Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Brake discs (rotors)

My 2012 Plus 4 has already had two new pairs of brake discs. Now, at 14k miles, the judder had returned especially noticeable when braking at speeds above 60mph.

I think there must be an underlying problem causing the discs to deform. BTW I don't rest my foot on the brake pedal when at a standstill so that's not the issue.

The car pulls up straight and there's no loss of braking effect, just an annoying judder when braking.

Any advice on what to check would be much appreciated.

Bob.

I am afraid that the brake discs have a reputation for warping, even when not subjected to racing.

The problem is that most of us replace them with another new disc , which also does the same thing. Apparently once the discs have been through at least one heat cycle which causes warping , it is most unlikely that they will suffer the same fate again (ask a metallurgist, I am no expert)

The optimum path seems to be taking the discs to a machine shop where they can be surface ground, and to refit your "reconditioned" units.

There is an alternative which can be done with the discs still on the car , and that is to take them to Uncle Melvyn , who has a disc brake surfacing machine . This may not be as good as a surface grinding , but it does work. I had mine done in this way and have had no further issues (and I m not known for being light on my brakes!)

Be very careful here as most discs have a wear allowance of only 1mm and the minimum amount an on car lathe can remove is 0.4mm per side of the disc. Therefore if the disc has done 10,000 miles it will have lost around 0.2mm to 0.3mm in thickness, therefore the disc may be below the minimum thickness after the skim.

On the market leading disc skimming machine manufacturers website, they advise garages not to worry about losing the sale of new discs and the fitting labour because the garage will be able to charge for the skim and as the disc will be so near to it's minimum thickness after the skim, the garage will still get the replacement disc job at the next service.

There was a thread on PH a while back about warped discs - here:

https://www.pistonheads.com/gassing/topic.asp?h=0&f=23&t=1691393&i=20

And another (which I've just looked for and can't find) suggesting brake dust adhesion to be the cause for judder.

I had the discs replaced on my Roadster as the brake judder was horrendous - I seem to remember some improvement was had by re-greasing the front suspension.

When I purchased new "Wilwood" brakes there were instructions for "Breaking In The Rotor" and "Breaking In The Pads".

Breaking In The Rotor: I would gently heat the rotor by driving at first slowly and bringing Morgan to a stop and then a bit faster and gently bring the Morgan to a stop etc. until the rotors were quite hot and then let them cool down until I could touch them with my fingers.

Breaking In the Pads: Same as "Breaking In the Rotor" but a more aggressive stop until I could smell the Brake Pads.

I think this procedure was to prevent warping the rotors. Not totally sure what Breaking In The Pads did, but the braking certainly improved.

My trick for setting the brakes up on my rally cars was to fit new brake discs, get them absolutely stinking hot, remove the discs, check for warpage, set them up in the lathe on a big faceplate and give them a light skim. Never had a problem with them warping in service after that!

Arwyn

Just had the same problem on my 2008 Roadster, turned out to be sticking pistons in the calipers. This was due to flaking chrome on the pistons surface which made them stick. The harder I braked the more it shuddered. They still worked well but was horrible to drive. fitted new discs and new pads and cleaned the pistons and lubricated them and they worked well for some a months and then the same problem was back on the way home from Malvern this year. On stripping the calipers down again I found two of the four pistons in each caliper were stuck. Spoke to Peter at Mulfab for his advice and he suggested a complete caliper referb with new discs and pads or new calipers and discs.
After looking into it I opted for new billet 4 pot calipers and new larger vented discs and braided hoses.
I fitted them myself, they are superb quality and now the car brakes and feels like a proper sports car should. Expensive but well worth the money and I am so confident and happy with the feel and the braking.

Many thanks for the very detailed and informative replies. I have tried to identify an on car skimming service that is closer to me (Somerset) than Uncle Melvyn but to no avail. I contacted Pro Cut and they say he's the only one and he developed the centre lock adaptor himself.

I will start the search for the fault and report back.
Bob.

There is an on car skimming service at Henstridge if that isn't to far from you.

Problem is that they cannot cope with centre lock wheels as there is no adaptor available for the Pro Cut lathe.