drum brake warping

carl

carl

True Classic
My previous 128 had a rear disc conversion. Since my current wagon is not built as a hot rod I left the rear drums on but rebuilt/replaced everything including some cheap eBay drums. One rear drum started pulsing bad and I had both new drums turned which got rid of the problem for a bit but now the rears are starting to pulse again.

Did I buy some really crappy drums that won't stay round with just normal urban driving or is there some other issue causing drum warpage?

carl
 
same issue

On one of my rear drums on my SL Coupe. Irregular wear was evident on the old drum and shoes. New parts cured it, but only temporarily as with yours. It would be great to figure out the root cause and resolve. Tweaked backing plate? Any insight or analysis methods well appreciated in advance.
 
brakes

I assumed cheap rotors but really I have yet to seriously lean on the brakes so don't see how that could be the cause. I jacked up the car and noted I had the e-brake adjusted a tad too tight as I could just hear the passenger side drum brushing the shoes. I backed off the cable tightness so it spun free and the brakes seem to be OK....no pulsing at the moment. Both instances of rear brake pulsing were caused by the passenger side brake. I guess I could rig up a test stand with a dial indicator to see if the drums are out of round, again.
 
Have you performed a brake bedding procedure?

Stop Tech has an interesting write up. Supposedly if you do not bed the brakes properly, uneven deposition of friction material on the rotor (or drum) is possible, causing uneven thickness variation. The result is a warped rotor/drum feel without them actually being warped. And if you replace parts and don't bed those in, you get the same result after a while.

At a previous job we performed Disk Thickness Variation testing for OEMs, to see how things were wearing after lots of Los Angeles driving. We were measuring variation in microns so it doesn't take much to screw up the brake feel!
 
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