Speedo drives

[Bozu]

All information about servicing, changing and problems with speedo drives here.


Bozu says

I found this in my spare parts that came with the car I recently bought:
http://www.ae86drivingclub.com.au/dcimages/6/9/1/1/68695.jpg

Can someone tell me which gearboxes these are for

[McLEVIN]

idk distributor shafts?

[timbo]

speedo drives and worm gears. the go in you gearbox to read your speed!

they should have 2 numbers on the nylon gear, e.g. 22 6, which means the nylon speedo gear has 22 teeth and the worm gear on the output shaft in the gearbox has 6. very handy to have al those as spares if you plan on changing your diff ratio.

edit: bottom three look like they are for t series boxes and the top im unsure, maybe a w series?

[70XIN]

looks like a T50 speedo drive, 3 T50 speedo drive gears/shafts

and up the top is definitely a W series speedo

[Bozu]

Don't you just love the feeling when the pieces of the puzzle fall in to place!
The previous owner of my car changed the T50box to a W57 box and T50 diff to a F series diff.
Thanks guys, your help is greatly appreciated!

But to get the technical part right, why do you have to change those parts if you change your diff?
I understand a different diff ratio changes the rpm when the speed of the car stays the same but I don't see why you have to change those speedo gears...

[70XIN]

Haha, yes it's good :)

The speedo takes it reading from the speedo drive, which is in the gearbox - when you change your diff, it speeds up/slows down the gearbox, which effects the speed the drive (and cable) spin - thus your speedometer is off.

Changing the speedo gear will account for this change, and make your speedometer right.

[timbo]

as seamus said. at $60 a pop for the nylon gears they are quite a handy bonus!

[Bozu]

Ah yeah I get it, I confused the speedo signal with the rpm signal...
The change in ratio has to be the opposite then of the change in the diff isn't it? If the gearbox speeds up you want the speedo drive to slow down and vice verse right?

Where is the rpm signal taken from?

[70XIN]

Exactly right :)

The tach is taken from the negative side of the coil - every time it pulses, it sends a voltage spike through the negative wire - your tacho works out how frequent they are, and magic happens ;)

[Bozu]

Straight out, don't muck around!

Thanks!

[Sam-Q]

Bozy I am making this a reference from the technical index, and I eddited your original post to suit, if you prefer it to not be then let me know and I will delete the whole thread.

[Bozu]

Bozy I am making this a reference from the technical index, and I eddited your original post to suit, if you prefer it to not be then let me know and I will delete the whole thread.

I have no problems with it, could be usefull information for others in the future!

[Jrad]

Adding some information here as it is in the index of technical threads.
Thought speedo cable questions would be an appropriate place to put this info as well.

If you are wanting to get a new speedo driven gear assembly, you need these two part numbers:

Sleeve that goes into the gearbox: 33404-16010 (comes as a sub-assembly including o-rings)

Gear - to suit a 3.9 ratio (stock):33403-19155 (comes as a sub-assembly including an o-ring and clip)
Other ratios are available with different part nubmers.

N refers to number of teeth in the nylon gear.

33403-19135 N=19
33403-19155 N=20
33403-19165 N=21
33403-19175 N=22

(To work out ratios/what you need etc. Look at this thread too: http://www.ae86drivingclub.com.au/forums/showthread.php/22529-speedo-gears )

Extra parts in the pic aren't needed. Didn't realise they came as sub-assemblies. So save yourself some cash.
36588



My question:
Do all manual AE86 have the same speedo cable?

Mine was originally 4AC and the cable seems too short. Am I missing something? Is this correct?
The bend is quite harsh and it doesn't seat into the holders.

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