Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Wavy Brake Discs on 4/4

Thanks for all the helpful comments, probably a lot to check and more than one possible reason to consider.
Good to know that the issue is not depending on the wideness of wheel/ tyre. (my wrong thought was that when considering a center locked but narrow wheel, a stronger leverage effect from the surface to the center of the wheel could effect a stronger lateral movement resp. force...also to the brakes).

Yes, brake reaction bars were mounted soon after I got her in autumn 2014.

Brake discs were every time changed in pairs. And the first 2000 or 3000 km after such a change she feels fantastically smooth when braking. She is not in use on trackdays etc. I drive her in a sporty manner from time to time. But she feels so light weight and I never had a car where the brakes had to "work" less than with her.

The front cross frame and the tie bars were checked the last time but in two weeks from now I again have a garage date and it should be checked again. I myself will have a look also.... if I can discover something wrong at all...now being TM expert At least the helpful acoustic test I can do.

The left side hub only (seen in driving direction) was changed when they again changed the discs in autumn 2016 for the last time.
This hub resp. the brake disc mounting threads on the hub were out of tolerance / center which caused really nasty, small but strong and sharp hits in the steering wheel when driving ca. 130 km/h and faster...if my words describe it somehow correctly. With the change of this hub the sharp hits are happily gone but the disc wobble and the bad quick pulsing pedal feel is back again.

When the wooble occurs it rises in a not linear way. First you feel that something is wrong and then it becomes stronger and stronger after 1000 km more.
My driving style even changed a bit when driving her. I don't brake so hard in front of curves but I drive smoother anf use the brake less and less if the situation allows. Which is a positive side effect in general.

Sospan, when the last change was made it was to see exactly this area on the disc the way you describe it. And perhaps it is no coincidence that the stronger shudder happens now after she was parked away since late October, only driven two short times until this march.
Anyway I will have to watch again the surface of the brake disc.

Jack the lad, my feel is also that the quality of hardware in general is worse than in the past.
They perhaps find better methods to give a product a better calculated period of working life span than it was possible in earlier times.
...Or the other possibility, a product is just cheap and low quality. I don't know if e.g. the brake discs of the 4/4 are also offered from different manufacturers with same disc size?

Or I must invest in ventilated brake discs and consequently wider brake calipers. It is more expensive but I have learned by three times now how long the standard solution will last (assuming no other reason would cause the issue). On the other hand regarding the brake force any ventilated discs on my little 4/4 are not a need, it would only make sense perhaps to prevent too much heat building up.

Hi Heinz,
I suffered warped discs some years ago on my aero8, the dealer put it down to putting the car away with wet brakes, there was a shadow of the pads on the inside of the discs causing the vibration when braking, the dealer skimmed the discs and refitted, whenever I washed the car I always then drove round the block to warm the brakes and hopefully dry them out before putting it away, I did not have any further problems after that.
Ian

+1
Use it or lose it!

I suffered wobbly disks on my motorbikes. I learned to "brake in" the disks carefully with slowly increasing braking force. This is dependant on how the disks were fabricated from steel or cast iron, and how the casting was done. I can not recall how many miles I needed to fully break in the disks.
Maybe this helps.

Is skimming discs an option in Germany?

Given your strict TÜV regulations on what you can and can't do?

But if they are skimmed on the car it should make the discs true as they'll ever be, even new ones can need it at times.

If you are worried about the quality of the actual discs fitted and are convinced they'll go wobbly again why not find some high quality ones you can trace to where they are made now?

Mark, I will ask my garage and also google if skimming is allowed here. It sounds to be a plausible treatment. I should find out who can make it when the discs are mounted.

Unfortunately Morgan front discs are Morgan specific, they are not used on anything else.

As supplied by the factory the castings are very green.

We have a lot of problems on the "production" racecars with the discs warping after they are used a few times in anger. However, once this has happened they can be skimmed true, and then seem to pretty much last forever.

All that said, I don't believe the discs are warping, but it is more likely they are suffering from pad pickup or pad shadowing on the discs after being used infrequently.
You can bead blast the discs to remove this pad contamination, but it will come back if the car continues to be used in a similar fashion.

Pad material can and will make a difference (I really don't rate EBC pads at all), as some are more susceptible to this than others
Most common pad materials used these days are designed to stop 1500 odd kg of heavily servo assisted daily driver
A light car like a 4/4 just doesn't use the material hard enough

Simon @ SiFab.co.uk

I have to say that I'm not sure if I could be responsible myself also. After a car wash I always drive some km to dry her but I never considered a stronger braking to dry the discs and pads as well.

Steer clear of the machines that resurface discs.

They take a minimum of 0.4mm off each side of the disc and if you look at the Mazda MX5 spec. I cannot find a similar Morgan spec it says something like 20mm original thickness at the front for the ventilated disc a minimum thickness of 18mm but a minimum thickness after resurfacing of 18.4 mm otherwise you are taking the disc down to the thickness it should be replaced at.