My speedometer is driving me nuts! Works sometimes.

[mrngbear]

On my 1976 CJ5 I cannot figure out what the heck is the problem with my speedometer. I have replaced the drive gear (with another used one) at the Transfer Case . I have replaced the spedo cable 3 times. All have made a slight improvement but in general, the problem continues.
I try to start a little long with the new cable and gradually shorten (then test), to the point of it not working because eventually, it becomes too short. Again I've gone through 3 cables. So once I get to the point that it seems close I stop...then
I can drive it all over town and the spedo works. Drive it 15, or more miles on the highway and it works until you start to slow down, then about 45-50MPH it indicates on the speedo that you are doing 25MPH or so (and continues to register way low until you stop (30 shows about 5-10, etc. etc), come to a stop and it will stay at 0 after stopping....until it sits overnight and the whole process begins again.

 

[Torxhead]

I would suggest checking for any slippage that might occur where the cable goes into the speedometer. Like remove the end that goes into the Transfer Case , hook it to a drill motor and look for a continuous reading on the speedo. After reassembly, disconnect the end that goes into the speedo and try to twist the cable. The cable may twist but should not turn, This could determine if the issue is in the drive mechanism or the speedo itself. I would think there are loads of used CJ speedo clusters where you live.

 

[mtnwhlr]

Speedo's wear out the one in my truck was fine up to about 45mph then it would jump a good 20mph. I replaced the cable and it still did it so I replaced the speedo with a used one and it works fine now.

 

[mrngbear]

I would suggest checking for any slippage that might occur where the cable goes into the speedometer. Like remove the end that goes into the Transfer Case , hook it to a drill motor and look for a continuous reading on the speedo. After reassembly, disconnect the end that goes into the speedo and try to twist the cable. The cable may twist but should not turn, This could determine if the issue is in the drive mechanism or the speedo itself. I would think there are loads of used CJ speedo clusters where you live.

I have performed both of these tests when installing a new cable but your post makes me think past the stupidity, I have never run a drill from the Transfer Case end AFTER driving and when the spedo is not working, after hwy driving (when the spedo is hot or whatever the cause for it not working)

Also Interesting..............when testing the cable from the spedo side after installs it seems tight with the gear, but thinking again I remember one time last fall when it quit, I pulled over in a parking lot disconnected at the spedo and drove around the parking lot holding the inner of the cable and was able to prevent it from turning, but was unsure if I might not be pushing the cable toward the Transfer Case enough to keep it engaged with the gear because I was driving with one hand and holding the inner cable with the other.

I'll drive it on the hwy tomorrow and after it quits on me check it from the Transfer Case side with a drill, and while hot and not working (probably first test) I'll find someone to help me (drive) while I check to see if I can hold the cable from the spedo end and keep it from turning (while keeping it engaged with the gear) while moving.

If these test are ok then hopefully as you and "mntwhlr" suggest perhaps
a new speedometer as a most likely fix.

 

[Lumpy Grits]

T'case drive gear is stripped.
LG

 

[mrngbear]

T'case drive gear is stripped.
LG

I have visually checked the drive gear and it looks good, and when trying to turn the speedo gear when engaged in case it cannot be turned. My failures have only occurred after hwy driving (when Transfer Case is hot). Finally... I checked the speedo gear/ drive gear mesh today, after failure when hot....and the speedo gear spins the drive gear freely(when hot only).

I had come to a previous conclusion that the drive gear was slipping on the output shaft and in an attempt to find a drive gear I was told on many occasions that that part is no longer available. I was finally directed to J&W Jeep in California. He had a used one but sells it only in a pair with the speedo gear. I decided to take the Jeep to a repair shop this morning, before spending $100, to see what they thought and they came to the same conclusion, the drive gear is slipping on the output shaft.
I called Neil at J&W Jeep to order the gears and he said he didn't think the gears were the problem unless there was a plastic drive gear and it was cracked but generally the Dana 20 had a metal drive gear and said he hates to sell something to someone if they might not need it. (awesome! 916-723-3950, I highly recommend them for used Jeep parts) He put me on hold and when he came back he said he spoke to Specialized Jeep in Sacremento and they said that I needed to add an output shaft "shim". I tried to find a listing for Specialized but could not and ended up calling a different place (Specialized Four Wheel Drive in Sacremento, Joe... 916-381-6735). Joe told me the same thing, saying that the pressure from the shims presses the gear up to the bearing to keep it from spinning free. He also said I might first try to tighten the yoke nut about 5 degrees before adding a shim (he also gave me a parts number for a shim kit for the model 20). I could not tighten the yoke nut at all so I ordered the shim kit.

If anyone has a breakdown schematic better than my "Junk" Haynes manual or experience removing the rear output shaft from the Dana, model 20 please help...I wing it a lot but would prefer not to.

I plan on ripping the rear output bearing cap off in the next few days to take the shaft out (so any quick thoughts would be appreciated) while waiting on the shims and so I can inspect the drive gear to determine if I might actually need it.


Thanks for any and all thoughts and help on this post,
Terry

 

[Lumpy Grits]

The gear might be loosing contact when the t'case gets hot.
Take the cable out of the t'case fitting, and put a small screwdriver into the sq drive of the cable slot.
When you try to turn the screwdriver in either direction, there should be little, to no movement.
Give these guys a call.
http://www.novak-adapt.com/
LG

 

[mrngbear]

The gear might be loosing contact when the t'case gets hot.
Take the cable out of the t'case fitting, and put a small screwdriver into the sq drive of the cable slot.
When you try to turn the screwdriver in either direction, there should be little, to no movement.
Give these guys a call.
Novak Conversions Home
LG

The drive gear cannot be turned ( and has only a very little play) when Transfer Case is cold.
Can be turned easily when Transfer Case is hot!.........................

I will try to contact Novak tomorrow,
Thank you!

 

[hagar]

Sounds like you have one of the early nylon drive gears.
Your symptoms regarding hot/cold confirm it.
You'll have to remove the rear output to replace it with an all steel drive gear.

 

[mrngbear]

Sounds like you have one of the early nylon drive gears.
Your symptoms regarding hot/cold confirm it.
You'll have to remove the rear output to replace it with an all steel drive gear.

Removed the output shaft today, saw the nylon gear (and, it was only halfway on the gnarled surface). Got a used all-metal drive gear from a local Transmission shop and WOOOHOOO! Drove about 50 miles on the highway and it works perfectly.

Thanks to all who contributed to my success!
Terry

 

[JeffP]

I ran into almost the exact same thing long ago.
What I eventually found was that some cables require a little rubber seal that goes inside the cup where it screws to the Transfer Case . ALL of the cables need to be tightened on that end to the point it feels like you are going to break something. I never understood why.
The problem is this... the driven gear has just enough end play that if not super tight (pushed in by the cable) it can move away from the drive gear just enough to either not work or give a false reading.
When under load the gear is somewhat held in place, when the load changes... like from the wheels coasting, the driven gear isn’t held tight against the drive gear!
Make sure you have that little rubber cup in the end of the cable then tighten the heck out of the cable nut with a 12 foot long wrench!