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[Torviki] How to get your speedo reading correctly


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#1 _CHOPPER_

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Posted 14 March 2007 - 09:33 PM

Firstly I will assume you have a speedo that needs 621 revolutions of the speedo cable to add 1 km to your odometer, or 1000 revolutions for a mile. This is true for Toranas and Kingswoods. It also applies to many other GMH vehicles. There is sometimes a number printed on the speedo face near the bottom. If it says 621, you're in business.

Secondly I will assume you have a Trimatic or an Aussie 3 or 4 speed gearbox.

Thirdly, I will assume you have either a banjo or a Salisbury diff.

If so, let's proceed.

There are three different gears on the gearbox output shaft.

6 tooth brown
8 tooth white
9 tooth blue

Then there are 8 different gears on the end of the speedo cable.

18 tooth tan
19 tooth pink
20 tooth white
21 tooth green
22 tooth dark blue
23 tooth red
24 tooth yellow
25 tooth light blue

Rare Spares don't list an 18 tooth tan gear, but I have one in my garage. The following is a list of the optimum tyre diameters for the various diff ratio/driven gear/drive gear combos. Tyre diameters are limited to what one would expect to see from the factory for 6 cyl and V8 Toranas and Kingswoods.

9 tooth blue drive gear:

2.60:1

19T 630.9 mm
20T 599.4 mm

2.78:1

20T 640.8 mm
21T 610.3 mm

3.08:1

22T 645.5 mm
23T 617.4 mm

3.36:1

24T 645.5 mm
25T 619.6 mm

8 tooth white drive gear:

2.78:1

18T 632.9 mm
19T 599.6 mm

3.08:1

20T 631.1 mm
21T 601.1 mm

3.36:1

22T 625.9 mm
23T 598.7 mm

3.55:1

23T 631.7 mm
24T 605.4 mm

3.9:1

25T 639.4 mm

6 tooth brown:

3.9:1

19T 630.9 mm
20T 599.4 mm

4.44:1

21T 650.5 mm
22T 620.9 mm

To work out your tyre diameter, there are many online calculators. Or do it yourself with basic maths as in the following example.

205/65R15

(205 x 0.65 x 2) + (15 x 25.4)

This will give you a diameter of 647.5 mm if you did it correctly.

#2 _ChiaLX_

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Posted 14 March 2007 - 09:40 PM

Can mods put this in a sticky or in the tech section. Very good info Chopper thanks for sharing. :spoton:

#3 _CHOPPER_

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Posted 15 March 2007 - 12:49 AM

If you are one of the few people who use light truck tyres, such as a 185R14LT 8PR, you will notice there is no profile in the tyre size. With sizes such as 175R13 or 185R14, they are generally an 82 profile.

#4 _MAWLER_

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Posted 27 March 2007 - 01:14 PM

You said Chop you were working on banjo and sals diffs. Is there any difference for 9" diffs? As the 9" is a very popular conversion, perhaps it would be helpful to cover it as well...

#5 _jap-xu1_

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Posted 29 March 2007 - 04:26 PM

great info for sure
i would have thought that the type of diff is irrelevant.
i mean they all turn a certain amount of times in relation to the driveshaft,brand or style of diff shouldnt matter

#6 _CHOPPER_

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Posted 29 March 2007 - 07:02 PM

The differences with the 9" is the ratios, which alters the results. I will not be compiling a list for all the various 9" ratios.

#7 EFI Torana Man

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Posted 27 September 2016 - 02:07 PM

Yep got 2.92 borgwarner th350 and 14inch tyres running the biggest driven gear that just fits in hole changed drive gear to suit now at 95km speedo says 85km got to get within 10%

#8 Bigfella237

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Posted 27 September 2016 - 03:21 PM

A 10yo thread resurrection, well done! ;)

 

We would need to know your exact rear tyre size to work out the revolutions per km, if you give me that then I'll crunch the numbers and figure out which speedo gears should get you close?

 

By the sounds of it you may need to pull the extension housing of the trans and change the driven gear too?



#9 kiwi-lilj

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Posted 27 September 2016 - 04:01 PM

What happened to chopper ?



#10 LHSL308

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Posted 27 September 2016 - 07:31 PM

What happened to chopper ?

 

Pretty sure he was banned a few years ago.



#11 gtrboyy

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Posted 27 September 2016 - 08:33 PM

Thread dig aye...haha

 

Tim the gears ol' chop chop posted about are for trimatic or m20 gearbox not for th350...no biggie.

 

google 'speedo gear calculator th350'

 

You'll need to know actual wheel diameter & both drive/driven gears then can work out which ones needed to correct speedo.



#12 rodomo

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Posted 27 September 2016 - 09:11 PM

He didn't get banned......he just dropped off the radar.................personal issues and the like.

#13 LHSL308

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Posted 27 September 2016 - 11:16 PM

He didn't get banned......he just dropped off the radar.................personal issues and the like.

 

Poor bloke. Hopefully he's doing better these days.



#14 Uncle Chop Chop

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Posted 09 October 2016 - 02:22 PM

I know John (chopper) from the mens shed. Its been 11 years since that car crash. Despite what all the doctors reports said, he is on the mend.



#15 _Ivan_

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Posted 23 November 2016 - 04:57 PM

i have 215/ 50/ 13 and it worked out to around 545 and I could not find that, as  am also running A W50 toyota box with 3.08 diff



#16 N/A-PWR

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Posted 23 November 2016 - 05:06 PM

Never knew that Vick,

 

 great news.

 

I know John (chopper) from the mens shed. Its been 11 years since that car crash. Despite what all the doctors reports said, he is on the mend.



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#17 Bigfella237

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Posted 23 November 2016 - 08:19 PM

i have 215/ 50/ 13 and it worked out to around 545 and I could not find that, as  am also running A W50 toyota box with 3.08 diff

 

Ivan, I entered your tyre size (215/50R13) into my calculator and I get 583 revolutions per kilometre (if that's what you're asking)?

 

I have no idea what speedo gears come in a W50 or where you would get different sized gears, but you should still be able to count the teeth... these are the closest I come to accurate with your tyre size and diff ratio:

 

If your drive gear is 7 teeth then the driven should be 20 teeth (speedo reads 100.5km/h @ 100)

If your drive gear is 8 teeth then the driven should be 23 teeth (speedo reads 99.9km/h @ 100)

 

Although with a Toyota box you might be better off looking at one of those speedo adapters that go into the cable?



#18 Uncle Chop Chop

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Posted 24 November 2016 - 01:47 PM

I think the Toyota boxes have more like 30 teeth on the driven gear, but don't quote me.



#19 Bigfella237

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Posted 24 November 2016 - 07:49 PM

Okay, as you can see the speedo drive ratio is around 2.875 to 1 for that particular tyre/diff combo, so if you have a 30 tooth driven gear then you need a 10 tooth drive gear (it actually comes out to 10.435 teeth so maybe an 11 tooth gear would do)?



#20 _ASLTO_

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Posted 29 November 2016 - 04:29 PM

Hey Drew,

I could do with your assistance mate !

Crunch this... I've got 205/60 R13's, 3:55 ratio diff, off a M20 box.. car is an LJ, red 6..

On the highway I'm doing around 3,000 rpm and the speedo's showing I'm doing around 130kph PLUS when I'm actually doing somewhere just above 100kph..

please help !

P.S. Don't know Uncle Chop Chop at all but.. Get better soon mate, it's people like you that have invaluable information that can pass it on the next generations of car enthusiasts..

#21 Bigfella237

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Posted 29 November 2016 - 07:50 PM

I've got 205/60 R13's, 3:55 ratio diff, off a M20 box.. car is an LJ, red 6..

On the highway I'm doing around 3,000 rpm and the speedo's showing I'm doing around 130kph PLUS when I'm actually doing somewhere just above 100kph..

 

G'day Ian (sorry, I thought we were shortening names here now),

 

It will depend on which drive gear is inside the gearbox, if you remove the speedo cable and look inside the hole you should be able to identify the colour of the drive gear on the output shaft. You may even need to change this drive gear depending on whether you can find an appropriate driven gear?

 

If you have the red 7 tooth drive gear, the closest I come is the dark blue 22 tooth driven gear, which should read 99.7km/h @ 100

 

Or if you have the white 8 tooth drive gear, the closest I come to is the light blue 25 tooth driven gear, which should read 100.3km/h @ 100

 

None of the other drive gears even get close with such a low diff ratio. Looks like the red drive gear is not available from Rare Spares but the white one is, along with a variety of driven gears... see here:

 

http://www.rarespare...OMPONENTS&pno=3

 

If your speedo is currently reading 130km/h @ 100 then I'd guess you either have a white drive gear with a pink driven gear, or a blue drive gear with either a dark blue or green driven gear?

 

EDIT: My gear ratio calculator says that with your tyre size, in fourth gear, a 3.55:1 diff should be doing 3,266 RPM @ 100km/h

 

A 3.36:1 diff ratio would be doing 3,091 RPM @ 100km/h

 

Tyre Size = 205/60R13
Tyre Revolutions = 552 per km
Gear Ratio = 1.00 : 1
Diff Ratio 2.60 : 1 = 2392 RPM @ 100km/h
Diff Ratio 2.78 : 1 = 2558 RPM @ 100km/h
Diff Ratio 3.08 : 1 = 2834 RPM @ 100km/h
Diff Ratio 3.36 : 1 = 3091 RPM @ 100km/h
Diff Ratio 3.55 : 1 = 3266 RPM @ 100km/h
Diff Ratio 3.70 : 1 = 3404 RPM @ 100km/h
Diff Ratio 3.90 : 1 = 3588 RPM @ 100km/h
Diff Ratio 4.11 : 1 = 3781 RPM @ 100km/h

Edited by Bigfella237, 29 November 2016 - 07:59 PM.


#22 Bigfella237

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Posted 29 November 2016 - 08:11 PM

Bloody hell, ran out of "edit time" again...

 

Just for interest sake, your shift points for that combo (at 5000 RPM) should be:

 

 

Tyre Size = 205/60R13
Tyre Revolutions = 552 per km
Diff Ratio = 3.55 : 1
5000 RPM in 1st Gear (3.05 : 1) = 50 km/h
5000 RPM in 2nd Gear (2.19 : 1) = 70 km/h
5000 RPM in 3rd Gear (1.51 : 1) = 101 km/h
5000 RPM in 4th Gear (1.00 : 1) = 153 km/h
5000 RPM in Rev Gear (3.05 : 1) = 50 km/h

 

Brians_Gear_Calc.jpg


Edited by Bigfella237, 29 November 2016 - 08:12 PM.


#23 _ASLTO_

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Posted 29 November 2016 - 09:22 PM

Thanks for that detailed info Andrew !

apologies for the abbreviation..

at looking at the gear shift chart I'm thinking that my box may be an M21 as I'm sure I get more speed out of 1st & 2nd then what the computer says, though I may be wrong. The upcoming recondition will tell..

I am going to look into the colours of the driven & drive gear this weekend now that you've given me the info I needed to try and sort it out.

Your also making me think with the final drive rpm's you've calculated that my tachometer might also be out? What checks can I do to verify that it's reading correctly?

Thanks again for al your help mate !

#24 N/A-PWR

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Posted 29 November 2016 - 09:32 PM

Go to a 5 km roadside marker 'Start and Finish',

 

 look at the speedo distance reading,

 

 do the 5 K, and re-check speedo distance reading.

 

 

If you have Miles, 5 K is 3.1 Miles :)



or the calc is 5000 divided by 1.6 = 3.125

 

 

 

 

When the correct gears are in,

 

 the distance reading is right, and the speedo speed reading is right.

 

 

Then if everyone is overtaking you, the speedo speed reading is wornout!


Edited by N/A-PWR, 29 November 2016 - 09:45 PM.


#25 Bigfella237

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Posted 29 November 2016 - 10:49 PM

looking at the gear shift chart I'm thinking that my box may be an M21 as I'm sure I get more speed out of 1st & 2nd then what the computer says

 

Are you absolutely sure you've got a 3.55 diff and not a 3.36?






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