fbekholden.com

EK283 wrote:Joe,

I have a full diff out of a sedan and maybe some brake drums if you want it, out of one of my wrecks yours if you need it.

Regards Greg

I might just... I think diff centre will be my main interest. Do you know what ratio? I’d consider something a little taller than my current 3.89s
Cheers Joe


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Hi J
I put a 3.55 centre in the original diff when I still had it in my FC before I went to the dunnydoor one, the 3.55 gave it better highway legs.

Still got the bloody thing under a bench somewhere I think.

Neil

FireKraka wrote:Hi J
I put a 3.55 centre in the original diff when I still had it in my FC before I went to the dunnydoor one, the 3.55 gave it better highway legs.

Still got the bloody thing under a bench somewhere I think.

Neil

Yeah, I’m thinking 3.55 would be about right. Shame you’re so far away!

I’m guessing 3.36 would be a little too far being as I’m mostly a city dweller, but 3.89 is gonna have the Grey wailing at 100kmh or above...


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Joe,

I have a 3.36 in my otherwise bog-stock grey-powered FC (185/70-13 tyres). If you're not going to be carrying loads in the ute, I'd recommend a 3.36.
The other factor to consider is the overall diameter of your tyres. I think the original crossplies were about 24" diameter. If your new tyres are this size and you will be carrying loads from time to time, then a 3.55 would be a better bet.

Rob

ardiesse wrote: Wed Apr 11, 2018 10:47 am Joe,

I have a 3.36 in my otherwise bog-stock grey-powered FC (185/70-13 tyres). If you're not going to be carrying loads in the ute, I'd recommend a 3.36.
The other factor to consider is the overall diameter of your tyres. I think the original crossplies were about 24" diameter. If your new tyres are this size and you will be carrying loads from time to time, then a 3.55 would be a better bet.

Rob

This is helpful, thanks.

After quite a bit of trial and error with 15" Commodore rims, my ex HT Monaro 14" rims and finally deciding I will run the original 13" rims (lol), the hunt is on for white band tyres to suit. As spotted elsewhere, the Maxxis 185/80R13 tyre is probably my pick. I currently have decayed 185/75s on there, but can't find this size in white band anywhere.
By my calculations, the Maxxis tyre will be about 24 1/2 inches diameter... so my gut feeling that 3.55 is the ratio for me probably checks out. And yes, there will be driving involving steep carparks loaded up with drums, amps, roadcases and guitars, so I'd still like a useful first gear.

Running the original gear box the challenge with changing diff ratio is to calibrate the speedo. I believe 48 FX FB driven gear does an acceptable job with tall tyres and 3.55 ratio. This is the only calibration option as far as i am aware, other than the after market speedo adjuster boxes which I no nothing about.


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The speedometer driven gear units were 22-tooth unit in FX/FJ Holdens (part number 7405060), and 23-tooth unit for FE/EK Holdens (part number 7405945). This change means that the speedometer cable speed for FE/EK Holdens is some 4.3% slower than the FX/FJ Holden cable.

Changing from a FE/EK Holden driven gear unit to an FX/FJ Holden unit will spin the speedo faster, making the speedo increase reading. This is what you want to do when lowering diff ratio (eg going from 3.89 to a 3.55 centre). However, the change from 3.89 to 3.55 is an 8.7% change, so the speedo gear-swap will only do half (4.3% vs 8.7%) of the change needed. A bog-stock FB/EK with a 3.55:1 centre and the FX/FJ speedo gear will still have a speedo error of 4.4%. This is inside the margin for most engineering changes (10%).

If you put smaller tyres on the rear end, then the speedo would get closer to being correct (kinda defeats the purpose of that gear centre change though...). You would need to run a 4.4% lower diameter than the original 13" tyres. Not sure what the original diameter was... there is a pair of old Olympic Airrides under the house with the spooders, but I've never measured them.

Cheers,
Harv

These days most of us have access to very accurate speed measurement in the form of satnav equipped smartphones. As a spatial professional I can confidently say the speedo apps are accurate to better than 1km/k using Doppler principle just like the old police radar. Sorry for hijack joe.


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Harv
I am just stunned about the information that you provided please tell me it was not all in your head .
As it make me feel so deficient!
And shows why forums like this are gold!

so - who has a FX/FJ speedo gear they want to sell ?????

Errol62 wrote:These days most of us have access to very accurate speed measurement in the form of satnav equipped smartphones. As a spatial professional I can confidently say the speedo apps are accurate to better than 1km/k using Doppler principle just like the old police radar. Sorry for hijack joe.


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Haha I’m with you mate, I’m not concerned about speedo so much - I have used Speed Box on the smartphone for a while now. I’ll note the actual speed against the EK speedo and remember that

That said, I’ll eventually swap out speedo drive if I can find one. Why not eh.


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smiffy60 wrote: Wed Apr 11, 2018 4:26 pmplease tell me it was not all in your head .

Nah, I did some research into crashboxes a while back, and copied most of that out of the crashbox Guide I wrote. My head is generally full of crap .

Blacky wrote: Wed Apr 11, 2018 4:41 pmso - who has a FX/FJ speedo gear they want to sell ?????

I may have one kicking around Blacky. I gave one to one of the FE/FC newstarters a while back, not sure if it was the last one I had. Remind me by PM next week (when I am home again) and I'll take a look in the spare parts department (EKmart, Western Sydney franchise ).

Cheers,
Harv

Harv wrote: Thu Apr 12, 2018 6:16 am I may have one kicking around Blacky. I gave one to one of the FE/FC newstarters a while back, not sure if it was the last one I had. Remind me by PM next week (when I am home again) and I'll take a look in the spare parts department (EKmart, Western Sydney franchise ).

Cheers,
Harv

Cheers Harv

You can "tune" up the speedo head somewhat. There's a small weight tab on the disc that you can alter an move around to change the balance of the disc against the magnetic drive. I have managed to get the speedo with a couple of km's reading compared to GPS. Everyone now seems to be very slow now compared to before .................no tickets yet

Craig Allardyce wrote:You can "tune" up the speedo head somewhat. There's a small weight tab on the disc that you can alter an move around to change the balance of the disc against the magnetic drive. I have managed to get the speedo with a couple of km's reading compared to GPS. Everyone now seems to be very slow now compared to before .................no tickets yet

Pic_0216_027.jpg

oooh, thanks for this Craig.

This looks like (a certain kind of) fun... but I’m not game to dismantle my speedo just yet, I think my impatience to get the car running and the major bugs ironed out will mean any tinkering will happen after I reach the holy grail (ie: registration)

So many neat little tricks I’m discovering through this forum, priceless info. Cheers.


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