Speedo Correction need assistance

[Da67goatman]

Breaking News, my speedometer is off, quite a bit.  Who would have guessed, only went from 31s and 3.08s to 33s and 4.10s.  So how do I go about changing the speedo so it reads more accurately?  I heard that there are gears inside the tail-housing that need replaced.  Trans is a 700r4.

P.S. it has 2 wires that go from trans to gauge, NOT a mechanical cable.

[topp]

You have an electrical Speedo....

There are adapters out there to allow the changes-
http://www.transmissioncenter.net/speedometer_calibration_______va.htm

[Da67goatman]

Yes its electronic, went over that in this topic,
http://forum.73-87chevytrucks.com/smforum/index.php?topic=16056.msg126424#msg126424
Speaking of, does anyone have a suggestion on how to adjust my odometer?

[topp]

The adapter adjusts the speed that registers for your gear/tire combo, hence the odometer works correctly as a result.

[Da67goatman]

Can anyone walk me through swapping gears with the trans in the truck still?  Thanks.

[Da67goatman]

No seriously, can someone walk me through swapping speedo gears in a 700r4?  that way I have some idea of what I'm doing.

[topp]

2 or 4 wheel?

[Da67goatman]

2wd, sorry I should have mentioned that.

[topp]

With an electric Speedo you don't have to change gears....

I posted a link.
http://www.transmissioncenter.net/speedometer_calibration_______va.htm

ELECTRONIC RATIO ADAPTOR


2nd, if you know what you have in it already, you may not have to change the drive gear, just the driven one.

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

[Da67goatman]

I can't justify spending $170 to correct my speedometer, its just not that important, but I would be willing to change gears.  If you walk me through changing them on a mechanical speedo, I can adapt to change them on my electronic, I have my contact at my local dealer on standby with the speedo gears.

[topp]

You need to find out what Drive gear is in there.
You may only have to change the driven gear.

Other than that.
Drop driveshaft
Drain tranny.
Remove tailshaft of tranny
Swap drive gears.
Reverse to reinstall.

[Da67goatman]

Update:  Pulled tail-housing off and there is only one gear and its on the Tail-shaft.  Took it to my most trusted GM parts people and they went back and forth on how to correct it and came up with a couple different ideas.  They had the $180 programmable one, and they remembered using a "comb" like circuit to correct the speedometer.  They have discontinued the combs, but I have them calling contacts to try and locate one.  They also recommended some local Junkyards to search through.  So now I have to put the trans back together and go parts searching, at least its a simple plug and play fix, when I find it.  I am posting some pics so you guys can watch out for this setup, its such a PITA.

[topp]

I believe the company of the link I posted sells them.....

That was one reason for the link....

[VileZambonie]

SPEEDOMETER CALIBRATION

The speedometer must be recalibrated when rear axle ratio or tire size is changed.

NOTICE: Do not touch the pins on the back of the instrument cluster or immediate damage to the cluster will occur.



Re move the cluster from the vehicle.
Refer to INSTRUMENT PANEL (SEC. 8C).
Plug the connector from the service kit (figures 20 and 21) into the back of the instrument cluster and momentarily touch the wires across the vehicle battery terminals.
The connector from the service kit should be used a maximum of 10 times.
It is not necessary to perform this step if the speedometer has been previously recalibrated.
Check the calibration chart using the vehicle axle ratio and corresponding tire size to find the appropriate pins to be removed from the clip.
The rectangular end of the clip is the top. The pins are numbered 1 through 8 from the top to the bottom of the clip. Remove the proper pins by bending them back and forth with long nose pliers.
Place the revised clip into the eight holes in the rectangular slot on the back of the cluster.
Install the cluster into the vehicle.
Refer to INSTRUMENT PANEL (SEC. 8C).

[Da67goatman]

Yes that comb thing is what I am in search of.  Anyone have one?  Sorry, but I can't seem to find anything on that web page, it could use some organization.