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To skim or not to skim etc?


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High speed braking (anything over 120 mph, autobahn only officer)  produces a noticeable shudder through the steering. This would seem to suggest a warped disc or two at the front.

 

Obvious answers seem to be new discs or skimmed, has anyone had this done? if so how good were the results?

 

Thanks,

 

Mike

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I would say it depends on your driving. if you do mainly motorways at high speed perhaps it would be best to buy good new ones. If like me you drive reasonably slow you can buy cheep discs of the internet that are ok. To have them skimmed would probably cost as much. Bye the way it does not mean it is the front brakes. I have just done my rear one done because I had a judder on braking hard. it was warped.

Stan.

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Yes I've had rear discs cause vibration issues in the past.

I would always advise new discs where possible. For the cost of them, it really isn't worth the hassle of removing the old ones, taking them to a machine shop, collecting them afterwards and refitting them with less metal to dissipate the heat generated from braking, especially high speed braking. It just invites brake fade.

I replaced my front discs and pads on my X Sport for £63. Not genuine parts but Apec, which are a good quality pattern part.

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Bye the way it does not mean it is the front brakes. I have just done my rear one done because I had a judder on braking hard. it was warped.

 

Hadn't thought of that Stan, thanks, How did you work out which one was warped?

 

It's just passed it's MOT and been serviced by Jaguar and neither of them picked up on it.

 

It was only when I visited head office in Hameln last week and thought I'd stretch it's legs that the problem became apparent.

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It's almost impossible to fail an MoT for brake condition. So long as they meet the performance test on the rollers they have to be practically in bits before they can be failed! Cracks can only be advised, as can thickness. Unless the pad material has fallen out or there are chunks of metal missing from the disc, it's not considered a fail.

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Good question. A tiny amount of warp can feel like a major vibration so it's really difficult to tell which is warped without measuring them.

I tend to go on the appearance. If the disc has a big lip at the top and/or bottom of the braking surface or has some bad corrosion then replace them. Be sure to check both sides of the disc as the outside can look perfectly good but the inside be corroded and pitted. This is generally caused by stiff or seized calipers causing one side to apply pressure on the disc whilst the other side does very little. In this case you need to strip the caliper guides out and clean them up, replace the pins if necessary and grease then up wirh copper grease.

General rule of thumb is if the discs look badly worn, corroded or 'lipped' then replace them anyway.

Also, low pad material or thin discs can can cause a warp-like sensation as the heat isn't dissipated and the brakes overheat. If the discs are clean but the pads low then replace the pads.

Brakes are more complex than people think and many factors can cause a myriad of symptoms, but generally, if they look bad bin them.

A warped disc will be felt at any speed, fast or slow, so if yours feel fine at lower speeds I'd say that the cause of the high speed braking 'warp' is down to low pads material, thin discs, or both

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I have had brake judder on other cars that can be felt through the brake peddle, I am very light on the brakes and I have a theory that that causes warping and judders, as my last 5 vehicle all had it.

Skimming is hard to recommend, when replacement disk are reasonably  priced.

If you skim the disks and you still have the judder you will be wondering if the machine shop was any good, changing them at least eliminates the possibility of it being the disks.

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There is a slight discolouration in what I can only describe as regular smudges on the osf disc so I have ordered a pair of Pagid discs and pads from Euro car parts at £67.20 each for the discs and pads at £36.97.

 

Call me paranoid but I didn't fancy Ebay when it came to brakes.

 

So, skinned knuckles and blasphemy for me this weekend!

 

Mike

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Front discs and pads are actually quite easy to do. Keep all the surfaces cleaned with a wire brush, chip away any uneven corrosion from the pad mounting slots and apply a small smear of copper grease to them and you'll be fine. It's a good idea to pull out the caliper guide pins and clean them and regrease them too. They'll pop out of the rubber seal if you pull gently. Keep them in the the same locations whe refitting. They are usually slightly different so make sure the top one is refitted in the top. Remember to also clean and copper grease the hub before fitting the new disc as there will be small amounts of corrosion under the old disc which will prevent the new one from fitting fully flush to the hub.

And the new discs come coated in a fine coating of grease to prevent them rusting. Be sure to wipe it off as thoroughly as you can from the braking surfaces prior to fitting the pads.

I also use the old discs and pads to lever the piston back into the caliper before I unbolt it all. It's easier than trying to do it afterwards and it doesn't matter if the old stuff gets damaged. A big, flat screw driver usually suffices

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Well, I've donated several bits of flesh to the cause and so far so good.

 

Not 100% sure yet because I've got to let the pads bed in but it feels ok at the moment.

 

Thanks again for all the good advice.

 

Mike

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Good on ya Mike.  I am just having to change my rear ones I still have a bit of judder. I thought that I had cured it with changing pads that where mutalated.   Its hard work when you are in very late seventies, love it though.

Regards

Stan.

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