'61 Coupe brake grinding

[MidModCad]

I'm having a weird problem with my front brakes.  As the car comes to a stop they are grinding badly, but only under specific circumstances.  No grinding when cold or during heavy use.  I recently had brake work done - new wheel cylinders and conversion to a dual master with higher pressure than stock.  The shoes were not changed at that time and still show plenty of meat left.  I've been told the grinding could be from sub-standard pads used on a prior brake job and recommendation was made to switch to Wagner brand shoes. Appreciate any opinions. 

[savemy67]

Hello MidModCad,

Is the noise a grinding noise like a grinding wheel or is the noise a chatter like dragging a heavy object across a floor?

Did the noise start after you had the work done?  If the work was done at a shop (as opposed to by you), did the shop recommend the Wagner shoes?  How is it that "higher pressure than stock" was determined?

After the new wheel cylinders were installed, were the old shoes arced, and were the drums turned?  If the shoes and drums were not touched, I would be skeptical that the new hydraulics are the cause of the grinding noise.

Your description of when the noise occurs should be able to be duplicated after the car has been driven and placed on a lift.  This should be done after a thorough visual inspection of the brakes at all four wheels, and a thorough audible inspection of the wheel bearings at all four wheels.

Some noises can be hard to diagnose.  Something other than the brakes may have failed coincident to the brake work.  Do you have the shop manual for your car?

Respectfully submitted,

Christopher Winter

[MidModCad]

Thanks for your detailed response, Christopher.  In answer to your questions:

The noise sounds like metal to metal grinding, but not chatter. The brake work was done a couple of months back, but the noise only started two weeks ago. 

The modern aftermarket dual master installed works with higher pressure than the stock system.

The shop did recommend Wagner shoes as they've had good results using them on drum brake classics.

The shoes and drums were not touched during the brake work.  Like you, I'm not sure why they would be the culprit.  The noise really only appears as the car is just coming to a stop with the weight transferring forward. 

Yes, it will be up on the lift to investigate more thoroughly next week. 

Update: Your mention of wheel bearings may point to an answer.  After a drive today with wheel covers off I found splatter that looks very much like bearing grease on the front right tire.  Will investigate.

And yes, I do have a 61 shop manual (with a GM library stamp on the cover!), but I could not find anything relating to my specific issue.

[Omarine]

Is it possible the drum and backing plate are touching cauising the dragging sound? Maybe someone tried to bang the drum off and slightly bent that backing plate into the drum for that metal to metal sound, or even a spring or some component inside touching the drum?

Cheers oscar

[35-709]

Yes, I'm wondering if a spring hasn't broken and is dragging.

[fishnjim]

Check to make sure the lining(shoe) is seated properly, it could be "chattering" on the backing plate.   Usually you get a shiny spot were it's happening.   They make a lube for that also.
I suspect noise is coming from one wheel?   
ps: If you're going to do a brake job, do a brake job, not half of one.   The drums should've been trued, new linings, brake parts, repack, etc..   
They can put a pressure reducer in for the excess pressure.   They did that on mine(modern dual with original drum brakes) to even out the front to back grab.   May also not be properly bled and some air in the wheel cylinder causing pulsation.

[MidModCad]

When the wheel cylinders were replaced the shoes, linings, etc. were checked and found in good cond.  The previous owner had recently done all of that but clearly had not rebuilt the wheel cylinders.  As mentioned, brakes worked fine after the job was done for a couple of months, then this grinding began.  When I brought the car back to the shop to have them check the noise it had disappeared. They pulled the drums and inspected at that time but everything checked out.  The noise returned a few days later so I returned and this time the grinding was evident.  That's when the recommendation was made to try different shoes.

Oscar, your theory is interesting, however the grinding comes and goes and seems most related to heat.  It's hard to explain the sound, but it's not a dragging noise.  It's a severe grind/shudder just as you pull to a stop - as mentioned, only when the brakes are operating in the middle heat range. 

Will check into the lining being seated properly and also wheel bearing, since I found grease splatter on the tire after driving without wheel covers.  Thanks all!

[savemy67]

Hello MidModCad,

Your shop manual should indicate the bore size of the original master cylinder.  If possible, you should find out what the bore size of the new dual master cylinder is.  Since hydraulic force is a function of cross sectional area, a 1/8" increase in bore diameter will result in a near twenty percent increase in hydraulic force given an original master cylinder bore of 1".  This significant increase may not be suitable for your car given that nothing else was changed.

Respectfully submitted,

Christopher Winter