How to calibrate the tac?? - Page 2 - ZR-1 Net Registry Forums

02-19-2008

VSS is only used to calculate speed, nothing else.

Paul Workman · 02-19-2008

Tiz a std 3.45 gear. That wouldn't affect the tac, as others have indicated.

DaveK · 02-19-2008

ahhh okay - I thought the vss signal was used on both, my mistake

Tom · 02-20-2008

I have seen this on a 90 ZR1, the problem was in the instrument cluster which had to be pulled and repaired. I would ask a local Chevy dealer where they send their warranty electrical repairs.

Jarek5_7 · 01-17-2009

mine tach in 1991 read twice as real rpm ;(

WVZR-1 · 01-17-2009

Tach calibration is done on the "main board" in the cluster. I've had conversations with a fellow who likely can accomplish it but he's not into the C4 clusters presently. He's pretty close to me and has offered to look at mine and with snapshots I've provided he's agreed with me which capacitors/resistors are responsible for the calibration. I just haven't had the opportunity to let him have at it. He does early stuff for many of the "resellers". The resellers that sell other than his product send theirs to him to correct when the one they sold fails.

The cluster can be sent to several cluster re-builders for the calibration and they usually come with a 1 yr warranty. There's not as many authorized service centers as there used to be but there are "responsible" people out there. A build should be something $235 to maybe as high as $350.

The error is sometimes conversational. When I bought my car I was told "stock everything". Seat of the pants it sure felt like it was "stock" but the tach reflected something that would have led a person to believe it had a gear! I checked it with my Tech1 and confirmed the error.

If you've an "error" now it will likely get substantially worse.

The tach can also be calibrated with a "box" similar to a Dakota digital. A plus to this would be you could occasionally re-calibrate it yourself. I've had conversations with a builder and it seems quite easily accomplished.

gbrtng · 01-17-2009

Check with these guys

http://www.instrumentclusters.com/

to see if they can "calibrate" a tachometer. They repaired a 91 cluster for me and
their work is good.

The tachometer is just an analog gauge which gets its input from the ECM - it's kind of like a voltmeter.

And the tach reading has NOTHING to do with the rear gears.

WVZR-1 · 01-17-2009

Quote:

Originally Posted by gbrtng

Check with these guys

http://www.instrumentclusters.com/

to see if they can "calibrate" a tachometer. They repaired a 91 cluster for me and
their work is good.

The tachometer is just an analog gauge which gets its input from the ECM - it's kind of like a voltmeter.

And the tach reading has NOTHING to do with the rear gears.

If your reference is to my post here's an example:

2500 RPM / 3.45 gear / 1-1 (4th) / 25.7 tire = maybe 110 MPH,

2500 RPM / 3.90 gear/ 1-1 (4th) 25.7 tire = maybe 98 MPH

If your car (stock) is at 2500 RPM in 4th gear and the speedo is something substantially less than 110 MPH with no speedo error there can be only a couple explanations, it's had a gear installed or it's got a tach error. Mine were numbers similar to these and I confirmed the tach error with a Tech1 reading both speed and RPM from ALDL connector. I didn't SAY the rear gear effected the tach's accuracy.

The Tech1 confirmed the "tach error" and also the fact the car I bought was "stock" at least in respect to the rear gear ratio.

gbrtng · 01-17-2009

Quote:

Originally Posted by WVZR-1

If your reference is to my post here's an example:

2500 RPM / 3.45 gear / 1-1 (4th) / 25.7 tire = maybe 110 MPH,

2500 RPM / 3.90 gear/ 1-1 (4th) 25.7 tire = maybe 98 MPH

If your car (stock) is at 2500 RPM in 4th gear and the speedo is something substantially less than 110 MPH with no speedo error there can be only a couple explanations, it's had a gear installed or it's got a tach error. Mine were numbers similar to these and I confirmed the tach error with a Tech1 reading both speed and RPM from ALDL connector. I didn't SAY the rear gear effected the tach's accuracy.

The Tech1 confirmed the "tach error" and also the fact the car I bought was "stock" at least in respect to the rear gear ratio.

My post was not in response to yours. Yours hit the list while I was typing.

XfireZ51 · 01-17-2009

The issue with our tach, like all the other electronic tachs since at least 84 is that the damn thing is slow to react. Get a shift light.

02-19-2008	#11
Jeffvette Guest Posts: n/a	Re: How to calibrate the tac?? VSS is only used to calculate speed, nothing else.

02-19-2008	#12
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: How to calibrate the tac?? Tiz a std 3.45 gear. That wouldn't affect the tac, as others have indicated.

02-19-2008	#13
DaveK Join Date: Jul 2004 Location: Sudbury, Ontario. Canada Posts: 1,533	Re: How to calibrate the tac?? ahhh okay - I thought the vss signal was used on both, my mistake __________________ 1991 #1516 Black/Black davidmkelly.com Author of fast-paced, sci-fi thrillers.

02-20-2008	#14
Tom Join Date: Jan 2004 Location: Southern CA Posts: 108	Re: How to calibrate the tac?? I have seen this on a 90 ZR1, the problem was in the instrument cluster which had to be pulled and repaired. I would ask a local Chevy dealer where they send their warranty electrical repairs.

01-17-2009	#15
Jarek5_7 Join Date: Aug 2008 Location: Radom, Poland Posts: 38	Re: How to calibrate the tac?? mine tach in 1991 read twice as real rpm ;(

01-17-2009	#16
WVZR-1 Join Date: Oct 2004 Posts: 1,884	Re: How to calibrate the tac?? Tach calibration is done on the "main board" in the cluster. I've had conversations with a fellow who likely can accomplish it but he's not into the C4 clusters presently. He's pretty close to me and has offered to look at mine and with snapshots I've provided he's agreed with me which capacitors/resistors are responsible for the calibration. I just haven't had the opportunity to let him have at it. He does early stuff for many of the "resellers". The resellers that sell other than his product send theirs to him to correct when the one they sold fails. The cluster can be sent to several cluster re-builders for the calibration and they usually come with a 1 yr warranty. There's not as many authorized service centers as there used to be but there are "responsible" people out there. A build should be something $235 to maybe as high as $350. The error is sometimes conversational. When I bought my car I was told "stock everything". Seat of the pants it sure felt like it was "stock" but the tach reflected something that would have led a person to believe it had a gear! I checked it with my Tech1 and confirmed the error. If you've an "error" now it will likely get substantially worse. The tach can also be calibrated with a "box" similar to a Dakota digital. A plus to this would be you could occasionally re-calibrate it yourself. I've had conversations with a builder and it seems quite easily accomplished.

01-17-2009	#17
gbrtng Join Date: Feb 2006 Location: San Antonio area Posts: 1,177	Re: How to calibrate the tac?? Check with these guys http://www.instrumentclusters.com/ to see if they can "calibrate" a tachometer. They repaired a 91 cluster for me and their work is good. The tachometer is just an analog gauge which gets its input from the ECM - it's kind of like a voltmeter. And the tach reading has NOTHING to do with the rear gears. __________________ “Buy the best example of what you want, and pay whatever it takes. That way, you cry only once.” ~ Bruce Meyer

01-17-2009	#20
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,683	Re: How to calibrate the tac?? The issue with our tach, like all the other electronic tachs since at least 84 is that the damn thing is slow to react. Get a shift light.