3.55 gear change - speedo gear difference?

[Ithnu]

I searched and found too many general responses. On other forums I saw someone mention that the 1993 cobra needs a 23 tooth instead of a 20 tooth speedometer gear that the GT/LX use. Is this the case? I thought the only difference in the tranny was the phosphate gears.

No I'm not debating 3.55 or 3.73. ;-) I'm getting 3.55s.

 

[NEOH1]

I have the 3:55s and changed to 23 tooth gear. GPS speed is as close as you can get.:beer:

 

[NEOH1]

By the way. I love the 3:55s but I think the 3:73s would be better for my combo at the drag strip. I had to shift into 4th right at the end.

 

[Ithnu]

Excellent, thanks!

My car may never see the dragstrip so I'm not super concerned about 1/4 miles times. I had a 1986 GT with a 2.73 but even with the 3.08 in the Cobra it just feels held back.

 

[Ithnu]

I ordered the Steeda 23 tooth today. I stopped at a Jeep dealer and the guy had no idea what I was talking about. He said all he could find was an out of production 24 tooth. The guy at the Ford dealer knew exactly what I wanted but said he only had the 21 tooth, as expected.

 

[DougM]

Which gear is needed for the 3.73:1 gears? I'm pretty sure I don't have the right gear. Would gears be different for a Tremec tranny?

 

[Ithnu]

I just put he 23 tooth in. There was a black 20tooth stock. The stock with the 3.55 gears was off 10mph at 70 and with the 23 tooth is now off by 5mph at 70.

An improvement yes, but still not accurate. I used 2 different GPS apps on my iPhone and drove by a speed limit sign with radar to confirm it.

 

[Mustanganatic]

I put 3.73s in my pace car with the red 21-tooth driven gear (at the end of the cable) and I'm off about 18% high. Found this chart (in the middle of the page) for the speedo gears in the Ford Racing catalong http://www.fordracingparts.com/download/charts/129.pdf I thought I had a 7 tooth drive gear, but obviously I've got an 8-tooth. The bad part is I've got to pull the tail shaft to change it to the 7-tooth drive gear :whine: A 23 or 24-tooth driven gear will still be off and also they tend to be weak with that many teeth and don't last long.

 

[Mustanganatic]

I never noticed the formula at the bottom of the page on that link I included above. I calculate out a 23.8 tooth driven gear. Googled it and Jeep has them, but out of production. Called a local transmission place and they have them. Hmmmm, may be worth a try... a hell of a lot easier than pulling the tail shaft! BTW, if you need to find your revs/mile on your tires, go to Tire Rack, look up your tire and the specs page has it.

 

[Ithnu]

I checked with a Jeep dealer too, also said the 24 tooth was out of production.

I'm going to call a speedometer specific shop and see what they can do. Maybe one of those reducer boxes. And then I can put the stock one back in so I don't have to worry about the 23 tooth wearing out.

 

[Mustanganatic]

Well, my bubble just burst I called Dacco Transmission parts for a 24-tooth speedo gear and he said he needs to know what tranny. I called Tremec and they said they didn't have that and to call D&D Performance. No such animal. They used to have a 23-tooth for the T-5, but they wore out almost immediately. Oh well, looks like I'm back to pulling out the tail shaft. Oh, BTW, I looked up the speedo gears for Jeep and they don't look anything like what goes into a T-5.

 

[Crock]

Go with a 6 or 7 tooth drive gear like mentioned above. Do the calculations for each and you may be able to use your existing 20 tooth.

 

[Mustanganatic]

Go with a 6 or 7 tooth drive gear like mentioned above. Do the calculations for each and you may be able to use your existing 20 tooth.

Right Crock, once I change the drive gear to a 7-tooth, the 21-tooth driven gear is correct. I read somewhere else that the '94 Cobras had a T45 tranny, but it's got a T5... apparently with an 8-tooth drive gear.

 

['93blownCOBRA]

Not sure if this helps any but I got this email the other day from LatemodelRestoration.com. I figure it might help a few folks out.

 

[Mustanganatic]

Hey 93Blown, that calculator sure does help. I didn't know that anything over a 21-tooth gear was available, but for giggles, I plugged in my numbers and it said a 23-tooth gear would work and showed one available from 50Resto. They're a bit pricey, but a whole heck of a lot easier than pulling off the tail shaft and changing the drive gear! Thanks for posting! :banana:

 

['93blownCOBRA]

Glad I could help out. I have learned a lot of things from this forum. Kinda neat when I can give back a little.

Here is a link to the calculator and the "How To" video:

http://www.latemodelrestoration.com...ail&utm_term=0_cb1e7fdfb3-4f8824a663-50744077