XK150 disc brakes
Are the original Dunlop round pad cylinders
          up to the job?
Page list

 
My car, when purchased in October 2013, was fitted with:

Front: Original Dunlop-branded 2-1/8" cylinders, with retractor pins and round pads, and with original-style pistons carrying the seal. Receipts showed that the cylinders had been bored and lined with stainless steel in March 2003. Discs were close to new.

Rear: Original Dunlop-branded 1-5/8" round cylinders, with retractor pins and 2-1/8" round pads. These cylinders too had been lined with stainless steel in 2003. Discs were close to new.

The master cylinder fitted to the car had been purchased in August 2012, and thus had been in service for just fourteen months when I bought the car.

The brake booster was the original Girling piston-style booster. After a few weeks of ownership the booster began to make a strange whoosh noise when the brake pedal was first depressed. A receipt showed the booster had been rebuilt in June 1999 near the end of the full restoration in South Africa.

The brake and clutch fluid reservoirs were each an after-market Guy Broad aluminium-bodied type, fitted in 2012, with standard Girling steel caps.

All things considered, the braking system appeared to have been well-maintained. However, some time after purchase, I discovered the front pads were not retracting properly due, I later found, the retractor pins not being fully free. Also, found later during replacement, one rear piston had seized in its cylinder. To dislodge the piston, I had to pressure up the cylinder (using water, nor air!) to 900 kPa (130 psi). 

After having endured the round pad cylinders' poor performance for nearly three years, in mid-2016 I made the decision, mostly on safety grounds, to replace the cylinders with modern types.

The car was fitted with new, modern-design, UK-sourced disc brake calipers. The front are four-pot, rear are two-pot. The front calipers use standard E-type Series 2 pads, and the rear use the later-version XK150 square pads.

I have included details of how the troublesome round pad cylinders with their retractor pins work.

 

Front brake calipers

Round pad cylinders

Brake booster replacement

Dual circuit braking system