Weak/Loose Swaybar Bolts

[TomoHawk]

One of the bolts on my swaybar was loose; i.e., it took little effort to spin out with the racket. The other three go in tight. I didn't see any stripped threads on the screw, but the threads might be just worn so I can't run the screw down tight.

What can you do to tighten up the threads on these bolts? I can get new bolts & see if those threads are tighter? what are those threads?

thx

[=Enigma=]

The bolts that mount the front sway bar to the body of the car on my 73' are M12 x 1.25 x 20mm hex bolts. Hope that helps.

[TomoHawk]

Mine look more like m8 x 1.25 x 40mm, and the tip is tapered for about 15mm. Odd buggers. Mine is a '78

[=Enigma=]

M8 sounds a bit small for a part taking on so much stress unless you have 4 per side. Just to be clear, my bolts are M12(head) x 1.25(thread pitch) x 20mm (length) CL8(strength) Hex Bolt and there are two per side. VicBrit show the same part for 240, 260 & 280Z's.

Sounds like yours may have been replaced at some point. Hopefully the thread or shaft diameter is the same as normal M12 or this may be your problem. It's even possible someone replaced them with non-metric parts or had to re-thread the hole. Many sway bar mounting brackets come with 1/2" bolts. I found a 1/2" bolt used for one of my motor mounts rather than the usual M12 x 1.25 x 25mm(I think).

Check if the other working bolts fit properly in the problem mounting point. If so just pick up a matching one at the HW store. If not, you may need to clean up the threads with a an appropriate tap. Sorry, you;re simply gonna have to get under the car

[jmortensen]

Mine on my 70 were 8 x 1.25 as well. They are small for sure.

[montoya_fan01]

M8 sounds a bit small for a part taking on so much stress unless you have 4 per side. Just to be clear, my bolts are M12(head) x 1.25(thread pitch) x 20mm (length) CL8(strength) Hex Bolt and there are two per side. VicBrit show the same part for 240, 260 & 280Z's.

Sounds like yours may have been replaced at some point. Hopefully the thread or shaft diameter is the same as normal M12 or this may be your problem. It's even possible someone replaced them with non-metric parts or had to re-thread the hole. Many sway bar mounting brackets come with 1/2" bolts. I found a 1/2" bolt used for one of my motor mounts rather than the usual M12 x 1.25 x 25mm(I think).

Check if the other working bolts fit properly in the problem mounting point. If so just pick up a matching one at the HW store. If not, you may need to clean up the threads with a an appropriate tap. Sorry, you;re simply gonna have to get under the car

This is confusing the issue of the bolt size..

Metric (actually ALL) bolts are not sized by the size wrench that is used on the hex head. Bolt size is related in diameter of the shaft, then thread pitch, then length of the shaft.

The bolts that secure the mount bushings on a 240z front anti-rollbar are M8 x 1.25 x ~ 20mm. I would suspect it would be the same on a 280, but I have never checked.

Tom: If the threads on the bolt don't appear stripped but don't tighten up when threaded into the captive nuts in the frame rails, then it is probably the captive nuts that are damaged/defective.

[=Enigma=]

Actually, most bolt shaft diameters DO coincide with the head size in that there is a standard ratio that is normally used. That is not to say that there are not exceptions, but they would be just that.

[TomoHawk]

On my car the heads are always bigger than the shaft. Most of the bolts with a 10mm hex head ( they bolt most every part under the hood made of sheet steel like heat sheilds, brake lines, fuel filter, carbon cannister, etc.) have an m6 thread. On my swaybar the heads are 14mm andthe shaft m8. There may be a consistency, but it must be proportional to the shaft.

[montoya_fan01]

Actually, most bolt shaft diameters DO coincide with the head size in that there is a standard ratio that is normally used. That is not to say that there are not exceptions, but they would be just that.

First of all I wasn't trying to rag on you, but instead to clarify your statement about "M12" for the benefit of anyone who might need to buy a bolt/nut.

Your statement quoted above is semi-accurate.

A bolt with an 8mm shaft dia is not called a M12 just because a 12mm wrench is used on it, and the reason is because hexhead sizes DO vary.

FWIW, a standard 8mm bolt/nut has a 13mm hex head, an 8mm JIS (Japanese Industrial Standard) bolt/nut, the type of bolt used on a Datsun, would have a 12mm hex head.

Thus size is stated in terms of the dimension that DOES NOT vary.

If someone goes to the store and buys a bolt/nut in the size you posted (M12 x 1.25 x 25mm), what they come home with will NOT fit the application we are discussing. If you order a M12 x 1.25 x 25mm bolt, you would get a bolt with a shaft diameter of 12mm. It's as simple as that.

[TomoHawk]

Is there a chart with the relationship between shaft & head?

[=Enigma=]

Montoya, you are in fact correct. I always thought the first measurement was the bolt head size. But after doing a little research, I see that I misunderstood the notation of fastener sizes. Thanks for the correction. And I didn't think you were ragging on me. I seldom take anything personally. Life is way too short for that.

http://www.boltdepot.com/fastener-information/Default.aspx

[montoya_fan01]

Montoya, you are in fact correct. I always thought the first measurement was the bolt head size. But after doing a little research, I see that I misunderstood the notation of fastener sizes. Thanks for the correction. And I didn't think you were ragging on me. I seldom take anything personally. Life is way too short for that.

http://www.boltdepot.com/fastener-information/Default.aspx

Enigma:

You are certainly not the first one to be confused (I may have been). I do admit that it is a bit confusing in that most of us (including me) when working on our cars DO think of bolt size in relation to the wrench we use on them.

The first time I was buying bolts to replace my oil pan bolts, and intake, exhaust bolts/studs and nuts I got a bit of an education from the salesperson at Lawson products. www.lawsonproducts.com

Tom:

Lawson has hardware spec'd by shaft diameter, thread pitch, length, and they also indicate head size. It took me some time to go through their info thoroughly and find what I was looking for, which was the identical size (completely) that came standard on my car even though I could not find the hardware in the gold cad, or yellow zinc (whatever) that Datsun/Nissan used. It was also a pain to order through them because they generally sell only to wholesalers and I had to get "approved" by the regional sales staff before they would accept my order.