I've got a '15 Z51 m7 w/ 56k miles. Just changed the trans fluid for what I thought was the first time during the life of the car. What I realized when draining it was that it was probably changed when the PO had the slave cylinder done under warranty. Anyway, I noticed the plugs were pretty darn loose when I took them out although not leaking.

When I went to reinstall the drain plug, I torqued it to 20ft lbs as per the spec, and it went a good bit further than where it was before I took it out. Didn't feel bad going in or anything, but it did seem like more torque than I would have put on it had I been just snugging it up by hand.

When installing the fill plug it was the same story, went in smooth, torqued to 20ft lbs which felt like a bit much torque. Later I noticed there was a curly q of aluminum at the entrance to the hole where the plug went in. I'm 99% confident it wasn't cross threaded (started it by hand and it was secure and smooth) or over torqued (started with a small torque wrench and went to 16 ft lbs (top of its range) then switched to a big torque wrench to get it to 20ft lbs (bottom of its range where they're known to be less accurate) , to ensure I wasn't blowing way past the spec).

Anyone else had this happen, and is there anything I should do about it? It doesn't seem to be leaking so I figure it's probably best to just leave it alone.

I figure there was maybe a burr on the drain plug thread that hadn't previously engaged since it was under torqued (or maybe I over torqued it a little).

 

I wouldn't worry about it. Probably just something left over.

 

I agree. It sounds like a one time anomaly.

 

Thanks for the input guys. I'll just keep an eye for leaks and if it seals there's nothing to worry about I suppose. I'll probably make a mental note not to reuse that plug next time I pull it out though, incase there's a thread burr.

 

Those plugs on the trans are pipe plugs. They go in easy by hand then start to get tight because the threaded opening actually decreases in diameter the further in u go that's how it seals along with the pipe sealant u see on the threads of the plugs u remove.

GM may have a torque spec of 20 ft/lbs. or whatever on those plugs but basically they screw in by hand and when it starts to get tight by hand u only need to go a bit more with the ratchet and it will be tight and won't back out or leak.

I'm thinking 20 ft/lbs of torque on those plugs is a bit much.

Tony

 

Yep. The only reason they have a torque spec is to keep ham fisted techs and owners from stripping the thread by over tightening.

The only real reason for torque specs is to ensure there is enough bolt /stud stretch to provide adequate clamping force. Obviously this is not a requirement for a drain plug.

 

Here's a good read about NPT pipe thread with pics so you get an idea what is going on there when you screw in the pipe plug to the trans case.

My feeling...…………...u overtorqued it even if you did use a torque wrench and put 20 ft./lbs on those plugs. You are lucky you didn't crack the trans case. I would buy 2 new pipe plugs from GM and take out those plugs, replace and this time snug them up and you are good.

http://blog.parker.com/what-are-the-...raight-threads

 

I started to realize they were probably pipe threads once I saw the curly Q. Weird/frustrating that GM and Tremec included a torque spec for these when that is possibly dangerous.

Would I really want to take these out and replace them now though? If they aren't leaking it seems like to me that I'd just be asking for trouble by taking them back out and replacing them if I don't have to. I was thinking I'd just leave them until the next time I needed to remove them for service, and then replace them with new plugs then.

 

Obviously if there's dammage to the transmission threads now it will still be a problem later, but it could be years before I have to take these out again and I'd much rather delay the issue that long if I can. Plus I'd have to refill the ATF. Is there any potential for *further* dammage by leaving them in? The only thing I could think of would be thermal expansion further causing excess loading, but aluminum seems to have a higher thermal expansion than steel (which I assume the plug is made of, not sure), so that shouldn't be a problem.

 

My worry is the stresses you are putting on the case in that area with the overtorqued pipe plugs. It may be ok now but with driving, bumps, heat and cool cycles on the trans it could be a problem down the road.

Maybe back off the plugs you have in there now so they aren't that tight. Get 2 new plugs and keep an eye on it for the next few weeks, if there are no leaks leave it till it's time to replace the fluid again and change them out then.

A word of caution, your 3/8" drive ratchet square bit fits in the fill and drain plugs kinda loose and only maybe 1/4 to 3/8 of the way into those plugs so make sure you have a good firm square pressure on it before you apply the torque to loosen it. If you slip you'll mess up the square of the plugs and you are in a whole new world of hurt.

Tony

 

Thats a great suggestion, thank you for the help! Hopefully if someone else is looking for the torque spec for these plugs they'll find this thread and not make the same mistake.

 

As noted, I cannot believe you have a problem. I always do them by feel, but I've been at it a looooong time. As for "loose" plugs, I seem to recall something here quite some time ago about such from the factory. Btw, my experience with dealer Svc. Depts. is that they way OVER-tighten plugs, if there's an issue, not leave them loose. All the best!