Handbrake bell crank

[JDNSW]

Today I was checking over the 2a for a pink slip some time before Christmas. I found that I needed to shorten the linkage between the handbrake lever and the brake, as the lever was reaching its travel limit before the brake was on very hard, but tightening the adjuster caused it to drag. So I should have been aware of the potential problem. After reassembling the linkage I pulled the brake on hard - and there was a loud bang, and no handbrake - lever free.

Investigation showed that the pivot for the bell crank had broken off. This is a shaft about 40mm long, 25mm diameter, and has the end turned down to 3/8" and threaded, being attached to a chassis bracket. The threaded section had broken off at the base of the thread, and had obviously been cracked halfway through long enough to rust inside the crack. I smoothed up the broken surface on the lathe, and bored it to 3/8" and fitted a 3/8" UNF bolt through it, securing it in the shaft with Loktite 609.

If you find the handbrake linkage is losing motion, this might be worth checking - you would not want the failure to happen when you use the handbrake as an emergency brake.

John

[Wolfman_TWP]

Is this the shaft that you are referring to??

Wolf

[JDNSW]

Is this the shaft that you are referring to??

Wolf

Yes. That's a nice shiny one - is it new? I would also comment, that unlike the one that broke, the thread does not go all the way to the shoulder.

John

[Wolfman_TWP]

Yes. That's a nice shiny one - is it new? I would also comment, that unlike the one that broke, the thread does not go all the way to the shoulder.

John

That is a pick that I got from LRSeries. But I do have a new shiny one..

Does the thread have to go all the way to the shoulder?? Or is the one in the pick ok/better??

Wolf

[JDNSW]

That is a pick that I got from LRSeries. But I do have a new shiny one..

Does the thread have to go all the way to the shoulder?? Or is the one in the pick ok/better??

Wolf

No, the thread does not have to go all the way to the shoulder - the attachment goes through the chassis bracket and a spring washer before it gets to the nut, and it would make sense to avoid the stress riser right where the shaft narrows and where the load is highest. Personally, I am not enthused about the design at all - there is quite a stong bending moment at this point, and it is not unusual for the chassis bracket to be bent a little.

John