My speedometer has been acting up over the last few months and wanted to know what ya'll think would be the best way to fix it.

First of all, the speedometer does not work when the car is cold. When it starts to warm up, the speedo starts jumping around, and once the car is warm, it works most of the time with some jumping.

I have taken the cable out and lubed it with some liquid graphite. After making quite a mess with that, installed the cable back in the car. The problem is still there.

So, should the entire cable be replaced or should the sending unit in the transmission be replaced? I don't think that the speedometer itself is bad because I hooked the end of the cable sending unit, spun it with a drill and the speedo worked just fine. I just don't want to start replacing parts if any of you have encountered and corrected the same problem.

Thanks in advance!!!

 

Try replacing the driven gear. They only cost around $9.00. My speedometer was acting up just about like yours and then finally quite working. When I bought the new gear I compared it to the one I was replacing. I could see a very slight taper on one section of the gears. The new one works great. I have an '81 4 speed which uses a 19 tooth natural color. You might need to pull the gear to find out what color you need. Good Luck.
Bill

 

He's right. The speedo gear may have teeth worn down.

 

if you have cruise control it could be the cruise unit on the left fender where the cables meet

 

I'll go ahead and get a new sending unit. $9.00 isn't expensive at all and I'm sure it does need to be replaced. I also have a 4 speed, so I'll see if it is the same as your 19 tooth unit.

By the way, I was under the impression that the coloring determines what gear ratio the car has, so the coloring may be different. Is this correct?

Thankfully, I do not have cruise control, so that is something that I don't have to troubleshoot.

Thanks for all of the responses and I'll pull the old unit tonight!!!

 

Ok, I pulled the gear sending unit and it has an 18 tooth, dark brown gear. It does not appear to be damaged. How can I tell if this is the problem?

Also, what rear gear ratio does this car have if it uses the dark brown gear? When the speedo was working, it always read a little faster than I was actually moving, so should I get another color?

 

Having this problem with the 71. I checked the cable (both lower and upper) by disconnecting from the transmission and placing an electric drill on it running in the counter-clockwise direction - everything works from there up.

I see the gear end in the transmission. There are 12 choices on Ecklers for this gear when I search for 1971 "speedometer gear" - it has an auto tranny.

Is the gear hard to remove (procedure please)? Is the only way to tell what gear you have by removing it first?

 

Andrew,

This could be caused by the rear end ratio having been changed from the original one or the fact that you are running shorter tires than came on the car stock. These gears are cheap, so if you go to the dealer and show him your gear (the brown one), he should be able to give you a different color gear to slow down your speedometer by using the brown one as a reference.

Ideally you should try to determine the ratio of the rear by counting the revolutions of the drive shaft with respect to one revolution of the wheel… 3.5 revolutions of the driveshaft to one revolution of the wheel equals a 3:50 or 3:55 rear ratio. With this information and the size tire you are running the dealer can look in his book and tell you what color gear you should need. Either way will work, one is just a little more precise than the other.

Because they are cheap, I would ask for the next two color gears to dial it in if the first one doesn't quite get it. Since even same size tires from different manufacturers can vary in diameter.

By the way, if this doesn't do it, there is the drive gear that is located on the output shaft and drives the nylon gear on the cable. It is also made of nylon and you'll need to remove the tail shaft housing (at least partially) to replace that gear. Do the easy stuff first… and cross your fingers.

Good luck… GUSTO

 

Need an answer from my previous post...

 

ttt

 

Only way I know of to tell which gear is to remove. follow cable to tranny. Should be about a 7/16" bolt holding a clip tight over the housing. Loosen it up and spin it out of the way. Housing with gear attached can the be pulled out (watch for falling transmission fluid). Gear can then be easily slpiied off of cable and out of housing. WHile you have it out, if you can get your finger in the hole, check position of drive gear on the tranny shaft. Mine had slipped forward and was not driving the gear on the cable. Assemble in reverse (isn't that what the manual says ) Good luck

 

Thanks. It's tight up there and the exhaust pipe is very close. I was wondering about "falling" tranny fluid too.