Speedometer Issues

[skisnokc]

We have recently purchased a 1978 CJ5 and the speedometer does not work, it would bounce up to about 40 intermittently or just read zero. this thing has a Muncie SM465 in it and the speedo gear is in the Dana 20 . Replacing the speedo cable did not fix it. pulling the cable off the speedo head and running the jeep the cable turns just fine. I also pulled the gear out of the housing and it looked okay. then I took the cable off the Dana 20 and chucked it up in my cordless drill and the speedo will run and hold any speed I want. I pulled the cluster and checked it over and the needle is free and smooth. I am new to the CJ's coming from my mall crawler JKU. any ideas or help is appreciated. thanks!

 

[mtnwhlr]

When I had this problem with my truck it was the speedo I had to replace it with a good used one

 

[gert]

Seems like there has been enough problems with CJ gauges that I have seen a web page dedicated to trouble shooting them, I wonder if your cable is not making contact with the speedo gear


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[mriplaybass]

Seems like there has been enough problems with CJ gauges that I have seen a web page dedicated to trouble shooting them, I wonder if your cable is not making contact with the speedo gear


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My thoughts exactly. Try disconnecting the cable at the Transfer Case , and see how far you can push it in. My guess is that it will go in far enough that it won't engage the Transfer Case drive.

 

[Lumpy Grits]

:ww:

X2 on check'n cable length.
Also-Lift the rear wheels and see if you can confirm the t'case speedo drive gear is really working.
LG

 

[Turbogus]

Same story on my '78 'Black Betty' replaced the cable with an Omix (made in China of course) and while the odometer turns the speedomter does not, I was told by another that it's on account of the cable going in to the back of the speedometer too far is the issue, other stuff has taken precedence so I haven't gotten to it yet. I'll be watching this thread for more.

 

[Hedgehog]

Lumpy has a point. The speedo drive gear is not held on it's drive shaft by anything other than friction between the gear and the shaft. No real mechanical connection between the two. The gear will have a tendency to slip on the shaft giving whacky speedometer readings.

Like others have mentioned, I had crazy readings until the cable was reset in the Transfer Case and properly tightened down. Now it's very consistently only ten MPH off.

 

[Belizean]

Sounds like my speedometer. Fluctuations of give or take each way 5 mph

 

[Hedgehog]

That is fairly common in these older speedometers.

 

[Lumpy Grits]

Inside the speedo is a coil spring that's in contact with the needle's shaft. This spring acts a as dampener to reduce/stop needle bounce. It either gets 'weak', breaks or both over time.
LG

 

[skisnokc]

I can disconnect the cable from the speedo and drive the jeep confirming the gear in the Transfer Case works fine and also in the reverse I can disconnect the cable from the Transfer Case while its connected to the speedo and chuck it up in my cordless drill and the cable will spin the speedo up to solid speeds, no bouncing needle at all. so if the cable works on the speedo and the Transfer Case why when I drive does it either not move at all or rarely it will twitch just abit.
my spidey sense says the cluster has to be bad but yet it works with a drill..

thanks

 

[Lumpy Grits]

Are you SURE that the cable is seated into the drive gear, inside the t'case when connected to the speedo?
LG

 

[Torxhead]

You could have a worn out gear in the Transfer Case , causing the cable to slip.

 

[Turbogus]

When I finally got into mine the shaft that goes to the clockspring dampner had broken. Being as mine is a '78 it took 18 months to find another speedometer head that matched mine. Here's a photo;

https://www.jeepz.com/forum/attachm...king-speedomters-wp_20161004_15_13_35_pro.jpg

https://www.jeepz.com/forum/attachm...d1490451394-speaking-speedomters-speedo-9.jpg

 

[Turbogus]

Got the speedometer installed last night, in the many months since I removed the old one I had almost forgotten how difficult it is to install the top mounting nutz, got one of them at least!

 

[Lumpy Grits]

Hope all works 'rite'.
LG

 

[JR74CJ5]

I can disconnect the cable from the speedo and drive the jeep confirming the gear in the Transfer Case works fine and also in the reverse I can disconnect the cable from the Transfer Case while its connected to the speedo and chuck it up in my cordless drill and the cable will spin the speedo up to solid speeds, no bouncing needle at all. so if the cable works on the speedo and the Transfer Case why when I drive does it either not move at all or rarely it will twitch just abit.
my spidey sense says the cluster has to be bad but yet it works with a drill..

thanks

You could have a worn out gear in the Transfer Case , causing the cable to slip.

On mine, the drive gear inside the Transfer Case , not the one you can change easily that cable attaches to, but the one on the shaft that spins that gear - after time it wore and slips. When I rebuilt my Transfer Case , I noticed it but didn't have the part and didn't want to wait - used a adhesive of some sort, either locktite or crazy glue or something (can't remember) to secure it better to not slip on the shaft.

https://www.jeep-cj.com/forums/f2/dana-20-spedo-gear-19725/

the plastic yellow gear is what I'm referring to - may be metal in yours.

Sounds like this may be your problem honestly, especially since you say it works great with the drill from Transfer Case hookup to cable. It will still spin showing good when you detach from the speedo and drive it because it does still spin, but enough resistance (like the speedo operation) and it will slip giving you inconsistent or no reading on speedo.

 

[JR74CJ5]

ah - just realized how old this was with OP's post date... oopsie

 

[hdgapeach]

ah - just realized how old this was with OP's post date... oopsie

No problem by me! Dang good info that hadn't been mentioned in the thread. Any of us might find it beneficial one day!

 

[Turbogus]

Only driver a couple of miles since swapping in that other speedomter and it's working fine, now on to the brake master cylinder...