Strange speedometer response while accelerating

mack4759

mack4759

Member
Need help diagnosing a speedometer problem. Up until a couple of days ago it has been working fine and was quite accurate. Unfortunately it is now acting up, while accelerating it reads 0, as soon as you let off of the accelerator it will then spin up to the current speed. When you accelerate or give it gas again it drops to 0 and repeats the process. I am guessing it is has more to do with the cable than the actual speedometer but I am not sure. Any tips on what to try or look for to diagnose this problem?

Note: The only thing that I can think of that may have effected it was a week ago the engine was raised and lowered a few times while repairing a motor mount. Also the speedo cable was resting on top of the muffler for a few days and about 60 miles.

Thanks!
 
Hi Mack,

Maybe look at it this way:

!. With current conditions, the cable will never get better with time, & can only get worse.

2. Remove it & investigate both ends & see if you notice any cable kinks & if it turns easilty with an electric drill.

3. If found unserviceable, which appears to be a possibility just get another one.

Hope this helps -- but why wait?
 
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Hi. I am not familiar with your car, but this would be caused by the speedo drive in the back of the gearbox being loose. Tighten the nut on the back of the mainshaft, and you will have it fixed.
 
Your drive shaft is moving back and forth. Which is dis in gauging the speedometer drive gear. You may need to check and see if the gear is to far back on the drive shaft. Maybe they forgot the snap ring on the drive shaft.
 
Maybe the square cable end at the speedo gear is loose enough to slip while accelerating but tight enough to hold after the stress is relieved. Again... pull the cable and check. You might find that you can pull that square end off by hand.
 
Thanks everyone for your help. It turns out the retaining ring on the speedo drive gear is missing allowing the gear to walk. It is very frustrating that the drivetrain will have to be pulled out over a .75¢ part. Would it be too wishful of thinking to hope that there is such a thing as a 3/4 snap ring that could be installed without removing the drivetrain?

Also, can anyone tell me how to remove the speedometer cable from the speedometer and the drive gear mechanism? I cannot figure out how to get the cable to release from either end. Thanks!
 
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mack4759 said:
Thanks everyone for your help. It turns out the retaining ring on the speedo drive gear is missing allowing the gear to walk. It is very frustrating that the drivetrain will have to be pulled out over a .75¢ part. Would it be too wishful of thinking to hope that there is such a thing as a 3/4 snap ring that could be installed without removing the drivetrain?

Also, can anyone tell me how to remove the speedometer cable from the speedometer and the drive gear mechanism? I cannot figure out how to get the cable to release from either end. Thanks!
Click to expand...

I was thinking the same thing about the snap ring. It would be woth a try to buy the snap ring and grind off the ends so you have about 60 or 65% left. Then remove the driven gear and housing to see if you can snap it into place. I don't have a tube handy to look at, so maybe this isn't even possible.:confused:

The top end of the cable should simply unscrew from the speedometer, then the inner cable can be removed.
 
Onone of my A,s the drive would move back & forth enough to disengage the driven gear.I was able to wind several turns of wire around DS behind gear to stop gear movement & speedo worked OK.On another car,the speedo quit & the problem was that the square drive hole in the driven gear shaft was worn out & free-wheeling on the cable.A new shaft fixed the problem.
 
mack4759 said:
Thanks everyone for your help. It turns out the retaining ring on the speedo drive gear is missing allowing the gear to walk. It is very frustrating that the drivetrain will have to be pulled out over a .75¢ part. Would it be too wishful of thinking to hope that there is such a thing as a 3/4 snap ring that could be installed without removing the drivetrain?

Also, can anyone tell me how to remove the speedometer cable from the speedometer and the drive gear mechanism? I cannot figure out how to get the cable to release from either end. Thanks!
Click to expand...

I had the exact problem once, it is an easy fix! Slide the gear out of position and use a sharp punch to make a raised burr on one or two splines. this deformation will make the gear hard to put back in position and will also keep it from disengaging again.
Rainmaker Ron
 
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