Tach Fixed
 

Well, I finally got the part I needed and got it installed. Thanks to 5.0 10 for posting the pic of the S-10 tach capacitor swap.
From that I was able to track down that capacitor on the Camaro tach.
It is right under the edge of the tach face at the 3250 RPM position, it is the larger of the 2 cylindrical items there. Just unsolider it from the PCB and install another capaciter .0033 uf 100VAC (Polyester film type). I got mine from Mouser Electronics http://www.mouser.com/ and the P/N for it is: 75-225P100V0. 0033
I was able to confirm through Winaldl that it was the tach that was reading incorrectly (by over 500 RPM), since both the ECM and Tach get the same signal from the distributor.
I put the new capaciter in the tach and fired it up and the RPM's are now reading right.
Hope this helps some others with this problem. And it beats the $125 that everyone wants to repair a tach.

~M~

I am a little dense and my ability with electronics minimal...could you put up a diagram of the board or a pic that shows which component(s) need to be replaced?

Also will replacing that component correct a v6 tach for an 8? I did a board search but didn't find any solid answers on the issue.

Yes it will make a V6 tach work in a V8. I did however give the wrong position for the component that needs changed. It is at the 3250 RPM position not the 5750 RPM.
I tried to take a picture but the face plate is too close to the board and throws a shadow over the spot.

What you are looking for is a red/brown item (Capacitor) out near the edge of the board, it is about 3/4" long and 1/4" diameter. There is a smaller silver diode sitting next to it. Just unsolider the capacitor and bend the ends of it's wires up while the solider is melted, then remove it one end at a time and install the new one in the same holes and resolider.

~M~

Thanks :D I'll give it a shot this weekend.

OK finally got to the electronics store, got a capacitor, soldered it to the board and swapped the board onto my guage...problem is when I fired up the car the thing read waaaay too high instead of dropping to where it should be, so I either got a bad board or the wrong capacitor :( back to the drawing board. I will probably solder the cap onto my current board, which I know works and see what happens.

Well after several trips to the electronics store, taking the dash apart half a dozen times and one burned fingertip :doh: I could not get the tach working, so I said **** bought a V8 tach from thirdgenparts and swapped the board onto my V6 tach....works like a charm. :) Funny thing is though, the capacitors on both boards are stamped with the same ratings...WTF?! oh well it works, I'm happy :)


Hmm I just realised my guage cluster is the biggest parts whore in my car I have guages and parts of guages from 4 different cars in there, but the best part is all the faces and needles match :)

The capacitor that Morley reccommended worked for me. Here are some pictures.

Here's a second one.

Hey what does it mean when your tach goes to like 3000 then kinda sticks and bounces around a little (200-300 rpm). Plus my speedo is off like 20 mph or so. More so the faster I go.

Any ideas???

does this work with the Firebird Tachs as well?

Something I found out about the Firebird tachs...it seems that just the face may be the only difference between the V6 and V8 units.
I installed some white face overlays last weekend, and just dummied them up on my old 86 V6 cluster first to see how they installed before attempting to demolish my 89 V8 cluster.
The 0 rpm point is in the same location on both faces. When straight up, the V6 tach reads 6000 rpm (with the V6), it is getting 6000 x 6 (36,000) pulses per minute at that reading. On the V8 face, straight up is only the 4500 rpm position, but it is still getting that same number of pulses per minute (4500 X 8 = 36,000).
This makes a cheap easy alternative to seeking out a V8 Firebird tach when swapping out a V6 for a V8. Find a V8 tach face, or install a set of V8 overlays and install them.

Pete

how about the GTA digital dashes??

I just converted my v6 tach to a work with a v8 by changing the .0068uf capacitor found under 5750 (above the oil gauge) to a .0033uf (332M) not the .068uf capacitor found under 3250. My gauge works Great with the v8 now.

I changed the .0068 cap to .0033 on two different tachs pulled from 87 and 89 irocs and they still read high. You don't want to change the .068 or it will peg! Ok so has anyone yet experimented with the resistance chip or measured it pin to pin? I have very different readings between the two tachs I have and one is reading higher than the other so maybe it can be adjusted down. I have no schematics to work with.

There seems to be some confusion here with which capacitor to replace. I have a v6 tach and need to convert it to a v8, which one do I replace, the 3250 one or the 5550 one?

Noone seems to know? I just got the capacitors in the mail and am confused which one to replace.

Re: Tach Fixed
 

can somone give me the capcitor ratings for a factory v6 tach need to convert a v8 tach to read right on a v6

Re: Tach Fixed
 

Can somebody explain what issues they were having with their tach that led them to determine that the cap was to blame? There is a very large thread devoted to the failed resistor issue, and from what I can see, this failed cap issue is producing some of the same symptoms. I'd like for us to be able to clarify specifically how to diagnose a faulty capacitor vs. a faulty resistor so that people with problems can be sure that they're doing the right fix.

Re: Tach Fixed
 

Because of the time that the tachometers have been around, I would suspect the capacitors. Electrolytic capacitors go bad over time and even open up at the top sometimes. Resistors are easy to measure when removed from the board but the resistance measured while part of a circuit only measures the least resistive path on the board and not necessarily the resistor you’re looking at. As far as I know they do not degrade over time and are less suspect. They can over heat, turn brown and crumble but that would be from extreme heat. Either one may become excessively hot while the circuitry is on but it still could be from surrounding components and not necessarily the one in question.

There could be issues with multiple capacitors going bad resulting in issues as well. The replacement of a resistor may be making up for the capacitors or other faults of the circuits. I can’t really comment on it any more specifically than that.

Re: Tach Fixed
 

I have a 87 v8 Camaro that I've tried this in, and instead of being way off it now instantly pegs out to max rpm after the capacitor swap, any thoughts? I ordered this one http://www.mouser.com/Search/Product...225P100V0.0033 as suggested in the OP

Do you think I should also try that 90-92 tach fix with the resisters?

[update]

I went ahead down to radio shack and got 2 of those 100k 1/2 watt 5% resistance resisters to try that fix. Few things to note, older models don't have a separate removable board, that white designed chip is simply on the tach board with the for mentioned capacitor swamped before so its a bit harder to get to and work with. I however managed to cut the 2 pins needed and sauder the two resisters on it.

The new problem is now instead of being pegged at 7k it bounces between 500-1000 regardless of what the actual rpm is. So that fix either doesn't apply or needs some adjustments to work with my 87's v8.

Re: Tach Fixed
 

I tried too. I ultimately just bought a working used tach and all is well. Naturally, the oil pressure gauge doesn't work correctly but at least the tach does.

Re: Tach Fixed
 

i tried this on my 1989 v8 tach.its now pegged at 7000.i wonder if this was a 'convert your tach from v6 to v8 post'the whole time.its also confusing.
[quote]
Yes it will make a V6 tach work in a V8. I did however give the wrong position for the component that needs changed. It is at the 3250 RPM position not the 5750 RPM.
I tried to take a picture but the face plate is too close to the board and throws a shadow over the spot.

What you are looking for is a red/brown item (Capacitor) out near the edge of the board, it is about 3/4" long and 1/4" diameter. There is a smaller silver diode sitting next to it. Just unsolider the capacitor and bend the ends of it's wires up while the solider is melted, then remove it one end at a time and install the new one in the same holes and resolider.
[end of quote]
is it the capacitor at 3250 or 5750?on my tach the silver diode is beside the 5750 capacitor.maybe morleys tach was different than mine.

Re: Tach Fixed
 

ok.i got my tach almost right now.i did as this post said.https://www.thirdgen.org/forums/elec...meter-fix.html .i ended up using a 100k and two 47k resisters.according to my scanner my tachs now right at idle,100 rpm low at 2000 and 200 rpm low at three thousand.close as i could get without using a variable pot.

Re: Tach Fixed
 

what was wrong with the tach that you had to change the capacitor. mines not working at all since the rebuild.

Re: Tach Fixed
 

Sorry to bump an old old thread. I just want to be sure im comprehending this right since im no electrical engineer.

To fix an 89 or earlier Tach all you need to do is replace a red capacitor near the 3k mark on the circuit board?

"The stock tachs in these cars are notorious for reading incorrectly. The usual problem with the 82-89 Camaro tachs is a capacitor located on the back side of the tachometer face."

Or do I need to do what it says here... to clip the 4 and 10 resistor pins? There is a white and black resistor on the earlier style tachs.
https://www.thirdgen.org/forums/elec...ml#post2836660

Re: Tach Fixed
 

I have the same question as chevyman. 88 305 iroc. Do i just need to replace the capcitor or do i also need to mees with the circuit board?

Re: Tach Fixed
 

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Re: Tach Fixed
 

i read ur the man on these 89 tach fixes. im either real tired or dumb but wht excatly do i need to do start to finish? mine is reading way high.

Re: Tach Fixed
 

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Re: Tach Fixed
 

Greg,
I just replace the resistor with a set value for the V8 cars found in one of the threads. Oh I found it. I used a 190k ohm resistor on it.

Can you change a V6 tach into a V8 tach with the same resistor swap or do you have to do other modifications to it? I have a 6000rpm tach and I don't know if it's a V8 or V6 tach. I assumed it was a V8 so I put the standard resistor in it for the V8's.

I found the thread:
https://www.thirdgen.org/forums/elec...-89-tachs.html

Re: Tach Fixed
 

My stock tachometer is twice as fast as the aftermarket tach we put on top of my dash. How would i fix this?

Re: Tach Fixed
 

https://www.thirdgen.org/forums/elec...-89-tachs.html

I did what Dimented did in his thread, but I went on ebay and bought the small 190k resistors so it would take up as little space on the board as possible. I snipped the leads on 4 & 10 IIRC, desoldered the leads, cut the leads as short as I dared on the 190k and resoldered them into the holes.

Re: Tach Fixed
 

I did the resistor fix today also and it worked great!

https://cimg3.ibsrv.net/gimg/www.thi...1a49b61178.jpg

Re: Tach Fixed
 

Nice!

I just grabbed a 200kohm resister packet because I wanted it to look factory. Glad you got it working again.

Re: Tach Fixed
 

Thanks, I was trying to get as close to 192k as possible. I used a 100k, and two 47k resistors spliced and soldered together (in the shape of the letter Z). Because of the 5% tolerance of the resistors, and each resistor being slightly under-value, I am at 190.8k ohms. I couldn't run it long yesterday because I have the transmission out and open headers, but it's only 200-300rpm off from from what my ECU says. WAY better than the 2000rpm variance that I had previously.