What gears do I have?
- Thread starter 1.8kmint
- Start date
Roland69
Sergeant Tangnet
jack the rear off the ground. put car in neutral. mark the driveshaft. rotate the rear tire 1 full turn while counting the # of rotations the DS makes
ie
2 and 3/4 =2:73
3 and a half=3:55
4 and a tenth turn=4:10
3 and 3/4=3:73
ie
2 and 3/4 =2:73
3 and a half=3:55
4 and a tenth turn=4:10
3 and 3/4=3:73
TRWXXA
Member
Your speed vs. RPM sounds like you have 4.10 gears, but we can't be sure your speedometer is accurate. You can't even that your tach is accurate -- they have been known to be way off from the factory.
The surest way is to do what Roland69 suggests. Only, you should mark the wheel and driveshaft, and have a helper rotate the wheel 10 times, while you count the driveshaft revolutions. The reason for turning the wheel multiple times is that it can be very difficult to distinguish between 3.1 revolutions and 3.3 revolutions. Or between 3.5 and 3.7 revolutions.
Whatever number you come up with, divide by ten. 31 revolutions = 3.08s, 33 revolutions = 3.27s, etc, etc. You may wish to do this a couple of times just to make sure you or your helper don't miscount.
The surest way is to do what Roland69 suggests. Only, you should mark the wheel and driveshaft, and have a helper rotate the wheel 10 times, while you count the driveshaft revolutions. The reason for turning the wheel multiple times is that it can be very difficult to distinguish between 3.1 revolutions and 3.3 revolutions. Or between 3.5 and 3.7 revolutions.
Whatever number you come up with, divide by ten. 31 revolutions = 3.08s, 33 revolutions = 3.27s, etc, etc. You may wish to do this a couple of times just to make sure you or your helper don't miscount.
KK thanks. I just wanted a rough estimate. I bought the car from a lady whos father owned it (supposedly trying to make a cobra according to her) and died so she just assumed it was stock. Soon as i drove it i knew something was up because it shifts way too good and has way more balls than a stock 5.0 with 121,000 miles.
TRWXXA
Member
Ooooops... I think I misread your post.
You said the the RPM was with your AOD in "DRIVE", not "OVERDRIVE", correct?
If it's in 3rd gear (1.00 : 1 ratio), then I calculate a gear ratio of 2.73 if your at 2000 rpm, and 3.08 if your at 2200 rpm. Both sound more plausible than 4.10s. 1992 AODs had an 8-tooth speedometer drive gear. It would be nearly impossible to get the speedometer even close to accurate with 4.10s in the rear. If you were pulling 2000 rpm, you'd be doing about 55 mph, but your speedo would probably read about 67 mph, if the previous owner even tried to correct the speedometer.
Here are the calculations I used, if you want to try them too:
Tire Height (inches) = Tread Width * Aspect Ratio / 1270 + Wheel Diameter
225 * 60 / 1270 + 15 = 25.63"
Rear End Ratio = Tire Height * 0.0000496 * Eng. RPM / Trans. Gear Ratio * 60 / MPH
25.63 * 0.0000496 * 2000 / 1.00 * 60 / 55 = 2.774 (closest to 2.73)
You said the the RPM was with your AOD in "DRIVE", not "OVERDRIVE", correct?
If it's in 3rd gear (1.00 : 1 ratio), then I calculate a gear ratio of 2.73 if your at 2000 rpm, and 3.08 if your at 2200 rpm. Both sound more plausible than 4.10s. 1992 AODs had an 8-tooth speedometer drive gear. It would be nearly impossible to get the speedometer even close to accurate with 4.10s in the rear. If you were pulling 2000 rpm, you'd be doing about 55 mph, but your speedo would probably read about 67 mph, if the previous owner even tried to correct the speedometer.
Here are the calculations I used, if you want to try them too:
Tire Height (inches) = Tread Width * Aspect Ratio / 1270 + Wheel Diameter
225 * 60 / 1270 + 15 = 25.63"
Rear End Ratio = Tire Height * 0.0000496 * Eng. RPM / Trans. Gear Ratio * 60 / MPH
25.63 * 0.0000496 * 2000 / 1.00 * 60 / 55 = 2.774 (closest to 2.73)
Roland69
Sergeant Tangnet
skunk21
Active Member
atuo's came stock mostly with the 2:73's also have seen alot with 3:08's. an option that could be ordered and is rare are the 3:27's. post your door code and we could give you the stock gearing if you don't have a door sticker or think the rear gears have been changed take roland69's advice, that will give the clear answer right there.
bynummustang
Seen my other Jackstand?
ryan218
In just 10 years, I'll be old enough to drive!!!!
mines got a 3.08 and in od it runs at 1,100 rpm..id say you got 3.55 maybe? maybe even higher? just pull the diff cover...rotate the tires till you see the engravings...
TRWXXA
Member
That's just it. I think he's saying he was running in D, not OD. To get 2100 rpm at 55 mph, in OD, with his tires, he'd have to have a 4.35 rear gear ratio.
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