Speedometer

Hi there. My speedometer has been jumping around a whole lot, and is not accurate at all. I recently replaced the speedometer cable, and made sure it wasn't getting kinked up. I got a drill and attached to the end of the cable and watched the needle go up. It seemed to be working fine. I'm pretty sure the speedometer gear in the t-case is good because it spins the cable like it should. Is this a sign of the speedometer itself going bad and needing replacement?

 

I've been trying to solve the same issue. I've been trying to figure this out for almost a year now, so I'll try to be as succinct as possible.

1. Replaced cable. When I ordered the cable from the store, they stated that they had two cables, a flexible and a stiff. I opted for the flexible. Lubed new cable, installed.
No change, symptoms just like yours

2. I read on the forum somewhere that the speedo could be lubed via a small hole on the top. Did that.
No change.

3. Did the drill test as you did, speedo worked great. Speedo was very smooth drill driven, counterclockwise.

4. I thought maybe the square drive hole that the cable fits into on the gear in the transfer could be rounded just enough to be causing the bounce. Checked. Nope.

5. ODO works fine, all day, every day. To me, that means the gear in the transfer is working.

6. It must be the cable, methinks, so I replace the cable with a "stiff" one. Things are much better. Now the speedo only bounces below 20 mph. However, I have yet to have the chance to check the speedo at higher speeds, (55+), with the 1st new (flexi) cable the speedo was kinda ok until it reached 40 or so, then it went bat crazy, often giving up and just kind of laying there. So I don't have much confidence in the "stiff" cable fix until I can do a full test.

6. On both of the replacement cables I found things work better if you just tighten the cable nuts finger tight, even loose.

7. On both replacement cables I found that the inner cable was too long to allow the outer sheath to seat properly on the transfer case, I had to cut some off the end of my inner cable to get it to fit properly. Yes, I've checked and double checked, I didn't cut off too much of the inner, the ODO continues to work properly.

8. My understanding is that the ODO is gear driven, on both ends. The speedo function is gear at the transfer, but some sort of magnetic clockwork voodolike thing in the speedo, which I have yet to comprehend.

There it is, the sum total of my knowledge and attempts to address the problem. Not much, I know. I really hope somebody has something more informative and hopeful.

With both cables I took great care routing, however, the flexi did get a melted area in the plasticote "protecting" the wound outer sheath. I was really hoping that this was the problem. The stiffer cable really required a lot more thought in routing, a hidden blessing, as it only has two very sweeping bends in it, no way it could be binding, no way to get hot.

I'm going to operate under my latest theory for a while, the theory that the new cable and sheath need to "break in" together for a while before they can operate with the smoothness necessary for a steady speedo read a lower speeds (inner cable rpm). Because after all this, if my wear in theory doesen't hold up, then I'm stuck dealing with faulty magnetic voodoo, and I don't have enough hair left to be dealing with magnetic voodoo.

Forgot to mention that early in the journey I installed an old school strap on tach, which I use for accurate speed measurement. I use the tables here: http://www.novak-adapt.com/knowledge/gearing.htm
So I have a pretty good idea of my speed, probably more accurate than the stock speedo.

But I'm determined to figure this out, I just HATE to replace original parts with crummy new repros. Especially when the repro gas gauges read backwards.

So much for succinct!

 

Wow! What a help! Sounds like we got the exact same problem. I've also noticed that my speedometer doesn't like to go over 45 too much. I believe I have the flexible cable you're talking about. Would you recommend getting the stiff one?

 

Stiff seemed to help, but still issues. It was worth the bucks to me to at least cover the bases. I've got my fingers crossed for the "wear theory". Hopefully, someone will chime in who has made it to the light at the end of the tunnel...

 

Mine has been doing the same thing or going up then hanging there. I haven't lubed the inside of the speedo itself yet, but did find that if the cable is finger tight/semi loose on the back of the speedo it seems to read pretty accurate. If it hangs up after stopping I can reach up under the dash and touch the cable upward and it re-zero's itself.

 

I just got a GPS and some velcro for the dash.

Replaced my tranny and xfer, didn't think to grab my speedo drive gear...gear in the new D20 makes it read about 20mph when I'm doing 45ish. (I got 3.73's).

 

I asked about rebuilding the jeep speedo's the other day. There is a good step by step teardown of the speedo here. But there is no step by step on lubricating and reassembley.

So that's what I'm working on now. I need to get the case and trim rings sandblasted and painted so I can get it back togheter. I have lots of picts. I can post a couple tonight so you can see how the magnetic magic hapens to make the speedo work.

From what I've learned of the speedo's, there is very little to go wrong. The cable comes into the back and spins a shaft. On the shaft is the gears for the odometer. If that works, then there is nothing wrong with your cables. It has to be either the mangetic dealie or the needle spring that returns it back to zero.
The magnetic dealie is a piece of metal shaped kinda like this "[" that is attached to the end of the thing the speedo cable attaches to at the back of the housing. The [ shaped thingie has a round, almost tuna can shaped thing that floats in space, but is not connected to it, that is attached to a shaft that has the tuna can on one end and the pointer on the other. The clearance between the [ and the tuna can is very little. As the [ thing spins, it sets up an electrical current by spining around the tuna can thing. They have to be close enough to set up the field but not so close that they touch.

In my speedo, there was a little build up of dirt and dust on the tuna can. I took some alcohol and put it on a rag that I gently wiped the tuna can off with. Once that was moving freely, I used a toothpick and a small drop of sewing machine oil to lubricate the shaft where the pointer turns.

I'll edit and post picts when I get home. it will all make since.

 

That would be most helpful

 

Sounds like more good info. Pics eagerly awaited!

 

This exact same issue was driving me crazy for over a year on my '75. Needle would bounce all over the place at any speed but seemed to smooth out at the higher mph...say 60 or so.

I also replaced the speedometer cable with no improvement. I began the search for the speedometer gear that the cable end screws into in the transmission. I figured that had to be the culprit. As noted in previous posts, a drill attached to the inner core of the cable gave a smooth reading from 0 up to 80, so that eliminated the cable and actual speedometer.

Well good luck finding that gear ! I finally gave up after calling about a dozen suppliers and junkyards. I had about decided just to disconnect it altogether cause it was so disconcerting watching it bounce around.

Tinkering around on day, I inserted the square end of the inner cable into the transmission housing and did not tighten it all. Just let it sit there with minimum pressure on it from a wire tie that kept the cable secure. Low and behold.....smooth as silk from the get go up to top speed (about 75). Fix involved cutting off approx 1/4 " of the inner cable and I still only hand tighten the knurled ring on the cable itself to snug it up.

I hope this solves your problem. Didn't cost a cent and I solved a problem that had really been bugging me. Made my day !!!

I hope it makes yours....

 

Mine does the exact same thing, I did a search and found a thread stating that the speedo cable is to long where it attachés to the gear in the transfer case. In this thread they said shorten the inner cable that it was sticking to far into the gear bottoming it out and putting the inner cable in a bind. This caused the needle to bounce and the speedo to show to slow a speed. I haven't had time to check it out yet but hopes it works.

 

Thanks springerfever,
I've already cut the inner cable by 1/4". It did make things better, as I reported above. I think I'll creep up from here in 1/8" increments. The 3 different inner cables I have are all different lengths, each guranteed to be the proper fit for a 75 by 3 different vendors. If I get it to work, I'm gonna pull the thing out and post the precise secret measurement for a 75/258. I really, really want to do the speedometer happy dance, I've been dealing with this forever. I'll report back tomorrow. Dark and Cold now.

 

farfle

No need to cut cable..Just insert square head into drive gear without tightening cable. Then go drive around. That should tell you if shortening cable length will correct the bounce...hope it works for you !!!

 

I have the same proble as all have cited here. I also have a new speedo head on the bench waiting for me to install this weekend. If clipping the cable a little fixes this problem, I guess I'll be eating the $60.00 for the new head.

 

Well, I cut another 1/4" off the cable and tried it out. Worked great, got rid of the bounce at low speed. Worked great until I hit about 45-50 mph, then it slowly dropped down to about an indicated 20 and floated there. (I was doing 50 or so according to my tach, corrected for tire size via Novak's online calculator.) So I guess if aallison doesn't post his internal speedo pics tonite, in the morning I'm gonna give it a shot of carb cleaner in the cable attachment hole in the back of the speedo. Maybe that will clean off the magnetic voodo device that he posted about.

Once again, The Little Red Irritant lives up to it's name.

 

OK guys, here is what I did. If this works, I'll post picts, then edit and explain it. I'll be picking up a sandblasting cab tomorrow and get on with the reassembley. I still need to get a fuel and temp gauge so the finished deal might take a few days. But here goes.

Crap, I just lost the whole darn thing. Try again......

OK, here is the speedo assemble once removed from the housing. There is a very good write up on getting this far. I referenced it in an earlier post in this thread. Anyway, on mine the speedo pointer was bent so it touched the face of the speedo up near the top as it spun around. I VERY CAREFULLY used a dental pick to bend up the pointer so it did not rub the face anymore. This was not noticable before dissambley. I also made sure I did not touch the face of the speedo. Later I found I could use a Q-tip and distilled water to very carefully clean the face. DO THIS AT YOUR RISK. I know of no way to repair the face if they paint is taken off.


The below pict shows the tuna can to pointer shaft. Darn I wish I knew the correct names for this stuff. Anyway, I used the toothpick to drop a VERY TINY amount of oil on anyplace I thought the shaft spun in bearings...or whatever. USE OIL VERY SPEARINGLY. Be careful to not get any oil of the speedo face.


OK, here is the "tuna can" and [ assembley I've tired to explain. The [ part is attached to the speedo cable end. This part seems to be lubricated by an oil port you can see just below the right arrow. On mine the port was packed with dirt. I used a dental pick to VERY CAREFULLY remove the dirt buildup. Use caution, it appears their is some sort of wick or filter in the bottom of this port. I used a toothpick and sewing machine oil and applied a very small amount. I also turned the shaft (where the speedo cable engauges the back of the speedo) a bunch of times just after applying a very small amount of oil. BE VERY CAREFUL TO NOT OVEROIL. On mine, the [ and the tuna can had dirt build up that prevented smooth, noncontact movement. As I understand it, the [ spins at the speed of the speedo cable since it is physically attached to it and magnets build up an electrical current between the [ and the tuna can. This electrical current causes the shaft to torque, moving the pointer on the speedo dial. The faster the speedo cable spins, the faster the [ spins, the greater the electrical current is built up by the magnets. The greater the current, the higher the pointer goes. Remember, while the cable spins at many rpm's, the most the pointer moves is something like120 degrees. In my case, their was dirt and dust build up between these two. I used alcohol on a Q-tip to clean off the tuna can and the [ so it would spin freely without touching.


Ok I hope this helps. I'll be be getting the parts of the housing cleaned and painted soon. I'be modifying the housing to fit a newer cj fuel gauge and temp gauge. I'll put the old faceplaces on the newer gauge so it looks like it's all orgional. There are a few other little things I'm trying to figure out. For instance, once you take the glass out, there is an old rubber seal that will fall apart in your hand. I found screen spline .75 dia, should make a good substitute. I'll also be replacing the light bulbs, one of (maybe all) of the little cardboard tubes that seperates the light from the light bulb.

If you have any questions I didn't answer, please let me know. I'll do what I can. If anyone has any better suggestions, please let me know. I'm just figuring this out as I go along.

 

Well shortening the cable on my certainly help smooth things out, but the speedometer still seems like it's at least 10 mph slower than I'm really going. It seems that the needle doesn't want to go over 45

 

Precisely Max. We're two peas in a pod. I'm gonna take a close look at my needle, to make sure it is not touching the face, like aallison's was. Good photo, aallison, I appreciate the effort. Unfortunately the pic didn't show the secret inner magnetic workings as I had hoped. Tomorrow, she's gonna get a shot of cleaner. If that doesn't work, I have one or two more ideas before I give up, but I'm gonna try things one at a time.

The scientific method and all.

I know we aren't the only ones with this problem. I suspect that the whole system is so delicate, that we could be dealing with a combination of factors.

Also, Max your profile states you are running 31 inch tires, the stock tire that my 75 came with measured an actual 27.5", my present tires are an actual 30.1. Throws off the speedometer by a percentage (gets worse as you go faster) You could easily be reading 5-7 mph low at 60 mph. If you have a tach, there are calculators that allow you to know how fast you are going pretty accurately by the tach. One is http://www.novak-adapt.com/knowledge/gearing.htm.

You might be in the ballpark...

 

Just for the record, I have the same issue with my 75. I bought a new speedo cable a couple weeks ago and have not had a chance to install it yet. Thanks for all the info....this is a very helpful thread ona topic that seems to be fairly universal in intermediates. Jeff

 

WOW, where did all those pictures come from?
Thanks aallison!

The edit is a wonderful feature.

When you're done, you've got to post a complete write up. Outstanding.