SDK Glock 18 firing issue

Hi everyone, I just replaced the piston in my Glock 18 and now it seems all out of wack.
It fires the gel then the slide goes back after the shot which then eventually it jams , 1st time the piston was stuck outside the cylinder (it came all the way out), now the slide doesn’t want to come forward to take it apart. I haven’t touched the gearbox either.
I checked the piston it’s the same size as the old one.

Did you put the spring retainer in the right position if it’s not sitting in right it will jam up

1 Like

It’s likely the front switch plate not in place properly and jamming the front spring.

I have it in as pictured with the notches facing bottom of slide

And the plate is in the grooves

Slide going back after the shot can be several things.
Front spring too stiff. Have you done a spring upgrade?
Battery not charged properly.

PS re Piston
I found in one instance that although looking the same, the slide guides on the piston were shorter than on the stock

I haven’t changed anything apart from the plunger. Never had this one apart before.
That’s why I’m stumped

Why the piston-cylinder change? Was something damaged?

Is it possible to use the old piston with/without the old rubber cushion in the new cylinder?

Piece in pic broke.
Took a couple shots and the sound changed so I took off top and that pice was broken


Probably a good excuse to upgrade

I bought several spare clear pistons early on so I could play with different designs but haven’t had one fail like that.

You can try something else.
Put a spacer inside the piston so the spring is compressed more.
Washers or grommets will do. Add 4-6mm to the spring compression.

I just fired a mag turned it upside down and its firing correctly , loaded another mag and same thing

Ok I’ll give it a go.
Might even strip it right down and put back together, that normally works for me at work

BTW, sometimes the leads coming out of the battery plug can interfere with movement of the tpiece.

If stripping it, be aware of these tidbits.

  • almost all issues are in the slide
  • there is not much to see or change in the gearbox.
  • there are many fine and fiddly wires running from the circuitboard plus the small connectors. These are easily bent, crimped and broken.

Tried the washer and its almost in time now, I’ll mess with the spacing and I think I should have it.
Thanks for that .

1 Like

Good to hear. :+1:
I have 8mm on one of them.

There seems to be a delicate balance between front and rear springs and the reverse cycle you spoke of, where it fires before the slide moves forward is usually because of that imbalance.
Same issue with the Beretta.

That’s interesting.
At least I learnt something today👍