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Speedometer gear? #2505136
06/06/18 11:10 AM
06/06/18 11:10 AM
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Doniphan, Nebraska
Lmopar69 Offline OP
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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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Pattison Texas
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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

Re: Speedometer gear? [Re: Lmopar69] #2505162
06/06/18 12:05 PM
06/06/18 12:05 PM
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Florida
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in tech archive there is a speedo pinion chart click it then click on auto trans and type in tire size and gear ratio to get tooth count needed.

28 inch tire?

I used a 225/75/15 tire size = 28.2 x 3.23 = 30 tooth pinion

sound about right as my M/Ts are 29x15x15 = 325x50x15 = 28" tall and I run a 3.23 with 30 tooth seems dead on in mine.

if your 28" is on tall side them a 31 tooth is next.

Re: Speedometer gear? [Re: Lmopar69] #2505167
06/06/18 12:19 PM
06/06/18 12:19 PM
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colorado
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savoy64 Offline
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google--dodge jeep speedo----enter the facts--including tire size and tranny gear ratios and you get everything....

Re: Speedometer gear? [Re: Lmopar69] #2505184
06/06/18 12:54 PM
06/06/18 12:54 PM
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West Coast, USA
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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)
Re: Speedometer gear? [Re: Lmopar69] #2505201
06/06/18 01:24 PM
06/06/18 01:24 PM
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Posts: 392
Doniphan, Nebraska
Lmopar69 Offline OP
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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] #2505216
06/06/18 01:55 PM
06/06/18 01:55 PM
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Florida
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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 Offline
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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.
Re: Speedometer gear? [Re: Lmopar69] #2505352
06/06/18 07:24 PM
06/06/18 07:24 PM
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Valencia, España
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With a Charger born in Chrysler assembly plant in Valencia, Venezuela
Re: Speedometer gear? [Re: Lmopar69] #2505369
06/06/18 08:39 PM
06/06/18 08:39 PM
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Posts: 392
Doniphan, Nebraska
Lmopar69 Offline OP
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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: Lmopar69] #2505389
06/06/18 10:10 PM
06/06/18 10:10 PM
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Hamtramck, PA
Alaskan_TA Offline
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The 32 is black (they are color coded also) I just installed one in a pals car.

32 tooth transmission gear pinion.JPG
Re: Speedometer gear? [Re: Lmopar69] #2505433
06/07/18 12:03 AM
06/07/18 12:03 AM
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usa
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lewtot184 Offline
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32's are pretty common.

Re: Speedometer gear? [Re: Lmopar69] #2505457
06/07/18 01:37 AM
06/07/18 01:37 AM
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Doniphan, Nebraska
Lmopar69 Offline OP
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Found a 30 in one of my automatics. That will do for now.


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Re: Speedometer gear? [Re: Lmopar69] #2505737
06/07/18 09:30 PM
06/07/18 09:30 PM
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Valencia, España
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Check ebay item 153042087853.


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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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Albany, NY
67SATisfaction Offline
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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
Re: Speedometer gear? [Re: 67SATisfaction] #2671954
06/30/19 02:44 PM
06/30/19 02:44 PM
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Sniper Offline
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Originally Posted by 67SATisfaction
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 sizes

Snipped 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.


pinion.JPG
Last edited by Sniper; 06/30/19 02:54 PM.
Re: Speedometer gear? [Re: Sniper] #2671993
06/30/19 04:39 PM
06/30/19 04:39 PM
Joined: Jan 2003
Posts: 7,538
Albany, NY
67SATisfaction Offline
The member whose name is actually Art
67SATisfaction  Offline
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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.. shocked

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
Re: Speedometer gear? [Re: 67SATisfaction] #2672002
06/30/19 04:57 PM
06/30/19 04:57 PM
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Grand Prairie,Texas
stumpy Offline
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Jack up the drivers side and you can cut down on fluid loss.

Re: Speedometer gear? [Re: 67SATisfaction] #2672010
06/30/19 05:23 PM
06/30/19 05:23 PM
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Bend,OR USA
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The early 727 push button speedometer gears are not interchangeable with the 1966 and later 727 whiney Way different in size shruggy


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Re: Speedometer gear? [Re: 67SATisfaction] #2672068
06/30/19 07:36 PM
06/30/19 07:36 PM
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Omaha Ne
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TJP Offline
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You could also have an inline ratio adapter put together similar to this
PICTURE LINK

they can speed up or slow down the speedometer. Google is your friend for a source. i have a local place that makes them up for us beer

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