Speedometer probs!? help please
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Old October 31st, 2007, 02:08 PM   #1
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Speedometer probs!? help please


I recently purchased an '85 GT and the speedometer didn't read anything at all, so i got a new speedometer gear put in (car has 3.73 gears and didn't have the right speedo gear) but it still isn't working right. The speedometer originally just sat at 0 mph, now the speedometer just acts funny... sometimes it will sit at 0mph, sometimes it will jump around constantly, and sometimes it is pegged all the way past 85 mph. anyone know what to do?
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Old October 31st, 2007, 02:38 PM   #2
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check the speedometer cable
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Old October 31st, 2007, 02:43 PM   #3
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The speedometer is mechanical, so you can eliminate electrical problems.

The problem could be the speedometer itself is broken, the drive gear on the output shaft of the transmission isn't in the correct location, or the speedometer cable is messed up. From the sounds of it, I think you have a bad gauge.
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Old October 31st, 2007, 02:43 PM   #4
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check it as in how? the shop that replaced the gear on the end of the cable didn't say there was any problem with the cable itself... he said it may be a gear inside the transmission that needed to be replaced as well, but he wants way to much monies to pull the transmission, so im trying to find out whats up before i call my granddad to get his mechanic to look at it for me (he lives about 2 hrs away, so i want to know most/all my options before i head out there. )
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Old October 31st, 2007, 02:46 PM   #5
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for 3.73's you need the red gear for your speedometer cable. If you go to ford and tell them the info on your car and just tell them you need the red gear, they should know what you are talking about. double check the connections in the tail shaft and in the back of the gauge, make sure the bolt that holds the cable into the tail shaft is tight. the chances that the gauge is broken is unlikely.

hope that helps
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Old October 31st, 2007, 02:50 PM   #6
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Oh and don't pull the tranny! i don't know what mechanic thinks that pulling the tranny will help but they are wrong. replacing this gear is easy and it can be done in 1/2 an hour with a floor jack and a 10mm wrench.
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Old October 31st, 2007, 02:52 PM   #7
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well my ford place must be full of dumbasses cause i told them my setup and they didn't know what they needed to give me o.O the only thing they had instock was a black speedo gear (20 tooth) and they had some 21 tooth gears on order. Its only like 8$ for the gear so i went ahead and got the 20 tooth gear. < i had read on the forum last week sometime that the 3.73 gears you needed the 20 / 21 tooth gear.
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Old October 31st, 2007, 02:54 PM   #8
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Originally Posted by fastford3388
Oh and don't pull the tranny! i don't know what mechanic thinks that pulling the tranny will help but they are wrong. replacing this gear is easy and it can be done in 1/2 an hour with a floor jack and a 10mm wrench.

he said that the tranny would need to be pulled to look at the gear that is inside the tranny (the gear that the speedo gear connects to) and yeah, he wanted 300$ just to drop the tranny.... i think i paid 200$ total in labor for my grandfathers mechanic to fully replace the tranny in my truck.
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Old October 31st, 2007, 02:55 PM   #9
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Your cable may be stiff or kinked and need some lubrication. If it is getting stuck, this may also explain the reason you needed a gear. You can pull the instrument cluster and gain access to the cable and can get some wd40 or light oil in it. That is a lot of work though if that is not your problem.
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Old October 31st, 2007, 02:58 PM   #10
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Originally Posted by nolife
Your cable may be stiff or kinked and need some lubrication. If it is getting stuck, this may also explain the reason you needed a gear. You can pull the instrument cluster and gain access to the cable and can get some wd40 or light oil in it. That is a lot of work though if that is not your problem.

its not getting stuck, it just doesn't give an accuratge reading. kinda bounces around anywhere from 0 -85+...... its getting really annyoing having to follow other people around so im not speeding everywhere i go
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Old October 31st, 2007, 03:04 PM   #11
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As it gets stuck it starts to twist up and then gets unstuck, that would cause jumping because it is moving fast and slow on the speedo end. If it really gets stuck good, it will twist up and break or the gears will strip out and the speedo will then not move at all. If you have long periods of no movement on the speedo, it is probably not the cable as it would have broken already.
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Old October 31st, 2007, 03:15 PM   #12
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but it doesn't seem to be stuck, it just goes whereever it wants.... i think i am confused though
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Old October 31st, 2007, 04:23 PM   #13
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If the cable is sticking or getting hung up.
Both ends of the speedo cable have to spin around the same amount of times. Assume you are going 40 mph, the cable at the transmission end may be spinning at a constant 100 rpm. The end at the speedometer may stop spinning or spin really slow for a short period and the cable builds up some tension, suddenly it breaks free and now spins 150 rpm to catch up with the other end and then gets stuck again. They still turn the same amount of times overall but the speedo end is erratic because it is getting caught up which causes your speedo to read erratic. This can happen on a much smaller scale and cause your speedo to bounce around and read all over the place. This extra cable tension can eventually cause the gear to strip out as well.

This may not be your your specific problem but it is one thing that it could be.
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Old October 31st, 2007, 04:50 PM   #14
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hope this helps mine was masking alot of noise and was inaccurite. now with the speedo cable the part that goes in the tranny is metal and the part that goes in the speedo is plastic. i heard that you can buy the all metal.i took out my cluster and found that the plastic peice was broken off in the gauge so when the cable turned it was turning the broken piece but, not like it was suposed to. so i took a small i mean small drill bit and SLOWLY drilled it into the broken piece in the gauge and then pulled it out. the lube up the new/used cable put it all back together. and know i can see how fast i am going when i am smoking the rice burns . hope that helps and i hope i was clear. it was in head.
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Old October 31st, 2007, 10:53 PM   #15
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If you gauge is sticking at 85, your gauge is bad, unless you are doing over 85.
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Old November 14th, 2007, 09:25 AM   #16
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I just put a new transmission (replacement) and new speedo cable and noy at about 75mph, my speedo reads 140+! A friend said that it needs time to "settle". True, or untrue?!
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Old November 14th, 2007, 09:28 AM   #17
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Originally Posted by sneezingfox View Post
I just put a new transmission (replacement) and new speedo cable and noy at about 75mph, my speedo reads 140+! A friend said that it needs time to "settle". True, or untrue?!
nope not "true" , you got something wrong in there. are you sure u have the correct speedo gear?
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Old November 14th, 2007, 09:38 AM   #18
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when i first got my car i took in out to see how fast it would go and when i got to 125 the needle just fell all the way past 140 and when i slowed down it came back out.....hasnt done it since
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Old November 17th, 2007, 11:28 AM   #19
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Yes, I am sure I have the right gear. I didn't change it. The only thing I changed was the speedo cable. I just found out however that the trans that I put in is out of a 92 gt. Mine is a 1989. WIll that cause any issues?
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Old November 18th, 2007, 10:07 PM   #20
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mine bounces around also, i put a new gear in for 3.55's and put the new cable in, about an hour job not so bad but make sure its the right one for your car (cruise contol or not) thats why mine bounces around they gave me one without cruise
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