Rear brake discs

Jul 19th, 2002, 15:02

Hello All,

How do you tell when the rear disc need replacing on a 850 ?

Do you go on the amount of polished disc remaining. I've been having probs with a rubbing noise and slight brake squeal and according to the old haynes manual one cause could be worn out discs ?

Cheers,

Craig

Jul 22nd, 2002, 23:35

Hi Craig

If you have access to a micrometer you can measure the thickness of the discs. The wear limit is 8.4 mm according to my manual so if they are close to or below that limit they should be changed.

cheers steve

Jul 24th, 2002, 16:15

Hello,

I thought the amount of polished surface remaining on the disc affected your braking performance ? On looking at mine one has a wider band than the other ?

Cheers,

Craig

sheerwater · Jul 25th, 2002, 23:59

Technically the replacement should be as stated due to the disc becoming thinner. The width of the polished surface is caused by rust.
The outer edge of the disc rusts. In so doing it causes a rough surface which in turn rubs the edge of the brake pad. This causes the brake pad edge to wear more and not make good contact with the disc i.e. a thinner band of shiny metal. Less shiny equals less contact than was designed for brake / disc contact equals uneven brakes. Why oh why do we spend £30 upwards changing brake pads and ignore the discs. My 940 ones were £40 for 2 delivered from eurospares. Peanuts compared with the security they provide. As a rule of thumb brake discs should be changed every 2 sets of pads but with newer pads wearing for 50k upwards this rule should be reconsidered. Theres nothing like the feeling of new pads and discs all round when you need to stop in a hurry and they are much cheaper than a new front bumper!!!! cheers Nigel

Jul 19th, 2002, 15:02	#1
cjboddy2 Guest Location:	Rear brake discs Hello All, How do you tell when the rear disc need replacing on a 850 ? Do you go on the amount of polished disc remaining. I've been having probs with a rubbing noise and slight brake squeal and according to the old haynes manual one cause could be worn out discs ? Cheers, Craig

Jul 22nd, 2002, 23:35	#2
Steve Morris Guest Location:	RE: Rear brake discs Hi Craig If you have access to a micrometer you can measure the thickness of the discs. The wear limit is 8.4 mm according to my manual so if they are close to or below that limit they should be changed. cheers steve

Jul 24th, 2002, 16:15	#3
cjboddy2 Guest Location:	RE: Rear brake discs Hello, I thought the amount of polished surface remaining on the disc affected your braking performance ? On looking at mine one has a wider band than the other ? Cheers, Craig

Jul 25th, 2002, 23:59	#4
sheerwater Master Member Last Online: Feb 24th, 2019 17:59 Join Date: Dec 2001 Location: Northampton	RE: Rear brake discs Technically the replacement should be as stated due to the disc becoming thinner. The width of the polished surface is caused by rust. The outer edge of the disc rusts. In so doing it causes a rough surface which in turn rubs the edge of the brake pad. This causes the brake pad edge to wear more and not make good contact with the disc i.e. a thinner band of shiny metal. Less shiny equals less contact than was designed for brake / disc contact equals uneven brakes. Why oh why do we spend £30 upwards changing brake pads and ignore the discs. My 940 ones were £40 for 2 delivered from eurospares. Peanuts compared with the security they provide. As a rule of thumb brake discs should be changed every 2 sets of pads but with newer pads wearing for 50k upwards this rule should be reconsidered. Theres nothing like the feeling of new pads and discs all round when you need to stop in a hurry and they are much cheaper than a new front bumper!!!! cheers Nigel

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