembly.
    7.) If you are going to the replace the cable housing, the next step is important. Tie a study string or wire to the VSS sensor end of the cable housing. This string or wire is to be used to fish the cable housing back through the maze of wires that is under the dash. If all you are going to do is replace the inner cable, you can omit this step.
    8.) Jack up the car, all 4 tires must be off the ground. Place jackstands under the car for safety.
    9.) Locate the VSS sensor on the driver’s side of the transmission tailshaft housing. The speedo cable housing will be secured in the VSS sensor with a hairpin clip Do not remove the clip!!!: The hairpin clip stays in place. If you remove it, the odds are that you will not be able to get the cable to stay in place on re-installation. Pull firmly straight back on the cable housing and it will come out. A considerable amount of effort may be required to get the cable out of the VSS sensor, but it will pull out.
    10.) Release the cable housing from the clips that secure it to the car body.

    Inside the car:
    11.) If all you are going to do is replace the inner cable, you can omit this step.
    The housing assembly can then be pulled out and the fish string or wire can be removed from the old cable housing and secured to the new one.
    12.) You can omit this step if you are replacing the cable & cable housing assembly.
    The inner cable can be removed by pulling it out of the housing assembly. Watch out for the lubricant so that you don’t get it on the car’s interior.
    13.) You can omit this step if you are replacing the cable & cable housing assembly.
    Lubricate only the lower part of the new cable with speedometer lubricant or graphite. Don’t use too much lubricant, or it will work its way up into the speedo head unit and damage it. Thread the inner cable into the housing, turning it as you go. When you are all the way in with the new cable, it will engage the VSS sensor and stop turning.

    Outside the car, replacing the cable housing assembly.
    The following steps are necessary only if you plan on replacing the cable & cable housing assembly.
    14.) Use the fish string or wire to feed the cable housing assembly through the dash wiring and out the cable hole in the firewall.
    15.) Secure the cable in the body clips, making sure that the cable isn’t rubbing against the exhaust pipe.
    16.) Push the cable housing assembly into the VSS sensor until it snaps in past the hairpin clip. Connect VSS wiring connector back to VSS sensor.

    Inside the car:
    17.) Push the cable housing back into the speedo head unit. You should be able to feel the white clip click into place.
    18.) Reconnect all the wires & connectors on the speedo head unit.
    19.) Re-install the cluster unit in the dash & tighten the 4 screws that hold it in place.
    20.) Re-install the cover for the ignition switch & turn signal.
    21.) If the car is up on jackstands, start the car, place it in gear & watch the speedo to see if it works OK. If you didn’t jack the car up, take a test drive.
  12. cdurbin

    cdurbin Active Member

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    As usual, you are the man! Thank

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