ZF5 Owners I need your help

mexicanjoe

Full Access Member
Joined
Aug 4, 2018
Posts
290
Reaction score
233
Location
texas
IF you are running a ZF5 transmission with a 4.10 final diff ratio, I need your help. On the ID plate of the ZF5 there is a speedometer code of some sort. If anyone can provide me with the code on your transmission I would sincerely appreciate it. Ford dealer is not helpful here.
 

Nero

HD Diesel nut
Joined
Jan 3, 2022
Posts
3,180
Reaction score
3,505
Location
OR
I have a zf with 4.10, I can check it this evening when I get home from work unless someone beats me to it.
 

ROCK HARVEY

Full Access Member
Joined
Oct 3, 2021
Posts
567
Reaction score
554
Location
Dayton OH
I checked but mine was blank, and I realized you need someone with a 2wd zf-5 since the 4wd ones have the Speedo gear in the transfer case.

Do you happen to know the color of your old Speedo gear? They’re color coded I believe.
 

Nero

HD Diesel nut
Joined
Jan 3, 2022
Posts
3,180
Reaction score
3,505
Location
OR
Ahhh yeah mine is 4x4, sorry mate
 

FrozenMerc

Full Access Member
Joined
Dec 21, 2018
Posts
297
Reaction score
539
Location
SW Missouri
I just did a ZF 5 spd swap into my '85 earlier this summer. 3.73 rear gears, and I think I used a 19 tooth speed-o gear. I keep a little drawer full of Ford speedometer gears just for this very reason. Try one, figure out the percentage that the speed-o is off and adjust the gear the same amount. In other words, if you have a 20 tooth gear and your speed-o is off 10%, go to either a 18 or 22 tooth, depending on which direction it needs to be corrected.
 
Last edited:

ROCK HARVEY

Full Access Member
Joined
Oct 3, 2021
Posts
567
Reaction score
554
Location
Dayton OH
I also just realized that from 1992 and up the Speedo reads off the rear axle, so you need someone with an 87-91 2wd ZF5 to check their tag.
 

mexicanjoe

Full Access Member
Joined
Aug 4, 2018
Posts
290
Reaction score
233
Location
texas
Alright crew, heres the story: I know Ive got a pink speedo gear with 19 teeth. AT 2100 rpm I show 66 mph but GPS says 59, therefore I think I need a 18 or 17 teeth gear ....
Am I correct in my assumptions? Most days I place the Iphone on the dash and read off of it the speed it shows. NOt great but better nothing.
 

Nero

HD Diesel nut
Joined
Jan 3, 2022
Posts
3,180
Reaction score
3,505
Location
OR
About 5~ mph off at that speed sound's accurate for factory calibration.
 

XOLATEM

Full Access Member
Joined
May 5, 2023
Posts
861
Reaction score
1,098
Location
Virginia... in the brambles
I don't trust the GPS and you prodded me to check my tire height and make a chart of RPM=MPH for my truck.

I have a 29 inch tire and 4.10 gear. The tire height was figured from measuring the loaded radius (center of axle to pavement) and doubled.

Center of axle to pavement =14.5 inches X 2 = 29 inches of tire height.

Once you have that, then you crank in the formula...


I don't have overdrive...yet...so the RPM's will be 24% higher than someone with the same tire and rear gear as me...but how it shakes out is this...

40 MPH = 1900 RPM

45MPH = 2150 RPM

50 MPH = 2350 RPM

55 MPH =2600 RPM

60 MPH = 2850 RPM

65 MPH = 3100 RPM

70 MPH = 3300 RPM

75 MPH = 3550 RPM

80 MPH = drastically shortened engine life...

If you have the same size tire and the ZF and you are figuring your RPM in overdrive (5th) then reduce these numbers by 24% (5th gear ratio.76-to-1)

Then...

70 MPH = 2508 RPM

60 MPH = 2166 RPM

50 MPH = 1786 RPM

40 MPH = 1444 RPM

I think that I am going to start looking for a ZF....

On the speedo gear...the last time I made a recommendation...I was wrong...but...I will try it again...

On the driven gear...

To speed up the speedo in relation to vehicle speed...you...reduce the number of teeth...

To slow down the speedo in relation to vehicle speed...you...increase the number of teeth...

I think that I have that right...we will see if the guys agree or not...

HTH...
 

IDIBRONCO

IDIBRONCO
Joined
Feb 5, 2010
Posts
13,406
Reaction score
12,460
Location
edmond, ks
To speed up the speedo in relation to vehicle speed...you...reduce the number of teeth...

To slow down the speedo in relation to vehicle speed...you...increase the number of teeth...

I think that I have that right...we will see if the guys agree or not...
Yes you're right.
 

mexicanjoe

Full Access Member
Joined
Aug 4, 2018
Posts
290
Reaction score
233
Location
texas
While this may not seem right I have measured the odometer against the mile markers on Interstate 20 I find the odometer to register 10% more than the distance traveled. Ive 2 different speedo gears coming soon : 17 and a 16 tooth driven gear ..... Ill find out which is closer to the right one! Ill keep you posted.
 

XOLATEM

Full Access Member
Joined
May 5, 2023
Posts
861
Reaction score
1,098
Location
Virginia... in the brambles
Alright crew, heres the story: I know Ive got a pink speedo gear with 19 teeth. AT 2100 rpm I show 66 mph but GPS says 59, therefore I think I need a 18 or 17 teeth gear ....
Am I correct in my assumptions?

I find the odometer to register 10% more than the distance traveled. Ive 2 different speedo gears coming soon : 17 and a 16 tooth driven gear


You'll want to go with a bigger one (with more teeth) to slow the speedometer down.
On the driven gear...

To speed up the speedo in relation to vehicle speed...you...reduce the number of teeth...

To slow down the speedo in relation to vehicle speed...you...increase the number of teeth...
You'll want to go with a bigger one (with more teeth) to slow the speedometer down.
 

Forum statistics

Threads
91,933
Posts
1,140,547
Members
24,755
Latest member
Jt64

Members online

Top