Gunsmithing 1911 Thumb safety issues

[Twisted300Win MAG]

Ok I removed the thumb safety on my STI Spartan V to install a scope mount just to give it a try. The pin on the safety that holds the grip safety snapped off. I removed it as I have done on several other 1911's with no issues. So I ordered a new factory STI safety from Brownells. After installing it I did a function check and with the safety engaged you can pull the trigger and the hammer will fall and force the safety lever down. I have disassembled and checked everything I can think of and still no change. Prior to this I Have had no issues with this pistol. The only change is the safety lever. Now I have not taken any measurements but visually it looks identical to the one i broke. Tomorrow I will take it to work and take some measurements, but I'm wondering if any of you have any ideas.

Thanks
Donald

 

[bptactical]

Check the height and configuration of the lug and fitting pad relative to the broken one. Hard to explain but if you look on the back of the safety there is a lug that goes through the odd shaped hole on the frame. That is the lug that blocks the hammer/sear. They do require careful fitting and from your description it sounds as if the hammer is bumping the lug. Take a sharpie or dykem and cover the lug. Reinstall and cycle the hammer and safety a few times and check for contact areas.
If the hammer will fall with the safety engaged the fitting pad portion is too short. You may have to try another safety or weld the pad back up and refit it.
You did not mention but did you do any filing/fitting to the new safety?
I would also be checking the condition of the hammer and sear as well, it is possible the leg of the sear is broken/ worn.

 

[Twisted300Win MAG]

Check the height and configuration of the lug and fitting pad relative to the broken one. Hard to explain but if you look on the back of the safety there is a lug that goes through the odd shaped hole on the frame. That is the lug that blocks the hammer/sear. They do require careful fitting and from your description it sounds as if the hammer is bumping the lug. Take a sharpie or dykem and cover the lug. Reinstall and cycle the hammer and safety a few times and check for contact areas.
If the hammer will fall with the safety engaged the fitting pad portion is too short. You may have to try another safety or weld the pad back up and refit it.
You did not mention but did you do any filing/fitting to the new safety?
I would also be checking the condition of the hammer and sear as well, it is possible the leg of the sear is broken/ worn.

I have already put dykem on the lug and the wear pattern is almost identical to the wear marks on the old one. The markings are a little lighter and when I took the beaver tail off and looked inside and it appears to be a little looser. You can push it up and it will hold the hammer when the trigger is pulled but there is too much play for the plunger to hold it up. I've had to file on safety's before to fit them to the sear and to get them to mate up with the slide and plunger. But I've never ran into one with so much play. The pistol has less then 400 rounds down the tube and all of the internals look good.

 

[bptactical]

Check plunger spring tension and free movement. Replace it or give the spring a tiny stretch if it is soft, you want the safety to snick crisply in place. Does the plunger bearing surface on the safety have the same dimensions and shape as the old one?
How far does the safety travel from full engage to where the hammer falls?
It should go to mid travel or so before it disengages, any sooner and it is rolling off too early IMHO. Build up the pad and refit it.
Exactly what looks loose when you have the grip safety out?

 

[Twisted300Win MAG]

The hammer and the lug on the safety have play in between them when the lever is engaged. That's what I meant by loose.

 

[EXTREMEPREJUDICE]

Well, what your describing is often caused by removing too much engagement material from the thumb safety when fitting. It can also happen when you stone too much off a sear or the sear is worn. A good test is to check for sear movement when the thumb safety is engaged and trigger pulled (there should be none.) I'm not familiar with STI but I've never heard of "drop in" 1911 parts, they always come a little oversize and require fitting. Perhaps they've sent one for a different model STI in error?

 

[Twisted300Win MAG]

I have not touched tithe internals of this gun nor did I file or stone the new part. I've replaced them before in other 1911"s and I've always had to fit then. This one snapped right into place and other then throwing a weld on it and reshaping it I can't think of any other fix. I'm thinking it was just a reject part. Ill know more on my lunch break when I can sit down and take a few measurements.

 

[TheShooter]

If a new 1911 safety drops in straight from the factory, I would be worried. I installed a new safety on my STI and filed forever before it fit.