Tach reading 1970LS6

[martyb]

Pretty sure my factory tach is reading high. 1970 LS6, M22, 4:10 rear end. 4th gear at 50mph tach is reading about 3100rpm, thinking that’s about 800rpm or more on the high side. Factory sized tires as well. Anyone seen this before, and if so what’s involved in making it accurate?

Thanks all

Marty

[ban617]

If I’m not mistaken the mph would be 60 @ 3,000 rpms with a 4.10.Does your transmission have the correct speedometer gear & has the speed be verified to be correct? I was thinking 3,000 @ 50 would be either a 4.56 or 4.88..

[martyb]

Speed has been verified by radar, speedometer is spot on.

[Remmag]

I just had my cluster from a 70 restored,my taçh was reading high (way high)
Per John at redline clock and gauge restoration there is a material (can't remember what it was)that breaks down over time and causes the tach to read high
This is what was wrong with my tach
I would suggest giving him a call

Good luck

[martyb]

So I bought an Autometer tach and hooked it up today, reads 3200 rpm at 60mph, so the factory tach is way off. Another project for another day!

[WILMASBOYL78]

With a factory F70/14 tire...you would be at 2621 rpm...at 50 with the 4.10 in high gear.

-wilma

[Burd]

It may just be a bad tach filter.

[martyb]

It may just be a bad tach filter.

What’s involved in changing that?

[SuperNovaSS]

Tach filters were late 70s. No filter on this one.

Jason

[martyb]

Tach filters were late 70s. No filter on this one.

Jason

It’s definitely reading way high, bad ground possibly?