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Help needed for future reference

Need someone to help me with this question for future reference

I have asked this on numerous forums but people don’t give me a simple answer just a massive description which don’t make sense.

The question is that if you can do it up by hand the bolt all the way to till the end of the internal thread female end and then can tighten it up its fine with a spanner .

Now if you were to cross thread the bolt will the bolt tighten up or just spin as some of the thread is stripped if you were to force it all the way from the moment the bolt starts to get stiffer and stiffer

I can see why you are not getting answers you want because if you don’t stop as soon as you realize you have cross threaded then what ever you want to stay in place might not do so.

Depends. Sometimes you get lucky and the bolt tightens up and stays there because the nut basically cuts itself a new set of threads on the bolt.

Other times you can’t get it tightened down at all, and now you have to get a new bolt or repair the threads.

Still other times it will seem to tighten down but it won’t hold.

Better to just do it right instead of wondering if you can get away with doing it wrong.

This is allot better answer then some of them is this the same principle if it was a bolt going into a female thread integrated in the engine and not a nut .

Also the first question about doing it up by hand e.c.t is this correct or not.

When you say it wont hold you mean it just spins.

sorry to be complicated but i’m actually getting some information and it just i’ve never felt what cross threading is or know when to feel it wrong when doing it up by hand .

Have you never tried to put a light bulb in crooked and noticed it did not want to turn. I am having trouble understanding what you are trying to ask. I suspect that you have already made a mistake trying to put a bolt and nut together.

Basically , I need to take out the brake servo and it quite a job and worried tht if I do this im not going to notice that ive done it or feel it and no i haven’t honest, people have said to me it will get stiffer and stiffer is this true .

people also said if you can do it up by hand all the way and then tighten it up all the way until it stops

then its fine

Correct, you cannot cross-thread by hand more than about a half turn.

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Maybe this is not a project for you. Mess up anything with brakes and catastrophe soon follows. Do you know how to bleed the brake system ?

Cross threading happens a lot with lug bolts. Some shops hurry up to get the wheels on the car without first starting the nut by hand.They also overtorque the nut making it impossible to change a flat.

One trick for blind insertion is to turn the fastener in the loosening direction while pressing in. It will drop slightly and click when the threads are lined up. Then hand tighten a few turns to ensure good thread engagement. You can tell it’s in if you pull back and it’s still engaged. I continue to tighten by hand until it is either too laborious or too tight to continue.

Look at the fasteners before inserting. If necessary, clean the threads with a brass brush or spray cleaner. Dirty threads just make it more difficult to tell if you have good engagement.

If you think you’ve started to cross thread because it’s hard from the get go… STOP immediately. Remove the fastener and examine the lead-in threads. You can use a jeweler’s file to clean them up before trying again. The worst mistake is to keep going, hoping it will get better or go away…


I find a thread file to be easier/faster in restoring damaged threads.


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Let me attempt to give you an answer. If the threads are not cross threaded, the the bolt is going in parallel to the hole. Imagine pushing a peg into a hole. If the peg is perfectly aligned with the hole, it goes in pretty easily. Now imagine trying to push the peg into the hole at a slight angle. Pretty soon the nose of the peg is trying to push its way into the side of the hole. The deeper the hole and correspondingly longer peg, the deeper the peg has to go into the side of the hole if it is to maintain that angle.

If the hole is shallow, once the peg pushes through the other side, it has finished distorting the hole so it gets a little easier, not as easy as if it were straight, but a little easier. There is additional friction from the pressure on the side of the hole due to the angle.

So if you had a hole that was not very deep, four threads for example, and you cross threaded the bolt, it would get harder to turn with each turn until you finished the fourth turn. Now you are through cutting new threads, but the bolt will still be harder to turn than a properly threaded bolt. A deep hole just keeps getting harder and harder until you just cant turn the bolt anymore or the bolt breaks off and now you have a bigger problem.

A cross threads bolt is not only trying to cut new threads, it is also going into the hole at an angle just like the peg above, so there are two forces working against you.

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If you have the room under the hood, and are fairly agile, you might be able to replace that brake servo . . . I assume you mean vacuum brake booster . . . without disconnecting any lines from the brake master cylinder

Cross threading is when the hole or nut meets the bolt or stud at enough of an angle that the different sides of the fastener don’t engage the same thread but are one thread off. If, after you break a fastener loose you can take it off easily by hand, you should be able to put it on easily by hand.
If, on the other hand if a fastener is coming apart where you have to use a wrench all the way, put some oil on the threads and take it almost all the way off then back in until you can spin it by hand.

This works for me in the heart of the rust belt so it will work anywhere.

I was going to mention what Twin Turbo did. The idea is not to get it started wrong. Once it starts correctly, it’s not going to cross thread. Once started incorrectly, all you’ll do is ruin the threads. Sometimes its hard to tell so sometimes you start it several times just to make sure and stop if there is resistance. It’s just second nature to me to first turn the bolt or nut the wrong way to catch the start of the threads, then proceed the right way. Particularly important on soft metals like brass. Sometimes no mater what you do, you wreck the threads due to junk or rust on them. That’s when you get the tap and die out, or Tester’s thread file.

Thank you for all the help , best answers I have got , slowly starting to make sense

So basically the bolt will be at a angle and will be pushing on the side of the female thread the nose of the
male bolt which I can understand will cause friction between the two as the male thread will want to try and go through the metal and out the other side Is this why you feel the force when turning as well as the stripping o the thread

One more question if you don’t mind answering it is, if a bolt had a slight resistant, then on the next turn it was easy to turn and then all the turns all the way up to the end was easy then is it okay or if the same situation occurred again on the same bolt and still went easy on the turns afterwards is it okay until the end.

Yes, it’s OK. A cross-threaded bolt will never turn in easily.

I was going to recommend this as well. I always do this and it’s never failed me.