Stripped Seatbelt threads

[tj21]

My new seat belt installation is not going as smooth as I hoped. I could not find torque specs for the bolts, and over torqued them, stripping the threads of both the bolt and messing up the threads in the floorboard.

 

I am planning on trying HeliCoil after researching this problem others have had with different cars. That way I can use the same bolts (I have extras). It looks like tapping and using a bigger bolt may not be possible, since seatbelt bolts are apparently all the same size. A standard grade 5 or 8 bolt would not work properly since the belt can not rotate freely when tightened down.

 

Does anyone know the size of HeliCoil I need? I know its 7/16", but I'm not sure if its 7/16-20 or another size, since I don't know what the "-20" even means.

 

If there is a better approach than this, please let me know. Is it possible to tap a new hole near the old one, and use a locking nut?

[aemsee]

The "20" is refering to thread pitch. The higher the number, the finer the thread.

 

Now, if you are unsure about the proper repair, save the cash and have a professional do this. We are talking about something that could potentially keep you from becoming a projectile. I personally would not trust a helicoil for this, and I'm not sure you could find one that is correct anyhow. The damaged nut should be cut out and a new nut and panel welded in to the truck. I am guessing this isn't going to happen.

 

Some of the guys on here can probably do the math for you (Sir Sam or Eagle) to let you know how much energy is generated by a sudden deceleration, like hitting a stationary object at speeds as low as 20 or 30 mph.

 

Don't short cut or do a hack job on this, you may end up regretting it. OK, off my soap box.

[jimoshel]

Usually when the bolt is in to where it should be, there is enough threads sticking out from the bottom to screw another nut onto.

[tj21]

The "20" is refering to thread pitch. The higher the number, the finer the thread.

 

Now, if you are unsure about the proper repair, save the cash and have a professional do this. We are talking about something that could potentially keep you from becoming a projectile. I personally would not trust a helicoil for this, and I'm not sure you could find one that is correct anyhow. The damaged nut should be cut out and a new nut and panel welded in to the truck. I am guessing this isn't going to happen.

 

Some of the guys on here can probably do the math for you (Sir Sam or Eagle) to let you know how much energy is generated by a sudden deceleration, like hitting a stationary object at speeds as low as 20 or 30 mph.

 

Don't short cut or do a hack job on this, you may end up regretting it. OK, off my soap box.

I understand the saftey-first approach, especially since safety is the sole purpose of the seatbelts. However....

 

The force on the bolt when in a crash is all shear. If I were to use helicoil, it would only need to prevent the bolt from pulling out, which is on a different axis than the primary force. I need to figure out whether helicoil can prevent the bolt from sliding out.

 

I suppose there is no easy answer for this, since it would vary by car and installation. If the bolt was not exactly perpendicular to the belt pulling on it, there would be more force pulling on the threads / helicoil. A large factor of safety would need to be used because of this.

 

An easier way to know it would work is if specs were available for helicoil strength vs strength of threads on stock welded nut. If helicoil > stock, then all is good.

[tj21]

Usually when the bolt is in to where it should be, there is enough threads sticking out from the bottom to screw another nut onto.

I was hoping for this as well, and looked for some locked nuts while at NAPA. But when I got home I saw that no threads were exposed. Perhaps if I found a longer shoulder bolt of the same grade this would work.

[jimoshel]

I have taken a bolt that fit the original threads with 3/8in or no shoulder and screwed a nut all the way on. Put the seat belt bracket on first. Screw the bolt into the hole until tight. Now go underneath and screw a second nut onto the bolt. Usually a 3in bolt will be log enough for this.Have at least 2 threads sticking out from the nut. If it's longer than that then cut off the excess. It will just rust and make it more difficult to remove at a later date.