Bouncy Tach, ...I tried the fix |
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Bouncy Tach, ...I tried the fix |
yeahmag |
Apr 28 2010, 11:04 AM
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#1
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
So once I got my 2056cc built the tach could no longer keep up and just flailed around worthlessly... Especially when running an autocross. So I finally got around to trying the 2200uF trick and now it's over damped... Sigh. Maybe I'll try a different variant of capacitor and see what happens.
Anybody else have a recommended type of capacitor for the application: http://en.wikipedia.org/wiki/Types_of_capacitor |
Dr Evil |
Apr 28 2010, 11:13 AM
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#2
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Send me your transmission! Group: Members Posts: 23,002 Joined: 21-November 03 From: Loveland, OH 45140 Member No.: 1,372 Region Association: MidAtlantic Region |
Maybe halving the farads will help?
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yeahmag |
Apr 28 2010, 11:17 AM
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#3
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
My EE friend thought that changing the type is probably a better bet. I have a rather large, polarized, electrolytic style - like you would use in audio. He was thinking of trying a non-polarized style.
It moves kind of like the old, mechanical ones you see on 20's and 30's race cars. Very jerky and then "sticks". |
Dr Evil |
Apr 28 2010, 11:24 AM
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#4
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Send me your transmission! Group: Members Posts: 23,002 Joined: 21-November 03 From: Loveland, OH 45140 Member No.: 1,372 Region Association: MidAtlantic Region |
Where did you get the info on the capacitor? I thought that the capacitor changed the RPM factor (like changing it from reading a 4 cyl to an 6 or 8 cyl). A large electrolytic one is not necessary. You can get a small capacitor at Radio Shack for a few cents and that should do it. The capacitor is basically acting as a clip on the RPM wave form. Like turning down the volume. Right now you are turning the volume down too far so a lower farad cap would give you a smaller time constant thus allowing more of the RPM signal through. You can see where changing the cap could dope the signal enough to stall it and make the needle rise slowly enough to match the RPM of a 6 or 8cyl.
I would think that gutting a universal tach and putting the guts into your case with your face and needle would be a more cost effective and time wise endeavor. |
yeahmag |
Apr 28 2010, 11:27 AM
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#5
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
It's just what the EE stock room on campus had... I've grown accustom to not really having to read the tach as I have a Mallory 6AL (rev limit) and can feel the engine really well.
That being said it would be nice to have something functional there... I'll try another, smaller cap first and see what happens. |
Dr Evil |
Apr 28 2010, 11:47 AM
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#6
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Send me your transmission! Group: Members Posts: 23,002 Joined: 21-November 03 From: Loveland, OH 45140 Member No.: 1,372 Region Association: MidAtlantic Region |
IIRC, the 2200uF was the one used to convert to a V8 tach.
I have heard of people greasing the needle shaft with some semi viscous lube to slow its bounce. This may also be a quick and simple solution for you. It would dampen the needle movement without changing the value. |
VaccaRabite |
Apr 28 2010, 11:52 AM
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#7
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En Garde! Group: Admin Posts: 13,465 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
Mine also bounces in the 2056. I just figured it was a function of me needing to be smoother in my driving - as the smoother I am, the less bouncy the tach is.
Zach |
JamesM |
Apr 28 2010, 11:53 AM
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#8
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Senior Member Group: Members Posts: 1,915 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
So once I got my 2056cc built the tach could no longer keep up and just flailed around worthlessly... Especially when running an autocross. So I finally got around to trying the 2200uF trick and now it's over damped... Sigh. Maybe I'll try a different variant of capacitor and see what happens. Anybody else have a recommended type of capacitor for the application: http://en.wikipedia.org/wiki/Types_of_capacitor I used a 2200uf cap that i pulled off of an old motherboard i had laying around, there are usually a bunch of them surounding the CPU. Works nice and smooth now however i also modded my tach to take the lower voltage output from a spark box. |
tat2dphreak |
Apr 28 2010, 11:54 AM
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#9
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stoya, stoya, stoya Group: Benefactors Posts: 8,797 Joined: 6-June 03 From: Wylie, TX Member No.: 792 Region Association: Southwest Region |
QUOTE Mine also bounces in the 2056. I just figured it was a function of me needing to be smoother in my driving - as the smoother I am, the less bouncy the tach is. (IMG:style_emoticons/default/agree.gif) same here more aggressive I drive, more it bounces |
yeahmag |
Apr 28 2010, 11:58 AM
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#10
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
So once I got my 2056cc built the tach could no longer keep up and just flailed around worthlessly... Especially when running an autocross. So I finally got around to trying the 2200uF trick and now it's over damped... Sigh. Maybe I'll try a different variant of capacitor and see what happens. Anybody else have a recommended type of capacitor for the application: http://en.wikipedia.org/wiki/Types_of_capacitor I used a 2200uf cap that i pulled off of an old motherboard i had laying around, there are usually a bunch of them surounding the CPU. Works nice and smooth now however i also modded my tach to take the lower voltage output from a spark box. I'm getting the feed off my Mallory 6AL. How or what mod's did you make? |
DNHunt |
Apr 28 2010, 01:02 PM
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#11
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914 Wizard? No way. I got too much to learn. Group: Members Posts: 4,099 Joined: 21-April 03 From: Gig Harbor, WA Member No.: 598 |
I'm not sure if this helps (free advice, take for what it is worth). I jumped a resistor to get the tach to accept the signal from an EDIS module. It also worked with a the tach out line from an SDS ECU. I haven't measured it but, I suspect both of the fedds I used were 5V.
Dave Attached image(s) |
Dr Evil |
Apr 28 2010, 01:04 PM
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#12
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Send me your transmission! Group: Members Posts: 23,002 Joined: 21-November 03 From: Loveland, OH 45140 Member No.: 1,372 Region Association: MidAtlantic Region |
Jumping a resistor makes some sense as well. It is like opening up the volts after it is doped down by the cap. However, it could lead to escaping magic smoke (IMG:style_emoticons/default/dry.gif)
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DNHunt |
Apr 28 2010, 01:06 PM
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#13
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914 Wizard? No way. I got too much to learn. Group: Members Posts: 4,099 Joined: 21-April 03 From: Gig Harbor, WA Member No.: 598 |
Magic smoke is still contained (knock on wood).
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BIGKAT_83 |
Apr 28 2010, 01:52 PM
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#14
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Senior Member Group: Members Posts: 1,798 Joined: 25-January 03 From: Way down south Bogart,GA Member No.: 194 Region Association: South East States |
The Tach is dampend with a pin coming off of the meter movement that rides in a small amount of grease or silicone. After time this dries and no longer functions.
I have cleaned the old grease out and used vasoline to replace it. It works great the trick is getting the right amount and put in the right place. I had done a write up on the old Yahoo porsche chevy group on how to do this and recalibrate the tachs for a V8 or 6cyl. With that being said I really think the best thing to do is shit can the 35 year old tach and get one from BIGMARK with up to date movements (IMG:style_emoticons/default/biggrin.gif) Bob |
Frost |
Apr 28 2010, 04:32 PM
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#15
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Frost Group: Members Posts: 75 Joined: 9-May 08 From: Houston,TX Member No.: 9,035 Region Association: Southwest Region |
My tach justo bounce then i start the car one day and it didn't work. I have a good sense of where the rpm is at so i dont really pay attention anymore.
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D1A3 |
Apr 28 2010, 04:47 PM
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#16
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Gruppe Neun Vierzehn Südosten Group: Members Posts: 362 Joined: 3-June 04 From: Atlanta, GA Member No.: 2,152 Region Association: South East States |
Had a similar problem and found the connection on the capacitor was not good. Cleaned it up, put a new connector on and works like a charm now...
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sgetsiv |
May 3 2010, 11:15 PM
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#17
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Former 914 Owner :( Group: Members Posts: 159 Joined: 20-June 08 From: Portland, OR Member No.: 9,192 Region Association: Pacific Northwest |
Remember that capacitors add in parallel. You can go from a 2200 uF cap to 2400 uF by wiring a 200 uF cap in parallel with the original cap. If they are electrolytic then they have a polarity and should be wired the same, + to + and - to -.
I just installed a 2315 engine in my ride and have the same bouncy tach issue. Need to get it dampened out so I'll be adding 200-400 uF at a time until I get the needle response I want. Steve |
yeahmag |
May 4 2010, 09:43 AM
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#18
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
After my PCA event on Sunday I noticed it's really not all that bad. It's actually quite functional in real world conditions. It still can't keep up with blipping the throttle and it also appears I didn't reset the needle quite right. It's almost 500 RPM off, so I guess I need to open it up anyway.
Someone needs to invent a variable capacitor for dampening purposes... I'd mount it outside the housing. Dreams... |
ClayPerrine |
May 4 2010, 11:07 AM
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#19
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Life's been good to me so far..... Group: Admin Posts: 15,515 Joined: 11-September 03 From: Hurst, TX. Member No.: 1,143 Region Association: NineFourteenerVille |
Just send it to North Hollywood or Palo Alto and tell them it bounces too much. They will fix it. (IMG:style_emoticons/default/biggrin.gif)
Some things are just worth the cost to have fixed. |
yeahmag |
May 4 2010, 11:16 AM
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#20
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
Thanks, but with the Mallory 6AL doing the rev limiting my money is better spent on tires and suspension right now (all things being equal).
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