Speedo gear calculator help..

[saladine1]

My VH had the small salisbury 2.68? ratio diff. We swapped the diff for a VL diff with 3.45 gears.
Now, when we took off the speedo gear, it was the green one with 21 teeth. We then installed the blue 22 teeth drive.
The speedo is now reading is way off.

So, can someone please tell me what the correct colour drive I need?

It's a Trimatic, with 16 inch wheels(225/60/16) and 3.45 ratio diff gears..

 

[dags061]

Do you run a 6 or 8 and how does it run with the 3.45 diff. I have one here and am considering putting behind a 253, 4 speed M20.Sorry cant help with speedo drives.

 

[rambunctious]

There are two gears that drive the speedo, one on the rear output shaft of the box called the drive gear and one on the speedo cable called the driven gear, and the fact you have increased the ratio by almost 28% may necessitate changing both to get a correct match.

I have a number of drive and driven gears that came from mostly trimatics in HQ HJ HX which may work but it will be totally dependant on the drive gear you presently have.
To count the teeth on the drive gear you must count the teeth on the flat of the gear not the edge.

You can try the old holden speedo calculator but it will still show your speedo to be out.
Here is the link Speedo gear Calculator

If you use 3.36 as a guide then according to the calculator you will need 20 tooth driven gear and 3.55 shows 21, so as I said, it has everything to do with changing the drive gear in the back of the box which is not a major job.

The other option is a speedo adaptor which mounts to the box and while I have never used one, I have heard they work.

I am on the other side of town to you but if you need to try some different gears, pm me and I will give you my contact. I am on the Sunny Coast for possibly the next two weeks but will then be back in Bris North.

And here is a bit more info which might keep you occupied for a while https://forums.justcommodores.com.au/threads/speedo-calibration.18655

Hope this helps and makes sense.

 

[ajvx01]

Please post up your answer as I plan on doing the exact same swap..

 

[vkberlina]

depending on your wheel & tire size this will affect the outcome I would buy a 20 and 21 tooth and see how close oyu can get it.

scott

 

[saladine1]

Ok, so, I've found out that the VH Trimatic has the blue 9 teeth drive gear and 21 teeth green driven gear. For my tyre and diff ratio specs, I'm going to need the 24 teeth yellow driven gear in order to get to 97/kph@100 which is the closest i'm going to get to being correct and safe.
Thanks everyone.