Why reusing lock-nuts is a baaaad idea [Archive] - SaabCentral Forums

: Why reusing lock-nuts is a baaaad idea


thaab
12th October 2011, 09:25 AM
So, on the weekend I acquired a new project car - a slightly weird monte carlo yellow vert that has good bones, and was in need of some TLC.

The PO had said that his mechanic had roadworthy failed the car on a few items, including the indicators not snicking off, and the horn not working.

Got a chance tonight to have a good look at the car, figuring that the indicator stalk needed to be fixed or replaced, and that there was an issue with the horn wiring or the contact between the steering wheel and column needed to be cleaned.

I was half right.

Started by taking the stalk off to check it out off the car. The cancelling mechanism seemed to be working ok, so I put it back on the car and had a closer look to make sure the nub on the back of the steering wheel was still there (I've seen these broken off in the past, which kills the cancel function). The nub was still there, but there was a 1/2 cm gap between it, and the plastic cancel lever that's attached to the stalk. And similarly the horn contact wasn't contacting the ring on the column.

Uh oh. The steering wheel wasn't seated properly. Taking the saab badge cover off the centre of the steering wheel revealed that the 23mm (or is that 22mm) lock-nut that keeps the steering wheel attached to the car had come loose, and was only a few turns away from coming completely off the threaded section. Major badness, especially since the PO had driven the car in this state for who knows how long :o.

I've no idea how this would have happened, but I'm surmising at some stage someone had the wheel off, and reused the nut, or didn't apply threadlocker when they reinstalled, or didn't torque the nut correctly, or just plain didn't check to see if the wheel was seated properly when reinstalling.

Needless to say I'll be grabbing a brand new lock-nut tomorrow, but I'm writing about it here to serve as a cautionary tale for those who would be tempted to re-use nylocks... here comes the finger waggle... Please don't :nono;

S900t8v
12th October 2011, 10:25 AM
An interesting story, glad you sorted the horn and indicator issue :)

In my opinion more likely someone didn't do it up at all. A nylock nut that has been used once, even 2-3x still has plenty of bite. If you can't thread a nylock nut on all the way by hand then there is still locking function. I have reused nylock nuts on not critical high vibration areas 5-6 times and they have been tight every time i've removed them. It's an insurance policy. I'm sorry but I'm skeptical. There is pretty much no way a nylock nut can become loose if you can't screw it on by hand (so bolt is through one side to other) It defies logic. Perhaps if they wd40ed it, even that I'm skeptical of.

I reused the nylock nuts holding the bearing/bushing caps of the lower control arms to the chassis. That was 12 months ago. About a month ago I had the wheels off and checked them with a torque wrench. Click click, as tight as I originally set them, Suspension nuts probably get the greatest vibration from the road and they were fine. I think a lot of other people on here have reused nylock nuts in various other applications. Sure it isn't recommended but I think it's a waste of cash. IF I owned a shop would I use new ones - Yes.

Re the steering wheel, If the nut had come off - the driver doesn't pull the steering wheel to turn, plus the angle of the column (about 60 degrees from horizontal) would make it extremely difficult to pull the steering wheel off from driving motion. In addition to this the teeth of the steering wheel (on mine at least) are a snug fit and it is difficult to pull the wheel off when you intend to. (Hence I guess Saab mentioning to be careful when removing and fitting the wheel not to bang it on as it can collapse the telescopic steering column.)

You hear of people reusing nylock nuts with no issues. Ensure they are torqued correctly and you will have no problems. It's like double insurance. If you are worried they might come loose give it an extra 5-10nm.

thaab
12th October 2011, 11:22 AM
Good points S900 - especially regarding how well the steering wheel is sometimes jammed onto the column, and its angle. The last wheel I took off required a jury-rigged puller to get it loose. This one, and a few others I've removed that were fastened correctly, not so much.

For me, though, it's a question of risk. Someone much cleverer than me has thought through and specified where critical fasteners should be used, their expected behaviour, and reusability. I'd rather not second guess those expectations for the sake of a few $$, but that's just me ;)

S900t8v
12th October 2011, 11:57 AM
Good points S900 - especially regarding how well the steering wheel is sometimes jammed onto the column, and its angle. The last wheel I took off required a jury-rigged puller to get it loose. This one, and a few others I've removed that were fastened correctly, not so much.

For me, though, it's a question of risk. Someone much cleverer than me has thought through and specified where critical fasteners should be used, their expected behaviour, and reusability. I'd rather not second guess those expectations for the sake of a few $$, but that's just me ;)

But of course, each to their own :) My dollars are carefully spent. I do use new ones where ever supplied! I like Permatex blue but still only use sparingly and rarely.

Sounds like you got a bargain with your car! It's funny how little things like that can get you a good deal. I had a guy break the ignition switch in a 900, I cut $525 off his price and got it for $225. The switch would have cost me 40 mins at a wrecker and $10-20 bucks!

li Arc
12th October 2011, 05:22 PM
I do re-use lock nuts, but I try to remember not to when using them on suspension parts. One guy in the project threads section had his tie-rod end nut fall off while rallying, that's definitely not good, and urged us all to replace nylock nuts with new. However, make sure you get good ones; I replaced mine on the tie-rod end last night and now it's stripped to hell. It wouldn't torque properly, and by the time I realized something was wrong, it wasn't coming out again. Even some persuasion with an impact wrench didn't help. I don't think it's the tie-rod end, since the threads are definitely built to withstand high torques, but either way, I think I'm going to have to angle grind it off and get new tie-rod ends. Because of some idiot who didn't QC the nuts properly.

Guess it's not specific to nylock nuts, but it's not the first time for me, whereas I've never had problems with normal nuts. Maybe I should junk this kit I got and buy them individually from those expensive boutique bolt shops.

li Arc

milos
12th October 2011, 05:26 PM
steering wheel attached to the car had come loose, and was only a few turns away from coming completely off the threaded section
There should be a spring washer that is supposed to keep the nut (and steering wheel) in place...

wbrook_ford
12th October 2011, 07:18 PM
I reused the nylock nuts holding the bearing/bushing caps of the lower control arms to the chassis. That was 12 months ago. About a month ago I had the wheels off and checked them with a torque wrench. Click click, as tight as I originally set them, Suspension nuts probably get the greatest vibration from the road and they were fine. I think a lot of other people on here have reused nylock nuts in various other applications. Sure it isn't recommended but I think it's a waste of cash. IF I owned a shop would I use new ones - Yes.

You hear of people reusing nylock nuts with no issues. Ensure they are torqued correctly and you will have no problems. It's like double insurance. If you are worried they might come loose give it an extra 5-10nm.

The torque applied is what keeps the fastener together, not the little nylon...

If you are worried they might come loose give it an extra 5-10nm.
^actually, don't do this. There is no substitute for proper torque.
Sure the extra oomph may be unimportant now, but when you strip some threads, break the fastener, or have it come loose due to over-torque, don't think the nylon will save the day.

S900t8v
12th October 2011, 08:19 PM
The torque applied is what keeps the fastener together, not the little nylon...

^actually, don't do this. There is no substitute for proper torque.
Sure the extra oomph may be unimportant now, but when you strip some threads, break the fastener, or have it come loose due to over-torque, don't think the nylon will save the day.

I don't think 5-10nm will break the average fastener, although I personally wouldn't bother. If you increase the torque the nut face bites further into the metal it's against and is less likely to move. Aside from a slight risk of damaging something slightly over-torquing is fine. Like I said, I have and will never bother doing that. The manufacturer knows what the optimum torque is.

In retrospect it was probably bad advice, a lot of people do go crazy tightening things. However 2-5nm is the error margin for cheap torque wrenches when you get into higher torque range. :lol:

thaab
13th October 2011, 06:06 AM
There should be a spring washer that is supposed to keep the nut (and steering wheel) in place...

Interesting - I didn't know that the washer is supposed to be sprung. there was a flat one under the offending nut. Speaking of which, I checked the state of the nylon insert tonight - it's pretty deeply thread grooved, so I suspect it's been on and off a few times.

There's also a splotch of red stuff on the outside and top of the nut: threadlocker, or a manufacturing marker that someone had correctly torqued the fastner?

Thanks everyone for your responses by the way - it's a pretty mundane topic, but I'm learning a lot from it.

c900
13th October 2011, 06:26 AM
There should be a spring washer that is supposed to keep the nut (and steering wheel) in place...

Yep it's a Belleville (wavy - literally) washer, and I've never heard of thread-locker being used for steering wheel nuts (referring to another post where that was mentioned).

Now one reason to be careful with nylocks over regular nuts is that a nylock when compared to a regular nut has less thread, so it's easier to make it strip the thread if over-torqued. Also if no anti-sieze (copper grease is what I use) is applied, that also can have an effect.

I use copper grease on all threaded fasteners unless a thread locking compound is specified which is only really needed for very few situations. It also helps protect against rust which is the #1 reason for snapping old fasteners (I find anyway).

Apparently the techie way to get hard to budge fasteners to release is hit with a hammer (or hit a punch held against it with a hammer) to break the thread bond, and slightly re-tighten prior to undoing.

Craig.

thaab
13th October 2011, 12:03 PM
I use copper grease on all threaded fasteners unless a thread locking compound is specified which is only really needed for very few situations. It also helps protect against rust which is the #1 reason for snapping old fasteners (I find anyway).

Thanks Craig. Sounds sensible, but does using the grease change the torque values for the fastener? If so, how do you calculate what the correct value to torque to is?

c900
13th October 2011, 09:50 PM
Thanks Craig. Sounds sensible, but does using the grease change the torque values for the fastener? If so, how do you calculate what the correct value to torque to is?

I have had some people tell me that using it does affect setting the proper torque but I just stick with the published torque settings and don't try to compensate. If you prefer to use something else, a little bit of oil works ok but I don't think that has the longevity of copper grease.

Craig.