SM465 wont shift?

[BlueK20]

Need some help, i am at a loss.

I have been driving my '78 K20 for about 2 months now, no issues at all, I have driven plenty of standard trucks and i dont ride the clutch.

except since the other day it started acting up

If i depress the clutch at a standstill the clutch acts like it should and i can put the trans into any gear (I always start in 2nd)

But once i get moving, the truck wont let me get out of gear without rev-matching, when i depress the clutch pedal it acts as it should, just the trans wont pop out of gear without rev matching, same goes with trying to pop it into gear, i have to rev match!

The weird thing is I have zero problems getting the truck to move, it moves no problem, i can stop at the stop light with the clutch in no problem.

I have adjusted the clutch linkage and it hasnt changed it at all

Any help?

 

[Smitch320]

Does your truck have a Slave? A few years back mine had some similar symptoms and it turned out the slave was bad.

Just a thought, though. I am no expert

 

[HotRodPC]

If his is still the Z bar linkage that comes OEM on the 78 models, then he won't have the slave. Should be adjustable Z bar manual linkage. It's sounding like you're not getting proper disengagement. You're getting enough to keep the truck from moving, but not enough to get the motor strain off the gears. If you've adjusted it and you're sure you're getting enough reach, but it's not releasing enough, it's almost sounding as if the some of the diaphram springs in the pressure plate are sprung or not releasing. How old is this pressure plate and clutch?

 

[BlueK20]

It's a Z bar, not sure on age of clutch and pressure plate, engine looks fresh but who knows.

I'm going to try and adjust it again but I have a feeling the plate is screwed

 

[HotRodPC]

It's a Z bar, not sure on age of clutch and pressure plate, engine looks fresh but who knows.

I'm going to try and adjust it again but I have a feeling the plate is screwed

That's what it's sounding like to me. If it's grabbing good, the clutch disk itself is still working, but if it's not releasing, then the pressure plate is not retratcting off the clutch disk. And you have plenty of clutch pedal right? No like someone used the wrong throw out bearing? There are 2 different types. A short and a tall. If have the short and should have had the tall, then that can be a problem, but in that case, your clutch pedal is only about 2/3 off the floor instead of all the way off the floor.

 

[HotRodPC]

This of course is so long as you're sure it's not a transmission problem. There are also known problems if the shift stick ball gets worn or roll pin wears, the shifter stick can drop to low into the shift rail and jam up the transmission. From your description, this seem to be the problem though.