13 replies to this topic

[Njc85]

Can anybody tell me what drive gear this is in my TH400

.


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[Bigfella237]

Dunno, can't see a 'steel' drive gear listed? According to the Old Holden calculator (which is now offline) there were only three different drive gears for a TH400:

 

Brown 15 teeth (Holden: 8629547 RS: n/a)

Orange 16 teeth (Holden: 8623311 RS: SG4018)

Red 17 teeth (Holden: 8629548 RS: SG4019)

 

Should be easy enough to count if you're able to turn the driveshaft, you need to count around one edge of the gear to see how many teeth start (or end) around the circumference, so you'll need to mark one of the teeth with a texta or similar then rotate the driveshaft one turn, counting as you go.

 

If you let us know the tooth count, diff ratio and rear tyre size I can crunch the numbers and hopefully come up with the closest driven gear, if that's what you're after?

[Bigfella237]

P.S. Just checked the Rare Spares website and it looks like they've discontinued all the drive & driven gears for the TH400 transmissions (at least they're no longer listed)?

 

http://www.rarespare...es & Components

[dattoman]

http://dev.chevymani...edo-gear-chart/

[arrimar]

The picture shows the output shaft, what is called the drive gear has already been removed.
Look online for references to output shaft variations rather than drive gears.
or,
count the splines along one edge of the gear.

Edited by arrimar, 18 April 2017 - 09:25 AM.

[Bigfella237]

~ what is called the drive gear has already been removed. ~

 

I'm guessing you meant to say "the driven gear"?

 

You can clearly see the drive gear in the photo, the driven gear would (normally) be attached to the cable.

[Njc85]

Thanks guys. Yes driven gear I have is a 35 tooth. Speedo is roughly out 20km/hr at 100km/hr.
So reads 120 but car actually doing 100.
265 50 15 tyres 3.55 diff gears.



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[arrimar]

Yes bigfella you're correct.

[Bigfella237]

Thanks guys. Yes driven gear I have is a 35 tooth. Speedo is roughly out 20km/hr at 100km/hr.
So reads 120 but car actually doing 100.
265 50 15 tyres 3.55 diff gears.

 

Did you ever get around to counting the number of teeth on the drive gear Nick?

 

Doing a few quick sums I'd *guess* it's currently a 15 tooth drive gear, which (with a 35 tooth driven gear) would give you a speedo reading of 119.7 @ 100kmh?

 

If so then as near I can figure, you either need a:

 

Yellow 41 tooth driven gear (Holden p/n: 1362195 Rare Spares: SG4007) for a speedo reading of 102.2 @ 100kmh

 

or a

 

Green 42 tooth driven gear (Holden p/n: 1362049 Rare Spares: SG4006) for a speedo reading of 99.7 @ 100kmh

 

Which way you go is up to you, note that a speedo will read slightly faster as the rear tyres wear too.

[V-SLR5000-P]

With a turbo 400 also be aware that you need the correct housing to hold the driven gear. A gear with more teeth has a larger diameter which moves its centre. The removable housing has cast into it the number range of teeth it will suit. As your adding 20% more teeth to the driven gear to slow it down you may need to change the gear housing too.

Edited by V-SLR5000-P, 23 April 2017 - 12:23 PM.

[Njc85]

Good info thanks big fella.
What's the equation you used to work those numbers?


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[Njc85]

Thanks V slr I did note on the housing what gears they can hold. I knew I needed a bigger gear to slow the speedo down just by how much I didn't know.
Now to get the rest of my slr gauges working.
Originally a six old owner fitted slr cluster but only volt Meter and speedo work


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[Bigfella237]

What's the equation you used to work those numbers?

 

It's all based on the OldHolden Speedo Caclulator, which used to be here but is now offline, but when it was working I crunched the numbers on a heap of different combinations and their calculator seemed to be based on 1042(ish) speedo cable rpm @ 100 km/h.

 

So working backwards, I figure out how many revolutions per kilometre your particular rear tyres do (a 265/50R15 has a circumference of 2029.5mm, which works out to roughly 492 revs per kilometre);

 

then convert that to a speed (492 x 100 (km/h) / 60 (minutes) = 820 tyre rpm @ 100 km/h);

 

then multiply that by the diff ratio to get drive shaft RPM @ 100 km/h (820 x 3.55 = 2911);

 

then divide that by the ratio of the speedo drive:driven gears and compare to the known cable RPM to see how it needs to be adjusted, for example yours was a 15:35 ratio, which gives us 1247.6 cable RPM @ 100km/h;

 

1247.6 is 119.73% faster than our target of 1042, therefore you speedo should have been reading roughly 120km/h @ 100.

 

Easy ay!

[Njc85]

Makes sense big fella. Cheers for that some great info. At least I know how to work it out now


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