1973 2000 gtv speedo 30km too slow!

[Jgjgee]

Hi all,
After lots of searching I have not been able to find a solution for my speedo reading and hoping someone who has experienced similar issues to me might be able to help!

The issue is that my speedo is reading 30km too slow. I have read lots of posts about a high speedo reading but not many that are too slow. Im running 15" wheels with 195/60/15 tyres. While I realise this is not factory spec, surely its not throwing the speedo out by 30km?

This is what Ive tried so far:
A different speedometer cluster (from a 1750) to check if it was a speedometer issue- Same reading approx 30km slow
Changed the speedo cable
Removed the speedo gear from the gearbox to check for missing teeth. All looks ok

I'm now starting to wonder whether I have a gearbox/diff miss match? The diff has the triangle that indicates its an LSD so I dont think its been swapped out.

Is it possible to have an incorrect speedo drive gear? The stamping on the spur gear reads 8/18. Is this the standard for a 2000 gtv?

Hoping someone might be able to shed some light!

Cheers
Jono   

[Balfa]

Following this thread Jono as I'd be interested to see how you resolve your problem.

I've got similar speedo inaccuracies but have given up and am just using a small gps speedometer on my dash (I know this isn't a solution, just saying).

[carlo rossi]

believe it or not what i did
is pulled the needle off the pin and relocated it
what has probably happened is someone has done this in the past
and not realised it
i did it by accident, mine now reads 8-10kmh fast
but thats a good thing for the [police

[ItalCarGuy]

The only reference I had seen to which goes in what was in a thread on the BB

https://www.alfabb.com/bb/forums/gearbox-transaxle-differential-propshaft/35434-speedometer-gear-drive-ratios.html

gear------outputyoke-----------rearaxle
19------------9------------------10/41(4.1)
21------------9------------------9/41 (4.5)
22------------9------------------9/43 (4.7)
18------------8-----------------10/43 (4.3)
13------------6-----------------10/41 (4.1)
22------------8------------------8/41 (5.1)

No guarantees that any of it is right though...

[Jgjgee]

The only reference I had seen to which goes in what was in a thread on the BB

https://www.alfabb.com/bb/forums/gearbox-transaxle-differential-propshaft/35434-speedometer-gear-drive-ratios.html

gear------outputyoke-----------rearaxle
19------------9------------------10/41(4.1)
21------------9------------------9/41 (4.5)
22------------9------------------9/43 (4.7)
18------------8-----------------10/43 (4.3)
13------------6-----------------10/41 (4.1)
22------------8------------------8/41 (5.1)

No guarantees that any of it is right though...

Thanks for the reply.  This is interesting.  If I'm reading it correctly, the stamp on my speedo drive (8/18) suggests it mates to a 4.3 final drive ratio. My understanding is that the 2000 GTV LSD had a final drive of 4.1. Assuming my diff internals are correct, I wonder if my gearbox is a non GTV. Would it be possible that the gearbox could be out of a sedan model such as the 2000 berlina which I understand had a 4.3 final drive?

If this is true, it might explain the number of speedo inaccuracies people encounter with the 105 coupes that have had boxes from a different model/year put into them. I wonder whether its possible to change the speedo gear to match the gearbox diff combination? 

Or,  I could be way off track focusing on the wrong areas to address the problem   

[Jgjgee]

Just reading through that thread again,

The only reference I had seen to which goes in what was in a thread on the BB

https://www.alfabb.com/bb/forums/gearbox-transaxle-differential-propshaft/35434-speedometer-gear-drive-ratios.html

gear------outputyoke-----------rearaxle
19------------9------------------10/41(4.1)
21------------9------------------9/41 (4.5)
22------------9------------------9/43 (4.7)
18------------8-----------------10/43 (4.3)
13------------6-----------------10/41 (4.1)
22------------8------------------8/41 (5.1)

No guarantees that any of it is right though...

Just reading through that thread again and it appears what I thought the issue was might actually be correct. The speedo gear is not correct for the 4.1 diff ratio (which I believe is standard on 105 2000 GTV). The only way to find out for sure is to test a 13/6 speedo gear but this will require the helical swapped out to correctly mesh with the 13/6  

[gebe1]

Hi Jono,
I have a 73 spider which was reading 10 km/h over at 100 km/h. After two visits to Lionel Otto Instruments in Brisbane we managed to get the speedo to read accurately at 80 km/h, but it under reads about 5 km/h at 40 km/h and over reads about 8km/h at 110km/h. Very frustrating. You now have me wandering if this is because of a mis match in gearing? Does your speedo error vary in the speed range?

[carlo rossi]

update i just pull the needle off aND RESET again
now im about 2 kmh slow or half a needle width close enough
found a speed indicator on the highway to verify