Hey friends,
I noticed on my SA2 calipers there is no nut on the end of the pad retaining bolt. Would it be wise to use the weakest loctite 222 (purple) on this bolt to make sure it stays in?
Very odd there is no nut on the end of this. They changed this in later calipers iirc. I am very careful about my brakes and don’t want a failure at speed.
Another option, not for the faint of heart, is to mildly deform the threads so there’s an interference fit. This can be done gently with a ball peen hammer, or my preferred method – vise grips! Loc-tite is potentially susceptible to heat, whereas mechanical interference is always there. HOWEVER…and this is a big one…anything that deforms the metal on one side, is also likely to affect the other side. And in the case of a strong bolt (steel) vs. soft holder (aluminum), it’s likely to happen and eventually lead to failure of the threads. So, caveat emptor.
The “proper” solution is a different design, with a through-hole and cotter / pin. You could theoretically do this fix, using a small drill bit (and tape to protect the threads) from the bolt side, then drill to tap size, and finish tapping through on that arm. This would be my preferred method. Drilling from the tapped side would be best to ensure alignment, but runs the risk of damaging the threads.
The reality is that the system likely works “well enough.” I’d use the loctite and forget about it. I would use a high-temp variety however.
At the risk of being pedantic - isn’t the nut built into the caliper where you show the red caliper?
I think using blue loctite should be fine, too.
Not a mechanical engineer - the load on the bolt is a bending load i.e. when you brake, the pads want to rotate in the same direction as the brake disk. The yield strength of the bolt will be easy higher than the bending load. The bolt will bend/deflect a little but I don’t see how it can overcome the thread friction of a properly tightened/torqued bolt.
I tend to mark bolts like this so it is very easy to tell if they have rotated.
Are you going to add the set screw to the safety collar?
I would go the loctite route. Purple is low strength, for M4 and smaller bolts so I would skip that. A liberal amount of 242 (blue) or a dab of red 262 or 271. The reds will withstand heat better and can always be broken with some MAP gas if you are having trouble at bolt removal time.
When you have the bolt out wire brush the old loctite off the threads and you can use a chaser on the caliper threads or a bolt with brake clean in and out a few times.
Calipers will put tension on the bolts when they go where a bridge would be as the pistons try to spread the caliper apart. How much? In cars you can tell when someone uses a bolt versus just a cotter pin. The rotational loads are normally taken by the edge of the caliper where the pad touches it.
Ted - I’m pretty competent with mechanical things but given this is the only caliper I have and I’m on a budget (more the budget part) I think I will try loctite.
Harjit - I haven’t taken this apart in a few years. It is possible the nut is in there and I’m just forgetting. Very odd design though.
Mark - I will definitely be adding the set screw to the safety collar. Ordering that next week with the set screw from a local shop. Marking it is an excellent idea.
Have to say guys, I thought I would get laughed at for asking such a seemingly basic question but I’m really happy with the cordial replies and information. I am really coming to love this forum and the group of people who post / respond here. So helpful. Thank you everyone!
Really good point.
In the picture, the caliper looks solid, so this spreading force shouldn’t show up on the bolt. Thoughts?
I don’t quite understand. Can someone dumb this down for me?
