Losing Fluid

I have spent the greater part of the Bank Holiday (albeit very contentedly) in the workshop, so it seemed like a pleasant idea to round it off with a trip to the pub in the Jag.  On the way home after dark, less than a mile from home, the low brake fluid light flickered hesitantly before illuminating permanently.  This was some surprise: The pedal still felt firm so it was unlikely that a pipe had fractured yet the behaviour of the warning light suggested that the fluid loss was quite rapid – more so than one might expect from a leaking cylinder. Furthermore I am in the habit of checking the fluid level once a week and it never goes down.  When we reached home I filled up the reservoir in the hope that only a partial bleed may be neccesary after rectifying the fault. This morning the reservoir was empty and there was a large pool of fluid under the Near Side rear wheel.

Knowing some of the history of the car I expected to find that one of the rear wheel cylinders was rust pitted and that the pads had worn sufficiently to bring the piston seal over the top of the damage.  Removing the cylinders revealed something I’ve not experienced before:  The car had benefitted with new pads and brake lines before we bought it and seems that the outer pad on the near side had not been correctly engaged with the piston. This had caused the piston to become more and more slanted in the cylinder as the pad wore unevenly, until the seal would no longer hold fluid.

The Dunlop design of caliper has a retractor mechanism which pulls the pads clear of the disc when the brakes are released and for this reason the backing plates on the pads have to engage with a button on the outer face of the piston so that they can be both pushed into the disc and pulled away from it.  I’ve never seen the results of driving with a pad which hasn’t been properly engaged; it’s potentially not that nice…..

This is probably a good moment to sing the praises of the Dunlop disc brakes. These days it seems fashionable to get rid of them and fit something more modern, but if they are in good order they work extremely well even by current standards. The ones fitted to the MK2 pull the car up very impressively with little pedal effort.  Interestingly the same brake fitted to the Series 1 E Type feels much less impressive: This is partly due to the rather lacklustre Kelsey Hayes servo fitted to the E Type compared to the Lockheed item on the MK2.  It may also, of course, be partly due to the fact that the E Type might need to be stopped from nearly 150 mph on those same brakes….

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