Pearl gets some modern Stopping power
Pearl’s wish list to Santa is never ending! But sometimes with a 60 year old car, Christmas has to come a little early at times. This time, a leaking front brake caliper dictated that brakes went to the top of the list, so what better opportunity than now to go “UPGRADE!”
The front brake kit, is from VA Spiteri, and is specifically for upgrading Mk2 & early E types. They advised that the rears didn’t need any alteration, but I happened to have a pair of S1 XJ6 rear calipers refurbished at the ready for that “rainy day”, (actually fitted at a later stage of the project), so I have common pads on all.
Bearings are good as gold, and will be re-used (after a repack with fresh grease), so they go straight into plastic bag to prevent contamination. The seal has to be removed to get the back bearing out, but they are only a few dollars at the local engineering supply store, so will be replaced (TC12124 – 1 3/4” x 2 ½” x 3/8”)
The hub needs to be held firmly to undo the disk bolts – and as the bolts have to be retightened with the new disk in place, it’s probably a good idea to have a plan to hold it firmly.
The disk and hub mating faces get thoroughly cleaned to ensure good ‘metal to metal’ contact for true running and heat transfer. (A surprising amount of heat is removed from the brakes via the hubs and wheels)
Then its time work fresh grease into the bearing cones , remount the hubs, fit up the new calipers and reconnect the brake lines ready for bleeding.
As I had another maintenance job pending for the rear end, it was easier to remove the complete rear axle and fit the rear calipers while it was out.
Installation is pretty straight forward, a bit of shimming is needed to center the XJ calipers to the disks, the Mk2 handbrake fits straight on (but need the XJ spreader forks as they are set slightly wider at the bolts) – and a bit of hand dressing to the pads for good disk contact.
Statutory compliance is an issue that must be addressed, as neither of these brake components were optional items when Mk2’s were in production, so they have to be inspected by Approved Vehicle Certifier (AVC) for a Tasmanian Modification plate to be affixed to the car.
The AVC has some neat kit now-days, which measure the applied pedal force, deceleration rates, & stopping distances at various speeds.
Pearl’s initial test failed miserably! The front brakes are so effective; they cause significant weight transfer, which then allows the more efficient XJ rear calipers to lock the rear wheels with surprisingly little pedal pressure (something I failed to consider, both Mk2 & XJ have the same piston sizes, so hydraulically are equal – the XJ caliper rigidity and pad design is just the next level up that caught me unawares!). The solution suggested by the AVC is to install an adjustable bias valve inline to the rear brakes to reduce the pressure.
Armed with some pedal pressure readings, I then resurrected that old MK1 pedal box out of storage to replicate the pedal pressures on the bench, so the Bias valve can be preset in the ‘ball park’ before installation – to be honest, I think if I had plumbed the rear brakes prior to the booster, it would have achieved similar results! (something to think about, if considering fitting a ‘dual circuit’ master cylinder).
While the Booster was out (to fit the bias valve) – I had been suspicious of it causing a bit of ‘brake dragging’ on occasion, First time (yes it came out more than once!) I noticed a perished hose from the air valve which I thought was the problem. Second time out, it got a new seal kit throughout (even though it looked all ok).
Eventually, the fault was traced to the master cylinder all gummed up and not returning fully at times. The pain doesn’t end there! The bore was also pitted, so needed S/S sleeved (not a fun job in my 100 year old lathe!).
On the bright side, the second brake test passed with flying colours – the preset pressure of the bias valve was bang on the money – my Tech teachers when I was an apprentice should be proud!
Onto the next job!
Grant Rodman
