Ford F834 Posted November 9, 2017 Share Posted November 9, 2017 I've been pouring over the Garagemahal web pages on speedometer drive gears and driven gears and I think I need help... My particular combination does not exist in the charts (donor was a 1982 with a Borg Warner 1345 and 3.00 axle gears). But I can see that the taller the gearing the more teeth were on the drive gear. The Warner TC got 6, 7 or 8 tooth gears, so my bet is on the yellow 8 tooth gear: E1TZ-17285-A.... Great. It's obsolete and I can't find one. Down the chart a ways in the 87/88 section it shows another 8 tooth gear for the 1345 that was for use with 3.08-3.55 gears, but the part number says "TBD". So was the E1TZ-17285-A replaced with something else? Would I need a different driven gear to go with it? I have not even tried to figure out the right driven gear yet for my oversized tires, but even if I am a certain % off it will be better than no speedometer at all. So any help with sources for the drive gear or possible brick nose substitutes would be appreciated. Also, the E1TZ-17285-A is not in the drive gear types chart, but the 7 tooth one is, and according to that it should be a type 12 gear. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 9, 2017 Share Posted November 9, 2017 Jonathan - What tires will you be running? I can do some math to figure out what gear you would need with a 7-toothed gear and then we can see if that is available. And, I’ll also look for the 8-toothed gear. Which reminds me, did you ever hear back from Bill/NumberDummy? I was traveling when you asked and had forgotten until now. Link to comment Share on other sites More sharing options...
1986F150Six Posted November 9, 2017 Share Posted November 9, 2017 Jonathan, I am certain someone will be able to answer your question and perhaps even supply the part, but I will share something that happened to me. My son's 1984 with manual O.D. was born with 2.47 rear gears. A change to 3.55 gears was rather dramatic. Before knowing about the different gear possibilities, the truck was taken to a shop which specialized in this sort of thing. At that time, they were the shop [Atlanta area] which calibrated the speedometers of Highway Patrol cars. They cut the speedometer cable and installed a small device which had internal gears [like a transmission] which adjusted the speed of the speedometer cable and certified the speedometer to read 55 mph @ 55 mph. This device has been in place since about 2000 and has had zero problems. Link to comment Share on other sites More sharing options...
Ford F834 Posted November 9, 2017 Author Share Posted November 9, 2017 Jonathan - What tires will you be running? I can do some math to figure out what gear you would need with a 7-toothed gear and then we can see if that is available. And, I’ll also look for the 8-toothed gear. Which reminds me, did you ever hear back from Bill/NumberDummy? I was traveling when you asked and had forgotten until now. Gary, I have 31x10.5's on there now. But they measure 30" when new, 29" when used up a bit. I hope to ditch these now that I found some 5 lug 16" rims and run 235-85/R16's which specify a diameter of 31.72". That said, for now I just want to get it working at a reasonable cost. Like I said, if it's off calibration I will worry about that once I get the tires and wheels. David, I have seen what you are talking about. They are ratio adapters. I was not aware that they are adjustable. They look to be ~$85-$150 in price, and may require special speedometer cables. If I can't get it close with the plastic gears then I will look into this once I have the bigger wheels. Link to comment Share on other sites More sharing options...
PetesPonies Posted November 9, 2017 Share Posted November 9, 2017 Gary, I have 31x10.5's on there now. But they measure 30" when new, 29" when used up a bit. I hope to ditch these now that I found some 5 lug 16" rims and run 235-85/R16's which specify a diameter of 31.72". That said, for now I just want to get it working at a reasonable cost. Like I said, if it's off calibration I will worry about that once I get the tires and wheels. David, I have seen what you are talking about. They are ratio adapters. I was not aware that they are adjustable. They look to be ~$85-$150 in price, and may require special speedometer cables. If I can't get it close with the plastic gears then I will look into this once I have the bigger wheels. There are two ways to calculate this. I can do or help with either. You can use a formula or some easy linear math. Do you know how much your speedo is off right now? There are apps for phones that will tell you how fast you are going. Link to comment Share on other sites More sharing options...
Ford F834 Posted November 9, 2017 Author Share Posted November 9, 2017 There are two ways to calculate this. I can do or help with either. You can use a formula or some easy linear math. Do you know how much your speedo is off right now? There are apps for phones that will tell you how fast you are going. Right now my speedometer does not work at all. I suspect the problem is the drive gear, as I felt inside the cable port and it feels worn like an apple core. So my plan was to replace it and see from there. I've done a LOT of gear ratio and rpm math but I've not done anything with speedometers until now. Link to comment Share on other sites More sharing options...
Ford F834 Posted November 9, 2017 Author Share Posted November 9, 2017 Right now my speedometer does not work at all. I suspect the problem is the drive gear, as I felt inside the cable port and it feels worn like an apple core. So my plan was to replace it and see from there. I've done a LOT of gear ratio and rpm math but I've not done anything with speedometers until now. Gary, I never did hear anything back from Mr. NumberDummy. Link to comment Share on other sites More sharing options...
1986F150Six Posted November 9, 2017 Share Posted November 9, 2017 Gary, I never did hear anything back from Mr. NumberDummy. Mr. NumberDummy is away from his computer until Friday. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 9, 2017 Share Posted November 9, 2017 Mr. NumberDummy is away from his computer until Friday. David - Are you working the Bill/ND thing? Jonathan - Using the spreadsheet that can be downloaded at Driveline/Transmissions/Speedometer Gears I ran calc's for the 6, 7, and 8-toothed gears, as shown below. (Note that it doesn't matter what you stick in for the "Speedo driven gear tooth count" in blue.) And the result is that a 6-toothed drive gear requires a 12-toothed driven gear. But the smallest I've seen is a 16, so this won't get even close w/o an adapter. The 7-tooth takes a 14, which still requires an adapter. And the 8 requires a 16, but even then it is reading 52 MPH at a true 60. Link to comment Share on other sites More sharing options...
Ford F834 Posted November 9, 2017 Author Share Posted November 9, 2017 David - Are you working the Bill/ND thing? Jonathan - Using the spreadsheet that can be downloaded at Driveline/Transmissions/Speedometer Gears I ran calc's for the 6, 7, and 8-toothed gears, as shown below. (Note that it doesn't matter what you stick in for the "Speedo driven gear tooth count" in blue.) And the result is that a 6-toothed drive gear requires a 12-toothed driven gear. But the smallest I've seen is a 16, so this won't get even close w/o an adapter. The 7-tooth takes a 14, which still requires an adapter. And the 8 requires a 16, but even then it is reading 52 MPH at a true 60. Gary, it looks like I will indeed need some kind of ratio adjuster when I go to the larger wheels and tires... but in the meantime if I use an 8 tooth drive and 16 tooth driven gear the speedometer should read exactly right (current tires measure 30"). As much of a horrible pain in the butt as it would be, I might even try to find a junkyard gear. I don't want to get too invested in this whole thing because I may switch transfer cases and add the overdrive later. If that happens I will need the drive gear that fits the overdrive, not the TC. Both Gear Vendors and Doug Nash use GM parts so I will be starting over. The ratio adjusters are a little pricey so if I buy one I want it to jive with the OD unit. 🙄 Link to comment Share on other sites More sharing options...
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