FC Speedo Calibration

[Airfireman]

Gday all,

Took my FC for a drive this morning to have Gas certificate and roadworthy completed and along the highway the speedo is reading 60mph and the GPS is saying 85km/h ???

I have the original 13" wheels so maybe it has a taller diff centre???

Would this change the speedo or any other suggestions???

Tim

FC purrrrrrrrrrrrs like a kitten  ;D

[Glenn 'Stinky' Stankevicius]

Sounds like you need to change the speedo drive gear, they come in a range of colours that change the speedo reading.
The trick is working out which one you need.

[Glenn 'Stinky' Stankevicius]

Here's a calculator that might be handy

http://codes.oldholden.com/Speedo/

[hsv-001]

Mate , first thing is you have the 13" tyres but not the original profile . Speedo cogs would be hard to find if that's the original crash box . If you are staying with what you have then look at diff gears and tyre profiles . Plenty of people on this forum can help you . Its been awhile since I ran stock gearbox and diff so I'm not sure what's available . I run 173 block and a borg-warner 5 speed ,336 diff gear but because I can only run 205/60 tyres on the 7" rims I had to shuffle through various speedo drive cogs to calibrate the speed. Haydn

[ACT59FC]

are the speedo drives on a holden Grey crash box the same as eh, hr, ht, hg ? Reason Im asking is I am considering replacing my 3.89 standard diff with a 3.55. I too have a set of 13" mags and can only get 205/60 R13s for them.

My poor old girl revs her guts out at 60mph with the standard rims and 185/75 R13s. I am hoping a change in diff ratio will do the trick.

Rod

[mcl1959]

In order to work out a solution we need to know engine, box, diff and wheel size. Original crash box only has one speedo drive ratio. Later boxes have a plastic drive gear which is easily changed.
Pretty basically, with a stock engine and box, if you drop the wheel diameter by fitting radials you can get this back by fitting a 3.55 or 3.36 diff.

Ken

[ACT59FC]

Ken Engine is stock standard 132 grey (tired....very tired) Gearbox is the stock standard FC crash box. Current diff 3.89.

I was lucky enough to purchase a set of cheviot hurricane 13" x 7 mags and was planning on running them while I take the original rims off to be sandblasted and powder coated.

Thanks for the info Ken. Just need to find myself a diff I think.

Rod.

[Rod]

Hi Rod (by the way great name champ),

I went through this many years ago and found two grey crash box speedo gears. The standard for FE/FC having 23 teeth and a 22 tooth gear from a 48-215/ FJ for 15 inch wheels.

Please have a look at this thread.

http://forum.fefcholden.club/index.php?topic=911.0

Cheers

Rod

[KFH]

When I fitted 185/80R 13 with the 3.89 diff the speedo reading was spot on.  With a 3.55 diff and a 22 tooth gear from an FJ the speedo reading again is spot on.

Keith

[ACT59FC]

Rod (your parents chose an excellent name for you) and Keith (who wasnt so lucky) thanks so much Ill keep my eyes out for an FJ speedo gear.

That post was an interesting read however you guys simplified it  :)

Regards Rod.

[mcl1959]

Thanks a Rod and Keith, I had forgotten about the FX FJ gear.

Ken

[Airfireman]

The diff gasket is leaking on my FC so a good time to pull out and have a look at ratio whilst repairing the leak.

As confirmed by members here at the Nationals I have the crash box fitted to the red motor.

Great info

Thanks

Tim

[rob_dav]

If you are running stock original rims you can get 155 13 tyres they are a light truck tyre /commercial tyre there are a few different makes. They are a 100 profile tyre and have a similar tred pattern to the original tyres.

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