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1977 280z Speedometer and Odometer Woes


ckurtz2

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Hey Guys,

       So I decided to start tackling the problem as to why my 1977 280z speedometer and odometer do not work. When I got the car the odometer had one less mile than it does now, so it at least worked for 1 mile. I never saw it working though.

      I would like to state that I am running a 81 280zx 5speed transmission and 88 turbo 3.7 LSD.

      To start, I first completely removed the inner speedometer cable at the transmission from it's sheath and inspected it. The cable is completely intact with the the square end for the speedometer and other end with the key for the transmission. I then pulled the speedometer pinion gear inside the transmission and the gears were lubed and perfectly intact. OK.

      So I went under the dash and removed the cable from the speedometer and inspected it. Looked fine. So I had a friend use a drill on the cable at the transmission end and spin it up while the cable was in the speedometer. Ok, going counterclockwise the odometer worked, but the speedometer did not. I would like to note the car was off with no key in the ignition. Does the speedometer use anything electrical, or is it completely mechanical like the odometer? It's weird the odometer was functioning but the speedometer was not. The speedometer moved to about 15mph and then stopped there stuck.

     Ok, so maybe the gauge is boofed, so I hooked the cable back up at the transmission and fired it up. I made sure the cable key seated into the speedometer pinion gear. Whelp, once again the speedometer nor the odometer work. This has me stumped.

     So #1 is it possible the speedometer cable failed in a way that when the cable is attached at the transmission it no longer spins the speedometer because it can't reach and pulls back out of the speedometer.

          #2 is it possible the speedometer pinion gear at the transmission is not spinning while the car is in gear. I have read that the 280zx and 280z housings are different for the pinion gears, and I honestly don't remember which one I am using in there. The gear is still completely intact and not damaged so it makes me assume nothing funky is happening there. 

         #3 is the speedometer purely mechanical or does it use an electrical aspect (besides backlight). I have never worked on speedometers so this is new to me.

Thank you in advance!

Edit*** Did some deep thinking and I'd note I probably drove around 1 mile on the original 4 speed.

 

Edited by ckurtz2
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2 minutes ago, ckurtz2 said:

is it possible the speedometer pinion gear at the transmission is not spinning while the car is in gear. I have read that the 280zx and 280z housings are different for the pinion gears,

 

3 minutes ago, ckurtz2 said:

is the speedometer purely mechanical or does it use an electrical aspect

Yes and yes.  There are two possible reasons that the cable is not spinning the speedo/odo parts.

1.  There's enough slack in the sheath that the drive cable can get jammed up and not engage correctly.  It helps to pull the inner cable out at the transmission and stick it in to its slot on the transmission end then push it back up toward the speedometer as you screw on the sheath end.  At least that helped me.  Apparently the speedo end seats more easily than the transmission end.  I think that I had also spun the propeller shaft while I did that.  I had the back wheels up.

2.  The housings are different.  The locking slots are oriented 180 degrees apart.  The gears are offset so if you use a ZX in a Z the gears won't mesh.  Look in the hole and you should be able to figure out which one you need.  You can also reorient it without locking it down and see if it engages.  Some people just grind a new slot in the housing when they do a transmission swap.  But it's pretty easy to swap the gears too.

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@Zed Head

All super helpful. Found the easiest way was to tighten the cable down on the speedo. Then get under the car and press the inner cable until you could feel it seat in the speedometer. Then attach to tranny. 

Anyways, success. Flipped it 180 degrees and both the speedometer and odometer came back to life. The drill must not have been spinning fast enough to engage the speedometer. I am just gonna go ahead and buy the housing and gear together, as I need the proper gear for the 3.7 instead of the stock 3.53 anyways.

The speedo is pretty bobbly, I also have read that this is usually due to friction and such inside of the speedometer cable housing. What is the best way to remedy this? 

Man it's been a good week. Fixed the car vibration and now the speedometer without spending much money🤪 unheard of for me. 

 

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Actually, my post wasn't about the easiest way.  It was about the best way to be sure both ends were correctly seated.  Your bobbly speedo sounds like the cable is not fully seated and it's rubbing on the inside of the sheath.  It's bound up.

Or it might be that you have a bad spot on the gears. 

At least you know that the parts all work.  

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