98 f-150 trans in 93 mark speedo fix?

[93luxurysnake]

I put the 4r70w from a 98 f-150 in my car an now my speedo reads 70 when im running 60 how can i fix this?

 

[chris2523]

probably need to change the speedo gear.

 

[93luxurysnake]

probably need to change the speedo gear.

which one should i use?... so i know what to rob one out of on my next junk yard endeavor

 

[svtlincoln]

Did you try maybe using the one from your original transmission?:thumbsup:

 

[93luxurysnake]

Yea an it was showing i was running 30mph when i was really doin more like 70!

 

[driller]

Study this... http://www.sccoa.com/faq/speedgr.html

There are 7 tooth and 8 tooth drive gears available in different variations of the 4R70W. It sounds like you possibly had an 7 tooth drive gear and now have a 8 tooth drive gear with the F150 trans? The 8 tooth drive gear would produce a 68.6 mph output at an actual 60 mph.

Pull the speed sensor and count the number of teeth on the speedo gear. Order a replacement with approximately 2 teeth less.

www.transmissioncenter.net

 

[93luxurysnake]

Study this... http://www.sccoa.com/faq/speedgr.html

There are 7 tooth and 8 tooth drive gears available in different variations of the 4R70W. It sounds like you possibly had an 7 tooth drive gear and now have a 8 tooth drive gear with the F150 trans? The 8 tooth drive gear would produce a 68.6 mph output at an actual 60 mph.

Pull the speed sensor and count the number of teeth on the speedo gear. Order a replacement with approximately 2 teeth less.

www.transmissioncenter.net

O yes thank you driller your the man!!!!

 

[tixer]

We made him President for a reason.

 

[93luxurysnake]

We made him President for a reason.

Yes I can see that:thumbsup:

 

[93luxurysnake]

an update i pulled the vss out of my trans today and i have the 8 spline drive with the orange 19 tooth gear what can i rob a green 17 tooth out of?

 

[Lvnmarks]

Your old transmission should still have the right one in it.

 

[93luxurysnake]

i tried the 17 tooth an it made it go 20mph off instead of 10 so i tried the 21 tooth an now it is 5 off what do i need to do to get it rite on?

 

[driller]

Your numbers are inconsistent. Let's walk thru this according to http://www.sccoa.com/faq/speedgr.html

The formula is:
Speedometer Gear Teeth = (Drive Teeth * Rear End Ratio * Tire Revolutions per Mile) / 1,000

It can be simplified to:
Speedometer Gear Teeth = (Drive Teeth * Rear End Ratio * 20.2) / Tire Height

Do you know your rear end ratio and tire height?

Let's assume 26.6" tire height for a 225/60-16 tire and calculate for different gear ratios.

Gear Ratio - Speedo gear teeth
3.08 - 18.7
3.27 - 19.9
3.55 - 21.6
3.73 - 22.7
3.90 - 23.7
4.10 - 24.9

If your tire size is different, you can calculate the tire height.

Tire Height = ((Tire width(mm)/25.4)*(tire series/100)*2)+Rim Diameter

Example (225/60-16):
Tire Height = ((225/25.4)*(60/100)*2)+16
Tire Height = (8.86*0.60*2)+16
Tire Height = 10.6+16
Tire Height = 26.6

Or you can use the following... http://www.sccoa.com/faq/tirecalc.html

 

[93luxurysnake]

ok recap i have a 93 mark viii with a 98 f150 4r70w and 3.55 gears out back and stock size tires i had the 19 tooth for the 8 spline drive in it and it was 10mph off now i have the 21 tooth for the 8 spline and it is 5 mph off if i am figuring correctly if i go with the 23 tooth for the 8 spline then from past experience it should exactly rite