Spedometer all wonky. Whats going on

[candymancan]

The spedo in my 90 Gw is acting weird. Its not wiggling slightly or anything like it would in the past..

Its litterally going from say 55mph to 50. Back to 55. Sometimes itll go from 55 to 45 then jump back to 55. And it wiggles a lot in between.

Its very strange.

[devildog80]

Check the cable inside the core. Might be dry and needs some lube.

[candymancan]

Isnt the cable.. Now its ddopping to 0mph and sitting at 0mph.. sometimes jumping back to say 55mph.

I think the spedo itself is going bad. Is that possible ? Is the spedo seperate from the odometer. So i can simply say swap a new spedo in ? Or are they one unit.. and ima mess up my mileage now if i swap a new spedo in

[letank]

Usually dry grease, you need a good lube down that cable, unless the sheath is damaged or frayed , or if the motion is prevented if the cable is somehow compressed somewhere.

[devildog80]

Can you drop the speedo cable off the head unit and have it hanging down under the dash where you can see it while driving? Watch it spin to see the cable slows or stops while driving. Would still wager the cable is the culprit, as you said, the head unit is magnetic. With the cable exposed, pull it out and make sure the ends are good and all lubed.

[candymancan]

How do you lube the whole cable ?

[90wagmi]

The cable would be a common failure point as others have mentioned.

You could also check the speedo gear and speedo drive gear in the transfer case. And make sure that the speedo gear cartridge is clocked correctly based upon the number of teeth in your speedo gear. The previous owner of mine had the speedo gear cartridge clocked incorrectly which resulted in the plastic speedo drive gear on the output shaft getting chewed up by the speedo gear which was too close. The opposite can happen too where the speedo gear will not make sufficient contact with the drive gear if it is clocked incorrectly and they are too far apart. Sometimes our problems are cleaning up the issues the previous owner created.

[letank]

How do you lube the whole cable ?

spray lube, such as motorcycle spray chain lube, it is sticky but flow freely, I have plenty of the off road version.

It is a foaming spray so it does splatter all over.

[sierrablue]

As @90wagmi said, the cable is the first thing I'd check--however on my dad's truck, when it started doing that, it turned out that the speedometer gears were getting stripped on the output side of the tcase.

Flip side, on the '71 when it started bouncing around all over the place, it was the cable fraying and ultimately breaking.

[devildog80]

First thing to remember before starting this process, is to mark the head unit, or transmission end of the core cable, so respective ends go back in the same way they came out.
To lube the entire cable, best to pull the cable core out of the outer casing, and inspect it for defects. If needed, NAPA has a build your own speedometer cable core kit, that you measure & cut to length.

Remove the top end off the back of the head unit. Remove the bottom fitting off the transmission. You should now be able to pull the core out, but if unable, you might need to remove the entire cable assembly out of the truck, so the cable can be worked better.

Once you have the core cable removed, take your air nozzle and blow out the core, while giving it a good shaking/flexing where you can (as it is still installed in the truck) while blowing through it.

Now use some gasoline or carb cleaner, to spray through the casing, to clean out any residuals/dirt/old dry lube from inside the core that did not come loose with the air. Hang it up by one end to air dry and drain for 24-48 hrs if you can. At this point, if you can, push a wire through the core. Idea is to "bore clean" the core of any oily residue. Cut a cotton swab small enough to fit inside the bore, and bend a loop on the wire to hold the swab, again that will fit into the bore of the casing. Make as many swap passes through the bore as needed, until the swab comes out clean. Not sure but a 22 caliber bore kit might work for this.

Next, to reassemble I recommend using dry graphite, as this will not attract anything dry like dirt, or wet lube with white lithium spray grease. Spray either into the core first, and manually coat the cable, before re-inserting into the core. Work the cable by pushing in and pulling out back and forth to distribute the lube completely through the casing.

Reinstall the cable on the transmission and head unit.

Make sure as advised above, to inspect the transmission gear alignment while cable is removed, to be sure that part is also serviceable.

[candymancan]

Well i did what you ssid. The cabke i can spin freely by fingers and i can push pull it out if the sheeth easily.. but i do feel some stickyness at points. And the cable itself feels sticky

Pulled it out fully and the cable feels sticky to the touch.. im on luncj for work so i didnt use gasoline to clean it etc lol.

I did use graphite lube.. put it back in. And it still wobbles all over the place. Besides cleaning.. im wondering if a liquid lube will work better like the lithium you mentioned. Ill try that when i get off work

[devildog80]

The graphite will probably stick to the gunk on the inside of the core, so might not do much good. I would spray some cleaner through it, to flush all the gunky stuff out, then clean the cable up good and pre lube with the wet spray before it goes back in.

[candymancan]

Well i cleaned it all up and used lots of lithium grease

Its still going from say 55moh to 30moh up down up down..then drops to 0 and stays at 0. Until i slow down to say 15mph then it goes back up but wobbly.

The odometer stops rolling i nkticed too when its at 0.

Here it is on video

https://youtu.be/laPbEb_OK40?si=NWGQve_ZsdURDG6e

[rocklaurence]

I just posted a video of my Speedometer and cable replacement. It could be the meter but is most likely the cable or the nylon tip of the cable that goes into the meter. https://www.youtube.com/watch?v=25hg-CK3iTE

[candymancan]

The tip i noticed had black streaks on it that i couldnt rub off

[devildog80]

Do you have this separate tip on the head unit end? I found this on my '84 GW when reworking the cluster. The point is actually square, and this inserts into the head unit, followed with the speedo cable behind it which then screws on. You can see where the base broke, so the square socket will not hold the tip of the cable anymore. My speedo cable system is 2 separate cables....lower - trans to speed control....upper - speed control to head unit. When I bought the replacement upper cable from BJ's, I had to remove this tip from the system, as the new cable was made to not need it.
If you have this tip, it could be broken at the base where the square tip of the cable engages as I found mine was, and was not engaged on the end of the actual cable.

20230618_113705 by Scott Weckerly, on Flickr

20230618_113720 by Scott Weckerly, on Flickr

20230618_163605 by Scott Weckerly, on Flickr

[candymancan]

My cable has that top that goes into the cluster. And it isnt broken. It just had a few black streeks on it.

The other end is just a open round end. Which goes down to what is the cruise control moduelle thingy, which is under the wireharness on the firewall. Then it goes from that to the transfercase.


I read online for these Jeeps on another forum the spedo uses magnets.. and they get weak and cause this very issue im having. Im wondering if this is the same issue.

But i will say day 1 i got this Jeep the spedo was a tad wiggly.. not horrible.. but i could hear it making noises in the unit itself. Until i lubed it years ago.

[rocklaurence]

I read online for these Jeeps on another forum the spedo uses magnets.. and they get weak and cause this very issue im having. Im wondering if this is the same issue.

Yes, it uses a yoke or "U" that spins over magnets in the gauge. Pretty cool non-contact system. The faster the yoke spins the greater the magnetic field that works against the gauge needle return spring.