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Old 08-15-2004, 20:22   #1 (permalink)
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XC Falcon speedo gear, which one?

i've got an xc falcon that i have recently fit a ford T5 (from an ED XR8) behind a 351C. Obviously the speedo gear needed changing, so i went and visited the local ford dealership, told them my situation also noting that i have a 2.92 diff ratio. They sold me a pink gear drive (19 teeth) and my speedo reads 110kmh when i'm actually travelling 100kmh. If anyone can accuratley tell me whether i need a brown (20 teeth) or a green (21 teeth) speedo gear it would be much appreciated!!!
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Old 08-15-2004, 22:04   #2 (permalink)
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Re: XC Falcon speedo gear, which one?

ok, no one is responding and i want to get a replacement gear today. Can I get some peoples opinions on whether my below math is logical as to which gear I should buy:

brown (20 teeth) = 1 extra tooth / current 19 teeth = 5.79% decrease in speedo cable revs. Therefore 110kmh x 5.79% reduces to 103.631 kmh

green (21 teeth) = 2 extra teeth / current 19 teeth = 10.52 % decrease in speedo cable revs. Therefore 110kmh x 10.52% reduces to 98.428 kmh

seems the green is probably a little more accurate (before g/box conversion my speedo read 96 when doing 100) so if no-one can trip up my math logic, i'll go buy GREEN.
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Old 08-15-2004, 22:15   #3 (permalink)
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Re: XC Falcon speedo gear, which one?

Sounds right. Do they make a 22 or 23 teeth drive? My mate runs the same rear gears as me yet his speedo's still 10k roughly out. He runs a 21 tooth gear.

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Old 08-15-2004, 22:25   #4 (permalink)
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Re: XC Falcon speedo gear, which one?

these is atleast one more, not sure it just goes to 22 or 23 though. the 21 tooth is supposed to be for a 3.43 diff ratio, so even shorter diff for the 22/23 teeth drive.
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Old 08-29-2004, 14:53   #5 (permalink)
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Re: XC Falcon speedo gear, which one?

I wouldn't be worried about the speedo being wrong. I seriously doubt the box will live long enough with a 2.92 diff to worry you.
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Old 08-29-2004, 15:44   #6 (permalink)
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Re: XC Falcon speedo gear, which one?

Yup. Be interested to see how long the T5 lasts behind a 351C, given that you can kill a T5 behind a reasonably strong 289 or 302w.....

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Old 08-29-2004, 15:50   #7 (permalink)
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Re: XC Falcon speedo gear, which one?

Don't forget that tyre sizes also affect speedo readings.
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Old 08-29-2004, 22:47   #8 (permalink)
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Re: XC Falcon speedo gear, which one?

"Be interested to see how long the t5 lasts behind a 351 C"

A V8 T5 is rated to a minimum of 250rwkw, and the guy I got the T5 from had it behind a 351C producing around 350rwkw. Please explain to me how a mild 351C would not last!?!?!
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Old 08-30-2004, 00:27   #9 (permalink)
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Re: XC Falcon speedo gear, which one?

The T5 in the XR6T is a higher spec version than the one you have, and I have replaced a number of them after 2000km with 270rwkw. The EDXR8 box was never good for that output, but you will help it live by running a lower diff, ie about 3.45.
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Old 08-30-2004, 19:48   #10 (permalink)
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Re: XC Falcon speedo gear, which one?

How did you manage to wreck the gearboxes? I've heard of one guy who stripped the input shaft of an XR8 box with a monster Clevo, but never heard of any problems otherwise! My mechanic ensures me that the gearbox could handle up to 300kw without any dramas, regardless of the diff ratio, and he is a vastly knowledgeble mechanic.
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