Speedo drive gears and ratio calcs for tyres

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Re: Speedo drive gears and ratio calcs for tyres

Postby Aidan » 12 Dec 2017, 07:58

footstuck wrote:I think I am possibly getting valve bounce at £87 :wink:
Just need to know the current Rotational value to calc how much less than £87 I need to prevent braking free of orbit. I also require a Temporary' safe value of maximum velocity, I can face the music with my chosen planetary expert when I have the funds available.
FD= 616 with .07 4th n 2058516's
Calcs to explain it, would be a good run through demo if any would be prepared please.
No naysayers at the result please :tsk
I intend to stay quiet close to the tyre size given


Electronic TDI
Taste the rainbow



Ah but which worm gear have you ?
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Re: Speedo drive gears and ratio calcs for tyres

Postby footstuck » 12 Dec 2017, 12:38

I just got a PM From Aidan :ok cheers buddy
The answer was so simple :idea , 'Borrow your mates 16" Diesel Syncro dash With Tachometer and drive it up the road'



Its all about the 16''s Baby :D
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Re: Speedo drive gears and ratio calcs for tyres

Postby silverbullet » 09 Oct 2019, 12:40

For reference.ImageImage

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Re: Speedo drive gears and ratio calcs for tyres

Postby irishkeet » 16 Apr 2020, 17:23

My speedo is not working and Ill need a new drive gear. 14" Syncro Caravelle with AVN gearbox and 4.86 final drive and 205R14 tyres, looking at the charts I will need either white or olive. Is there any way of knowing for sure, it would be nice to have it ready to fit if possible. cheers :mrgreen:
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Re: Speedo drive gears and ratio calcs for tyres

Postby silverbullet » 16 Apr 2020, 17:31

Olive 8/18 is the odd one, the only "8" ratio.

Check the front diff code.

The white gear is almost certainly the one you need.

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Re: Speedo drive gears and ratio calcs for tyres

Postby silverbullet » 16 Apr 2020, 17:36

PS the tables in the parts listings have to be read line by line, each speedo ratio listed does NOT cover all the tyre sizes and diff ratios in that block, just the ones on that line.

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Re: Speedo drive gears and ratio calcs for tyres

Postby irishkeet » 17 Apr 2020, 16:04

Cheers Ian.........I was hoping to have the answer today but I can not get the drive gear out of the diff.

Ive removed the diff, can get it to turn around but very tight......any tips on removing would be appreciated :ok
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Re: Speedo drive gears and ratio calcs for tyres

Postby Aidan » 18 Apr 2020, 12:13

helps to have a spare old speedo drive cable you can use the 27mm hex cap to pry against once you have punched out the roll pin that retains the drive sleeve, 5mm parallel punch to punch out the roll pin after soaking with plusgas or other suitable penetrating oil/rust breaker, it is easy to break the case using the wrong tools, if your punch is too small it can go into the roll pin and expand it till the corner breaks off the case, also easier if you remove the nosecone where the VC lives to give you good access so you can hold the punch straight and get good thunk with the heavy hammer on the punch without twating your fingers or getting them trapped against the nose cone, Stand the diff on the fat end and a piece of 3x2
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Re: Speedo drive gears and ratio calcs for tyres

Postby irishkeet » 18 Apr 2020, 14:53

Aidan wrote:helps to have a spare old speedo drive cable you can use the 27mm hex cap to pry against once you have punched out the roll pin that retains the drive sleeve, 5mm parallel punch to punch out the roll pin after soaking with plusgas or other suitable penetrating oil/rust breaker, it is easy to break the case using the wrong tools, if your punch is too small it can go into the roll pin and expand it till the corner breaks off the case, also easier if you remove the nosecone where the VC lives to give you good access so you can hold the punch straight and get good thunk with the heavy hammer on the punch without twating your fingers or getting them trapped against the nose cone, Stand the diff on the fat end and a piece of 3x2


cheers Aidan, I have spent ages trying to get the speedo drive out with no joy. Roll pin is out and I can get it to turn but its very stiff. I was chatting with Gordon today and he had the idea of nose off to access the speedo drive from inside, bloody thing wont budge :roll:
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