Author Topic: Stop tach & speedo needle bouncing  (Read 159 times)

Maxthe222

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Stop tach & speedo needle bouncing
« on: August 12, 2019, 12:08:52 AM »
Ok next one on the list:

Every since a certain "someone" thrashed the car after I specifcally said not to, the speedo dial (and sorta the tach) wobble a fair bit while driving. Now when I first got the car, the speedo wouldn't wobble as much. It was also 13-25 km/h off. I fiddled witht he fuse box and wiring a bit, and it kinda made a difference for a little bit, then when back again. It was a bit more accurate and wouldn't bounce as much. I really don't think it's the speedo gear, I still have a 2.56 rear and I don't think it's ever been changed. Do they break? When i'm going near 80kmh an hour it is more accurate, and also at around150-160km/h it's accruate.  Someone in passing mentioned it was de-magnetised or something about magnets? And that It needs to be calibrated? Not sure what exactly is the problem. I also noticed that the speedo background light is barely visible at night, where as the tach is very clearly visible. Not getting enough current? Whaddyas think?
1979 T/A Y84 WS6
1979 F/A W72 WS6
1971 Formula 400 4-Speed

Casey

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Re: Stop tach & speedo needle bouncing
« Reply #1 on: August 12, 2019, 03:13:34 AM »
Speedometer cables do wear out, tach could be connections or something in the ignition system like the coil or distributor.  Though it seems in older cars the speedo and tach aren't rock solid steady like they are in even 90's cars much less the entirely digital stuff today.  Old analogue stuff isn't ever 100% stable, think of it as character. :lol:

TAchris

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Re: Stop tach & speedo needle bouncing
« Reply #2 on: August 12, 2019, 12:34:53 PM »
Had similar problem with mine regarding the speedo.
I took it off the back of the clocks and pulled the cable out of the sleeve.
Straightened any bends and smeared grease on the cable as I slid it back in.
That worked for me.

My lights also were pretty dim.
A put a new circuit board on the back and slightly higher watt bulbs back in
This might sound strange but I also stuck chrome wrap on the inside of the clock
Housing to reflect the light to make it even more brighter.

Not sure about the tach, again mine was faulty, input a new one in and it was fine.

Good luck
The joys of owning a classic ????

80_transam

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Re: Stop tach & speedo needle bouncing
« Reply #3 on: August 13, 2019, 05:18:45 PM »
Not sure on the spedo issue, but for the tach issue both times my tach started bouncing around my ignition module went out a short time later. The last time 3 hours from home.....I now carry a spare ignition module with me. Not saying it is the issue for sure, but the ignition modules go when they get overheated / not applying the heat sync paste (or from due to cheap aftermarket quality) so if someone trashed on your car and got it really hot and your tach is now bouncing around, you ignition module may be on the way out.
« Last Edit: August 13, 2019, 05:21:15 PM by 80_transam »

Maxthe222

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Re: Stop tach & speedo needle bouncing
« Reply #4 on: August 13, 2019, 05:41:03 PM »
????????????

Could be..... Well the whole dash is coming out to totally clean all the electronics, so I will have the check that out. Is that the clear-ish plastic box on the steering column?
1979 T/A Y84 WS6
1979 F/A W72 WS6
1971 Formula 400 4-Speed

Re: Stop tach & speedo needle bouncing
« Reply #4 on: August 13, 2019, 05:41:03 PM »

80_transam

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Re: Stop tach & speedo needle bouncing
« Reply #5 on: August 13, 2019, 05:52:29 PM »
Nope, its in your distributor, when you take your distributor cap off it looks like the image below. As, already mentioned could also be the connection at the distributor as well.

« Last Edit: August 13, 2019, 06:11:06 PM by 80_transam »

Grand73Am

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Re: Stop tach & speedo needle bouncing
« Reply #6 on: August 14, 2019, 04:12:43 PM »
For the speedometer, as TAchris mentioned, the speedo cable probably needs to be greased. You can disconnect the cable at the transmission and pull out the inner cable, grease it with some wheel bearing grease, and shove it back in and reconnect it. When you shove the cable back in the sheath, rotate the cable a little since it will have to line up with a square hole in the back of the speedometer to be able to go all the way back in. They often smooths out the speedo needle.

As for speedo accuracy, start by seeing if your odometer is accurate. See what your odometer is now, drive 10 measured miles, and see if your odometer is now 10 miles more. If it does, you know your odometer and transmission speedo gears are correct. So, that just leaves the speedometer. If it's not right, you'd have to take it out and send it to a speedo shop so they can recalibrate it to be accurate to the marks on your speedo face. It works off a spinning magnet, so they de-magnetize the magnet and re-magnetize it until it's accurate.

Or, you could try buying another used speedometer, for your year of car, and hope it's accurate. The year of car makes a difference, since for example, a 78-79 uses a 100 mph speedo, and an 80-81 uses an 80 mph speedo.

For the dim lighting in the cluster, you probably have some bad bulbs in the dim areas. And the originals are dim anyway, so using brighter bulbs will help. I think original bulbs are 194's. You can use 168's which are brighter, or use 194/168 LED replacements, which are brighter still. You'll have to pull the cluster out, at least part way, to get to the bulbs to change them all.
Steve F.

b_hill_86

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Re: Stop tach & speedo needle bouncing
« Reply #7 on: August 14, 2019, 06:01:12 PM »
Could also use a gps speedometer app on your phone to check the accuracy of your speedo. Assuming that’s accurate.
-Brian-

1977 Trans Am 400 4 speed

Maxthe222

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Re: Stop tach & speedo needle bouncing
« Reply #8 on: August 14, 2019, 06:14:31 PM »
Well that's how I figured it was at least off. I'd be doing 60 kmh according to the Speedo, and I'd be getting overtaken. I got my brother to get one of those Speedo apps and even considering a margin of inaccuracy it was still pretty off.

G/A I like your idea, I'm going to look into that grease thing, should be a good idea to do it anyway as maintenance
1979 T/A Y84 WS6
1979 F/A W72 WS6
1971 Formula 400 4-Speed

b_hill_86

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Re: Stop tach & speedo needle bouncing
« Reply #9 on: August 14, 2019, 10:24:08 PM »
After you grease it you may want to see how it’s routed. My cable is probably old but it was routed in a way that caused it to bounce at 30ish or below, the. I moved it so it was not making any sharp turns and the bounce about went away. After the trans came out at a shop I haven’t found that sweet spot for routing again but it’s something to consider.
-Brian-

1977 Trans Am 400 4 speed

Maxthe222

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Re: Stop tach & speedo needle bouncing
« Reply #10 on: August 21, 2019, 05:28:14 PM »
Entire dash (will probably have whole other thread about that too) is now out and in the process of now rectifying everything back there, and found out why the gauges weren't doing so good. A lotta corrosion back there. Not like turbo rusty, but stuff is going brown and it's pretty dirty. Circuit Board was pretty boofed. Will likely need to be replaced. (Don't tell anyone, it's still the original numbers matching barn find circuit if they ask.) Zinc plating and cleaning the plastic too. the dash guy said it might also be the speedo cable too, so i'll definitely grease that pig up and give it a real good clean out. I think that cable is fine, but the cable that goes from the transmission shiftier is super kinky, not sure if that has anything to do with it.
1979 T/A Y84 WS6
1979 F/A W72 WS6
1971 Formula 400 4-Speed

mz-formula

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Re: Stop tach & speedo needle bouncing
« Reply #11 on: August 22, 2019, 05:21:31 AM »
Not sure on the spedo issue, but for the tach issue both times my tach started bouncing around my ignition module went out a short time later. The last time 3 hours from home.....I now carry a spare ignition module with me. Not saying it is the issue for sure, but the ignition modules go when they get overheated / not applying the heat sync paste (or from due to cheap aftermarket quality) so if someone trashed on your car and got it really hot and your tach is now bouncing around, you ignition module may be on the way out.

Nope, its in your distributor, when you take your distributor cap off it looks like the image below. As, already mentioned could also be the connection at the distributor as well.



If you really need to keep one of these as a spare, due to frequent failure, I would be looking to another manufacturer.  Accel lost absolutely all of my confidence in products.  Spark plug wires where the jackets tore off super easy... As in when pushing them into the Accel looms, and 2 failed modules in 2 different cars.  One a 4 pin in the firebird, where it just died, the other a 7 pin in my Cadillac, where the timing fell apart after 35mph.    Pertronix makes an awesome reliable 4 pin module that is stock replacement, don't recall what I used for the 7 pin anymore, but at the time, Pertronix did not have a 7 pin avalible, they do now.

Re: Stop tach & speedo needle bouncing
« Reply #11 on: August 22, 2019, 05:21:31 AM »
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