How to fix your speedo the factory way ...

[Sprinter]

After you have changed your wheel size, or diff ratio or put in a new GB (T or W is what I have experience with) you will often find that your speedo is out of calibration. The way the factory addresses this is to change the speedo driven gear in the GB (and sometimes the worm gear!!).

The following has been shamelessly copied from an article by NZ toyophile Phil Bradshaw (http://home.clear.net.nz/pages/phil....peedo%20Drives). It explains how to calculate which driven gear you need taking into account wheel circumference, diff ratio and speedo gearing.

The following applies to T series gearboxes (T40 - T50) and the W series (I have a W57 that I tinkered with). I have done these changes to both T50's and the W57 (in case you think this is just speculation).

Speedo Drives
The standard speedo drive comes directly out of the gearbox tail shaft housing. If you have a really tight transmission tunnel then a VDO etc angle drive can be used to allow the speedo cable to lie parallel to the gearbox. Many automatic RWD Celicas etc had a factory angle drive that will mate with a T50 etc - and it costs a lot less from a wrecker than a VDO stockist...

Speedometer Drive Corrections
If you change your overall tyre size or diff ratio, or mate the gearbox to a completely different speedo then you will need to make a speedo error correction. My thanks to Neil Fraser for the following information:
"The gearbox speedo worm drive ratios I know of include 5 x 19, 6 x 20, 6 x 22 etc. (ie 5 starts on the worm gear and 19 teeth on the driven gear). Most speedos are 637 rpk, 675 or 1000 rpk (revs per km). So lets say that to cover 1 km of distance your output shaft at the gearbox will turn how many revs?

Say a tyre diameter of 590mm: Circumference = 22/7 x .59 = 1.854m
Axle revs: 1000/1.854 = 539.37
Output shaft revs: 539.37 x 4.11 = 2216.8284
Say your speedo is 675rpk (should be written on back somewhere) - required speedo cable revs: 2216.83/675 = 3.284, so therefore best ratio is about 6x20 (3.33)

The small gear will have written on it the number of starts on the worm it would be compatible with (ie 5 or 6). Using a 5 start gear on a 6 start worm is always terminal. The worm slides off easy enough but requires practically stripping the whole gearbox…"

Now I have just performed a straw poll of all the AE86 dash clusters I have (ADM, JDM, UK and Canadian) and they all translate to 637revs = 1 KM. Note that the UK cluster reads in MPH so its 1024 revs = 1 Mile.

One BIG caveat: this applies to mechanical speedo's such as AE86, TE72, etc etc. There are many other ways to correct your speedo but this way meant I just had to swap one gear in the gearbox.

Hope this helps those of you with speedo problems.

Denis

[brett_celicacoupe]

the other option is to screw in a MX83 grande or soarer electric speed sensor. they fit all the w5x boxes.

then buy a VDO 5" speedo and calibrate it

[skiddz]

the other option is to screw in a MX83 grande or soarer electric speed sensor. they fit all the w5x boxes.

then buy a VDO 5" speedo and calibrate it

what if ya have a T50 box? then what?

if there is an electronic speedsensor that fits a t50 id love to know cos it means i can run a speed sensor to the ecu and consequently a check engine light which would be the bomb and a half

[brett_celicacoupe]

i ~think~ T50 and W50 are the same. though not too sure, hence why i didnt mention it.

try searching

[Sprinter]

Nope - T50 and W5X are different. I believe the electronic sender uses a different setup on the output shaft from the gearbox and no T50's had an electronic sender.

Denis

[rob1]

Not sure who makes it but you can buy a unit that converts a mechanical drive to elec. Used when aftermarket ecu needs a speed input and using older type box.

[worldwalker]

thanks brett, needed to know where I could get a sensor.

[The Witzl]

Not sure who makes it but you can buy a unit that converts a mechanical drive to elec. Used when aftermarket ecu needs a speed input and using older type box.

Correct, you can get them from "Mobile Instrument Services" in blacktown [Sydney]. I think they are a VDO unit, and they provide 4-pulse per revolution output.

[Norbie]

Does anyone have a list of possible speedo drive gear combinations? I want to integrate this into my wheel size and gearing calculator.

[oldcorollas]

for K series boxes there are 5/19, 6/20 and 6/21 (in KE1x, KE2/3x, and KE7x respectively)
KE1x has a different speedo rev/mile than the later rev/km... botht he 6 worm drives are same, but the 5 worm drive is a different diameter. 20 and 21 will work with same 6 tooth drive.

[Sprinter]

Here is what I have in my list:

T Series boxes
5/18, 5/19, 5/20, 6/20, 6/21, 6/22

W Series boxes
9/31, 9/32, 9/33, 9/34, 10/31, 10/35, 11/23

If you have a working EPC they have the various ones listed if you dig deep enough.

I have also attached a spreadsheet I wrote a few years back allowing you to enter the current wheel size data, gearbox ratios and wheel size variations (to prototype different wheel/tyre combinations). You need to enable macros and when you select the Main tab it should display. When you press the Run button it calculates the change in speed if you change to the specific wheel/tyre combinations. Really handy if your trying to work out what speed your doing after changing wheel configuration.

The Speedo gear tab has the calculations I mentioned at the start of this thread. Enter the wheel details, diff ratio and dash RPK and it will calculate the Speedo Cable Revs. Match the cable revs to the gearbox ratio and your done

HTH

[Negative Boost]

Great stuff!! This will come in handy, thanks.

[74sLeeka]

great info.. thanks alot..

[black86]

great info! are the rear ends that come in an sr5 corolla 3.909 and 4.11? i believe i have an sr5 tranny in my GT-S w/ a 4.3 rear end. im trying to get it all corrected.

195/60R14 (stock) T50 transmission:

the 4 possible final drives along with their worm/drive gear
3.909...would be 6x20
4.11.....would be 6x21
4.3......would be 6x22

at least the worm gear is the same.. phew...

funny thing is i went to the dealer for a new speedometer drive gear and they gave me a 19 tooth gear... my dealer sucks.

[parrot]

http://www.ae86drivingclub.com.au/fo...howtopic=14843

Jonny Rochester contributed this post.