Brake failure

[frankieb]

Hello everyone,
Had a very scary incident on the freeway, the bolts securing the back disc brake snapped and the disc brake cracked in pieces , the rear shock housing securing the brake caliper cracked and broke of,suddenly driving at 60 and no brakes!!! scary moment,slowed the car by downshifting and rubbing the front end of car to the cememt divider on the freeway,finally the car came to a stop.You feel very helpless in a small fiberglass box while 18 wheelers speed by you. what would cause the bolts to snap like that , where they just rusted out and fatique,or just bad luck. I had the rear suspension rehauled completely last summer,could that be the cause of the failure,. Like to here your comments. Cheers

[billwill]

It seems incredible that both bolts broke, so my first thought is that whoever overhauled your rear suspension used some ordinary steel bolts there instead of high performance bolts.

Another thought is that perhaps they were not done up tight and some sort of rocking motion put undue stress on the bolts.

Or perhaps they had been done up too tight, so that the bolt had actually stretched to near breaking point.

I presume you were applying the brakes at the time they broke, not just driving along.

[Quart Meg Miles]

It could have been a fatigue failure of the caliper bracket promoting a cascade of the other problems. Have a look at the broken casting to see if it shows dirt along the break where it had penetrated an old crack.

Similarly, check the broken edges of the disc which might show the typical shell pattern of fatigue in iron.

Any one failure would break up the whole area so we may never know the cause though Bill raises legitimate points. I rarely change my bolts when replacing the doughnuts but I do torque them properly and it seems unlikely that a proper garage would fail to and they should have used new bolts and nylocs, as the manual states.

What model was it, age and mileage? Do you drive hard on the brakes?

[reb53]

Put up a few photos, one photo being worth a thousand words etc.

( Besides which I'm kinda curious to see this mess....).

[frankieb]

It s a 1968 elan 2 I will try to take pictures of the mess,I do suspect it has something to do with the new suspension not being installed correctly. the reason I installed a new suspension last year was that the left rear bolt that holds the shock cylinder to the top anchor unwinded and the cylinder dropped and the rear tire and suspension collapsed,luckly I was not driving very fast,that s the same side that my bolts broke off. Maybe that has something to do with the housing and bolts breaking. The collapse of the suspension might have cause some stress on the wheel hub and bolts.

[billwill]

Of course if the brake disk shattered and a chunk fell out, when the disk pads closed into the empty space with the car at 60 mph, the resulting forces on the caliper & bolts & everything would be enormous and would easily break the bolts. In my opinion.