Squealing could be caused by a number of things.

1) Dust in the drums. As the shoes wear down, the dust produced builds up in the drums. This could cause squealing when braking.

2) Cheap linings. Low-cost linings do not withstand the heat build up well after repeated stops, especially in city driving. When the linings get hot they are known to squeal. This is also accompanied by reduced braking and increased braking effort on the driver's part. That is, you need more distance to come to a stop and the brake pedal does not feel as firm as it should. And the driver does not feel as confident when braking. Basically, the heat produced with cheap linings causes the linings to glaze. Thus the squealing, and the decreasing braking efficiency.

3) Hard linings. This is a situation more common with buses, trucks, taxis and the like. The harder lining does not break down as easily as the regular linings (also the cheaper linings). Thus there is more squawking when coming to a stop. Also, the drums wear more, as they are taking more of the wear than the linings do compared with using regular linings.

4) Other causes include distorted brake shoes, bent backing plate, broken or weak brake shoe return springs or retaining springs, or saturated linings (caused by leaking cylinders).

[On the possibility that the noise could be from a bad differential, and a mechanic's diagnosis that the differential, not the brakes, is the problem).

Basically, a differential goes when the gears get worn out. As to how you would know when it needs replacement, it would either be a failure or increasing noise from the differential. Bearings and seals can be replaced, but they, normally, would not result in the whole unit needing replacement. If they cannot repair, or replace it, they are not the mechanics they claims to be.

The next time you get your oil changed, make sure they check the differential fluid level. Low fluid level is the major cause of differential failure.

Bill Greer added:

I agree with all of Bill Watson's comments and here are several more ideas, for what its worth:

• sometimes brake squeal is nothing more than dust and dirt build up inside the wheels. take your car thru an automated car wash or hose down the backside of all four wheels for 2-3 minutes each.
• your automatic brake adjusters may not be working. take your car to a brake shop and ask for just a brake adjusment...not a repair job. some shops will do this free.
• live with it til you need new brakes [assuming new pads were installed]...brake squeal is usually temporary and will go away as brakes wear in more.
• rear differential noise is not uncommon in older cars. if the oil level is correct they can go for years before the noise finally gets to you. check the oil level and live with it...til you find a new mechanic.
• the noise you are hearing is probably a bad wheel bearing and not the differential. If you coast in neutral at 35mph and the noise is there its likely a bad wheel bearing. Fit is ASAP.

Other possibilities are a rear u-joint or pinion bearing going bad. A shop inspection can find these.

Tannon Weber added:

On 9.25" rear ends common to the late seventies and early eighties B and R bodies, the axle bearings rode directly on the axle housing rather than on a hardened steel insert. The downside of this is that if the surface inside the axle housing is messed up then the axle might not be repairable simply with new bearings. It is important to check this if there is rear end noise or more heat than there should be.

Disc brakes

Sometimes, disk brake calipers "stick" or clamp down more firmly than they should. This is a common problem with age, but it can affect brand new calipers. When a brake is squealing, check all four pads to make sure none are unusually worn.

More information

For detailed instructions on replacing disc brake pads, click here.

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