tach noise after cable replacement

[Robert C.]

'67 SB.

After replacing it - it squeaks. This is the correct length cable from LI Corvette.

So far, the only thing we found was removing tension on the tach assembly stopped the noise.

I removed the cable from the distributor side and spun it with a drill - tach inside was fine, no noise.

When we pulled the cable on the firewall side up a little, the noise at the tach stopped.

The tach also seemed to move a little in the cluster.

So, to me, this said we have too much tension or pressure on the back of the tach housing - only question is how to correct it ??

I'm hoping this stops after some driving and the cable heat cycles in the engine bay.

I think the "gradual S bend" GM intended is hard to do in practice.

Maybe modern materials are stiffer than the originals ? Anyone run into this before ?

Thoughts ? Advice ?

Bob

[Gerard F.]

Re: tach noise after cable replacement

Bob,

Take a look at this thread from the archives:

https://www.forums.ncrs.org/showthre...ghlight=Dimple

I found that with a replacement distributor on my 67/327/300/4 speed, the dimple in the drive gear was reversed to the #1 rotor position. In order to set my initial timing (6*B) with that situation, there is a fairly sharp bend in the tach cable.
By lining up the dimple with the #1 rotor position there was less bend in the tach cable, and it allowed me to use the shorter cable (about 25", I think). The difference is about 14 degrees.

The pictures in the thread are my original distributor, one with the dimple correctly lined up, and one with the dimple reversed. For a base engine 67 with manual transmission, the correct initial set should be with the vacuum can pointing about 45d clockwise from axis of the engine. Now if you have a PG/AIR car with an initial set of 4d A, the dimple has to be reversed to the #1 rotor position to get to 4d A.

Also, you should check that the cable is properly lubed. If you do have excessive bend in the cable, the longer cable will help.

[Robert C.]

Re: tach noise after cable replacement

Don't seem to have that sharp a bend.

Tach cable is almost straight back to the firewall from the distributor, with a gradual bend into the firewall hole.

Vacuum advance cannister is positioned correctly. The distributor gear is lined up too.

Now I'm wondering if I should try the longer tach cable ? I thought this would make the problem worse which is why
I grabbed the correct lengh LIC tach cable after researching it on NCRS.


DSCN1353.jpg

[Dan H.]

Re: tach noise after cable replacement

High Robert, one thing you should check when changing cables is the length of the protrusion into the tach socket. If it is too long, it will bind up etc. Compare your old cable to the new one for dimension. Make sure it is not bottoming out in the tach. You might try loosening the tach cable nut to see if this helps. In any case, make the ends equal to the old cable.
Dan

[Gerard F.]

Re: tach noise after cable replacement

Bob,

That bend at the firewall looks OK to me.

Check the bend under the console. I have a little tie strap on mine to reduce the radius of the bend in that location.

Also check your tach drive gear. When they become worn or are too loose, they tend to move back and forth along the cable. But it is more of a clicking sound.

[Robert C.]

Re: tach noise after cable replacement

I have to admit, the LI Corvette replacement was spot on. I did check one end ! The other end on the old cable was the part that broke.

The tach does work - actually works just fine except for the noise. Good point about loosening it up.....not that I
cherish the thought of getting in there again.

I had it finger tight and snugged it down a 1/8 turn with long nose pliers.

Let me give that a shot, I post back tomorrow.

[Robert C.]

Re: tach noise after cable replacement

Inside, it almost runs parallel to the steering column.

Now I'm wondering if the tach is damaged ? I'm going to try and loosen up the nut a bit first on the tach side.

When I got it finger tight, I snugged it a little bit more with needle nose pliers, maybe a 1/8 turn. Maybe it is too
tight.

Then again, when I spun it with the drill it was quiet as a mouse and the needle was steady which gets me back to the
cable is pressing on the tach housing. When I had the cluster out, I think researched where the cable was routed
and this one didn't match the AIM.

I know I found some photo's on NCRS at one point........ughhhhh..........thanks for your help

[Gerard F.]

Re: tach noise after cable replacement

Bob,

Here's a thread which seems to be the very same problem:

https://www.forums.ncrs.org/showthre...ght=tach+cable

It doesn't say how or if the problem was resolved. Why not ask Dennis if he ever resolved it.

[Robert C.]

Re: tach noise after cable replacement

Dan "the Man" Holstein !!!

I loosened the nut maybe a 1/4 to 3/8 of a turn and the noise is gone.........thanks a million !!!