N/S Front wheel makes a noise

[RSW]

Hello to all,
I've done a bit of work on brakes and wheel bearings before so I know what sort of noise to listen for when parts wear but I'm not sure about this one.

When I drive the car the for a sustained period, after a while the N/S front wheel makes a noise. The noise sounds just like that of a failing clutch release bearing (TO bearing) but it lasts for longer.

I can make the noise stop by pushing the brake peddle, but it soon reoccures.

It dosen't sound to me like a traditional wheel bearing sound as these tend to make a humming sound. This sound is more like a higher pitched sound created by a vibraton.

I am not familiar with the bearing arrangement on the 911 and thought I post this before I start taking things appart.

It behaves like it is something to do with the rake but sounds like it could be a bearing?

All comments and previous experiance welcome.
Many thanks in advance.

Richard

[Roy M]

Richard

I had a similar problem and it was a sticking caliper. On mine I could see the 'rattle' marks on the pad itself. Try and establish a side (it was the n/s on mine too but the diagnosis was complicated by a bearing failure on the same side - a bearing which had only been fitted by a specialist 200 miles before!) and pull the pads.

I rebuilt my calipers for the cost of a seal kit (about £11 a side) and have had no problems since

[RSW]

Hi Roy,
Thanks for that.
I'll look into stripping down the caliper.

Where would I look to find information on how this is done? is it in the Bentely manual?

Rich

[AirCooledExcellence]

Rich,

There's a good tech article here:

http://www.pelicanparts.com/techarticles/911_caliper_rebuild/911_caliper_rebuild.htm

It's an easy job, good luck!

Cheers

[RSW]

Thanks Tim,
I've just printer and read the artical.
Its good to know the fix is a relativly simple job.

One question - the 20 degree angle, there must be something on the piston that lines up with the template is there? Its not too clear from the photos.

Rich

[AirCooledExcellence]

Rich,

There's an indent in the top of each piston. Once you get a good look at the calipers all will become clear....

Have you got Wayne's book, that's got some good pictures.

Cheers

[RSW]

Tim,
Thanks again - i do have Waynes book.
I'll have a look throught it tonight - I just thought I'd pop the question as the noise seemed to be getting worse on the way in this morning.

Thank for all the help.
Rich

[Roy M]

Richard - been away from my desk on Business (suppose I've got to work sometime).

I found mine incredibly easy. Main points were I had access to compressed air which made things a lot easier (although I did put one caliper back on and used the hydraulic pressure to free a piston) and I had a couple of 'frozen' brake line couplings. I ended up making new short pipes (a single flare) and putting on new flexible brake lines (they were so cheap - about £9 each - it was a sensible precaution). Bleeding was no problem and I did the 'thin bit of wood in the caliper' trick to get the brakes up to pressure - longest part of the job was waiting for the paint on the calipers to dry!

If I was planning to do it this w/e I would spray penetrating oil on your brake line couplings tonight and tomorrow to make things easy. I also found a set of welding clamps (like Mole grips with extended grippers) useful to hold one piston in whilst exerting pressure on the other.

A dead easy, really satisfying, job to do.

[RSW]

Thanks Roy - I appreciate the encouraging words.
I drove mine home last night and after a while it began to make the high pitched drone (not quite a squeal) again.

I swervered the car from left to right and the noise came and went.

I'm sure it is the problem - this could be why my brake efficientcy was way down but passable on the MOT.

Thanks
Rich

[RSW]

PS - can the pistons be bought seperatly?
I can see me having a problem if one of them is damaged.

Rich

[Roy M]

Don't know - mine had some slight corrosion which I polished off with Brasso and they were fine. If you have a bad piston (and I'm fairly certain you won't) there's a place in the Porsche club magazine who'll do a reconditioned caliper for about £60 a side. If the piston's gone I'd probably go that route in case the bore was damaged.

As I say I'm sure it will be ok but the place is called Classicar Automotive (01625) 860910 if you need them (they will probably come back prettier than if you do them yourself though!)

[RSW]

Thanks Roy - thats very helpful

Rich

[Neilk]

Rich,

I have a couple of tips for you...

If you decide to rebuild the calipers, you can easily make your own 20 degree triangle rather than buying the "tool".

If you don't have a protractor, use MS Paint or any other graphics program and draw a straight line, shift that line 20 degrees and draw another straight line that intersects the first line. Print it out and copy the triangle onto cardboard. Voila, your 20 degree template.

To get the pistons out, remove the brake pads and put a really thin piece of wood in place of the brake pads. Pump the brakes until pads touch the wood. Remove the brake caliper and see how much you can move the pistons. If they still seem a little tight, then slowly press the brakes until one of them is a little loose. Then get a c-clamp and clamp the loose piston to keep it in place and start pressing on the brakes so that the other piston will loosen. Once the pistons are loose, remove one of the bleed valves from the caliper, disconnect the caliper from the brake lines and screw the bleed valve into the brake line on the car so that the whole system doesn't drain out. Rebuilding is easy, just follow the tech article.

[Roy M]

One other thing worth doing is to depress the brake pedal by about an inch just before you take off the lines - this will stop the weeping which would normally occur from an unpressurised system. I used a couple of steel right angles (B&Q, Wilkinsons etc) to form a U and a length of wood jammed between the seat and the brake pedal. Worked so well its's in my tool kit now!