How to install speedometer correction gears

I am in the process of a differential rebuild with 4:10 gears install so I purchased a set of speedometer correction gears from Marc Haibeck (ZR-1 Specialist). Being a novice myself I figured I would share this for the others novice folks that like to do things themselves as I do (mostly because I can't afford to pay someone and also because of my location).

Anyway, assuming all the other things from car jacked up safely to exhaust removed and driveshaft removed, etc., etc. mine was done with the trans of out the Z and just tilted to its side and supported with some pieces of 2X4s.

1. Remove the 10mm bolt on the Vehicle Speed Sensor



2. Gently pry the edge of the sensor in equal locations around the sensor and remove it. If your trans is in the car, approximately 1/4 of a liter will drain out according to the ZF Doc's instructions.



3. Turn the shaft so you can see the tab at a good location to press down on and push the drive gear toward the rear and slide off the output shaft. I used a small screwdriver to reach in and push it until it came of the back end where the driveshaft goes in. Be careful because the clip shown can easily fall from its location, but you should have no problem retrieving it if so.



Here are the new replacement corrections gears from Marc. White is the drive gear for the output shaft and blue is the driven gear for the vehicle speed sensor:




4. Put the new drive gear in from the rear sliding it over the output shaft and use a long thin object to push it forward. I used a long, thin flat screwdriver. Once you get the slot lined up on the gear to the tab, use one hand to hold the clip and press down into the slot as you push the gear forward with your other hand until it goes all the way in against the washer and you will hear a click. Attempt to push the gear back to ensure it is locked in place and turn the shaft if you need to double check and ensure it is locked.



5. Replace the driven gear (blue) and clean the seal (replace if you have a new one) and all the areas inside the housing and the sealing area for vehicle speed sensor. I applied a very light coat of clean oil.
.

6. Gently put the vehicle speed sensor back in and use the clamp as a guide to where it is placed in reference to the clamp/hold down. Verify by looking into the tailshaft with a light and you will be able to see your drive gear and driven gear meshed and you can turn the shaft to see the gear engagement. Ensure the spacer is on the bottom of the hold down and tighten the 10mm bolt.

Top off your oil, etc., etc. and reverse the process of removal for other items. Here is the written info that I used from Bill Boudreau's site:

Changing the Speedometer Gears on the Vehicle
NOTES: The C4 Corvette Vehicle Speed Indication System (VSIS) uses a pulse-signal-reference generated from the Vehicle Speed Sensor (VSS). The VSS, when equipped with a 15 tooth (T) drive gear (on output shaft) and 42T driven gear turning the VSS combined with a 3.45:1 differential ration, produces 4000 pulses per mile traveled. The VSIS is calibrated to 4000 pulses equaling one mile. When the differential (final drive) ratio changes, so does the pulses generated over each mile. To correctly recalibrate the VSIS signal pulse rate back to 4K/mile either the drive and/or driven VSS gear(s) must be changed or a black box Electronic Ratio Adapter (ERA) installed. Both cost around $140.
DIRECTIONS:
- Raise vehicle and safely support on jack stands.

Remove or Disconnect
- Exhaust.
- Driveshaft-to-pinion strap bolts (8mm).
- Driveshaft. (little to no oil should leak out).
- Vehicle Speed Sensor 10mm bolt.
- Vehicle Speed Sensor.
Note: Roughly 1/4 of a liter of oil will drain out of the transmission.
- Driven gear from Vehicle Speed Sensor.
- Drive gear off of output shaft.
To do this, you will need to rotate the shaft until the speed sensor drive gear clip is visible.
Push in on the locking tang of the clip then slide the driven gear back and off of the output shaft.
NOTE: The speedo drive gear will clear the extension housing tail bushing and seal.
Leave the washer in place for the new speedo drive gear.

Install or Reconnect
- Speed Sensor Drive gear and locking clip.
- Driven gear onto Vehicle Speed Sensor.
- Vehicle Speed Sensor.
- Vehicle Speed Sensor 10mm retaining bolt.
- Driveshaft.
- Driveshaft-to-pinion strap bolts (8mm).
- Oil into the transmission to replenish what was lost.
Note - add oil through the fill plug hole until it runs back out of the hole.
- Exhaust.


So there you have it, my little contribution that may or may not help anyone. I am a visual person so it would have made it easier for me having seen this first even though this is very easy to do and a slow person like me took maybe 20 minutes to do this taking photos and being meticulous. Even I can do it and I am not a caveman, nor did I stay at a Holiday Inn Express.

[Hammer]

Excellant Craig, Thanks. You should contact Dwight and have him get this in the Heart of the Beast. Would make a great article for the mag.

[xlr8nflorida]

Originally Posted by Hammer

Excellant Craig, Thanks. You should contact Dwight and have him get this in the Heart of the Beast. Would make a great article for the mag.

Why do some cars with the 410's have the speedo calibration box?

John,

Thanks for the kind comments, but I don't really know if this is that worthy. I was just trying to share with pictures.

Xlrn8florida,

Based on the ZF Doc, I think it is just a matter of choice in the last sentence. For me I prefer the gear (manual) method and feel I don't have to worry about accuracy with electronics for the box breaking:

Changing the Speedometer Gears on the Vehicle
NOTES: The C4 Corvette Vehicle Speed Indication System (VSIS) uses a pulse-signal-reference generated from the Vehicle Speed Sensor (VSS). The VSS, when equipped with a 15 tooth (T) drive gear (on output shaft) and 42T driven gear turning the VSS combined with a 3.45:1 differential ration, produces 4000 pulses per mile traveled. The VSIS is calibrated to 4000 pulses equaling one mile. When the differential (final drive) ratio changes, so does the pulses generated over each mile. To correctly recalibrate the VSIS signal pulse rate back to 4K/mile either the drive and/or driven VSS gear(s) must be changed or a black box Electronic Ratio Adapter (ERA) installed. Both cost around $140.

[Jagdpanzer]

When installing the correction gears with the transmission still in the car I find it helpful to mark the area around the tab slot of the white drive gear with a black majic marker. This makes the slot much easier to see when lining it up to slide over the drive tab.


Another tip is put some heavy grease on the back side of the drive tab to help hold it in place on the transmission output shaft while installing the drive gear.

Originally Posted by Jagdpanzer

When installing the correction gears with the transmission still in the car I find it helpful to mark the area around the tab slot of the white drive gear with a black majic marker. This makes the slot much easier to see when lining it up to slide over the drive tab.


Another tip is put some heavy grease on the back side of the drive tab to help hold it in place on the transmission output shaft while installing the drive gear.

Thanks for adding in these great tips.

[flyin ryan]

Originally Posted by Hammer

Excellant Craig, Thanks. You should contact Dwight and have him get this in the Heart of the Beast. Would make a great article for the mag.

He's right Craig, you should. To the guys who have not yet ever done it, it IS worth it! I feel guilty sometimes for not writing something to contribute . John (Hammer) has a good idea for once...must be a new year or something . John knows I Luv him

Originally Posted by flyin ryan

He's right Craig, you should. To the guys who have not yet ever done it, it IS worth it! I feel guilty sometimes for not writing something to contribute . John (Hammer) has a good idea for once...must be a new year or something . John knows I Luv him

Thanks Ryan. It would be the first thing I ever contributed to. It is harder for the knowledgeable folks to imagine how a novice thinks sometimes. I really don't know enough to contribute much as all of this is a first most of the time for me. I sure do use the heck out of all the advice I find here and otherwise on the internet; I have no idea what I would do without it. It would be nice it share something or help if possible. Maybe I'll try to document the battery relocation project I am doing too.

[tomtom72]

Craig. This is a sweet write up, and the tips from Jagdpanzer on the "in car" situation are sweet added info!


Happy New Year Fellers!