Tach not working
Thread Starter
Racer
Joined: Apr 2010
Posts: 352
Likes: 1
From: Central NJ
Tach not working
I just recently finished up a bigblock swap onto my 74 and now the tach doesn't work. I went with an MSD distributor (with the mechanical tach drive), 6al-2 and a Pertronix coil (it was already in the car) instead of the old ignition system. I have the tach cable running from the distributor to the back of the gauge. Is there anything I'm missing? I always thought the tach ran off that single cable.
My speedo hasn't worked after the swap either but I'm not sure if the 2 can be related in anyway. The connections on both ends of the gauges are secure
My speedo hasn't worked after the swap either but I'm not sure if the 2 can be related in anyway. The connections on both ends of the gauges are secure
Safety Car
Joined: Oct 2007
Posts: 3,729
Likes: 267
From: Austin Texas
Corvette of the Year Winner 2017
2016 C3 of Year Finalist
does the cable rotate with the engine running ?
the Dist. tach drive internal gear, can unscrew from inside the dist.
or they can be stripped / not rotating.
opps my info about the drive is for a stock Dist.
the Dist. tach drive internal gear, can unscrew from inside the dist.
or they can be stripped / not rotating.
opps my info about the drive is for a stock Dist.
Pro
Joined: Apr 2008
Posts: 681
Likes: 11
From: Carson City MI
I just recently finished up a bigblock swap onto my 74 and now the tach doesn't work. I went with an MSD distributor (with the mechanical tach drive), 6al-2 and a Pertronix coil (it was already in the car) instead of the old ignition system. I have the tach cable running from the distributor to the back of the gauge. Is there anything I'm missing? I always thought the tach ran off that single cable.
My speedo hasn't worked after the swap either but I'm not sure if the 2 can be related in anyway. The connections on both ends of the gauges are secure
My speedo hasn't worked after the swap either but I'm not sure if the 2 can be related in anyway. The connections on both ends of the gauges are secure
Thread Starter
Racer
Joined: Apr 2010
Posts: 352
Likes: 1
From: Central NJ
Connect a drill to the tach cable and run it in reverse to see if the needle moves. If so, your issue is in the distributor connection. The speedo would be a separate issue, but can be tested in the same manner however, that may run forward rather than reverse. You didn't possibly get the 2 cables mixed up did you?
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
The MSD distributor has a special sleeve that you have to slip into the distributor's tach drive crossgear before you connect your tach cable to the distributor. If you do not slip the special sleeve into the gear drive, your cable will not engage with the drive gear: the gear will just spin without driving the cable.
Lars
Lars
Thread Starter
Racer
Joined: Apr 2010
Posts: 352
Likes: 1
From: Central NJ
The MSD distributor has a special sleeve that you have to slip into the distributor's tach drive crossgear before you connect your tach cable to the distributor. If you do not slip the special sleeve into the gear drive, your cable will not engage with the drive gear: the gear will just spin without driving the cable.
Lars
Lars
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
The sleeve is supplied with the distributor loose in the box in a little plastic baggie, so unless you took it out of the baggie and installed it, it's not in there. It would be difficult to see it with the distributor installed in the engine/car, since you can barely see the tach drive fitting on the distributor: You might be able to get a mirror down there to see if the sleeve is installed in the tach drive. The sleeve will often fall out when you pull the tach cable off, so you gotta' watch it... I have no idea why MSD decided to use this little sleeve adapter, since they are frequently lost or not installed, and the tach drive is useless without it.
Thread Starter
Racer
Joined: Apr 2010
Posts: 352
Likes: 1
From: Central NJ
The sleeve is supplied with the distributor loose in the box in a little plastic baggie, so unless you took it out of the baggie and installed it, it's not in there. It would be difficult to see it with the distributor installed in the engine/car, since you can barely see the tach drive fitting on the distributor: You might be able to get a mirror down there to see if the sleeve is installed in the tach drive. The sleeve will often fall out when you pull the tach cable off, so you gotta' watch it... I have no idea why MSD decided to use this little sleeve adapter, since they are frequently lost or not installed, and the tach drive is useless without it.
EDIT: I came across something on their website that sounds like what you're taking about. Is this it? http://www.msdignition.com/product.aspx?id=5595&terms=Tach%20drive% 20adapter
Last edited by Condo_454C3; May 15, 2014 at 03:03 PM.
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Drifting
Joined: Mar 2011
Posts: 1,347
Likes: 121
From: Kernersville NC
Unfortunately for me I did not install the distributor so I am not sure if the engine builder ever did install it. I'm looking on the MSD website and I cannot find a replacement part. Do you know if they sell one?
EDIT: I came across something on their website that sounds like what you're taking about. Is this it? http://www.msdignition.com/product.a...rive%20adapter
EDIT: I came across something on their website that sounds like what you're taking about. Is this it? http://www.msdignition.com/product.a...rive%20adapter
Thread Starter
Racer
Joined: Apr 2010
Posts: 352
Likes: 1
From: Central NJ