89 Speedometer broken

BlueTuner · 11-30-2009, 03:09 AM

The Speedometer on my 89 is broken, it will go up but not to the right speed. It will say 3mph but i will be going around 25-30mph, it gets up to about 20mph, but i would be going around 65mph. My Turbo timer when showing the speed is also the same it will show what the speedometer shows. What could be wrong. If its the cables, do you have to remove the dash to see the cables? how to I get to the speedometer cables.

cre · 12-01-2009, 07:38 AM

Your problem is indicative of a broken speedometer cable, broken speedometer or a slipping driven gear. The cable is the most common, so let's focus on that....

The speedometer cable is a two segment unit (three on an automatic equipped MKIII). I'm going to assume we're dealing with a 5 speed, because I like them and since you didn't indicate otherwise. The lower segment is the easiest to access and as such is where I would begin. The speedometer cable connects to the driven gear in the transmission toward the center of the transmission (lengthwise) on the passenger side and just a tiny bit above the level of the floorboard. About 18" from the transmission you'll find the union between the upper and lower segments. Disconnect this while leaving the transmission side of the lower cable attached. Now, (you'll need tools for this, can't remember whether it's a male or female end at that union) you want to try and spin the spindle of the lower segment. If the cable is good and the driven gear are good, the cable shouldn't spin at all... if it does spin, then disconnect the other end of the lower segment and while holding one end still try to spin the other again... if it sping, the cable's bad, if not, then climb back under the car and try to spin the spindle sticking out of the driven gear's housing. If you can spin the spindle it's time to drain the transmission and pull the driven gear.

If both of those test out fine it's time to pull the gauge cluster and test the upper cable segment. This is easily handled if you have an assistant. Have your assistant hold the spindle (which connects to the speedometer) in place with a pair of pliers (be careful not to chew up the surface, it's soft material) while you try to spin the cable from below... if it spins you've found the problem... if not, it's the speedo... unless you've somehow miss diagnosed the first three parts (gear, lower and upper cables).

Double check your results when testing the cables, sometimes a broken cable will still posess enough friction to feel firm but slip under any real load... no need to grab the vice grips and break what wasn't broken though... I'll leave it to you to find the place in between. In some cases you'll pull one of the ends from its mating surface and the borken bit will slide right out of the sheathing... I love it when that happens... unthread one union, pull apart and PRESTO! diagnosis complete!

Speedo cable assembly: http://www.cygnusx1.net/Supra/Librar...spx?F=8301&P=3
Speedo driven gear: http://www.cygnusx1.net/Supra/Librar...spx?F=3304&P=1

Good luck!

Today's tip: Posting ALL relevant data (such as what transmission) in your thread, will really help us help you.

11-30-2009, 03:09 AM	#1
BlueTuner Intake Join Date: Nov 2009 Location: Englewood, Ohio Posts: 41	89 Speedometer broken The Speedometer on my 89 is broken, it will go up but not to the right speed. It will say 3mph but i will be going around 25-30mph, it gets up to about 20mph, but i would be going around 65mph. My Turbo timer when showing the speed is also the same it will show what the speedometer shows. What could be wrong. If its the cables, do you have to remove the dash to see the cables? how to I get to the speedometer cables.

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12-01-2009, 07:38 AM	#2
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Your problem is indicative of a broken speedometer cable, broken speedometer or a slipping driven gear. The cable is the most common, so let's focus on that.... The speedometer cable is a two segment unit (three on an automatic equipped MKIII). I'm going to assume we're dealing with a 5 speed, because I like them and since you didn't indicate otherwise. The lower segment is the easiest to access and as such is where I would begin. The speedometer cable connects to the driven gear in the transmission toward the center of the transmission (lengthwise) on the passenger side and just a tiny bit above the level of the floorboard. About 18" from the transmission you'll find the union between the upper and lower segments. Disconnect this while leaving the transmission side of the lower cable attached. Now, (you'll need tools for this, can't remember whether it's a male or female end at that union) you want to try and spin the spindle of the lower segment. If the cable is good and the driven gear are good, the cable shouldn't spin at all... if it does spin, then disconnect the other end of the lower segment and while holding one end still try to spin the other again... if it sping, the cable's bad, if not, then climb back under the car and try to spin the spindle sticking out of the driven gear's housing. If you can spin the spindle it's time to drain the transmission and pull the driven gear. If both of those test out fine it's time to pull the gauge cluster and test the upper cable segment. This is easily handled if you have an assistant. Have your assistant hold the spindle (which connects to the speedometer) in place with a pair of pliers (be careful not to chew up the surface, it's soft material) while you try to spin the cable from below... if it spins you've found the problem... if not, it's the speedo... unless you've somehow miss diagnosed the first three parts (gear, lower and upper cables). Double check your results when testing the cables, sometimes a broken cable will still posess enough friction to feel firm but slip under any real load... no need to grab the vice grips and break what wasn't broken though... I'll leave it to you to find the place in between. In some cases you'll pull one of the ends from its mating surface and the borken bit will slide right out of the sheathing... I love it when that happens... unthread one union, pull apart and PRESTO! diagnosis complete! Speedo cable assembly: http://www.cygnusx1.net/Supra/Librar...spx?F=8301&P=3 Speedo driven gear: http://www.cygnusx1.net/Supra/Librar...spx?F=3304&P=1 Good luck! Today's tip: Posting ALL relevant data (such as what transmission) in your thread, will really help us help you.