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Unread 12-26-2013, 10:45 PM   #1
SouthernGypsy
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Speedo Gear

While changing the fluid in my 1983 CJ7's T-5 today I took them time to pull my speedo gear to see what I had in it now, mine is RED and marked 26, and a count of the teeth verify that it has 26 teeth.

My speedo shows 5 MPH slower than my actual speed and I need to correct it for 30x9.50x15 tires to correct the speedo with my 2.73 gear ratio.


Now that I know what gear is in it now, can anyone tell me which gear I need to order to correct my speedo, and who sells them?
-

img_1413.jpg  
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Unread 12-26-2013, 11:50 PM   #2
Spieg8
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Lots of threads on this if you search...

Here is the formula (works better when you mesure at highway speeds);

speedometer reading / GPS reading X current tooth count = accurate tooth count

Example 1 –
60 mph on speedometer and 65 mph actual on GPS. You need to speed the speedometer up so you need a gear with fewer teeth.

60/65 = .923
Multiply this by your current tooth count (34 in this example).
34 x .923 = 31.38

A 31 tooth gear would be the closest. Speedometer would read just slightly faster than actual speed.
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Example 2 –
65 mph on speedometer and 60 mph actual on GPS. You need to slow the speedometer down by installing a gear with more teeth.

65/60 = 1.083
Multiply this by your current tooth count (34 in this example).
34 x 1.083 = 36.83

A 37 tooth gear would be the closest. Speedometer would read just slightly slower than actual speed.
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Unread 12-27-2013, 12:16 AM   #3
SouthernGypsy
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Thanks, and Yes, I have a 26 now and I am thinking I need a 24 tooth, but want to verify it if anyone runs 30" tires with 2.73 gears and knows for sure.

The other problem is I can't seem to find a listing for 24 teeth gears anywhere online. I found they they DO exist, but no one seems to stock lower than 26 tooth.
That's actually what I was doing when your post came through, sitting here searching for a 24 tooth.

I can't even find a color or part number listed specific to Jeeps but I think it's the same long shaft speedo gears the Chrysler vehicles take in which case per a chart I have saved from my 'Cuda I believe a 24 tooth would be a white gear with the original Chrysler part number 3410024, but can't find one of those for sale.


Teeth/Color/Mopar Part #

24 WHITE 3410024
25 BLUE 3410025
26 RED 2538926
27 WHITE 52068149
28 BLUE 52068150
29 BLACK 52068151
30 YELLOW 52068152
31 GREEN 52068153
32 BLACK 52068154
33 YELLOW 52068155
34 GREEN 52068156
35 ORANGE 52068157
36 RED 52068158
37 WHITE 52068159
38 BLUE 52068060
39 GREEN 52068061
40 ORANGE 52068062
41 RED 2538941
42 WHITE 2538942
43 BLUE 2538943
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Unread 12-27-2013, 10:05 AM   #4
wm69
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24 tooth works for 31x10.50 with 2.73's. I have them in two of my three Jeeps. They are out there, but not easy to find. I got both mine on ebay. You also have to get the 21-25 gear housing if you want to use anything lower than a 26 tooth.

This place has the housing and a 25 tooth gear, but they're $50 each (ouch).

http://www.transmissioncenter.org/sp...e_and_jeep.htm

Use search terms "Mopar speedometer gear" when looking too. If you're patient you can find them on ebay cheaper than the place linked above.
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85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT

85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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Unread 12-27-2013, 11:19 AM   #5
SouthernGypsy
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Thanks. I already have the correct housing, now if I can just find the gear at a reasonable price.
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Unread 12-27-2013, 01:31 PM   #6
wm69
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Out of curiousity, at which speed did you measure the 5mph difference? In my experience, the higher the speed, the greater MPH difference you will see.

I do know that my 2.73 Jeeps both are running 31's, and a 24 tooth gear got me almost dead accurate, so I would think that a 25 would be closer to working with 30x9.50's. I don't recall what the stock gear was on either of my 2.73 equipped Jeeps was (one came stock with 235/75/15 and the other came with 205/75/15 so they were different gears from the factory dependant on OEM tire size). There used to be a gear applet for speedo gears, but it doesn't work anymore.
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85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT

85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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Unread 12-27-2013, 01:57 PM   #7
Matt1981CJ7
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WM69 is correct. The gauged speed difference will be a simple ratio.

For example, the ratio between 30" and 32" tires is 32/30 = 1.0667

So, 1.0667 is your multiplier. At 25 mph on the gauge, your true speed is 26.68 mph (25 x 1.0667). At 70 mph on the gauge, true speed is 74.67 mph (70 x 1.0667)

Hope this helps,

Matt
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Unread 12-27-2013, 08:00 PM   #8
Brewski
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I know your question is asking for help on a gear but I will add, the link listed above by wm69 http://www.transmissioncenter.net/sp...n_______va.htm also has a ratio adapter available for $62 as an option. After failed attempts and frustrations with buying gears, I ordered their ratio adapter. It works great and is a simple 5 minute install. The only downside was the lead time for it. It took many weeks to receive it. All you do is GPS your vehicle at 55 mph and compare that to the speedo reading. Do the math to know what % increase/decrease you need.
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Unread 12-28-2013, 07:52 AM   #9
big_o_tom
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Ive always wanted to fix my speedo, its 15-20 mph off. Thanks for the link above, I'll be calling them monday!
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Unread 12-28-2013, 11:55 AM   #10
SouthernGypsy
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Quote:
Originally Posted by wm69 View Post
Out of curiousity, at which speed did you measure the 5mph difference? In my experience, the higher the speed, the greater MPH difference you will see.

I do know that my 2.73 Jeeps both are running 31's, and a 24 tooth gear got me almost dead accurate, so I would think that a 25 would be closer to working with 30x9.50's. I don't recall what the stock gear was on either of my 2.73 equipped Jeeps was (one came stock with 235/75/15 and the other came with 205/75/15 so they were different gears from the factory dependant on OEM tire size). There used to be a gear applet for speedo gears, but it doesn't work anymore.

If I can find them I actually want one of each, a 24 and a 25, because I plan on keeping 30's on my Limited but want to put 31's on the Laredo later on.
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Unread 12-30-2013, 11:53 AM   #11
wm69
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Quote:
Originally Posted by big_o_tom View Post
Ive always wanted to fix my speedo, its 15-20 mph off. Thanks for the link above, I'll be calling them monday!
If you have a 78 you have a Dana 20 so an adapter would be about the only way of fixing yours.

If you have a Dana 300 Tcase the gear is a lot cheaper and more durable.

I have an 83 GMC with SM465 tranny and it's eaten a couple of those adapters. They get pricey when you have to buy more than one!
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85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT

85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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Unread 12-30-2013, 11:57 AM   #12
wm69
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Message this guy. He gets new gears in from time to time. I told him I needed a 24 and after a bit he told me he had one and I got one of my two from him.
http://www.ebay.com/itm/MOPAR-SPEEDO...ht_1429wt_1362
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85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT

85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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Unread 12-30-2013, 01:00 PM   #13
SouthernGypsy
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Quote:
Originally Posted by wm69 View Post
Message this guy. He gets new gears in from time to time. I told him I needed a 24 and after a bit he told me he had one and I got one of my two from him.
http://www.ebay.com/itm/MOPAR-SPEEDO...ht_1429wt_1362

Hahaha, now that's a funny coincidence! I actually did message that same guy a couple of nights ago and he said he gets them time to time but didn't have one right now. I wrote him back and asked if he could let me know if he got one in and he said he would. I figured he'd be like a lot of volume eBay sellers who say that but then quickly forget and just assume you will constantly check their auctions, it's good to know he's one of the ones that really will remember to write back
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1983 Jeep CJ-7 Limited 4.2L ~ Daily Driver, Prepping for a 2 month Tour of America Summer 2014.
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Unread 12-30-2013, 02:00 PM   #14
JrTjK
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partsmike.com sells them, too. That's where I picked one up for my last Jeep.
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