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Author Topic: Do speedometers actually break or stop working?  (Read 6300 times)

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Offline TRAN5AM

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Do speedometers actually break or stop working?
« on: June 30, 2006, 08:47:16 AM »
I bought my '78 with a non-functioning speedometer. Before I go looking for a replacement on eBay or my local junk yard, how likely is it that the speedo is actually broken? Before I take apart the dash, is there anything else that could be the problem, and how do I check for it?
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Offline eroc022

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Do speedometers actually break or stop working?
« Reply #1 on: June 30, 2006, 09:45:35 AM »
hmm not sure how top check the mechanics of it but id check to see the cable from the tranny to the speedo is in good condition and actually connected to both.....
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Eroc
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Offline TRAN5AM

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Do speedometers actually break or stop working?
« Reply #2 on: June 30, 2006, 11:52:11 AM »
I'm not much of a mechanic. Is that something easy to spot/find?
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Steve Frey

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Offline eroc022

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Do speedometers actually break or stop working?
« Reply #3 on: June 30, 2006, 12:07:25 PM »
yeah just pull out the cluster and theres a cable attached to the back with   kinda a clip type thing but heres a pic of how it should be connected to the tranny....



and how it should be connected to the speedo

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Eroc
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Offline ta78w72

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Do speedometers actually break or stop working?
« Reply #4 on: June 30, 2006, 03:20:19 PM »
Anything can break.  But as suggested elsewhere, the first thing to suspect is the cable.  You can verify the problem by pulling the cluster.  But I'd first check to make sure the cable is connected at the back of the cluster and at the transmission.  If it appears that the cable is connected correctly, you could pull the cluster.  Or, if you can reach in and disconnect the cable, try rotating the speedo neck to see if the needle moves.  If it does, you might as well replace the cable.  Be careful on your routings to avoid angles.

Now I'll ask what I should have asked at the beginning.  Did the speedo quit? or does it jump and make a noise?  Does the odometer work?  I assume it doesn't.  

If you end up pulling the cluster, are your gauges working correctly?  If not you can address those issues at the same time.
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Offline Eagle 1

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Do speedometers actually break or stop working?
« Reply #5 on: June 30, 2006, 05:55:08 PM »
The first question is, does the car have cruise control?
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Offline ta78w72

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Do speedometers actually break or stop working?
« Reply #6 on: June 30, 2006, 07:06:46 PM »
Maybe it did but got hacked out :D

That would explain it!  

By the way TRANSAM, we can take you through how to pull the cluster.  It's not that hard.
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Offline Eagle 1

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Do speedometers actually break or stop working?
« Reply #7 on: July 01, 2006, 11:02:58 AM »
If it had cruise control, there is going to be two cables to check plus the cruise control regulator.  I would suspect any of these before I would the speedometer.   Alot of times the cruise control regulator will bind up due to wear and age causing the lower cable from the ccr to the trans to break.
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" He done good didnt he Fred?"
"I'm in pursuit of a black Trans Am. He's all mine so stay outta the way."

Offline ta78w72

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Do speedometers actually break or stop working?
« Reply #8 on: July 01, 2006, 12:46:45 PM »
I'm not sure how common cruise control was in 1978.  I see very few at the salvage yard.  It would be an interesting statistic.
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Offline 81BlackTA

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Do speedometers actually break or stop working?
« Reply #9 on: July 02, 2006, 12:57:18 PM »
I would unscrew the cable from the trans and spin the inside small cable by hand while someone watches to see if the speedo hand moves in the dash. If the hand moves, then its got to be the trans tailshaft gear/cog. If the needle doesn't move, move to the next connection point. If the cruise is missing and the cable goes directly to the back of the speedo, pull the cable off the back of the speedo and again have someone spin the cable from the transmission end and see if the cable spins on the speedo end. If the cable spins on the speedo end, its most likely the speedo gauge. If it doesn't spin where it hooks to the speedo gauge, the cable is bad.
Good luck!
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Offline TRAN5AM

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Do speedometers actually break or stop working?
« Reply #10 on: July 03, 2006, 09:16:29 PM »
Yes, it has cruise, but it does not work.

Neither the cruise or the speedo worked when I bought it.

I'll check all the cables first. Thanks for your insights!
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Steve Frey

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Offline ta78w72

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Do speedometers actually break or stop working?
« Reply #11 on: July 03, 2006, 10:09:23 PM »
Eagle made that call!
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Offline Eagle 1

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Do speedometers actually break or stop working?
« Reply #12 on: July 04, 2006, 01:02:55 AM »
I would check the cruise control regulator.  Unscrew both cables at the cruise control regulator, mounted on the drivers side inner fender well.
Then using your fingers, spin the cruise control where the cable from the trans hooks up.  The other part of the ccr that goes out to the speedometer  should spin freely.  If is doesnt, then you have found your problem.
If that checks out ok, get a buddy to help you.   Have him watch the speedometer while you spin the cable end at the cruise control.  The speedometer will should move depending on how fast spin the cable.
If thats ok, then try this.   Have him walk along beside the car and watch the cable coming up from the trans while you pull forward a few feet, slowly.  The cable should spin.  If it dont, then either your lower cable is bad, or possibly the gear inside the trans that turns the cable.  (not likely though, but possible).
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" He done good didnt he Fred?"
"I'm in pursuit of a black Trans Am. He's all mine so stay outta the way."

Offline TRAN5AM

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Do speedometers actually break or stop working?
« Reply #13 on: July 04, 2006, 02:30:13 PM »
Okay, here's the deal.

The Cruise Control had been previously removed, however, there is a cable running from the speedometer to the transmission.

I pulled the instrument cluster, disconnected the cable from the speedometer, and was able to turn the speedometer by hand. This would seem to confirm the theory that is it a cable problem.

I then went under, and disconnected the cable from the transmission. I was going to turn the tip by hand, and have a helper see if it was turning at the other end, but it was bound up.

I traced the cable as it ran between the frame and floor pan and found that where the cable turns upward in front of the pan, the cable was frayed and kinked. Basically it is shot and needs to be replaced.

Now my question is, since the inner cable was unable to turn at all, what is the likely hood that it stripped or otherwise busticated the "Sleeve and Seal Assembly" or the "Speedo Gear" at the transmission, as shown in Fig 8-87 as posted by eroc022 ?

If so, are these NAPA Auto type parts, or do I need to start scrounging around junk yards?

Thanks for your help guys.
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Steve Frey

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I saw it in a cartoon one time, but I think I can do it!"

Offline ta78w72

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Do speedometers actually break or stop working?
« Reply #14 on: July 04, 2006, 04:19:59 PM »
If I were you, I would buy a new cable and housing and see if that solves your problem.  Chances are it will.  But be careful about running it.  Make sure you run it like the original.  It could be that whoever installed that cable didn't follow the original route and that's why you have the problem.  You should be able to see where the cable runs in the car by taking out the carpet guard under the base of the steering column and by pulling back the carpet.  You can't have tight bends in it or your speedometer won't work.

I've had the speedometer jump and make noise and tried to pull the cable out of the housing and grease it.  That didn't work for me.  The best solution was to replace the entire cable and housing.

I've found that these gauges are pretty reliable and if they quit or don't register correctly the problem is usually not with the gauge itself.
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