speedo gears

[JDM-086]

i know this has been posted on the old forums and iv'e tried searching for the thread with no luck, wondering if someone can link me.

- i'm after the thread about changing the small speedo gear in your gear box so that your speedo will read accurately when putting 4.3 diff gears into an 86 with an adm t50. needed info on which parts are needed, the part numbers and instructions on how to do so... all of this was in the previous thread so if it still exists that would be awesome..

thanks in advance
Dario

[timbo]

http://www.ae86drivingclub.com.au/forums/showthread.php/18462-Speedo-worm-gear-T50-4.3diff-ratio

[JDM-086]

cheers, wasnt the thread i was after but still somewhat helpfull.... although im still a little confused.. that helps if i was running 4.1, im too shit to work out what i need to get my 4.3 reading correctly... id be ordering the parts from toyota so i dont mind if i cant get it out of another car..

[JDM-086]

from reading that, i came to the conclusion that all id need is the 22 6 drive gear, which is what is present in a jdmt50? making my speedo read correctly with 4.3 diff gears? i shouldnt need to change the worm gear as i was running an original adm ae86 t50 which should be 20 6? so the worm gear in mine should work fine with the 22 6 drive gear?? amirite?

[Oly AE86]

Speedo Drive Ratio Corrector

Bought from Castlemaine Rod Shop http://www.rodshop.com.au/

Order Page >>> http://www.rodshop.com.au/order_forms/SPEEDO_CORRECTOR_ORDER_FORM.pdf

I bought one of these, easy to install with to touching of the gearbox.

[marvin]

Here are the part numbers (from the old thread):

Plastic gear
33403-19135 N=19
33403-19155 N=20
33403-19165 N=21 (not specifically a AE86 part)
33403-19175 N=22

Metal worm gear
33481-12030 N=5
33481-14040 N=6

According to the old thread, Australian AE86 comes with 22:6 and 19:5, depending on the tire size, and 22:6 being more common.
Here in N. America, the GTS models having 185/60/R14 tires seem to commonly come with 19:5 speedo gears.

Formula:
speedo gear ratio = (1000 x Diff)/(pie x D x 637)
Diff = final drive ratio
D = diameter of tire, in metre

e.g. switching to 4.78 final drive (43/9)

speedo gear ratio = (1000 x (43/9) )/(3.14 x 0.580 x 637) = 4.11

In theory, 20:5 or 21:5 would work. However, I mean in "theory" ... For those running 4.78 final, please read on further. I wrote this (http://www.dorikaze.net/showthread.php?t=20513) 2 years ago after upgrading to 4:78 final. Here is an excerpt:

The 4.78 final drive and 20:5 speedo gears have been installed for 2 months now, and I started noticing that the indicated speed is somewhat higher than the actual speed, at least more than the 2.7% I anticipated. So I borrowed a GPS, and to my surprise, found out that the indicated speed is 10% higher!

Previously I calculated the speedo gear ratio to be 4.11. Between 20:5 and 21:5 ratios, I chose the first one because it would give me a more conservative speed, roughly 2.7%. But 10% is indeed a bit excessive and quite annoying even when I'm driving in the city.

At this point I was pulling my hair, so I phoned Brian at 86tuning. Brian explained that the speedometer in a 20+ year old car isn’t very accurate to begin with (~ 5%), and typically it gives a higher indicated speed. By going with the more conservative 20:5 ratio, I have essentially doubled the safety factor. Had I chosen a 21:5 (= 4.2), the indicated speed would be roughly 5% higher than the actual speed, which is more reasonable.

However, to compensate for my inaccurate speedometer, I would need to change the driven gear to from 20 to 22 teeth, i.e. 22:5 = 4.4!!

After solving the puzzles, I bought a 22-teeth driven gear (p/n: 33403-19175). First, it’s still available from the dealer. Second, it works with the 5-teeth metal drive gear. Third, I checked against the GPS afterward and confirmed the speedometer to be accurate.

Lesson learnt:

You will need 21 or 22 teeth depending on
(1) speedometer accuracy: before deciding on speedo gears, check how inaccurate your speedometer using a GPS or similar device. For instance, mine is off by 7%.
(2) tire size: The tire size is another factor. The figure in the example (0.580m) is only an average dimension. For your reference, my 195/50/15 tire has a diameter of 0.576m.

cheers,

marvin

[timbo]

marvin ftw! top work.
http://t3.gstatic.com/images?q=tbn:ANd9GcQk_A1ZqsivuudFjckuYMHjaX9r2hzIR JjGPDLleEh_jjJ7mo4&t=1&usg=__fTg8DHY2Q4y-5esyFCopOXEtK3A=

[JDM-086]

lol dam thats so complex... ill have to work it out. all ADM ae86's came with 13" wheels so im going to assume they were all 22:6. im currently running a 15" rim and my speed reads about 5km off up to 100km, then more the faster u go. im thinking of gettin the 22:6 drive gear

[Oly AE86]

Buy the ratio convertor above, nothing complex at all :D