Speedo is off 15km how to fix

[mrp69]

hey guys

 

my speedo is out about 15km out

how can i fix this??

 

and were could i possibly take it in sydney and what sort of dollar figure will it cost to fix??

 

peter

[Hunter]

Have you changed the running gear in your zed from original?

 

Read this link, it contains different cog sets for different ratios.

 

http://www.viczcar.com/forum/index.php/topic,2698.0.html

[nat0_240_chevZ]

find the right colour speedo gear for the g/box and will fix it.

[mrp69]

 

well car has a v8 with a supra 5 speed and recently changed the diff to a 3.54

 

peter

[Zeddophile]

my speedo is out about 15km out

how can i fix this??

 

Is it 15km out at all speeds, or 15km out at 100km/h (or some other set speed)?

 

If its the latter, and you didn't change the speedo drive gear in the gearbox when you changed the diff, most likely you just need to fit the correct speedo drive cog for the 3.54 diff. 

 

If its the former, have a look and see if you can move the needle inside the speedo around on its pin so that it reads correctly.  This may result in it reading 15km/h when standing still, but it will be right when you're moving!  I did this trick on my Alfas' tacho.

[mrp69]

15km out at all speeds

 

comfirmed it with my GPS

 

i thought everytime i drove it "F**k people are driving so slow around me" lol

 

will try and work out what cog my car has and get back to you guys

 

peter

[260Coupe]

If you are running a Supra 5 speed then you may have to source the speedo drive from another Toyota box.........

[Zeddophile]

15km out at all speeds

 

comfirmed it with my GPS

 

i thought everytime i drove it "F**k people are driving so slow around me" lol

 

will try and work out what cog my car has and get back to you guys

 

peter

 

if its always the exact same 15km amount out at all speeds (ie. reads 25 when doing 40 and 100 when doing 115), changing the drive cog isn't going to fix it.

 

If you say for example you have a rolling diameter of 600mm in your tyre, doing 3000 rpm with a 3.9 diff with a 3.1 gear ratio (random numbers I picked to illustrate the point, but should be close to the ballpark!), you're doing 28km/h.  Change the diff to a 3.54, and you're now doing 30.7km/h.

 

Keep the numbers the same except for the gear ratio, make it .8 for a rough 5th gear.  With the 3.9 diff, you get 108 km/h, with the 3.54 you get 119.

 

The point is, that at lower speeds, the inaccuracy isn't as noticeable as at higher speeds, because it is a percentage of your actual speed thats not being shown.  If you had a 4.1 diff before, a 15km/h difference AT 100KM/H would be feasible, but it would be about 7km at 50km/h.  Swapping the cog may get it to read right SOMEWHERE, but it will still be out everywhere else.  Maybe if you only drive on the highway, that could be a good fix, and just get it reading correctly at that speed, but otherwise, you need to come up with another solution.

 

My Alfa speedo reads 5km/h low across the board.  I just drive 5km/h faster, but if I wasn't so lazy, I would pull the speedo out, and lift the needle off the pin coming out of the mechanism, and move it up 5 km.  I did it with my tacho to get it reading about right, but you can actually pull Alfa gauges apart, I can't remember whether you can remove the front off a Zed speedo to get at the needle or not.

 

However, I believe you probably have two problems - one being the drive gear is wrong (not by a heap, maybe its a 3.7 drivegear), and also that the needle isn't quite in the right spot.  Check with your GPS again and see if its always exactly 15km out, or whether maybe at 100km/h its out by 17, and at 40 its out by 13?

 

The other thing is, as 260 coupe says:

If you are running a Supra 5 speed then you may have to source the speedo drive from another Toyota box.........

 

This is an excellent point which we all completely missed - the nissan colour codes you've been given above are likely to be completely irrelevant in this case, and you will have to see what diff ratios the supras had to see whether any other speedo drive options are available!  Unless the nissan item has been retrofitted......

[stevo_gj]

I think Zeddophile is right, if your 15km/h wrong across the board then your needle is probably in the wrong spot.

 

It is very easy to remove the Taco (I did it myself and I know next to nothing about cars), take it apart (just a few screws) and adjust the needle. To adjust the needle, I find its easiest to take the needle off, the spindle will return to the zero position, then carefully place the needle on facing the zero direction. Of course being very careful not to scratch your precious gauge face.

 

[Hunter]

Just say your car is travelling at 100km/h and the speedo is reading 110km/h that it is out of wack by 10%

 

In this case the car travelling at 60km/h the speedo will be reading 66km/h; again out by 10%

 

SO YOUR CAR IS OUT BY A PERCENTAGE NOT BY 15km/h accross the board.

 

If I were you I would work out the ratios with your current setup or just use your GPS as your speedometer