Mark Allanson
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| posted on 25/11/03 at 10:32 PM |
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Swapping different T9 speedo drive cogs
Can this be done without chanding the internal worm? I have a 3.75 diff - the donor had a 3.92 running on 185 65 14 tyres, I worked out that by using
185 70 13 tyres I would have a 2.2 mph over read on the speedo at 3000rpm. I could change to 185 60 13's and read 2mph under.
If I could change to a larger toothed drive, I could guarantee a SVA pass on the speedo, and use the tyres that I want to.
Also anyone know how many teeth as standard an '89 sierra 2.0i would have?
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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paulf
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| posted on 26/11/03 at 10:46 AM |
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I am also looking into this at present ,as far as i know so far there are two drive worms and a choice of 4 pinions available which are suposedly
interchangable. I think the drive worms are the same diameter but with a different no of starts to them effectively giving a different gear ratio, the
problem is knowing which one you have fitted to start with.
I have been considering jacking up the back of the car and running the engine at a measured RPM and noting the speedo reading and then working out the
mPH per engine revs to give a check of speedo calibration. It would just need an accurrate tacho and a spreadsheet with diff ratio and rolling dia of
tyre.
Paul.
quote:
Originally posted by Mark Allanson
Can this be done without chanding the internal worm? I have a 3.75 diff - the donor had a 3.92 running on 185 65 14 tyres, I worked out that by using
185 70 13 tyres I would have a 2.2 mph over read on the speedo at 3000rpm. I could change to 185 60 13's and read 2mph under.
If I could change to a larger toothed drive, I could guarantee a SVA pass on the speedo, and use the tyres that I want to.
Also anyone know how many teeth as standard an '89 sierra 2.0i would have?
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Mark Allanson
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| posted on 26/11/03 at 09:02 PM |
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I've got a really nifty spreadsheet, which I modified from one gathered off the net. I put in a trye size calculator and the gear ratio's,
and it will give the actual speeds in any gear at any rpm. All I need to know is the number of teeth on the worm & cog - either that or go for 185
60 13's!!
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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paulf
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| posted on 26/11/03 at 11:55 PM |
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I also have a spread sheet off the net , it gives wheel and tyre sizes and one size of sierra drive gear you can modify it for different ones and i
found with a 3.89 diff and 18570 tyres i require a 25 tooth gear assuming the drive worm is as listed on the spreadsheet. I need a spreadsheet to tell
me MPH per 100 revs with a 3.89 diff and 185-70-13 tyres, i can then do a check to find what speedo drive ratio i have and what to change it to. it is
easy to work out the difference in percent of a 25 tooth gear as opposed to a 22.
Paul.
quote:
Originally posted by Mark Allanson
I've got a really nifty spreadsheet, which I modified from one gathered off the net. I put in a trye size calculator and the gear ratio's,
and it will give the actual speeds in any gear at any rpm. All I need to know is the number of teeth on the worm & cog - either that or go for 185
60 13's!!
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