450SLC Dragging rear brakes – part 1

For the last couple of years I have noticed a noise from the rear of the 450SLC while driving.   At first I thought it might be a wheel bearing or some kind of bushing.   I mentioned it to my mechanic and he took and look and it wasn’t any of those things.

Last time I took the car on a longer drive, the noise was getting worse, and I noticed after I returned the rear wheels were hot to the touch.   Too hot to touch.    I realized that my noise had been dragging rear brakes all along.

Both sides were hot the touch, so it wasn’t just one bad caliper.    I went back and checked my maintenance records for the car and saw that the brake hoses were last changed in 2003 when I purchased the car, and one of the hoses changed again about two years after that.  16 years is about all the life that can be expected form these hoses, so I decided to replace them.   I also thought it would make sense to replace the master cylinder, as it is more likely to be causing dragging rear brakes on both sides.     Unlike when I had a similar problem with the Jag, the brakes were not locked hard on, just dragging.

Today, I did some further inspections.   I removed the rear wheels and looked at the condition of the calipers, pads and rotors.

Dragging rear brakes - calipers, pads and rotors

The rotors were still within the spec from the workshop manual.   The hoses looked old, and not particularly flexible.   It was also quite hard to push in one of the pistons to remove the pads, even with caliper disconnected from the brake system.     This led me to remove the caliper for further inspection.

It was the same story on the other side.   Removal of the calipers showed that the heat had made the seal rather crispy.

Rear calipers

These calipers can be rebuilt.  I may just replace them as the pistons don’t look great and the heat may have done other damage.   I am not sure if it is to do with the heat, or the 16 years on the car, but I found it almost impossible to remove the flexible hoses.  Even using the flare nut wrenches I managed to damage one of my hard lines.   I have liberally soaked the other side in penetrant to see if that will help when I get the new calipers.

While I was at it, I also replaced the master cylinder.    The brake fluid looked pretty good from a visual inspection.   I was quite surprised how much vile black fluid there was in the rear chamber of the reservoir once I removed it.   This is even after a flush about 18-24 months ago.

Dragging rear brakes - changing master

Some stained old shirts helped me protect the paintwork from the brake fluid.   In contrast with the flexible hoses in the rear, the lines were easy to remove from the master.   The coolant expansion tank needs to be unscrewed to get the master out. It does not have to move very far, so it does not need to be emptied.

new masterNext steps are to remove and replace the hoses from the rear, fit new calipers to the rear and replace the front hoses while I am at it.   At this point I do not have any indication that the front calipers need to be replaced or rebuilt.  This is covered in part 2 and part 3.

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