Have you ever heard of these gears??

[FordRacing302]

I jacked up my rear end the earlier today to check my rear end gear ratio and I was surprised as to what I found.....It doesnt even complete 2 axle rotations for 1 wheel revolution, I figured the gears to be about 1.70 - 1.80:1 gear ratio...Has anyone ever seen this in a 7.5 rear end before??? You would think with those kind of gears and an overdrive tranny your car would be good for 150 - 160+ MPH

 

[HISSIN50]

Axle and wheel rotations should be equal (the wheels are an extension of the axle).

You should note DS turns per ONE wheel rotation.

Good luck.

 

[HISSIN50]

And you would need serious power to reach those speeds with that kind of gearing. I mean serious.

 

[FordRacing302]

Sorry bout that, I meant driveshaft instead of axle...And I doubt my tires could hold up to those speeds anyhow

 

[Michael Yount]

You miscounted....

 

[speedytang]

In a Fox nothing under a 2.73

 

[sgarlic]

Wow, with gears like that, you could be practically at idle RPMs at 65mph!

 

[I_AM_CANADIAN]

You miscounted....

 

[Maryland Stang]

You miscounted....

I can attest to adults miscounting or even completely forgetting how to count altogether. I always see it in my daughter when she's talking to my granddaughter.

"I'll give to you five to put that away...one ...two...three...four...four and a quarter...four and a half..."

She never gets to five.

 

[timewarped1972]

isn't there some thing where if the differential is in a mode where one wheel is not locked ( like when you be going around a corner) that it could read incorrectly?? seems like i'd had this problem before and i tried it with one wheel still on the pavement, or something like that, lol.it's late maybe its just me...

 

[FordRacing302]

I gaurantee that I didnt miscount, I went out there about a month ago and tested and got the same results, but back then I was skeptical and thought I had done something wrong, So I finally got off my lazy butt and checked it again with the same results...Also the previous owner said the car's rear end was good for 170+ MPH, I thought he didnt know what he was talking about, but now I know what he meant

 

[Michael Yount]

OK. Let's try it like this then. Here's how the gear ratio actually occurs -- it's the ratio of the number of teeth on the ring gear divided by the number of teeth on the pinion gear. For example, the 7.75" Dana30 rearend in my car has 41 teeth on the ring gear and 11 teeth on the pinion gear. Do the math -- 3.727:1 ratio -- 3.73 gear. With the same ring gear a 10 tooth pinion gives you a 4.10 rear end, and a 9 tooth pinion gives you a 4.56.

If you think you counted turns correctly here are the implications. You say you're certain you have a 1.70:1 rear gear ratio. On a 7.5" ring gear if you do some simple math, what you'll discover is that the pinion gear would have to be SO BIG to accomodate the number of teeth it would have to have to achieve that ratio, that it wouldn't fit in the housing.

So, we all know there's an error in your counting. You can insist you're correct if you like -- or you can get back out there, jack the car up, and count again --- so you can discover that somewhere along the way you MISSED one turn of the driveshaft. The result is that the DS turned about 2.7 times and you have a 2.73:1 rear end in it --- just like about 99% of every 7.5" rear-ended Mustang ever built.

Just a guess though.

 

[Michael Yount]

....and btw, even with the 2.73 rear gear that's actually in the car, IF you had enough HP (which you're not even close to) it's PLENTY long to achieve 170 mph.

 

[CManT1914]

An even easier way of telling is, what RPM's are you turning at 70mph in 5th gear? Around 1750 is 2.73's like we're pretty sure you got.

EDIT: Oh, and if you had 1.73's, you would'nt be shifting outta first until 70mph, 2nd at 120. Theoretically 5th gear would be good to 350mph!!

 

[Michael Yount]

May be 'easier' but with inaccurate tachs and speedos it may not tell you much that's accurate...counting turns is the ONLY way to be sure.

 

[85_SS_302_Coupe]

Wow 1.70....that's like a salt flat gear..lol I agree though, count the shaft rotation. I didnt read all the replies but a string tied around the drive shaft helps to keep count.

 

[CManT1914]

May be 'easier' but with inaccurate tachs and speedos it may not tell you much that's accurate...counting turns is the ONLY way to be sure.

It's gotta be more accurate than his counting ability, lol.

 

[rd]

The lowest gear I know about is 2.26, that was used in some 79 to 82 cars, before overdrives were used. This would most likely have come with a C4 trans. I had a 2.47 in the Capri as original.

 

[Foxfan88]

this is kind of off topic but did you ever notice all the 2.3 mustangs were giving the 3.73 rearend, they are so weak they cant use a a 2.73 rear.

imagine how slow a 2.3 would be with 2.73 O_O

 

[outlawjay]

If he doesn't have traction-lock, which I doubt he does then he is probably counting right, but without the traction lock this way of measuring gears doesn't work.