Speedometer doesn't work at all. Where to start?

[MisterB]

My fuel gauge right next to it works, but the speedometer is totally dead. I checked behind the gauge to make sure the speedo cable is plugged in, and it is. Other than that, I'm not sure what else to check?

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[1985c20]

Follow the cable and make sure the other end is connected to the transfer case if 4wd or the transmission tail housing if 2wd. Could also pull the cable off the back of the speedometer and go for a drive to see if the inner cable is spinning

 

[QBuff02]

If the cable is good and depending on your configuration, i'd say the little plastic bushing at the connection to the trans or transfer case is shot or broken. It's a common problem over time they wear out or split and the cable just has nothing to grab to turn anymore. Easiest thing to do is unhook the cable at the connection at the trans/t-case and hook a drill to it and turn it and have someone watch to see if the speedo works in the cab. Also if it has the 90 degree adapter down below, sometimes you can unhook and remove the adapter and redirect the cable to direct connect and "cut out the middle man" so to speak. We did that on my buddies '78 just a few weeks ago. and then literally last week while driving down the highway mine acted up, bounced around a few times and just quit. When I got home I pulled the cable off down at the transfer case and found the cable had broken off right at the coupler. So, complete new cable is in my future.

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[ali_c20]

Try to get a quality cable...I tried pioneer, atp and omix adar. They all suck. No matter what I did I always had a jumping speedo needle. Tried an original from a friends truck: no bouncing. Next will be ac delco which is 4 times the price of the other cables or oer.

 

[MisterB]

If the cable is good and depending on your configuration, i'd say the little plastic bushing at the connection to the trans or transfer case is shot or broken. It's a common problem over time they wear out or split and the cable just has nothing to grab to turn anymore. Easiest thing to do is unhook the cable at the connection at the trans/t-case and hook a drill to it and turn it and have someone watch to see if the speedo works in the cab. Also if it has the 90 degree adapter down below, sometimes you can unhook and remove the adapter and redirect the cable to direct connect and "cut out the middle man" so to speak. We did that on my buddies '78 just a few weeks ago. and then literally last week while driving down the highway mine acted up, bounced around a few times and just quit. When I got home I pulled the cable off down at the transfer case and found the cable had broken off right at the coupler. So, complete new cable is in my future.

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Awesome. Thanks

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[78C10BigTen]

Mine is also dead, put a new cable from the trans to cruise transducer and still nothing. Could also be a bad drive or driven gear inside your trans/t-case depending on if your 2wd or 4

 

[MisterB]

I bought a new speedometer cable today. I removed the cable from the transfer case to inspect it and the square shaft was broken off and the cable was all wound up. So, I removed the old cable and installed the new cable to the back of the speedo. Connected it to a drill, and low and behold the speedometer worked. So, I finished running the cable all the way to the transfer case. Removed the broken pin from the old speedo cable and hooked up the new speedo cable rk the transfer case. Buttoned up everything and took it for a drive, but it still doesn't work.

What's this plastic piece it connects to? Maybe it's bad. Where can I find one?

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[Dysco]

Generally if the speedo works with a drill, the problem is gears inside the adapter on the t-case. As you can see, you can take off the adapter and get new insides,Pretty or a different adapter cheap. Counting the teeth is helpful before buying. Rock Auto has them.

 

[MisterB]

Generally if the speedo works with a drill, the problem is gears inside the adapter on the t-case. As you can see, you can take off the adapter and get new insides,Pretty or a different adapter cheap. Counting the teeth is helpful before buying. Rock Auto has them.

So is it called a Transfer case adapter?

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[MisterB]

After more research, it is called a speedometer drive (or driven) gear. I also probably need a new housing for it (plastic piece that goes between speedo cable and transmission that speedo cable plugs in to). To complicate matters, I'm running 35" tires now, which means I could have gotten this all plugged in and fixed, and found out that my gauge is off my like 20 MPH. So, I have to determine my gear ratio and then do a calculation between that and my tire size and it'll tell me what driven gear size to order.

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[MisterB]

Update. I decided to try something. As I was driving today, I could hear something spinning back behind the speedometer. I decided to check the cable was in all the way. Turns out it was not. I needed to push it quite a bit further until that metal holding tab clicked. Took it for a ride, and the speedometer works, and it's accurate! I even verified it with GPS. A PO must have installed the proper drive gear to take in to account the bigger tires, but then the speedometer cable broke at some point.

So, between the time I tested the cable on the cluster with a drill, and me running the cable out the firewall and down to the transmission, it came unplugged just enough that it didn't work.

It's so nice to finally have a working speedometer.

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[1973c10]

Update. I decided to try something. As I was driving today, I could hear something spinning back behind the speedometer. I decided to check the cable was in all the way. Turns out it was not. I needed to push it quite a bit further until that metal holding tab clicked. Took it for a ride, and the speedometer works, and it's accurate! I even verified it with GPS. A PO must have installed the proper drive gear to take in to account the bigger tires, but then the speedometer cable broke at some point.

So, between the time I tested the cable on the cluster with a drill, and me running the cable out the firewall and down to the transmission, it came unplugged just enough that it didn't work.

It's so nice to finally have a working speedometer.

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It is always nice to get something fixed

 

[Scott91370]

It is always nice to get something fixed

Especially when it's a FREE fix!

 

[MisterB]

Especially when it's a FREE fix!

Close. I still had to replace the speedometer cable, because it was all wound up and snapped off at the transmission end, but it was only like $20 for a good one from NAPA

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[Kevin McDermand]

I need to check mine. It jumps around and gets way off the faster I go.