Ok, I know I've posted replying to others about how much I liked the electronic recalibrator from Zip Corvette. It's time for me to eat my words. I mounted up my D44/3.45 this morning and all was well. In fact, so well that I mentioned to a friend I was waiting for the problems to start any time. Well, they did. I hooked up the recalibrator and the speedo was eratic. I switched the VSS wire I was using from the yellow wire to the purple one. This didn't do anything. The speedometer was reading the same as if the recalibrator wasn't hooked up. I switched the wires going into the calibrator and it was the same. The only way I haven't tried was using the yellow wire and switching the wires going into the calibrator.
Does anyone have any suggestions about this calibrator? Which wire is the signal wire from the VSS?

TIA,
Chris

 

Ouch! Wish I could help you man, I sent my compeuter to reflashed by a pro. Too many bad expereinces with Hypertech, etc.

Good luck.

 

His '87 speedo isn't ECM controlled like your '95. Nothing to "flash" on the '87. That expensive re-cal box isn't necessary, either. If you are running a stock tire size, let me know which size and the "before" ratio. I can give you some GM part numbers that will correct your speedo for, reportedly, under $45.00 cost.

RACE ON!!!

 

It's an 88, but its the same as the way the 87's were. I was going to go with the gears, because I didn't want to have to pull apart the driveshaft and tranny tailshaft.
BTW, I will probably end up ordering the speedo gears anyway and doing it the old fashioned way. What's the part numbers for the gears going from a 3.07 auto to 3.45's? Will I need a new VSS also?

Chris

 

Your 3.07, 1988 auto should have:

Drive gear: Red, 17 teeth, pn, 8640517.
Driven gear: Green, 42 teeth, pn, 25513049.
Sensor: 25007339.

OOPS! It looks like I spoke out of turn. My 1984-1989 Corvette parts book doesn't show the 3.45 ratio. Only the 3.54 ratio. I could, maybe, do a ton of math, and research some other parts books, but it would be a lot easier if someone on here has a Corvette book showing the 3.45 gears. Sorry. The above numbers ARE correct for the 3.07's, so you can compare the correct 3.45 parts to see what is different. I think you will be able to reuse your sensor.

RACE ON!!!

 

The yellow wire is the signal wire, purple is the signal ground. I just installed the Dakota Digital SGI-5 Universal Signal Interface Unit $80 on my 88 to correct for 3.73 gears and it works fine. I followed the set up instructions for application #2 for an 8kppm-4kppm signal using ouput #1 (ac). Are you sure you have good power and ground connections? I used the ign lamps power feed, pink and black wire(C16) and black ground (D1) with no issues.

Good luck.

 

The power and ground wires were good, I used a multimeter to test when I did the hookup. I ended up ordering the Dakota Digital unit. Hopefully this works. I think the Zip one must've gotten busted durring shipment back to the states.
Thanks for the help. If you have any other setup tips on the dakota digital one, let me know.


Chris

 

I just tested my speedo calibration with the Dakota Digital Interface installed, with respect to a Race Locic V-box gps-based data acquisition unit.

The Initial calibration was very close indeed, within 1% at 110 kph,
(109 kph indicated vs 110 actual according to the Vbox). The Mph readings were just as good, but permitted higher resolution for test purposes. Unfortunately I-75 traffic at lunch time did not permit convenient testing at 100 mph.

The cal ratio I used was simply 3.07/3.73 = 0.823. So I set the DD to the closest value available 0.821. I have now increased it by one step to 0.826 since my testing indicated I was a bit low (109 kph indicated vs 110 actual). I know its silly to worry about < 1% error, but if you can correct it, why not. Now its dead nuts (within the precision of the display). If in doubt, you may want to round up, instead of down.

By the way I'm running an 88 4+3 (3.73) with Nitto drag radials P275/40ZR 17s rated for 811 revs/mile.

My testing with the Vbox indicates that the factory speedo calibration is very good as well, and a simple ratio division is all that is required for an accurate calibration.

Installation notes: I installed mine hidden under the upper dash panel, simply attached with velco to the top of the center the hvac ducts, since this location is close the the cluster connectors and is relatively easy to access by removing the upper dash.

I'm impressed with the product. :thumbs: