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90+ odometer/ tripmeter design&function?

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    90+ odometer/ tripmeter design&function?

    Hi!

    I've been bemoaning my poor fuel economy --calculated by resetting the tripmeter each time I get gas, and dividing the previous reading by the #miles traveled-- when I noticed something interesting today.

    The tripmeter was frozen at 110.8 for at least 2 miles. It rolls every 1/10th mile, and I definitely went more than 1/10th, much more, and it didn't move. I am pretty sure the odometer did roll over for them, but not certain upon reflection. It doesn't roll over every 1/10th, so you can't watch it move the same way. It resumed again later, or it must have, because when I got to work it was 112.

    So obviously the gears are good.
    And, I replaced the gears with the modern plastic ones just three weeks ago, so.
    And the cable must be doing something too.

    How precisely does the electric tripmeter (and odometer) work? Is it a motor, that receives pulses like a tachometer? If the motor is weak, could it end up turning more slowly or seizing intermittently?
    Again, as per the title, this is a 90+ electric tripmeter, not the all-mechanical cable of -89.
    I'd like to know what can cause this, so as I get into diagnosing I know something of where to look for this symptom.

    OTOH my fuel economy might still suck badly for other reasons, just because I've noticed, once, in many months, that the tripmeter was frozen briefly, does not mean it's frozen often enough to explain 10 months of 12mpg averaged.

    #2
    it "should" be accurate to whatever speed the speedometer is showing. But it is driven by separate electric motors.. so there may be variance.

    as for causes... if the new gears have tighter tolerances and are not allowing free movement, you may need to add some lithium grease, graphite, or other dry lube or plastic gear lube (readily available from everywhere custom RC cars are... and on-line).

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)

    Originally posted by gadget73
    ... and it should all work like magic and unicorns and stuff.

    Originally posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

    Comment


      #3
      yeah, I confirmed again today: froze for 7 miles straight, then resumed turning over (just the trip meter)

      Comment


        #4
        Not to hijack this thread, but I was doing a search on the odometer gear installation, and this came up. Anybody have the instructions for replacing them? I did it on a 97 Mustang, but the company I bought them from (PATC) gave great instructions. I forgot about them till I was looking for the instructions for the ones I bought (on Ebay.)

        Any help is greatly appreciated. I hope to do it this weekend. By the way, I have a 91 LS.
        Last edited by Bigbullitt; 12-27-2012, 11:58 PM.
        1991 Grand Marquis LS.
        2001 Mustang Bullitt (bought new)

        Comment


          #5
          Odometer gear instructions are here: http://www.odometergears.com/product...rquis+90-97/60 last PDF link on the page for both trip and regular odometer gears. I've done 3 of the four in my two '91s. Can be a bitch to press the worm drive gear onto the shaft, I ended up using some channel locks to pinch it on, carefully.
          Last edited by sxcpotatoes; 12-28-2012, 06:39 AM.
          ,
          Slicktop '91 GS HO 4.30 rear. '82 Mark VI Tudor HO, '90 F-150 XLT, '62 project Heep, '89 Arizona Waggin' and '88 donor in PA, getting combined.

          Comment


            #6
            Thanks, that's the same one I printed, but they give TMI, lol! What do you need to take off? Headlight knob and it looks like several screws hold the instrument panel on. Once those are out, does it just lift off? It looks like there's a panel that runs the length of the dash below it, does that need to come off?
            1991 Grand Marquis LS.
            2001 Mustang Bullitt (bought new)

            Comment


              #7
              One skinny trim piece on either side of steering wheel, then out come screws, then entire dash plastic/fascia comes off. THEN you can access the various screws/bolts that hold in the entire cluster.
              ,
              Slicktop '91 GS HO 4.30 rear. '82 Mark VI Tudor HO, '90 F-150 XLT, '62 project Heep, '89 Arizona Waggin' and '88 donor in PA, getting combined.

              Comment


                #8
                Originally posted by sxcpotatoes View Post
                One skinny trim piece on either side of steering wheel, then out come screws, then entire dash plastic/fascia comes off. THEN you can access the various screws/bolts that hold in the entire cluster.
                Is that skinny piece just pushed in? In other words, can I just get a good grip and pull?
                1991 Grand Marquis LS.
                2001 Mustang Bullitt (bought new)

                Comment


                  #9
                  yes. it just snaps in... pull up gently but firmly on one end until that pops free... then you can ease out the rest of the clips with less trouble.

                  Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                  rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)

                  Originally posted by gadget73
                  ... and it should all work like magic and unicorns and stuff.

                  Originally posted by dmccaig
                  Overhead, some poor bastards are flying in airplanes.

                  Comment


                    #10
                    I just replaced mine a few weeks ago on my '91 MGM, +1 for what sxcpotatoes said.

                    You need the headlight knob removed before the dash plastic/fascia will come off. I pried the top edge of the fascia out a little then was able to get a long enough torx driver (t20 I think, or maybe t15) into the little vent above the switch to get the top screw out for the headlight switch mounting plate. Then I was able to pull the whole switch out enough to easily unlock the knob and pull it right out.

                    Also I'm sure the OP has fixed the issue by now, but if not is it possible a small piece of the old gear accidentally left behind could be the problem?
                    Last edited by VicCrownVic; 12-28-2012, 10:08 PM.
                    Vic

                    ~ 1989 MGM LS Colony Park - Large Marge
                    ~ 1998 MGM LS - new DD
                    ~ 1991 MGM LS "The Scab"
                    ~ 1991 MGM GS "The Ice Car"

                    Comment


                      #11
                      Thanks for the help. I'm going to document it with pictures and text for anybody in the future doing it. I'm guesstimating it'll take about 2 hours to complete (for a first timer?)
                      1991 Grand Marquis LS.
                      2001 Mustang Bullitt (bought new)

                      Comment


                        #12
                        Okay. Done. A bit of a pain and of course, I got too into it to document it. One thing I noticed is that if you take off the panel directly under the steering wheel (by the fuse block,) access to the headlight knob release is very easy. Also, the mounting tab for the tripmeter motor was broken, so I had to try to tie strap it on and I don't know if it will hold. The instrument housing itself is showing its age and a lot of the mounting tabs were cracked. I don't know if either of the repaired parts will work until I drive it on Monday.
                        1991 Grand Marquis LS.
                        2001 Mustang Bullitt (bought new)

                        Comment


                          #13
                          Could always just roll your own...

                          Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                          rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)

                          Originally posted by gadget73
                          ... and it should all work like magic and unicorns and stuff.

                          Originally posted by dmccaig
                          Overhead, some poor bastards are flying in airplanes.

                          Comment

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