tach quits working in 4th gear?

[292farmer]

ok so i searched the forum tried some ideas and nothing seemed to work. in 1st 2nd the tach will work fine, occasionally in 3rd and all the time in 4th when i hit 2500-2600rpms the needle sticks, the motor keeps going up in rpms, but tach stays at 2500/2600rpms and wont move till i drop the rpms below that. the tach is a sunpro 2-5/8" the motor is a 292 stock ign. tranny is a sm465. what can be causing this all wires are tight, the switch on tach is at 6cyl, is this a tach problem or an problem at the ign/coil side i need to address? if its tach i could care less but if its an ign problem want to solve it. thanks everyone sorry for long post.

[292farmer]

also forgot at roughly 2500 the motor starts to sound lean(i think) it sputters and bucks a bit. now im thinking its not lean but an ign problem.

[Huck]

If the motor rpm continues but the tach stops at a given number--well da--it's the tach but take the tach apart before throwing it out. COuld just be a piece of crud in there.

[72BlckButy]

had the same thing on my '72. Never got around to fixing it because I sold the truck.

[fdbdw]

I would start by borrowing a tach from a buddy and hook it up and see what happens before you start diving into other things, if the other tach works fine you know were the prob is, if not run some new wires and get a good clean ground and go from there. always start cheep and easy

[292farmer]

yeah i figured it was the tach, which if it is i don't care, i just thought maybe the coil was losing power or wires are going bad which i do care about, see if i can borrow tach just to check. was looking for ideas in case this was a precursor to a common ign problem. thanks for replies guys!