Speedometer gear help

[Ford F834]

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.

[Gary Lewis]

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.

[1986F150Six]

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.

[Ford F834]

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.

[PetesPonies]

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.

[Ford F834]

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.

[Ford F834]

Gary, I never did hear anything back from Mr. NumberDummy.

[1986F150Six]

Mr. NumberDummy is away from his computer until Friday.

[Gary Lewis]

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.  

[Ford F834]

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.
🙄

[Gary Lewis]

Interesting.  I get that you'll be indicating 61.916 @ a true 60.000 MPH.  But, that's close enough for me.

Anyway, maybe you can get it going with soon and it'll work w/your current tires.  And then, as you said, when you do the O/D do the tires at the same time and adapt to that.  

[Ford F834]

Gary, in your calculators you have 3.07 entered as the final drive ratio. My rear axle is 3.00 so that's probably where the variance is coming from.

[Gary Lewis]

Good catch.  With 3.00 I get 60.504.  

[Ford F834]

That's what I get and it will work for me if I can find the gears!

[Gary Lewis]

I can't find that gear either.  But I submitted a question to Midwest Transmissions to see if they have it.  They don't show to even have parts for the 1345, but they do for the 1356.  In fact they have an 8-toothed gear for the 1356, but it is brown.

[PetesPonies]

No ratio adjuster needed, thats where the simple linear math is used. But I need a starting point. You need to drive the vehicle with a working speedo . .  and know which driven gear you have in place.

[Gary Lewis]

Pete - That’s just the point. The speedo doesn’t work and it appears it is the drive gear. So he’s just figuring out what gear he needs. Unfortunately it looks like one that is hard to find.

[1986F150Six]

Gary Lewis wrote

I can't find that gear either.  But I submitted a question to Midwest Transmissions to see if they have it.  They don't show to even have parts for the 1345, but they do for the 1356.  In fact they have an 8-toothed gear for the 1356, but it is brown.

Would this work?

http://dennis-carpenter.com/speedometer-drive-gear/p/E0TZ-17285-B/

[Gary Lewis]

David - I did a search for the one Jonathan thinks he needs, E1TZ-17285-A, and got the same one and thought yippee!  And then I realized it is E0TZ-17285-B. 😩

A few months ago I wouldn’t have had a clue why you can do a “verbatim” search for “E1TZ-17285-A” and find E0TZ-17285-B. But now that I’ve been trying to boost the search results of this website I know - someone put E1TZ-17285-A in the meta data for the page, so that’s what Google thinks is on the page. 😡

I’m going to call Dennis Carpenter and complain because those part numbers don’t interchange. Further, they show the application as for all 1980-86 trucks. But there are 9 other gears for those trucks, so that is inaccurate.

[Ford F834]

Unfortunately Gary is right, that gear won't fit the transfer case. The 1345 takes a type 12 gear:



I actually went into the Cottonwood Ford dealer today rather than just the phone call. The guy searched dealerships nation wide and it is unobtanium. Looks like I will have to junkyard it or install one of my overdrives and hope I have better luck sourcing those drive gears. 🙄

Thank you David, for helping me look!