willcox tach board
Thread Starter
Cruising
Joined: Jun 2015
Posts: 12
Likes: 0
From: Toronto ON
willcox tach board
Hello,
Last year my tach froze at 1900 rpm, I replaced the tach board and it's working better, but I've noticed a few behaviours I wouldn't mind a comment on
1) occasionally, particularly on startup the needle flips completly over to a few thousand past redline, as if the magnet polarity has pulled the wrong way or something. After enough sweeps of rpm it typically comes back
2) apparently my cold idle is about 600 rpm, and hot idle is about 200 rpm. Some days it's more like 400, some its just over zero. Not sure what it actually is as a number, but the car idles fine, definitely the problem in the tach not the engine
3) running the numbers 100 kph, 27" tires, 3.08 rear end (That's not 100% certain, that's why I started looking into this) the rpm should be ~2500 but it reads ~2900 some days, ~3100 others
4) the tach is beautifully smooth, zero gitter jumps or oscillations. Does behave oddly at low voltage and during crank but zero complaints about motion, just that the values seem off. Not off by massive amounts, but off.
Way back when I was into electronics, I have a power supply and oscilloscope and function generator. Is there a way to check the distributer / filter output to see if that is logical? I don't have a timing light unfortunately I know some give readouts. Thanks,
Last year my tach froze at 1900 rpm, I replaced the tach board and it's working better, but I've noticed a few behaviours I wouldn't mind a comment on
1) occasionally, particularly on startup the needle flips completly over to a few thousand past redline, as if the magnet polarity has pulled the wrong way or something. After enough sweeps of rpm it typically comes back
2) apparently my cold idle is about 600 rpm, and hot idle is about 200 rpm. Some days it's more like 400, some its just over zero. Not sure what it actually is as a number, but the car idles fine, definitely the problem in the tach not the engine
3) running the numbers 100 kph, 27" tires, 3.08 rear end (That's not 100% certain, that's why I started looking into this) the rpm should be ~2500 but it reads ~2900 some days, ~3100 others
4) the tach is beautifully smooth, zero gitter jumps or oscillations. Does behave oddly at low voltage and during crank but zero complaints about motion, just that the values seem off. Not off by massive amounts, but off.
Way back when I was into electronics, I have a power supply and oscilloscope and function generator. Is there a way to check the distributer / filter output to see if that is logical? I don't have a timing light unfortunately I know some give readouts. Thanks,
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
It sounds like there is an issue somewhere for sure, 200 rmp idle is impossible. You can test the signal from the distributor but I doubt that is the issue. You might by-pass the filter and see if the problem remains... for the board to flip like that almost sounds like something is spiking it. Sometimes it can be that one of the retaining nuts isn't seated too. Usually when I install the board I tighten the nuts up, then back them off a bit and re-tighten them.
It could be a movement issue, it could be a board issue... The best way for me to know is for me to have the tach here... So if you'd like, send the tach to me and I'll test your tach movement and then match calibrate the board to your tach. That is the best way... No charge, just the return shipping.
-Willcox
It could be a movement issue, it could be a board issue... The best way for me to know is for me to have the tach here... So if you'd like, send the tach to me and I'll test your tach movement and then match calibrate the board to your tach. That is the best way... No charge, just the return shipping.
-Willcox
Last edited by Willcox Corvette; Apr 16, 2016 at 10:47 PM.
Racer
Joined: Mar 2003
Posts: 282
Likes: 0
From: London
On the subject of the Tach board ... I'm currently having an issue that has me a bit puzzled.
I fitted a replacement Tach board, as my original board was reading WAY too high... but as yet I've not been able to get the new board to function properly. I assumed it was a faulty board so I sent it back and got a replacement ...but I've having exactly the same problem with this one.
Essentially, I've followed the fitting instructions... and everything is fine up to a point. When I switch the ignition on, the Tachometer needle goes to zero on the dial, as expected. When I crank the engine however, the needle jumps down below zero ... then once the engine is running, the needle just sits at zero again, no mater how much i rev the engine.
I tried re-fitting the old original board again, and it worked just fine (apart from reading too high).
I've checked all the nuts through the board are tight and in the right place... and it all seems fine.
I'm pretty competent when it comes to fitting stuff like this... but I'm obviously doing something completely stupid!?
Does anyone recognise these symptoms and know what might be wrong?
Thanks.
I fitted a replacement Tach board, as my original board was reading WAY too high... but as yet I've not been able to get the new board to function properly. I assumed it was a faulty board so I sent it back and got a replacement ...but I've having exactly the same problem with this one.
Essentially, I've followed the fitting instructions... and everything is fine up to a point. When I switch the ignition on, the Tachometer needle goes to zero on the dial, as expected. When I crank the engine however, the needle jumps down below zero ... then once the engine is running, the needle just sits at zero again, no mater how much i rev the engine.
I tried re-fitting the old original board again, and it worked just fine (apart from reading too high).
I've checked all the nuts through the board are tight and in the right place... and it all seems fine.
I'm pretty competent when it comes to fitting stuff like this... but I'm obviously doing something completely stupid!?
Does anyone recognise these symptoms and know what might be wrong?
Thanks.
Racer
Joined: Mar 2003
Posts: 282
Likes: 0
From: London
So .... I actually figured this one out for myself 
It was the Tachometer Filter.
Once I bypassed the filter, the replacement tach board seemed to work fine. The odd thing is that the original tach board still gave a reading with the filter in place ... but the new board didn't like it for some reason.
I'm not exactly sure what the filter does ... but I'll maybe try getting a new one, or just leave it out
It was the Tachometer Filter.
Once I bypassed the filter, the replacement tach board seemed to work fine. The odd thing is that the original tach board still gave a reading with the filter in place ... but the new board didn't like it for some reason.
I'm not exactly sure what the filter does ... but I'll maybe try getting a new one, or just leave it out
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
It sounds like there is an issue somewhere for sure, 200 rmp idle is impossible. You can test the signal from the distributor but I doubt that is the issue. You might by-pass the filter and see if the problem remains... for the board to flip like that almost sounds like something is spiking it. Sometimes it can be that one of the retaining nuts isn't seated too. Usually when I install the board I tighten the nuts up, then back them off a bit and re-tighten them.
It could be a movement issue, it could be a board issue... The best way for me to know is for me to have the tach here... So if you'd like, send the tach to me and I'll test your tach movement and then match calibrate the board to your tach. That is the best way... No charge, just the return shipping.
-Willcox
It could be a movement issue, it could be a board issue... The best way for me to know is for me to have the tach here... So if you'd like, send the tach to me and I'll test your tach movement and then match calibrate the board to your tach. That is the best way... No charge, just the return shipping.
-Willcox
Last edited by JimLentz; May 2, 2016 at 04:12 PM.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
So .... I actually figured this one out for myself
It was the Tachometer Filter.
Once I bypassed the filter, the replacement tach board seemed to work fine. The odd thing is that the original tach board still gave a reading with the filter in place ... but the new board didn't like it for some reason.
I'm not exactly sure what the filter does ... but I'll maybe try getting a new one, or just leave it out
It was the Tachometer Filter.
Once I bypassed the filter, the replacement tach board seemed to work fine. The odd thing is that the original tach board still gave a reading with the filter in place ... but the new board didn't like it for some reason.
I'm not exactly sure what the filter does ... but I'll maybe try getting a new one, or just leave it out
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I had odd symptoms after replacing my defective tach board. I tested it with 12 V before installing it and all looked good. I installed it on my '77 and then noticed very erratic behavior and after removing it again found one of the nuts was loose and tightening it up permanently fixed the problem. The board is a pain to get to in my car.
Your right, the 75-77 tach is a royal pain to get in and out.
This is a common problem and one we'll address when we re-shoot the new installation video. When I install them in the shop I tighten the nuts down, back them off a bit and then tighten them down again.
Willcox
