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Post by 60sFordGuy on May 25, 2009 21:28:06 GMT -5
After changing the 2 spd tranny to C4, with 3.00:1 rear gears, my odometer is clocking 1.25 miles for each driven mile. Will I need a driven gear with more teeth or less teeth? I didn't change the gear on the cable before connecting it to the tranny. I don't recall what color the stock one was, and didn't count the teeth. B4 I began the replacement process, I had bought a variety pack of gears, so have 5 or 6 new gears to choose from, and would like to select the correct one without making several guesses. Have most of the bugs out of the new install, and am noticing a considerable improvement of power - might be enough to get me into trouble if I don,t be careful!! The aluminum radiator is a great improvement. I have a 185* thermostat, and it is running about 175* on the gauge when the electric fan kicks in. With the speedo gear situation, and running the engine while parked, for adjustments I can't get an accurate mpg check yet. I've put about 200 miles on it, and will try to rack on at least 500 before I take it in for paint. I may get the A/C charged tomorrow.
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Post by ca on May 26, 2009 2:12:32 GMT -5
got a foggy head here tonite=(vicodin/fiorinal cocktail ), but i'ma thinkin you need a 20% reduction in teeth,right? so if you got a 20 you need to go a 16??? geeze that don't sound right. probly best to use a calculator and a formula.here's a link to TCI's calculator- www.tciauto.com/Products/TechInfo/speedo_gears.aspif thats to big of a pain then post the info you have and we can figger it out in the A.M. Ford Motorsports says-Driven Gear Teeth = (Drive Gear Teeth x Axle Ratio x Tire Rev. Per Mile) / 1000 Ford auto trans speedo gears= 16-teeth-blue (D0AZ-A),17-teeth-green (C7SZ-A),18-teeth-gray (C7SZ-B),19-teeth-tan (C7VY-A),20-teeth-orange (C8SZ-B),21-teeth-purple (D0OZ-B)
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Post by Meteorgirl on May 26, 2009 10:03:17 GMT -5
To slow the speedo down you need to ADD teeth not subtract them. If you have less, the cable spins faster. More teeth, it spins slower. I believe you say it's registering too fast (far) right? When I changed from the 2 speed to the C4 I needed 2 more teeth to get it right as I made a slight change in tire size also. Here is a link to a chart on our club website for the gears. www.fabulous50sford.com/mr/mr-7.html
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Post by 60sFordGuy on Jun 23, 2009 15:28:09 GMT -5
Okay - I changed the speedo gear from 16 teeth to 18 teeth, and I'm now clocking 1.1 miles for each mile driven. My current tire size is 205/70-14. If I change to a 19 teeth gear, would it be too much of a change, or do I need to go to a different tire size? If tire size is changed, would I likely go to a 215/70-14, or possibly 225/70-14? I have a 19 teeth gear, which would be less costly than replacing tires. As long as I'm clocking more miles/more speed, I can mentally calculate actual, and would be less apt to rack up tickets. When I still had the MM2, I was clocking the same as now (1.1/mile), so it calculates 60mph = 66mph on the speedo, 65mph = 71.5mph on the speedo, 70mph = 77mph on the speedo, etc. MG, what tire size are you running, since you only mention "a change" in size? Also, MG, do you have any more info on the Sept Winnipeg show? Due to computer change, I lost your contact info, so would appreciate if you would PM me.
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Post by Meteorgirl on Jun 23, 2009 21:48:21 GMT -5
Dug through the old notes. I actually used a 20 tooth gear and have 215/75-14 tires. I also have 3.25 gears which makes it different than yours. I think the 19 tooth will put you very close but still a little under, if you have a 20 it would be almost dead on.
You had 16, went to 18. dropped from 1.25 to 1.10.
16 / 18 = .888 1.25 * .888 = 1.11
16 / 19 = .842 1.25 * .842 = 1.05
16 / 20 = .80 1.25 * .80 = 1.00
There is only 1.5 mph diff at 60 mph between 205/70 & 215/70.
There is only 3 mph diff at 60 between 3.00 diff with 215/70 & 3.25 diff with 215/75. The latter is slower (actual car speed)
Hope this helps. Put in the 19 if you like the little leeway on the speed, leave the tires alone.
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Post by 60sFordGuy on Jun 23, 2009 23:22:05 GMT -5
Thanks, MG!!
If I had any mathematical talent, I MIGHT have come up with that formula, so am grateful for that info. I'll check to see if I have a 20 tooth gear, and install that. Mental calculations make it easier to add the 1/10th to actual speed for reading the speedometer (for my simple mind), and not needing to change tire sizes will be much more affordable. Another drawback for changing tires is my Magnum 500 wheels require lug-centric balancing, and a shop that can do that is hard to find in this area.
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Post by 60sFordGuy on Jun 26, 2009 20:18:53 GMT -5
Installed the 20 teeth gear today, and (by highway mile markers, rural cross roads at one mile intervals, and timing to the second with speedometer needle on 60mph) I'm racking up 1.0 miles in 60 seconds, each mile, at 60 mph, thanks to the calculation forumulas that MG sent ;D !! I'm also running at 2500 on the tach at 60 MPH. We are sooooo lucky to have her knowledge, and willingness to share it with us. I'm hoping to thank her personally one day, possibly at a function that is to occur in Winnipeg in September. I had hoped to have the Merc painted by now, but, due to some setbacks during my recent 5.0/C4 conversion, have had to delay that. Seems like a good time to do it will be after the "driving season", when it would normally be parked for the winter season. THANKS AGAIN, MG!!!
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Post by Biggie Smalls on May 20, 2015 18:17:00 GMT -5
Bump
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