Speedo inaccurate

[Minotaur]

Howdy
I have found out the hard way that my speedo shows a lower speed than i'm actually doing. When the speedo says 50, i'm actually doing 60, 100 is 120. The ratio seems to be constant so I suspect it's a gearing problem or something like that. I have an SL but had the instrument cluster changed to a berlina (with tacho) some years ago and I was wondering if this could have anything to do with the problem?
Thanks.

[VS Omega]

Do you have the factory wheels or some bigger aftermarket ones? Aftermarket ones can throw it around a bit

[Minotaur]

I have 15" rims on the car - it's what it came with when I bought it. I'm not sure that a single inch extra in diameter could account for a 20% discrepancy in the speedo though. But who knows?
Thanks.

[Bax]

Theres two speedo's.

But the only different between the actual units are the series 2 calais cluster and then theres the standard speedo unit. If you look at the two dashes you can see the increment change. When I put my cluster in I broke the old calais speedo part and I replaced it with a normal part. That put my speedo heaps out.

Apart from that I'm not sure.

[jimrichards1964]

Howdy
I have found out the hard way that my speedo shows a lower speed than i'm actually doing. When the speedo says 50, i'm actually doing 60, 100 is 120. The ratio seems to be constant so I suspect it's a gearing problem or something like that. I have an SL but had the instrument cluster changed to a berlina (with tacho) some years ago and I was wondering if this could have anything to do with the problem?
Thanks.

if you have changed tyre diametre or diff ratio, even gearbox then the speedo DRIVE GEAR in the gear box maybe to small tooth wise. I had same problem with my m75 borgwarner as my speedo was out exactly 25% at all speeds because the gearbox was from a 4 speed with a 7 start gear in the box when i needed a 9 start. The m75 suited the starfire and the 2,8 blue only the other m75's had the 9 start gear in it. I got the smallest one on the cable at 20 tooth as they dont make a 17 anymore like the powerglide ones from Brouham's. If you go to get a smaller cable gear it may not be listed for manual or auto, just give them the brand ie; borgwarner and ask for tooth size as too much info confuses cov's and repco. The 9 starts are completely unavailable any where, but a bmob in ozzie park re-calibrate speedo for $80.00 if you remove speedo from the front, dont do it the hard way and remove dash. They set it up to suit your wheel diameter, axle ratio, etc. But the speedo will only suit that setup and gearing. Take speedo out, measure off 20 metres on road with chalk and count exactly how many times cable turns, this will help the speedo people. Really hope I may of saved you some time and hassles. Regards jimmy.
jimrichards1964@westnet.com.au if I can help further, why did my VL start to miss then die then would not turn over? Is it a common thing if so what, computer, fuel pump, I know starter crook as solenoid is look and sounds like eggs cooking when youn try to crank. Any links you know of that may help? try original speedo first as the bell spring tension may be different good luck fellow commodore owner

[jimrichards1964]

I have 15" rims on the car - it's what it came with when I bought it. I'm not sure that a single inch extra in diameter could account for a 20% discrepancy in the speedo though. But who knows?
Thanks.

its actually 1/2 inch from axle to road making an error of about 3 kph, 1 tooth out can at 100 make a difference of 15-18, mine at 80 on the speedo meant i was doing 100 because of only 2 teeth on the DRIVE GEAR on the output shaft not thwe cable one, good luck

[albino1986]

lol i also found out the hard way, twice in one night lol

is there any way to avoid these fines if you can prove the descrepency of the speedo and say you didnt reliase it or wil they just laugh at you lol

[Minotaur]

I think the problem with that is... proving your speedo is inaccurate might lead to a defect notice instead of a speeding fine :/