speedo pinion news

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speedo pinion news

Postby silverbullet » 07 Oct 2019, 18:21

We're going to manufacture another batch of our syncro speedo pinions, each ratio being made in batches of 30 for convenience.
There will be the popular 8/21 for 4.86 final drive vans and probably some 8/19 for the 5.43 axles too.
We have stock of the 8/20 so we won't re-stock them for now.
This time round we would also like to include a quantity (30 off) of the most popular 16" type for the 6.16 final drive vans (the ratio escapes my memory!)
It's unlikely that we would ever make any for the (very rare) 5.83 axle, but if we do it will probably be a one-time offer.ImageImage

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Re: speedo pinion news

Postby Aidan » 08 Oct 2019, 06:21

21/8 is 5.43 ratio Ian along with 20/8, 4.86 ones are 18 and 19. 19 is 205 tyres so probably most useful
6.16 use 19/7 which is also used for 5.83 with 205 tyres
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Re: speedo pinion news

Postby silverbullet » 08 Oct 2019, 07:21

Thank for clarifying, I was writing without my lists to hand!
Any demand for either of the /9 ratios or the 18/8?

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Re: speedo pinion news

Postby silverbullet » 08 Oct 2019, 08:27

ETKA lists three 9/## ratios for ADM, AHU and AHT diffs
9/20, 9/21 and 9/22Image

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Re: speedo pinion news

Postby silverbullet » 08 Oct 2019, 12:25

FYI We will be making 8/19 (white), 8/21 (red) and 7/19 (brown) this time around.

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Re: speedo pinion news

Postby syncropatrick » 09 Oct 2019, 08:49

I'll check what 16" ratio I have then let you know.
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Re: speedo pinion news

Postby silverbullet » 09 Oct 2019, 12:27

They will be a few weeks yet, my advice is to keep an eye on Brickwerks shop in November.

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Re: speedo pinion news

Postby silverbullet » 09 Oct 2019, 12:31

Here's my annotated list to help identify the correct speedo pinion for a given diff code:ImageImage

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Re: speedo pinion news

Postby clift_d » 09 Oct 2019, 12:44

Great! thanks for that.
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Re: speedo pinion news

Postby syncropatrick » 12 Oct 2019, 15:32

syncropatrick wrote:I'll check what 16" ratio I have then let you know.

I'm being dim. Help!

Box rebuilt by Aidan in 2010 and changed to final drive 5.43.
However all I had at the time for the speedo drive was from the old final drive - a brown 18/8. This was been fitted to get speedo working, with the knowledge it'd never be accurate.

So now I have a 5.43 box, which would've come with a grey speedo pinion (yes ?) with had ? teeth, and the correct brass one to buy from BW is a ? with ? teeth.

Help!
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Re: speedo pinion news

Postby Aidan » 13 Oct 2019, 09:52

Patrick all you can choose from are the four 8 drives,the 18 you have is a 4.86 14" ratio tyred for 205R14Cs; normally undererads slightly on factory tyres: on 215/75/15 should be about right on speedo and under read on odo, but you run bigger tyres so it's difficult to get better with an 8 drive, really as a 5.43 16" you should be running on of the 9 drive variants to best match your tyres, that necessitates changing the drive cog on the pinion shaft as well.
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Re: speedo pinion news

Postby silverbullet » 12 Nov 2019, 08:06

I could talk to the gear cutters and see if it's possible to cut a pinion to 8/17, that would give a positive speedo correction factor of approx. 1/18 or 5.5% over the 8/18 which should accommodate the largest of tyres.

A bigger tyre turns slower for a given road speed (greater circumference means less turns to cover each km or mile) making the speedo read low. So the speedo pinion has to be turned faster to read correctly.

To do this it must have less teeth to increase its rpm and increase the reading for a given worm drive (in this case, 8 teeth driving)

I'll try and work out a equation to calculate the closest suitable ratio for a given diff, tyre and worm drive but it won't be easy or necessarily helpful if it throws up impossible drive ratios.

PS they are made from BRONZE (specifically wrought aluminium bronze, the toughest available of that material group and selected for its mechanical durability)

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Re: speedo pinion news

Postby syncropatrick » 12 Nov 2019, 13:00

:ok
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Re: speedo pinion news

Postby silverbullet » 12 Nov 2019, 19:59

So here's an example:

Take my Caravelle with 4.86 diffs and originally fitted with 205/70/14 tyres.
Speedo pinion is 8/19 (white) as standard.

The wheels will rotate 798 times for every mile (see pics below for tyre comparison)
The propshaft will rotate 798 x 4.86 times = 3878.3 times
The speedo pinion will rotate 798 x 4.86 x (8/19) = 1633 times

1633/1600 = a speedo over-read of just 2% as standard.

Changing to 215/75/15 tyres:

The wheels will now rotate 729 times per mile, a reduction of 9.5%
So the speedo pinion needs to rotate 9.5% faster to compensate and still read true road speed.
Changing to an 8/18 pinion gives
(8/18)/(8/19) = 1.055
A gain of just 5.5%, so the speedo will still read around 4% low, but its as close as you can get.

Of course, we all know that speedos read more than the original 2% low as calibrated.

The above Caravelle on part-worn 215/75/15 read within 1mph at 70 according to the satnav, suggesting that new tyres would make it slightly under-read, so this needs to be allowed for along with variations in tread depth and tyre carcass size.

Confused?

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