Changing speedo gears (4L60/700-R4)

 

This is a fairly simple procedure. First, you need to determine what speedo gears you need.  There are many "gear calculators" out there, to tell you the drive/driven gear tooth count, or they tell you what color you need.  I replaced my speedo gears since I went from 2.73s to 3.73s and this is a large step, wich would have resulted in about a 15 MPH error in the speedo.

 

If you are putting in 3.73s, I can tell you that you need the gray drive gear, and light blue driven gear.  Part numbers:

25513052; 8642620

After you get the gears you need, you will have to remove the Torque Arm and Driveshaft.  There are only two bolts holding the T/A on, and it will slide right out of the bushing.  Then the driveshaft bolts are 11mm to remove the two U-joint straps and remove the shaft. 

This is a back view of the tranny with the T/A and Driveshaft removed.  You will need to remove the "sleeve" if it has a speedo cable, and the "VSS" if it has an electric speedo.  This is a 10mm bolts, and simply pry it out. 


Here is my VSS with the old "red" gear installed.  It simply pulls off, and slide the new gear on.  It should slip on and off easily.  On the right is the new Lt Blue gear.


There are four 15mm bolts that hold the tailhousing on.  Once you remove the bolts, the tailhousing will pull right off.  Pull straight back so you don't scratch the driveshaft support bushing.


Here is the "drive" gear.  It is almost pressed on.  There is also a retaining clip to keep it from moving around on the shaft.


You must be careful in removing the gear, so you don't damage the clip.  You will need to press in on the end of the clip, as you move the gear off the shaft.  Like said earlier, it is almost pressed on the shaft, so you will need something to help you remove the gear.  I use a 32mm wrench to "tap" it off the shaft.  If you don't get the gear to clear the clip, you will damage the clip.


Here is a close-up of the clip, so that you know what you are working with.  I know what you will think when you tap the gear off and the clip goes flying.  "OH no, there are TWO holes in the output shaft, and I didn't see which hole the clip went into".  Relax.  When you go to put the drive gear on, install the clip in the hole towards the FRONT of the car, then install the tailhousing on the tranny, and make sure the VSS hole is centered on the drive gear. 


I used the same 32mm wrench to install the new gear.  It can be tricky, because you need to line the clip hole of the gear, to the hole in the output shaft.  It has to be lined up perfectly, because once the gear is installed, it can not be rotated on the shaft.  Remember, put the clip in the foward hole, and VERIFY the VSS hole is CENTERED on the drive gear.


If you had a leaking output shaft seal like I did, now is the perfect time to replace it.  Its real easy now, since you don't have the output shaft in the way.  You will need to order the seal, and tailhousing square-cut seal (shown here) when you order the gears. Once this is done, re-install the tailhousing.

 

Put the VSS (or sleeve) back in the tailhousing. You may need to turn the output shaft to get the two speedo gears to mesh.  Once installed, you will need to hook the electrical connector back up (or put the speedo cable back on).  Re-install the T/A and driveshaft, and thats it.

 

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