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myer
07-13-2008, 04:58 AM
XF SV8
As previously mentioned I get the most annoying high pitched squeal that appears to be comming from the rear brakes, most particularly from the left hand side.

This happens when the car has been driven for around twenty minutes. If you depress the brake pedal slightly the noise goes away but returns as soon as you release the pedal.

I have been told by one member that the dealer replaced both rear discs, calipers and pads and the problem is now resolved. They suspected faulty pads, scoring the discs and sticking pistons in the rear calipers. The car has been to the dealer and the issue is unresolved!

My car has covered 4000 miles and there are slight ridges in the rear discs. Any others had this problem....?

jagular
07-13-2008, 12:05 PM
high pitched squeal is almost always from the edges of the pads. The most common cause is incorrect pad deposition during break in. Uneven pad material deposition sets up the slip/stick friction cycling that causes the high frequency squeal.

If you overheat the brakes before they are properly bedded in or, paradoxically, bed them in too gently you will often get this phenomenon. The higher the brake pad spec the more likely this is to occur.

If you already have more than 500 km (300 miles) on your brakes try re-bedding them. 10 successive stops from 60 mph (100 km/hr) reaching ABS activation levels should re-bed your brakes, and actually try not to stop between braking events as this can cause "imprinting" which is a major cause of the symtpoms you describe. You have little to lose by trying this as the only other cure is to remove the pads, skim the rotors, sand the pad faces and reinstall. Dealerships will simply put new pads and discs in as this is cheaper for them. Inside 500 miles you will have the same problem if in fact it is a bedding in issue.

There is no doubt the SV8 is overbraked for marketing reasons, the front brakes are basically "look at me" brakes. This means the rear brakes in particular will be really loafing. Most braking effort is done by the front brakes on any car, due to weight transfer, and those huge front discs on the SV8 are just overkill for almost all North American driving conditions.

The standard car uses the same diameter discs front and rear, effecting the correct brake balance by smaller rear calipers and thinner rear discs. The X Type used a similar philosophy. This means the standard car uses more rear brake in the sense that the rear brakes will get hotter than on the SV8 under most driving conditions.

My base spec car gets all of the wheels nice and dirty with black brake dust which means the base spec brakes are set up correctly. In my experience you can have nice quiet dust free brakes or good brakes but not both.

myer
07-13-2008, 12:21 PM
The high pitched squeal only occurs when I am not depressing the brake pedal! When I do the noise stops.

jagular
07-13-2008, 07:42 PM
the only normal way the brakes can make noise is from the pads touching the rotor and the only way the pads can touch the rotor hard enough to make noise is if the pads are stuck against the rotor. Only a sticking caliper or emergency brake could do that.

Are you sure it is brake noise? Could something else be touching the rotor? Mind you, if so then why would applying the brakes make the noise go away?


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