csherman

I have a 69 that we almost done with about to give back to the owner
New dash, new interior etc.....
The tach is inop -
I disconnected the cable - hooked a drill to it and spun it backwards and the tach went to 1000 rpms
I also confirmed the cable is latched in its "clip" at the back of the dash
I feel the tach is good
- I removed the distributor - and took out the tach drive - figuring the gears were stripped or ???
- When I spin the dist in my hand - the drive spins
- I took it apart anyway - gears are good - grease on them I dont see an issue
- greased them both up - put it together
- Installed the dist and made sure the cable is more inline with out a "S" in it -
- Turned over but didnt start - No tach movement - I would have thought the tach would move while under starter....
- Before I light this back off and try to re time in
- What am I overlooking???? Or should I light it and see if it runs
- I also moved my spark plug wires back one hole in order for the tach cable to be more inline - before it had an S in it and was against the firewall
- Engine is a 427 435 4 sp
Thanks
Chris

Big2Bird

Start it up.

ClothSeats

Did you connect your drill to the cable near the distributor after disconnecting it from distributor, or did you connect your drill directly to the tach behind the dash? I am just asking this dumb question in order to rule out the possibility of a broken cable.

Jebbysan

Is the receiver for the cable at the distributor rounded out? Is the end of the cable square?

Jebby

csherman

I connected the drill to the cable near the dist - yep - I was trying to rule out a broken cable or disconnected cable - I think I did verify I connected it correctly and it works. - That is what I thought too at first.

csherman

It doesnt look to be - but it could be - the cable is new and square - If the tach doesnt work after this fire up - I will repull the dist and replace the receiver/ drive

jackson

Sometimes ... when the tach gears(shaft & cross) are Effectively stripped and cannot drive thru the cable's friction ... sometimes there'll be a teeny bit of teeth left ... just enough to turn the crossgear's square hole/receiver ... but not enough bite to drive the cable's load/friction ... just enough to fool ya. T shirt


Stick a little ignition screwdriver in the hole and ... see if ya can turn the cross gear ... or ... careful ... try & hang on to it when ya crank it over.

FWIW ... that's a .104" square drive ... it's about .104" from one side to the other ... and about .147" from one corner to the other.

Big2Bird

I doubt it.

csherman

I pulled the distributor and replaced the gear and bushing assy
I will refire it and retime it

Gale Banks 80'

If the Cable is new then like every other reproduction part there is a chance that it was made wrong. Is the square end of it that goes into the Distributor the wrong size ? Either to big or small.

jackson

Like Big2Bird said ... doubt it.

Because most Mechanical Auto speedo / tach instruments employ a magnet & drag cup ... there is No direct coupling between rotating cable & needle. The magnetic pulsing drag at very low speed is not sufficient to overcome instruments' hairspring.

https://www.howacarworks.com/accesso...a-speedo-works

Big2Bird

That is the part that sucks about this hobby.
50% trash.

jackson

Yup ... s'pose I yam

A10pilot

This happened to me !

TOM B1

When I had my tach drive dist. in my 69 I had that problem and fixed it. I done the exact diag. steps you did.
What I found is that when It was spining or just connected. the steel cable would DROP OUT of the square slot and fall
down in the cable housing, just enough for it to not grab. this is a very little drop. I sent back 2 reproduction cables before I just ordered the repair
kit and cut it myself. worked like new till I modified the whole car and went a full electronic F.A.S.T. 2.0 system
Good Luck: Tom

csherman

I removed the dist and replaced the tach gear and reinstalled it
I am going to push it out and re time it tonight
Hope that was the fix
We shall see.
I will also check the engagement - hard to tell - cramped quarters

csherman

Update
I had the dist in and out 6 plus times
I changed out the tach drive with C Central parts - several times
and no change
Diagnoses - the drive cable inside is too short - it is just too short to slide into the drive
I ordered a longer cable and will install hopefully just replace the drive cable with taking the whole cable out....

Big2Bird

Bummer. They used to sell just the core you could cut to fit. Those days are long gone.

67:72

Not sure if you are referring directly to Corv. Central no longer selling the core, but they are readily available through regular places like Autozone and Summit. Speedo cable core is the same diameter and ends as far as I can see.

Big2Bird

Good. I did not know. Thx.