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Old 10-01-2005, 09:31 AM
Mellman99 Mellman99 is offline
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Default Speedo stopped working and check engine light is on

I have a 1983 Conquista, 305 with the TH350 tranny. 195k on the body, transmission was replaced about 20,000 miles ago, engine was done at 130k.


Was driving home yesterday and my speedometor just stopped working. for the past few months it has been "bouncing" a lot. I.E. during acceleration or decceleration it'll bounce around 10-15mph from the speed i'm actually traveling. But last night it just stopped working all together. What are common culprits? I'm assuming/hoping it was just the speedo cable that broke somehow (el has 195k on it, think the spedo cable is original) But shortly after the speedometer stopped working, my check engine light came on. Does the limited computer in my 1983 elky have any communication with the speedometer cable?

Please help!

Thanks in advance.
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  #2  
Old 10-01-2005, 12:33 PM
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Robby85 Robby85 is offline
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Yes, the cable probably did break. Culprits could be binding drive gear at the transmission or a worn cable casing. The cause is seldom that the cable itself has worn out so I would inspect carefully. Don't know about your year but my '85 has two cable's connected just outside of the firewall. Might be left over from when GM used cable driven cruise units. And yes, I think the check engine light could be related to this. I think (but I'm not sure) there is a "speed" sensor on the speedometer where the cable attaches to feed the computer.

Good luck,
Robby
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Old 10-01-2005, 05:21 PM
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Robby, the check engine light is due to the speed sensor not getting a signal from the speedometer when it quit working the speed sensor is a small light diode that plugs into the back of the speedometer and is secured by a small screw. The most likely problem with the cable is it stripped out the gear fitting at the transmission any good trans shop can sell you a new one to match your ratio you will need to lube your cable which needs to be removed from the top you might have to replace the cable sometimes they break strands and start to unravel. Harald K
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Old 10-02-2005, 06:49 PM
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Great,

Thanks for the responses guys. Heres another question about the speedo cable and how it attaches to the tranny. You mentioned it binding at the tranny - my transmission is leaking fluid - somewhere. The only spot I could find fluid on the outside was where the speedometer cable goes into the transmission. It was quite loose so i tightened it down. It seems to have stopped the leak - butperhaps it was tightened too much?

And yes - my cruise control is cable driven. The cable comes up from the tranny, into the CC box, then up through the firewall to the dash.

Any easy way to tell which cable might be bad? Is the cable going up to the dash also a cable? or just a light?

-Matt
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Old 10-02-2005, 10:03 PM
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If the cable housing was a loose as you say, it's possible that you put the cable in a bind when you tightened the cable nut. Loosen and remove the nut and confirm that the end of the cable is seated in the nylon gear in the transmission, then re-tighten the nut. Another idea is to try the cruise control. If it works it will probably be the cable between the cruise control unit and the speedometer. If it doesn't work, probably the cable between the transmission and cruise control unit.

Good luck.
Robby
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Old 10-03-2005, 04:31 PM
GoGoPWR GoGoPWR is offline
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Question related to this thread.

about a month ago, my speedo which always bounced a bit quit working all together

Leading up to this, I went to park on a hill headed downward about a 10 degree incline, put it in park, hadn't put the parking brake on took foot of the brake the car rolled forward, heard a clunk. It had done this once before on a real steep driveway right after I had replaced the tranny w/ this 350 w/ a shift kit.

Went to start it up, speedo still working fine, drives fine, about a half hour later (may have been there since then but didn't notice it) I hear a tick, tick, tick, as the car is rolling no matter how slow or fast, butthe tick accelerates as the car does, about 20 minutes later, the speedo is jumping all over the place and stops all together, oometer still works but no speed indication.

At first i thought the tick was from my UV joint, but after having a buddy roll it slowly by while i listened for where it was coming from, determined it was the tranny. Now I'm thinking it is the speedo gear in the tranny.

If I disconnect the speeo cable the one from the cruise control to the tranny (At the cruise control end) the noise goes away. I would have thought the speedo gear would be rotating regardless of whether it was connected on the other end as I believe (memory might be faulty) that the rod in the cable spins regardless of being connected or not.at the cruise.

The noise is definitly coming from the tranny and not the cruise unit.

Any Ideas, I have a speedo cable that goes direct from tranny to speedometer I could try but the ends on it won't let me just do a direct swap of the exising cable leaveing the cruise connnected.
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Old 10-03-2005, 05:58 PM
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Couple of years ago my 87 Olds G body's speedometer was bouncing all over as well. When it finally quit working the check engine light came on about 2 munites or less immediately afterward. Traced the speedo problem to a bad/busted cable. Once that was fixed and I reset the check engine light (by removing the battery's ground cable for 60 seconds) everything was hunky-dory.

Hope your repair is that simple.
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Old 10-05-2005, 08:14 PM
Mellman99 Mellman99 is offline
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Thanks guys, hope to get to this this weekend, been a crap-tastic week

unfortunately my cruise control has stopped working for the past few years, so i can't really use that to test it.

I'll check out the suggestions made and hope my autozone/Napa/local tranny shop has the parts needed in stock.

Thanks!
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Old 02-09-2009, 09:33 PM
Ted Dubree Ted Dubree is offline
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Default Speedometer stopped working check engine light came on.

My speedometer does not work either. Disconnect the speedometer cable at the transmission, chuck the cable end up in a reversible drill, ( use reverse) with the door open you will be able to see the speedometer function when you apply speed to the drill motor. If it works , wallah there you have it, the drive or driven gear is bad, if not go to the cruise control box disconnect the top cable, connect drill, have someone observe the speedo function, If it works. EXCELLENT, if not sorry I couldn't help. The check engine light comes on when the engine is at a certain temperature, speed, and the torque convertor isn't locked up, because it doesn't get the signal from the speedometer to lock up. I'm going to pull the tail shaft housing tomorrow to check out the drive gear which isn't meshing with the driven gear. May we both have sucess.
Ted Dubree
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