Speedometer gear?
#2505136
06/06/18 11:10 AM
06/06/18 11:10 AM
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Joined: Oct 2010
Posts: 392 Doniphan, Nebraska
Lmopar69
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OP
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Doniphan, Nebraska
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My speedo was dead perfect with 3.91 gears. I swapped in 3.23s last night to make it a bit more cruiser friendly. Anyone know which speedo gear I need to put in now? Is there a calculator out there that helps figure it out?
So my best guess from what I have found is with a 28" tall tire and 3.23s I will need a 31 tooth green gear.
Laine
Last edited by Lmopar69; 06/06/18 11:20 AM.
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Re: Speedometer gear?
[Re: Lmopar69]
#2505151
06/06/18 11:40 AM
06/06/18 11:40 AM
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Joined: Aug 2011
Posts: 2,843 Pattison Texas
CSK
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confirm what gear you have now & then do the math
1968 Charger COLD A/C Hilborn EFI 512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim 2020 T/A 392 Stock 11.79 @ 114.5
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Re: Speedometer gear?
[Re: Lmopar69]
#2505184
06/06/18 12:54 PM
06/06/18 12:54 PM
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Joined: Mar 2007
Posts: 3,275 West Coast, USA
jbc426
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Download a GPS based speed app on your phone, take the car out and compare indicated speed with the phone app at 30, 60 and 90 mph, do the math to calculate how much of a tooth decrease /increase you need.
Be sure to take 3 or more readings from slow to fast. and pick a range that is closest to where you drive most.
ie {@ 30mph indicated, GPS shows 25mph = 1.2
1.2 x what you have in there now = adjusted tooth count count.
For me, Freeway speeds can be hardest to judge consistently when the car has overdrive.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Speedometer gear?
[Re: Lmopar69]
#2505201
06/06/18 01:24 PM
06/06/18 01:24 PM
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Joined: Oct 2010
Posts: 392 Doniphan, Nebraska
Lmopar69
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This one is a 3 speed manual trans. From what I can tell, either a 30 or a 31. Time to start pulling speedo gears out of all my transmissions that I have sitting around and see if I can find one.
Thanks for the help fellas.
Laine.
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Re: Speedometer gear?
[Re: Lmopar69]
#2505266
06/06/18 03:34 PM
06/06/18 03:34 PM
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lewtot184
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I use a 32 with 3.23 gears and 27.5" tires. I think the speedo may be slightly fast with this combo. something to keep in mind is the factories had the speedo's set a little fast and the feds forced them to provide accurate speedometers. I think the factory charts are some what off in favor of the factories and their warranties.
Last edited by lewtot184; 06/06/18 03:36 PM.
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Re: Speedometer gear?
[Re: Lmopar69]
#2505369
06/06/18 08:39 PM
06/06/18 08:39 PM
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Joined: Oct 2010
Posts: 392 Doniphan, Nebraska
Lmopar69
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I found a 34 in a 4 speed I have laying around. Thats the closest Ive found to what I need. So far still no 31 or 32. More to check. ;-)
Laine.
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Re: Speedometer gear?
[Re: NachoRT74]
#2671950
06/30/19 02:30 PM
06/30/19 02:30 PM
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Joined: Jan 2003
Posts: 7,538 Albany, NY
67SATisfaction
The member whose name is actually Art
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The member whose name is actually Art
Joined: Jan 2003
Posts: 7,538
Albany, NY
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Are switching speedo gears the only reliable way to adjust an inaccurate speedo?
I used the calculator chart above to get an estimate of 27 teeth I should need with 225/70-14 tires and a 2.76 rear diff ratio.. I'm coming up with 6.2" sidewalls, plus 14" rims = 26.4" tire diam. With a 2.76 diff, the result is 27 teeth for the speedo gear.. is that how it works?
The speedo in our '65 with cable-shift 727 automatic is indicating about 10% too fast (reads 90mph when actual is more like 80). I'll pull the current gear and compare number of teeth in the car..
Thanks, - Art
Last edited by 67SATisfaction; 06/30/19 02:44 PM.
65 Satellite hardtop 361/4bbl console 727 2.76 67 Satellite convert 383/2bbl column 727 3.23 67 Lancia Fulvia Sport 1.3 Zagato. Alloy body, 1.3L V4 DOHC 4-spd 67 Lancia Fulvia Rallye 1.3. Alloy panel, 1.3L V4 DOHC 4-spd 71 Alfa Romeo GT Junior 1300 Zagato, 1.3L 4cyl DOHC hemi 5-spd 82 Alfa Romeo GTV6 2.5L SOHC hemi V6 5-spd transaxle 75 Maserati Bora US spec 4.9L DOHC hemi V8 5-spd ZF 77 Maserati Khamsin Euro spec 4.9L DOHC hemi V8 5-spd ZF 07 Aston Martin DB9 6.0L DOHC V12 6spd transaxle
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Re: Speedometer gear?
[Re: 67SATisfaction]
#2671954
06/30/19 02:44 PM
06/30/19 02:44 PM
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Joined: May 2019
Posts: 6,175 nowhere
Sniper
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Are switching speedo gears the only reliable way to adjust an inaccurate speedo?
I'll use the calculator chart above to get an estimate of what teeth count I need with 225/70-14 tires and a 2.76 rear.. then compare to the current speedo gear in the car..
The speedo in our '65 with cable-shift 727 automatic is off by about 10% too fast (reads 90mph when actual is more like 80). So if I count the teeth on the current speedo cable gear, I figure I have to find a replacement with 10% fewer teeth. is that how this works?
Thanks, - Art That chart is not accurate for the 65 style speedometer pinions. Conversion to modern tire sizesSnipped from the 65 Plymouth FSM Looks like you need a 17 Orange pinion, assuming you don;t already have that. The coverage spread is kind of wide. Brewer's has used, $80.
Last edited by Sniper; 06/30/19 02:54 PM.
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Re: Speedometer gear?
[Re: Sniper]
#2671993
06/30/19 04:39 PM
06/30/19 04:39 PM
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Joined: Jan 2003
Posts: 7,538 Albany, NY
67SATisfaction
The member whose name is actually Art
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The member whose name is actually Art
Joined: Jan 2003
Posts: 7,538
Albany, NY
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Thank you, That's a tremendous time saver - I have the FSM too and will have a close look. Based on the tire sizes on that FSM chart, it looks like my speedo reading is high due to smaller tire size I've chosen. That would make sense because nothing else was changed from stock. If I recall correctly, all the tranny oil will want to leak out when I pull that gear & cable coupling with the O-ring out of the tranny case... or maybe that was the shifter cable... ..either way I'll double check the FSM before I start.. ...it's been 4 years since I finished the resto and I shouldn't trust my recall on such details.. Thanks again, - Art
Last edited by 67SATisfaction; 06/30/19 04:44 PM.
65 Satellite hardtop 361/4bbl console 727 2.76 67 Satellite convert 383/2bbl column 727 3.23 67 Lancia Fulvia Sport 1.3 Zagato. Alloy body, 1.3L V4 DOHC 4-spd 67 Lancia Fulvia Rallye 1.3. Alloy panel, 1.3L V4 DOHC 4-spd 71 Alfa Romeo GT Junior 1300 Zagato, 1.3L 4cyl DOHC hemi 5-spd 82 Alfa Romeo GTV6 2.5L SOHC hemi V6 5-spd transaxle 75 Maserati Bora US spec 4.9L DOHC hemi V8 5-spd ZF 77 Maserati Khamsin Euro spec 4.9L DOHC hemi V8 5-spd ZF 07 Aston Martin DB9 6.0L DOHC V12 6spd transaxle
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