Timing problem, and tach problem
Thread Starter
Safety Car
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Timing problem, and tach problem
to make a long story short, I timed my 74 L48 with a dead plug, :o oops, well I changed the plug this weekend, and tried to time it again today, I took my vacuum advance off (plugged it) and set it to 8*, I reconnected the vacuum advance and the timing just dropped out the a$$, it went down to (for simplicity lets say the numbers on the bottom of the gauge are negative) -4* and it sounded TERRIBLE! so we said screw it and just timed it with the vacuum advance and set it to 4* (why 4*? because dad is very controlling and I was thinking I would just re do it this weekend the right way with my friend) so I took it for a short drive and it was sounding better, but I looked down and my tach gauge was sitting comfortably at 0.............
so my question is whats my timing issue and how did I screw up the tach? I know it feeds off the dist, but Im not too sure where the connection is
Miles
so my question is whats my timing issue and how did I screw up the tach? I know it feeds off the dist, but Im not too sure where the connection is
Miles
Instructor
Joined: May 2009
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From: salisbury missouri
ok i have a 1980 and my tach input comes from a wire that plugs into the distributor cap.electronic tach
some older vetts ran a cable from the distributor (like a speedometer cable i think).mechanical tach
not sure which kind you have,not up to date when they went to electronic on all vetts.
im pretty sure you have an electronic tach so check the two wires that plug into the distibutor.one is the hot for distributor and the other is the tack wire i think see if it is not pluged in all the way.
cant comment on the timing
hope i helped with the tach problem
some older vetts ran a cable from the distributor (like a speedometer cable i think).mechanical tach
not sure which kind you have,not up to date when they went to electronic on all vetts.
im pretty sure you have an electronic tach so check the two wires that plug into the distibutor.one is the hot for distributor and the other is the tack wire i think see if it is not pluged in all the way.
cant comment on the timing
hope i helped with the tach problem
Thread Starter
Safety Car
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well I just went out there to do a vacuum test and my tach is working fine, do you know what would make it be completely unresponsive and then work just fine? about a week ago it was fluctuating about 100-150RPM then it was working fine again, then it quit and now its fine again
killer, I think 74 was the last year for mechanical tach, I know it was the last year for a points dist
Miles
killer, I think 74 was the last year for mechanical tach, I know it was the last year for a points dist
Miles
Instructor
Joined: Aug 2008
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From: Warner Robins Georgia
yup, last year for the mech tach. If it's fluctuating, you may need to grease the cable or possibly you jarred it loose messing with the disty..... also the drive gear is more than likely going bad.
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Melting Slicks
Joined: Mar 2008
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From: Meriden CT
I don't see how plugging the vacuum advance back in lost you some timing. If it's to a ported source you should see no change at idle. If it's to a manifold source, you would see an immediate increase of 15 degrees at idle (or whatever the vac advance full capacity is).
Is the distributor loose? Maybe simply plugging it back in moved the distributor.
AFAIK the tach cable enters the distributor housing at the bottom. Maybe loosening the distributor clamp disturbed the cable connection.
Is the distributor loose? Maybe simply plugging it back in moved the distributor.
AFAIK the tach cable enters the distributor housing at the bottom. Maybe loosening the distributor clamp disturbed the cable connection.
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Instructor
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From: Warner Robins Georgia
Look at the back of your disty at the top of the shaft and you'll see a cable coming out. That is your tach cable. The gear inside that spins again the main shaft wears out due to lack of lubricant. The gears grind and eat away, usually tearing up its adjacent gear on the main shaft. Both have to be repalced.
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http://www.zip-corvette.com/Zip/prod...4D752E8BFFF64B
Im guessing this is what I need? could someone post a link to whatever I need to be able to grease the cable and gear? (aside from the actual grease gun)
Miles
Im guessing this is what I need? could someone post a link to whatever I need to be able to grease the cable and gear? (aside from the actual grease gun)
Miles
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well, I think that Ive actually found the problem, let me run another question by you, when your tach cable is screwed firmly into the distributor, you shouldn't be able to pull the cable out of the fitting right? because mine comes right out, the metal piece that is crimped to the actual rubber cable has simply released the cable, this shouldn't happen correct?
is there any way to fix this without replacing the whole cable? I cant imagine that to be a simple job, seeing as though you would have to loosen/remove the dash panel, is there somewhere that I can find a new fitting and just crimp it to the old cable?
Miles
is there any way to fix this without replacing the whole cable? I cant imagine that to be a simple job, seeing as though you would have to loosen/remove the dash panel, is there somewhere that I can find a new fitting and just crimp it to the old cable?
Miles
Last edited by randommj; Jul 19, 2009 at 09:50 PM.
Race Director
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You don't need special tools to grease either a tach or speedo cable. It's done the old fashioned way- by hand.
You may or may not need the gear in question. Take apart the dizzy to see. If so, then you will also need to replace the main shaft of the dizzy that has the matching gear as DLCorn mentioned. Both are damaged.
You may or may not need the gear in question. Take apart the dizzy to see. If so, then you will also need to replace the main shaft of the dizzy that has the matching gear as DLCorn mentioned. Both are damaged.
Le Mans Master
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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Hi Miles, its been a while since I replaced the tach cable but I think the cable slides into the housing from the speedometer end. Once the cable is in the housing it should not pull out from the end that goes into the distributor.
I'm glad you took the time to troubleshoot the problem instead of just replacing one part after another. PG.
I'm glad you took the time to troubleshoot the problem instead of just replacing one part after another. PG.
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where can I get a replacement piece circled in the picture that I can just re crimp to the cable?
pete, Im to poor to just replace things all *****-nilly lol, nice car though, it looks familiar.....
Miles
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Miles,
You can unscrew the coupler that holds the side gear in place. If any teeth are missing form it, as Mike stated you'll need both the main shaft and the tach gear. You should also check the clearance in the upper and lower bushings as well as the main shaft run out.
In the back wall of your distributor will also be a nylon button. It will be inserted in a hole in the back of the distributor exactlyw here the cross gear would ride. Make sure this button is on place.
From what you say, your cable is the problem and not the distributor. The crimped portion of the cable should not be able to move in and out of the metal end. The end is not available separate.
You may try to re-crimp this and see if it holds.
Willcox
You can unscrew the coupler that holds the side gear in place. If any teeth are missing form it, as Mike stated you'll need both the main shaft and the tach gear. You should also check the clearance in the upper and lower bushings as well as the main shaft run out.
In the back wall of your distributor will also be a nylon button. It will be inserted in a hole in the back of the distributor exactlyw here the cross gear would ride. Make sure this button is on place.
From what you say, your cable is the problem and not the distributor. The crimped portion of the cable should not be able to move in and out of the metal end. The end is not available separate.
You may try to re-crimp this and see if it holds.
Willcox
Le Mans Master
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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Now I understand the problem, the black housing has separated from the round nut that attaches it to the distributor. Do like Willcox says and try to re-crimp it. That should work for a while. When you do need a replacement I think your local Chevy dealer will have that part, sold as a set, cable and housing. PG.
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A new tach cable is less than 20 bucks. Replacing parts *****-nilly is always a dumb thing to do no matter how much money a person might have.
Former Vendor
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
