Speedo gear tooth difference

[Sixtyeight]

Hi,

Since I'm correcting all the dash meters now, I run into a misinformation regarding the Speedo gear tooth difference...

When my speedo reads 40 I'm actually doing 50. So I need to gear up 10 mph. I used the search engine of the site but I find threads with the following info on what difference one tooth makes on a speedo gear...

** one tooth equals 2-3 mph
** one tooth  on the gears is about 4-5 miles per hour
** one tooth on the gears is 5MPH
** one tooth on the gears is close to 7mph

Can anybody confirm which one is right?

Would be great! 

Thanks,

Jeroen.

[alfaitalia]

None!.... adding or subtracting teeth wont increase or decrease by a set number of MPH across the speedo range....it will add or subtract from the reading by a  certain amount at a certain speed but different amounts at other speeds....so it might gain you 2 mpg at 20mph or 10mph at 80 with adding the same number of teeth.

[Sixtyeight]

Ok, that's clear!

In that case does anybody have experience with how many tooth I have to add / reduce in my situation? My speedo reads 40 when I'm actually doing 50...

Thanks

[Nacho-RT74]

speedo moves by inertia and magnetism, is not a direct drive shaft movement. Odometer is a counter and is a straight relationship with speedo gear, through the wire and gears inside the speedo.

Your speedo could need a spring adjustment into the assembly to make the needle to read closer to reality, but the real relationship will be given by the odometer, to know if you are really way off or not.

That's aside the tables around to select the propper speedo gear  with relation between wheel diameter and axle ratio

[Nacho-RT74]

This is one of the many tables around to find the propper speedo gear you could be needing into your tranny to adjust your reading. Begin with that if you have the correct one first, or not. Then the speedo itself

http://board.moparts.org/ubbthreads/ubbthreads.php/ubb/download/Number/135055/filename/7390568-Speedogeartoothrequirements.jpg

[Sixtyeight]

I know how the speedo meter works and I used the tables to get me where I'am now. But having done all that I'm 10 mph off on 50 mph. That's why i need to now what difference a tooth makes  to determine my adjustment...

Jeroen.

[alfaitalia]

Don't think you are reading or fully understanding the previous posts....no offence.....If you adjust the number of teeth to get the reading right at 50mpg....it could be wildly out at other speeds....so overall no real improvement. Different teeth number will probably not cure your issue and will throw your odometer off. In my experience a new speedo is the likely cure.

[cdr]

check the Odometer 1st & see how far off it is.

[Bronzedodge]

   If you have a highway with mile markers it's fairly easy.  Go 10 miles and compare the odometer to the mile markers.

[XH29N0G]

The reason for checking the odometer reading is that will check the function of the speedometer.  If both are off (low or high) then it is a gear. 

If you are sure both are off, and that it is a gear, you can use the table Nacho posted a link to (or this one http://www.mymopar.com/speedometer.htm) to figure it out.

If you know what rear ratio and tire size you have, then just pull off the chart. 

If you do not know the rear you can figure it out, or you can simply adjust by % and cross reference the charts.  For instance it you are reading too low by 20%,  you would switch from the gear for a 3.23 to a 4.10. which is also ~20% different.

What color speedo gear to you presently have?

[A383Wing]

I know how the speedo meter works and I used the tables to get me where I'am now. But having done all that I'm 10 mph off on 50 mph. That's why i need to now what difference a tooth makes  to determine my adjustment...

Jeroen.

one tooth is about 5 MPH......try a gear with 2 less teeth, that should speed your speedometer needle up higher.....

[Sixtyeight]

Thanks, that indeed was the question!

Will try that, thanks! 

Jeroen.

[alfaitalia]

..well it was the answer you have been wanting to get....some of the OTHER replies were in fact the correct answer though. So now you might have a Speedo that's correct at 50 but wrong everywhere else and an inaccurate odometer...so...problem solved.

[cdr]

..well it was the answer you have been wanting to get....some of the OTHER replies were in fact the correct answer though. So now you might have a Speedo that's correct at 50 but wrong everywhere else and an inaccurate odometer...so...problem solved.

Yep!!!  on my car the odom is spot on, but the speedo is off,40 & below is spot on,,50 & up it is of by 6 %.

[Nacho-RT74]

The first step is match the speedo gear on tranny with your wheel diameter and axle ratios. Make the maths to get the number of teeth you need over your actual setup is irrelevant having the tables already done to match the setup.

THEN it you still have the speedometer off, take care of the odometer to check what is really wrong.

[Nacho-RT74]

If you drive by an hour at 60 MPH it means your odometer will get 60 miles more.

Since is hard to keep a firm speed driving by an hour, with just 5 minutes driving at 60 MPH you should get 5 miles more on odometer. And check for that on higways marks ( assuming highways are correct LOL )

[Sixtyeight]

Ok, when the odometer is correct. Is it possible to correct the speedo itself?

Jeroen.

[XH29N0G]

I would see if you can find a speedo shop (redline gauges, or some others also do this).  The mechanism is pretty simple and it could be dust binding the mechanism, a weak hair spring, or  something with the magnet.  If you are adept and maybe lucky you may be able to fix it.  I tried to fix two and they would read correctly at one speed, but none of the others (AND I didn't just move the needle to one place and fix it there).  Ultimately, I bought an expensive repop version from Classic (I think) and installed it.   

[Nacho-RT74]

Yes! You can readjust the needle return spring. Get a drill with reverse speed with a fixed and known speed and conect it to the speedo ( I used an old speedo wire )

The  speed rate is 1000 rpms at 60 mph. If you have a 800 rpms drill, make the maths

[Nacho-RT74]

Here is a fix I made with a kilo speedo I found for my car when I got an incident with it when the bushing got broken

http://wichargerguy.proboards.com/thread/19119/patiente-pays-brock-thing-help

And how I calibrated back the return spring

Read it up to the end