Topic: catastrophic rear brake failure--what the hell just happened???

[jessezm]

Well I'm glad I'm able to sit here and type this, because after getting home and looking at my bike I'm astonished it wasn't any worse...   So yesterday I put in a new clutch and barnett springs and new rear brake shoes on my cb400f/466.  I took it out for a nice ride tonight after dinner, and about 10 miles into it on my way home, there was a sudden jolt from the rear somewhere, almost like I ran over something with only the rear tire.  At first I thought the chain had skipped a tooth, but I adjusted it on the tight side and didn't think that could be it.  It didn't happen again and I was headed straight home so I kept going, and when I got off the highway I could hear parts hanging down banging about about, and went to apply some rear brake and there was nothing there. 

I made it home no problem but inspection showed some major failure.  The brake rod had snapped near the rear, and the part of it attached to the brake arm was literally wrapped like spaghetti around the axle spacer. The brake arm itself was contorted and unrecognizable, and the brake plate had turned so that the bolt hole for the straight arm that holds it in place was pointing up, and the bolt had totally sheared off.  One spoke was bent to the point of being loose, and another is slightly visibly bent.

So, what the hell just happened???   I was doing about 85 mph.  It was as if the brakes suddenly locked into place against the hub and broke loose, taking out the rod, brake arm, and stay all at once without locking up the rear wheel.  I'm a bit shaken but also really frustrated!  Those parts are going to be a pain to collect...  and I still have no idea what happened.  One other thing possibly of note was that the brake plate didn't want to move back into position until I loosened the axle nut a little.  But it wasn't any tighter than usual (I think the sudden jolt must have tightened it up).  Thoughts?

[754]

Sounds like the flat bar piece that connects the backing plate to swingarm let go.. think it isd called a torque arm.
 Did you have original bolts on each end?? if not sometimes cheap lower grade bolts cans tart to wear thru and let go(shear off) , or just plain shear off.
 When the torque arm lets go the brake rod will wrap around til it  (usually)breaks.

[jessezm]

That sounds like exactly it.  They were stock parts, but I just had it apart yesterday.  If I didn't tighten it enough and the nut vibrated loose, that would explain it.  I just got the wheel apart and there a chunks of my new shoes ground off along the inner edge, but no other damage inside.  The brake plate spins freely but it looks like it's out of round, like it's oblong or something.  Are they supposed to be perfectly round besides the elongated part that the torque arm attaches to?

[754]

The 750 ones are not..sorta a bit of a flange or skirt on lower side..

[Really?]

I am glad that you are here to tell this story!

[jessezm]

I am glad that you are here to tell this story!

Gah me too!  Could have gone either way. 

[splitt]

It sounds like you lost the front bolt on the brake arm stay. The jolt that you felt was when the brake arm stay stuck into the concrete. You're lucky that the brake arm stay bolt sheared off and didn't try to give you it's best impression of a pole vault. When you had it apart, did you make sure that the bolts on the brake arm stay had the cotter pins in place? You didn't attempt to reuse an old cotter pin, did you?

If anything is even questionable at all, just replace it, no matter the cost. Just ask yourself, how much is your life worth?

Glad your OK.

[Don R]

I've seen the drum brake lining separate from the brake shoe.  That could cause the brake to lock and possibly cause your problem. Check that too.

[Spanner 1]

Splitt +1, exactly IMO.

[steam-powered man]

the nuts at each end of the brake rod should be secured with cotter pins, i use blue loctite there too. glad you made it home.   

[jessezm]

It sounds like you lost the front bolt on the brake arm stay. The jolt that you felt was when the brake arm stay stuck into the concrete. You're lucky that the brake arm stay bolt sheared off and didn't try to give you it's best impression of a pole vault. When you had it apart, did you make sure that the bolts on the brake arm stay had the cotter pins in place? You didn't attempt to reuse an old cotter pin, did you?

If anything is even questionable at all, just replace it, no matter the cost. Just ask yourself, how much is your life worth?

Glad your OK.

The front bolt is still attached, thank god.  It was the rear bolt that seems to have come off.  I remember looking at it and wondering why there was no crush wahser--just a real thick washer.  Not I realize there must have been a crush washer missing.

[jessezm]

the nuts at each end of the brake rod should be secured with cotter pins, i use blue loctite there too. glad you made it home.   

Yep, you're right.  I wish I had slowed down a bit and looked more closely.  I didn't have a lock washer or a cotter pin on the back side of the brake rod.

[KingCustomCycles.com]

If the 550 is like the 750, the rear has a rubber cushion washer, plain washer, cotter pin or clip, and special bolt with a large diameter shank.  Yhe nut is only tightened enough to squeeze the rubber and then secured with the clip or pin.  A locknut won't do it, even if you could find the correct metric thread.  My bobbers are rear brake only, for the most part, I pay attention to this stuff. 

[jessezm]

If the 550 is like the 750, the rear has a rubber cushion washer, plain washer, cotter pin or clip, and special bolt with a large diameter shank.  Yhe nut is only tightened enough to squeeze the rubber and then secured with the clip or pin.  A locknut won't do it, even if you could find the correct metric thread.  My bobbers are rear brake only, for the most part, I pay attention to this stuff. 

Well mine is the 400, but yeah, it's got the same setup, looking at the parts fiche.  Now I've got to find a bunch of parts to put humpty dumpty together again.   I guess this would be a good time to have the head work done.  I was really looking forward to riding my bike to Barber, but that's not in the cards anymore...

[Duke McDukiedook]

Yep, don't forget the cotter pin!! I am sure a lot of people do.

[seanbarney41]

...this same thing just happened to an aquaintence of mine on a cb400...he was not going as fast, but when it happened it made the pedal spring up and bruise his foot...

[jessezm]

...this same thing just happened to an aquaintence of mine on a cb400...he was not going as fast, but when it happened it made the pedal spring up and bruise his foot...

Man I got of lucky the more I think about it.  I've already ordered all the parts I need to replace, just wish I had prevented it in the first place by using the proper parts...

[MoMo]

You are very fortunate-that should have been catastrophic...Larry

[MikeKato]

Bump on this thread so everyone does a check to make sure they do not get killed from the lack of a 5c cotter pin.

[BobbyR]

+1 on the cotter pin. Loctite is no replacement for a cotter pin.

[ncstatecamp]

Are you guys talking a cotter pin through a hole in a bolt or a pin rather then bolt?

[MCRider]

Are you guys talking a cotter pin through a hole in a bolt or a pin rather then bolt?

The OEM shoulder bolt is driled for a cotter, from the factory.

[bjbuchanan]

the nuts at each end of the brake rod should be secured with cotter pins, i use blue loctite there too. glad you made it home.   

I think a cotter pin got left out, more than one? The jolt was the rod winding up totally and binding til it just bent out of the way.

There is a cotter pin at the pivot under the frame at the front of swinger, and cotter pin on brake stay bolt. You gotta have both