I disagree the case will turn at different speed depending on your gear size right .
If your theary is corrct you would never half to enter gear size in the programmer to calb. the spedo this is always nessary.

Street3285 changed only his gears and now the spedo is off.

 

hahaha ok man. please explain to me how changing a gear ratio can affect the speed of the case. do you even know how a diffential works?

 

Not exactly I'm trying to understand here.
just doesent make since that the gears change the spedo if your correct ?

 

Wow! This has gotten lively! I didn't know the speed was measured from the rear. Used to be, it came from the front. Boy, am I a "fossil". :o

And I just got used to no spark plug wires, distributor, or throttle cable too!

So, what we really need to know is where the rotations are measured. If it's on the rear axle, only the tires count. But, if it's somewhere else, the differential comes into play too.

So, where's the flippin' sensor?

- Jack

 

on top of the rear diff. it reads off of a tone ring which you can see in this pic right behind the crown gear.

 

Adam, forgive me. I clearly don't know as much about differentials as you do. Crown gears and tone rings are as meaningless to me as perhaps Sidewinder growls, Bullseyes, IPs, TOTs and Popups might be to you.

So, what you're saying, if I take what you just said in context with the other posts, is that the sensor is reading axle revolutions, right?

And, if that is the case, only the tire size matters for the speedo.

But, unless I'm VERY wrong, the axle ratio has a big effect on when the transmission decides to shift. Right?

- Jack

 

correct it reads the same speed as axle revolutions. not driveshaft revolutions as other posters seem to think.

 

My statement that gears will change the speedo, comes from the exact experience I am having with my truck. I am just telling you how I see it.

Next time, try not being such a smart $ss to other members and myself.

 

sorry, i am an arrogant *****. its a disease.

 

Well as a certified Ford Tech I will tell you that any change of tire size or gears changes the speedo. The tone ring is for the ABS function, not the speedo, the speedo comes from the OSS,(output shaft speed).

 

wrong. only on vehicles with cable drivin speedometers. the rear speed sensor also is the signal for your cruise. unplugged cruise will not work. the OSS on the transmission controlls shift points under normal acceleration which is why edge has the option to change this. when the rear sensor is unpluged you will get your speedometer reading from one of the front wheels. if you still do not belive me, disconect your rear sensor and go outside and do a brakestand. your speedo will not move untill the front wheels do. PS im a ford tech also....

 

Well maybe you need to reveiw your online training, its www.fordtechservice.com if you forgot the address. The tone ring is for ABS, Ford still uses 3 channel ABS, so thats why the tone ring is there. And a brakestand??? Thats hard on the trans. and converter, but maybe you forgot that too. Change the gears in your truck, and tell me how accurate your speedometer is. And WTF is a crown gear???? Are you refering to the ring gear??? And cable driven speedometers??? How many 4r70w's, 75w's, 5r110's etc. do you see with cable speedometer?????

 

ever seen the vss on a 97? cable drivin
http://www.thedieselstop.com/forums/...mittent-41620/
looks like another ford tech who thinks your wrong. log into OASIS and check the workshop manual under description and operation. you have some reading to do my friend.

 

Agreed. Here is what oasis says:

Speedometer
The instrument cluster (IC) receives the vehicle speed sensor (VSS) signal from the PCM over the communication network. The PCM receives the VSS signal from the output shaft speed (OSS) sensor. The PCM monitors the VSS input and sends it to the instrument cluster (IC) over the communication network. With the VSS input, the instrument cluster (IC) provides the speedometer with a corresponding pointer movement.

The VSS:
is gear driven by the transmission.
sends a signal to the PCM indicating vehicle speed.

Output Shaft Speed (OSS) Sensor
The output shaft speed (OSS) sensor is a magnetic pickup, located at the output shaft ring gear, that sends a signal to the PCM to indicate transmission output shaft speed. The OSS is used for torque converter clutch control, shift scheduling and to determine electronic pressure control.

So in my mind, if you change gear ratio's, the output shaft speed WILL change due to the different gear ratio - thus changing your speedometer calibration, which is why you have to recalibrate the pcm to the correct gear ratio to keep your speedometer accurate.

The tone ring is going to spin at the exact same speed whether you have a 3.55, 3.73, 4.10, 4.56, 4.88, etc. etc. But, the engine speed (rpms) will be different due to the fact that the driveshaft rotations have changed due to the different gear ratio. If the driveshaft speed has changed, so has the output shaft speed, which will affect the speedometer.

If the speedo got its signal from the tone ring, then changing gears would not affect it. But it gets it from the OSS, so yes, gears will change your speedo until it is recalibrated.

 

Haha this is getting good.