Speedometer Gears

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ScramblerCJ8
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Speedometer Gears

Post by ScramblerCJ8 » Mon May 06, 2019 8:22 am

Hi guys, this is a technical question. I did a GM powertrain conversion on my 1989 Jeep yj, won't go into details about it but need to replace speedometer gear to match the actual speed. Transfer case is a 241c with a slip joke eliminator kit, 5:38 gears and 38 inch tires, witch actually only measure 37 inches. Look at some charts and found very little information, just one that indicates that a 40 tooth output shaft gear will fit but does not mention the one that drives the cable/vss.
So, any help on the right direction will be greatly appreciated.
Thanks.

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derf
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Re: Speedometer Gears

Post by derf » Mon May 06, 2019 8:42 am

On the 241 donor, does the sender have a gear in it that meshes with the gear on the tail shaft? Or is it a stubby piece of plastic that just points at a bunch of what look like splines on the shaft?

If the sender has the gear, you can swap it out. I worked up a chart to tell you which one to use. viewtopic.php?f=11&t=11623

If it's the direct VSS on the tail shaft (i.e. no gear), I don't know if it's possible to swap out to a gear driven speedometer without swapping out the whole tail shaft.


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ScramblerCJ8
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Re: Speedometer Gears

Post by ScramblerCJ8 » Mon May 06, 2019 5:55 pm

Thanks derf, the donor 241c unit came out of a truck with 4:10 gears and 33 inch tires.
its a cable driven unit, I just got a vss speedo cable combo unit from Dakota Electronics.
So I have the twp plastic gears, one on the final drive shaft of the t case and the other one that meshes and drives the cable.
The question was, do I need to replace both gears, the one on the final drive shaft and the one that drives the cable, or just the one on the final drive?
The chart I found calls for a 40 tooth gear on the final drive shaft, but does not mention the other gear?
Your chart is better, has more choices, mine is the last one.

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derf
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Re: Speedometer Gears

Post by derf » Mon May 06, 2019 8:09 pm

You should be able to just swap out the gear on the sender. The one on the tail shaft should be ok.

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Cecil14
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Re: Speedometer Gears

Post by Cecil14 » Mon May 06, 2019 9:05 pm

ScramblerCJ8 wrote:Thanks derf, the donor 241c unit came out of a truck with 4:10 gears and 33 inch tires.
its a cable driven unit, I just got a vss speedo cable combo unit from Dakota Electronics.
So I have the twp plastic gears, one on the final drive shaft of the t case and the other one that meshes and drives the cable.
The question was, do I need to replace both gears, the one on the final drive shaft and the one that drives the cable, or just the one on the final drive?
The chart I found calls for a 40 tooth gear on the final drive shaft, but does not mention the other gear?
Your chart is better, has more choices, mine is the last one.
For what it's worth, I have never seen anyone call for replacing the gear on the final drive, only the one that drives the cable. The whole idea is that one could replace that small/inexpensive gear and adjust for a lot of different combinations.
1983 J-10 - 4.6L(MPFI)/CS130D/Hydroboost/NV3550/D300/44/44/3.54/Disc-Disc/32s/42 gallon 'burb tank


mlaver
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Re: Speedometer Gears

Post by mlaver » Tue May 07, 2019 6:25 am

I just added an underdash gps speedometer easy install doesn't matter what gear ratios or tire size.
L.


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ScramblerCJ8
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Re: Speedometer Gears

Post by ScramblerCJ8 » Tue May 07, 2019 9:02 am

Thanks for the info, now just got to find the right speedometer drive gear and replace it.

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Cecil14
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Re: Speedometer Gears

Post by Cecil14 » Tue May 07, 2019 9:10 am

mlaver wrote:I just added an underdash gps speedometer easy install doesn't matter what gear ratios or tire size.
Doesn't help with FI computers, either. GPS speedos are awesome if you're staying carbed, though.
1983 J-10 - 4.6L(MPFI)/CS130D/Hydroboost/NV3550/D300/44/44/3.54/Disc-Disc/32s/42 gallon 'burb tank


Topic author
ScramblerCJ8
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Re: Speedometer Gears

Post by ScramblerCJ8 » Thu May 30, 2019 4:56 pm

Thank you guys, I had the local off road shop order me one, took almost three weeks to get it. My Jeep Wrangler has a SB 350 TBI and a 700R4 tranny.
The ECM needs to see VSS signal or the check engine light will come on, and the stock speedometer needs a cable to operate. With the 40 tooth gear it will read close enough to real and the cable won't wine.
I'll let you guys know once I get it install and road tested.


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ScramblerCJ8
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Re: Speedometer Gears

Post by ScramblerCJ8 » Tue Jul 09, 2019 1:36 pm

Ok, got the speedo gear swap and road tested. No more whine from the cable but speedometer still reads almost double the actual speed, a clue why the odometer reads over 250k.Found a NOS speedometer on ebay for 160 bucks, offered 100 and offer accepted.
Installed and road tested, just 1 mph off from my gps.
I'm satisfied and considered it fixed.
Thanks again.

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Stuka
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Re: Speedometer Gears

Post by Stuka » Mon Jul 15, 2019 7:47 am

Glad you got it figured out. Sounds like the original speedo had a weak spring in it or something?
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