according the the data plate - my truck has the "desirable" 3.08 gearing.

maybe one of you Ford gurus can tell me what the ratio is when overdrive is off.

thanks

 

Depends on your vehicle and which transmission...

 

thanks for responding.

really? does it matter whether it's a 4.6 or 5.4, F150 or F250? and can that really change the overdrive ratio?

ok - it's a F150 with 4.6. all I know about the transmission is it's an auto - and probably the cheapest, lowest one Ford could get away with in 1999. how would I know which transmission it has?

 

I believe there may be a misunderstanding here.
The rear gear ratio is seperate from the transmission.
When the transmission is in it's third gear on most of these units, the transmission ratio is 1 to 1 making the final (to the road) 3.08.
However in overdrive, the OD ratio is often .77 (or it would not be an overdrive)
If you multiply 3.08 times .77, the final 'to the road' ratio would be 2.3616.
The modifier to this would be when the converter is out of lockup. This condition usually adds about 300 rpm to the motor's speed to account for the fluid slip in the converter.
An out of lock condition is also actually a gear ratio change the motor sees due to the fluid slip. The total ratio at the road could be calculated by the change in rpm with all other gearing constant.
So when you ask about gear ratio, be awhere of the conditons and what OD ratio the transmission has in oder to arrive at the "final" drive ratio at any given time.
I should also add that the distance from the rear axle to the road is part of the final ratio such that a change in tire diameter changes the final ratio to the road at that point as well as even tire pressure raising or lowering the same distance. One does it by rolling distance as well as axle to road distance, the tire pressure make only the distance change for the same tire diameter and sleightly changes the rolling distance.
More to it than meets the eye when all the parts are taken into acount.

 

Yes, it matters since, with the identification, I can go right to the correct page in the manual and look up the data. Without the identification, I'm not even going to open any book since I don't know which book to open.

The 1999 4R70W gear train ratios are as follows (assumes TC locked):


Gear Ratio
1st 2.84 to 1
2nd 1.55 to 1
3rd 1.00 to 1
4th 0.70 to 1
Reverse 2.32 to 1

Perform the calculations Bluegrass gave to determine overall ratio from engine to ground.

 

whew!!! too much information. so, if I pickup a ring and pinion set - will it have a disclaimer that says the ratio may or may not be what you think you are buying??

Bluegrass 7 and projectSHO89, I appreciate y'alls attempt to explain this to a knucklehead.

my curiosity started when I switched the OD off when running about 70mph. I noticed an increase in engine rpm. that got me to wondering about the axle ratio, and it the advertised ratio was based on the OD on or off.

ok, last question - can the OD be defaulted to always be off?

 

The axle ratio is always the same once installed. If you order a 3.55 or 3.73 R & P set, that's what you'll get. Keep in mind that if you have a 4X4, you need to change BOTH axle ratios.

OD cannot be easily defaulted to off - you don't want that anyway. If you think you do, you're likely mistaken. If you STILL think you want that, you're still mistaken.

The 3.08 ratio with OD is great for fuel economy for a road warrior. However, if you want towing power or want to go rock climbing, it's not going to work out well.

 

You can always turn OD off with the switch at the end of the shift stalk each time you drive. When off, it lights the lamp in the stalk.
The PCM will always automaticaly return it back 'on' everytime you start the motor.
The switch is a dc signal voltage sent to a set of dedicated input terminals to the PCM software for what to do with the electric OD control in the transmission.
If your OD ratio is .70, then times 3.08 = 2.156. Even lower (faster) yet for the same road speed and engine rpm.
Gear ratios are all in relation to the engine rpm, torque band and what application you prefer to maximize performance for. It also affects fuel mileage in an inverse way most of the time.
Good luck.

 

well boys.... thanks for the answers. I really don't plan to replace the ring & pinion - as I just drive the truck in town, never towing.

however (as noted in another post) I have a problem with the heater core leaking. I've got to cross that bridge.