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My speedo is about 10% off - any ideas?

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sciroccojim

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Discussion starter · #1 ·
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I just changed the clutch and put a groovy .80 5th in my 85. Put it all back together and it's off. Here are the details:
1. I didn't change the r&p...stock 3.67...should be....
2. Gear on cable end is red...as it should be.
3. 120 mph VDO, high miles
4. Smooth movement (ex-lax) - no bouncing, skipping, noise....
5. 175/70-13
6. Car is going faster than speedo reads
7. Just got the car on the road...musta been that way before I R&R'd the trans.
8. Checked the speed with GPS and a stopwatch...it's off
9. 9A
???????
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Anyone ever have a speedo that was just off?
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#2 ·
Re: My speedo is about 10% off - any ideas? (sciroccojim)

I was a little afraid to click on this post, it sounded like you were pulling your bathing suit down a little.
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Anyway, i'm thinking a cheapo fix would be to pull of the needle and reposition it to try to compensate but that would be gues work. Other than that, I'm thinking you just might need to get a new one, but that would suck. You could take it to a speedo shop and have them calibrate it.......
 
Discussion starter · #3 ·
Re: My speedo is about 10% off - any ideas? (webthread)

thanks, but it's 10%, not 10mph. Moving the needle won't work. I'm gonna swap the cluster from my 88 to test, but I'd rather not if someone has a suggestion.
Breathe deeply and look into the Hasselhoff:
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#5 ·
Re: My speedo is about 10% off - any ideas? (sciroccojim)

I've always tried to think of a way to compensate for my innaccuracy of 10% too fast, but thus far have come up with nothing. So I guess I have no advice, so why am I posting this?
-Rob
 
#6 ·
Re: My speedo is about 10% off - any ideas? (robw_z)

just lift the needle off the peg, match it to the mark on the VDO guage...and set it...thats that. If it's still off (because you already did this) JUST SET IT BACK/FORWARD ANOTHER TOOTH (increment).... My 1980 used to have an 85mph speedo. I put a 100mph VDO guage in. I did the above and had it accurate to within 1-2mph all the way up to 99mph. My old neighborhood has those digital readouts that clock your speed. So..thats how I checked the accuracy of mine.
If it truly is 10% off from 0-120mph that means everything is accurate...just not preset properly.

It just occured to me...this is only valid if the speedo is like it is on the MK1. I dunno how the mk2's are.
-Other Rob



Modified by MK1Scirocco1980 at 8:08 AM 10-10-2005
 
Discussion starter · #7 ·
Re: My speedo is about 10% off - any ideas? (MK1Scirocco1980)

Quote, originally posted by MK1Scirocco1980 »
to the mark on the VDO guage...

Thanks, but are you saying I should move the needle to the proper speed line on the face? Won't that just change the reading by X miles per hour across the board? Mine is off by 2 or 3 mph at lower speeds and 9 or 10 at higher speeds.
 
#8 ·
Re: My speedo is about 10% off - any ideas? (sciroccojim)

Quote, originally posted by sciroccojim »
Thanks, but are you saying I should move the needle to the proper speed line on the face? Won't that just change the reading by X miles per hour across the board? Mine is off by 2 or 3 mph at lower speeds and 9 or 10 at higher speeds.

Your best bet is to change the needle position. I believe this will change the reading by percent and not just x amount across the board.
Its been a long long time since I had my speedo apart but it works by spinning a magnetic disk(connected to the speedo cable) which tries to rotate another disk(more like a pan if I remember right). This pan is what the needle is connected to. There is no mechanical connection like gears ect. between the cable and the needle. The pan also has a coiled spring like in a old clock which acts as counter force to bring the needle back to zero.
Repositioning the needle will put more preload on the spring. As MPH go up more preload is put on the spring so you should have more percentage of reduction at higher speeds.
Remember I said this was a long long time ago. I think I may have even smoked dope back then but I don't remember
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#10 ·
Re: My speedo is about 10% off - any ideas? (sciroccojim)

Wow. My memory is not too bad after all. I knew I was saving this crap for over a decade for something. Just found a pair of tail lights and other plastics goodies in the same box.
Coil spring is under face plate.
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Blue disk has a metal ring which is magnetic in one spot.It spins inside the pan shaped disk.
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Also note the broken red gear with JB weld for the odometer. It still holds but the larger gray gear just inside the housing is now spinning.



Modified by GDR at 11:50 AM 10-10-2005
 
Discussion starter · #12 ·
Re: My speedo is about 10% off - any ideas? (GDR)

Quote, originally posted by GDR »
Wow. My memory is not too bad after all. I knew I was saving this crap for over a decade for something. Just found a pair of tail lights and other plastics goodies in the same box.
Coil spring is under face plate. Blue disk has a metal ring which is magnetic in one spot.It spins inside the pan shaped disk.

Interesting.... so , the odo is direct drive and the dial magnetic, yes?
That would mean that if my odo is correct, but speedo is off, I can assume it's the coil spring/magnet action, whereas an innacurate odo means I should save myself trouble and look elsewhere.
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EDIT: Thanks for taking the time to break this down!
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#13 ·
Re: My speedo is about 10% off - any ideas? (sciroccojim)

Quote, originally posted by sciroccojim »
Interesting.... so , the odo is direct drive and the dial magnetic, yes?
Correct.
Quote, originally posted by sciroccojim »
That would mean that if my odo is correct, but speedo is off, I can assume it's the coil spring/magnet action
Correct
Quote, originally posted by sciroccojim »
whereas an innacurate odo means I should save myself trouble and look elsewhere.
Not really. The gear is just slipping and can be glued. The outer red gear is almost always split but will still work. When the inner gray gear slips its a major pita to fix but can be done.

Quote, originally posted by sciroccojim »
Thanks for taking the time to break this down!
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No problem. That was the stock 85mph that needed to be thrown away anyway.
BTW I think your later speedo has a plastic housing vs my early metal housing but it still works the same.


Modified by GDR at 12:52 PM 10-10-2005
 
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