How to figure out what gear ratio in rear end? - Mustang Evolution

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Old 03-16-2015, 09:08 PM   #1
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How to figure out what gear ratio in rear end?

Is there a way to find out the rear end gear ratio without having to jack it up and mark the driveshaft? I don't have any jack stands available here and don't trust the factory jack enough to crawl under the car with that being the only thing holding it up.


Also wondering if the Cobra's stock suspension is lower than stock GT? my 04 was bone stock I was the 2nd owner and some old lady had it before me so I know it was unmodified, it was higher off the ground than this Cobra is. might it have lower suspension or was the cobra lower from the factory?
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Old 03-19-2015, 04:37 PM   #2
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Anyone?
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Old 03-19-2015, 04:56 PM   #3
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Originally Posted by 99 RioRed SVT View Post
Is there a way to find out the rear end gear ratio without having to jack it up and mark the driveshaft? I don't have any jack stands available here and don't trust the factory jack enough to crawl under the car with that being the only thing holding it up.


Also wondering if the Cobra's stock suspension is lower than stock GT? my 04 was bone stock I was the 2nd owner and some old lady had it before me so I know it was unmodified, it was higher off the ground than this Cobra is. might it have lower suspension or was the cobra lower from the factory?
There is a sticker on your differential. Just park on an incline and crawl up in there lol

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Old 03-19-2015, 05:19 PM   #4
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There is a sticker on your differential. Just park on an incline and crawl up in there lol

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thanks ill check that out, but my point is to find out if that's what is in there. the sticker can say one thing but the insides can be different.
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Old 03-19-2015, 05:39 PM   #5
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thanks ill check that out, but my point is to find out if that's what is in there. the sticker can say one thing but the insides can be different.
You can Mark your axle and rotate tires and count how many rotations it takes for one full axle rotation.

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Old 03-19-2015, 10:57 PM   #6
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You can Mark your axle and rotate tires and count how many rotations it takes for one full axle rotation.

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Don't you mean driveshaft? The axles are going to rotate at the same rate as the wheels. It's the driveshaft that rotates at a different rate.

OP, AmericanMuscle has a chart for each of their gear sets that shows you what RPM you should be at for certain speeds. You can use this to determine what gears you have without putting it on a lift and doing the rotation method. Here's a link to the 3.73 set. Ford Racing 3.73 Gears. If you click on Tech Specs, it'll show you the chart. I would say drive at 65mph in 5th gear and annotate what RPM you're at, then refer to the charts on the site to figure out your gear ratio.
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Old 03-19-2015, 11:44 PM   #7
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Don't you mean driveshaft? The axles are going to rotate at the same rate as the wheels. It's the driveshaft that rotates at a different rate.

OP, AmericanMuscle has a chart for each of their gear sets that shows you what RPM you should be at for certain speeds. You can use this to determine what gears you have without putting it on a lift and doing the rotation method. Here's a link to the 3.73 set. Ford Racing 3.73 Gears. If you click on Tech Specs, it'll show you the chart. I would say drive at 65mph in 5th gear and annotate what RPM you're at, then refer to the charts on the site to figure out your gear ratio.
Yes lol thanks for the catch

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Old 03-20-2015, 07:45 PM   #8
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Thanks WhoDat. yeah I thought natestang07 meant the driveshaft but since the main thing I was asking was how to find out without doing that I just waited to see for another tip.
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Old 03-20-2015, 07:49 PM   #9
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after looking at the specs of that link, it cant be 3.73s my RPMs are lower at all speeds than that. at 80 im doing about 2200. only reason I know 80 is because Im new to San Diego and got the car from El Cajon and dad was showing me how to get back and he likes to drive fairly aggressive and I was trying to keep up so I didn't miss an exit. so im guessing they are 3.55s? or is there another ratio between them? I only know about the following rear end ratios: 2.73,3.27,3.55,3.73,3.90,4.10,4.33,4.56,5.14,5.56.
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Old 03-20-2015, 07:51 PM   #10
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Anyone have info on the suspension? I know for a fact its about 2- 2 1/2inches lower than my 04 GT. but the dealership said it was factory other than short throw shifter but I have my doubts about that...
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Old 03-20-2015, 08:09 PM   #11
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2200 at 80mph in 5th gear could be 3.55s or 3.31s
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Old 03-21-2015, 05:35 PM   #12
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2200 at 80mph in 5th gear could be 3.55s or 3.31s
Thanks. yeah today on way to Costco I set cruise control at 70 and it was dead on 2k rpms. its got pretty good pick up too, so I don't think they are too long of gears. id say probably 3.55s, anyways thanks for all the help!
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Old 03-21-2015, 05:48 PM   #13
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Anyone have info on the suspension? I know for a fact its about 2- 2 1/2inches lower than my 04 GT. but the dealership said it was factory other than short throw shifter but I have my doubts about that...
Can not find any direct comparison between a cobra height and normal gt height. I did see that the stock ratio was 3.27 though.

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Old 03-21-2015, 05:53 PM   #14
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Cobras were lowered 3/4" from the factory I believe. If it's that much lower than the GT then it's cut or aftermarket springs.


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Old 03-21-2015, 06:03 PM   #15
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Cobras were lowered 3/4" from the factory I believe. If it's that much lower than the GT then it's cut or aftermarket springs.


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I thought so, they aren't cut I know that, so they gotta be lowering springs. I just knew that it was too low to be factory. its low enough that I have to take speed bumps and driveways at an angle or it hits.
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Old 03-21-2015, 11:39 PM   #16
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Factory gear ratio is 3.55 om the Cobras so you more than likely have that. Does your car look as low as mine? Mine is lowered 2.5" on an 04 IRS
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Old 03-22-2015, 12:27 AM   #17
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Factory gear ratio is 3.55 om the Cobras so you more than likely have that. Does your car look as low as mine? Mine is lowered 2.5" on an 04 IRS
Hm I keep finding 3.27 for the stock ratio. 3.55 would make a lot more sense though

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Old 03-22-2015, 12:40 AM   #18
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Factory gear ratio is 3.55 om the Cobras so you more than likely have that. Does your car look as low as mine? Mine is lowered 2.5" on an 04 IRS
it looks pretty close to that but mine still has stock 17s so its hard to tell for sure, but looking at the side skirt its about how low mine looks to the ground. BTW your GT looks bad ***, love the spoilerless trunk I want to do that to my cobra.
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Old 03-22-2015, 12:47 AM   #19
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Hm I keep finding 3.27 for the stock ratio. 3.55 would make a lot more sense though

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me as well. the Terminator had 3.55s factory, but as far as the 99 I keep finding 3.27s but my rpms are off of the tech sheet I found so I think it has 3.55s instead of factory 3.27s. I also learned that my cobra was the first year of the IRS although it used the brackets for a solid axles so its not as good as the IRS in Terminators.
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Old 03-22-2015, 12:51 AM   #20
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Factory gear ratio is 3.55 om the Cobras so you more than likely have that. Does your car look as low as mine? Mine is lowered 2.5" on an 04 IRS
Also what rims are those? love how they look, im thinking of getting some like that and painting them black... duno its still a while before ill have the money to mod it. right now im just enjoying being a Cobra owner
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Old 03-22-2015, 01:57 AM   #21
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Hm I keep finding 3.27 for the stock ratio. 3.55 would make a lot more sense though

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All Cobras are 3.55s if I remember correctly.





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it looks pretty close to that but mine still has stock 17s so its hard to tell for sure, but looking at the side skirt its about how low mine looks to the ground. BTW your GT looks bad ***, love the spoilerless trunk I want to do that to my cobra.
Heres some 17s on my car for reference, and thank you. I loved that car a lot. I waffled a lot on the wingless look, some days I liked it other days I would out the spoiler back on.




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Also what rims are those? love how they look, im thinking of getting some like that and painting them black... duno its still a while before ill have the money to mod it. right now im just enjoying being a Cobra owner
The 18s were SVE Drifts off of Latemodel Restoration. They sell black ones as well as the silver I had
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Old 03-22-2015, 02:52 PM   #22
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All Cobras are 3.55s if I remember correctly.







Heres some 17s on my car for reference, and thank you. I loved that car a lot. I waffled a lot on the wingless look, some days I liked it other days I would out the spoiler back on.






The 18s were SVE Drifts off of Latemodel Restoration. They sell black ones as well as the silver I had
yeah that looks like my cobra. its got to have lower springs then. I take it by "loved that car" you don't have it anymore. ill look up those rims. the only way I would keep the spoiler is if I moved it back to the edge of the trunk, I HATE how far forward it is. but id rather just have it gone, my 04 didn't have a spoiler and I loved how it looked. if I did do a spoiler im really taken by the Saleen 3 piece wing. otherwise no spoiler. (im ready for the flak about a Saleen wing on a Cobra )lol
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Old 03-22-2015, 05:20 PM   #23
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yeah that looks like my cobra. its got to have lower springs then. I take it by "loved that car" you don't have it anymore. ill look up those rims. the only way I would keep the spoiler is if I moved it back to the edge of the trunk, I HATE how far forward it is. but id rather just have it gone, my 04 didn't have a spoiler and I loved how it looked. if I did do a spoiler im really taken by the Saleen 3 piece wing. otherwise no spoiler. (im ready for the flak about a Saleen wing on a Cobra )lol
Yep, sold the car earlier this year. I'll get something nice again a few years down the road. I moved mine back about 1.5" and I liked the look a lot. The Saleen wing is sweet so you won't get flak from me
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Old 03-23-2015, 12:06 AM   #24
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Yep, sold the car earlier this year. I'll get something nice again a few years down the road. I moved mine back about 1.5" and I liked the look a lot. The Saleen wing is sweet so you won't get flak from me
i got a question about moving and deleting spoiler (without buying new trunk lid) howd u deal with the holes from the spoiler? on my 96 GT when I took the spoiler off I just covered them with duct tape but that looks tacky as hell but that car was rough so I didn't care. this one is nice and I don't want to do something tacky like that...
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Old 03-23-2015, 12:19 AM   #25
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http://www.moddedmustangs.com/forums...s/57169?page=1

https://www.google.com/search?q=must...80692364741189
Maybe you could get those to,work for your 99

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Old 03-23-2015, 12:25 AM   #26
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Spoiler Delete Plugs

https://www.google.com/search?q=must...80692364741189
Maybe you could get those to,work for your 99

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Thanks man, I didn't even know they made those! not real expensive either.
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Old 03-23-2015, 12:26 AM   #27
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Thanks man, I didn't even know they made those! not real expensive either.
Nope not at all. And if they don't work I'm sure you can wander down to a parts store and find something That works

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