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

Graeme, thanks for birthday wishes What you describe meets exactly my experiences. When driving slow there is no issue. But when braking down from ca. 100 km/h or more I have the same strong shudder, most of it around 90 or 80 km/h. The (young) mileage of your car is also comparable to the intervals of the need to change my discs. It is very helpful to know that also cars with wider tyres like yours could be affected. Therefore my idea to swap to 185/70/15 is probably not the first solution. Perhaps it could be a heal to look at different discs which will be of same size etc. As I said I never had this issue with my Roadsters or my former P4SS, each of them driven more than 22.000 km.

One addition Graeme, let check the wheel play also before you dig deeper. If your car has so young mileage a too wide wheel play could be the cause of brake issues as I noticed it on other Mogs. It could expand during the first 10.000 km.

If it were the width of the wheels causing this, then all cars with narrow tyres and wheels would regularly suffer this.

Maybe inadequate cool down of the discs? Unlikely unless you are racing it.


Are the calipers squarely sitting on the discs, when the pads have been removed are they thicker one side to the other or top to bottom?

No unusual tyre wear I take it which would indicate wheel geometry issues?

If the discs are sitting square and true on the hubs, and the run-out is within couple of thou when measured with a dial gauge, then the only other thing I can think of is that the bracket that holds the disc caliper isn't true to the disc, as Mark says.

I note you've only had one hub replaced - has the other been accurately checked? you only need one side to be out.

My money is on one of the discs not lying absolutely flat and true on the hub, you will get this effect if there's the slightest amount of wobble, even a thousandths of an inch at the hub will produce it.

Either way, it's not going got be anything to do with having narrow wheels.

Heinz,

You describe the problem as a strong shudder. It is possible that the problem is not caused by warped disks.

This symptom can also be caused by damage or breakage to the front crossframe.

The first check is to ensure that the two diagonal tiebars that form part of the crossframe are not broken or loose. These tiebars run from the bottom tube to the top and prevent the crossframe from flexing everytime the car is driven over a bump or the brakes are applied. Use a spanner or similar to hit the tiebars - the sound should be that of a sharp 'ping' not a dull sound. It is the same principle as a piano tuning fork.

The second check is to ensure that the crossframe mountings and tiebars that run from the bottom of the crossframe to the bottom chassis flange are neither broken nor loose.

Finally, check that there is no damage associated with a minor accident such as anything that is bent such as the crossframe tubes, stub axle or wheel. Checking the crossframe tubes is quite easy: remove the wheels and look through the length of the tube with your eye - you will see if it is bent. It is not a major task to straighten the tube.

Good luck!

The symptom could be replicated by a few things, warping discs being just one so it's worth double checking all mountings.

I can't believe all the discs you've gone through over the years are all poorly machined.

Hard braking makes the discs very hot, and can warp if you hold the brakes on when stationary immediately after. Coming down off a hill and holding the car on the footbrake at the junction at the bottom, that sort of thing.

A dial gauge and some double checking down there is needed I think. It's certainly not the thinner tyres or wheels as Tim says.

Do you have brake reaction bars ?

Late birthday wishes too....

I suffered from warped discs with my last Morgan - a new 3.7 Roadster. They had to be replaced under warranty. I've owned enough cars to know about cold water and hot discs - it wasn't this. Nor was it caused by driving like a loon. To be honest I have no idea what caused it, but it happened all the same.

It was definitely the discs - lift the wheel, rotate and you can feel the catch on the pads.

A lot of the disc brakes are made in China and not that well . I purchased a set and had to remove them as they had a tiny warp you could feel it through your foot . Some garages have a machine that takes a a tiny amount off the disc while on the car but sounds more like you need to shop about for quality in both disc and pad.

Heinz, how clean are the discs? Is there any signs of areas where the pads have stayed in contact leaving a pad shaped area visible?
If the car has been idle in the garage for a while then the small pads gap to the disc may lead to this area being affected. Many owners report brakes sticking slightly after a period of non use. This sticking can leave a rough/lightly corroded area where the pad meets the stationary disc, and this then shows up as a shudder, especially at any sort of speed. I had this many years ago on a car after a period of non use. New discs and pads needed!