Jaguar XJS: Seized Brake Calipers Renovation

Main function of this junk is based on expansion of polyurethane inside of the piston when squeezed between carriage bolt’s head, washers and stud coupler nut (also known as “long nut”). The other two stud couplers should provide sufficient grip to the counter-spanner – just jam those two hard against each other somewhere in the middle of the carriage bolt, above squeezing nut (if you’re over 60 – use Loctite or Superglue). The end of the carriage bolt can be connected to the slide hammer (highly recommended). I chose 200mm carriage bolt providing some leverage to wobble out the piston. 30mm wheel was picked to fit 30.9mm ID pistons from rear inboard brake calipers. With this configuration you should have enough clearance to the bottom of the piston and grabbing force. The calipers on the photos below went like a poop through the drain.

Slightly seized brake pistons.

Se the photo attached, rear brake calipers shown. You need one tool above or:
1.    Strong flat screwdriver (something better than your Draper)
2.    Really solid locking pliers (Irwin, Bahco)
3.    Good results on the gym (under 50) or strong grandson (Jaguar Lovers)
4.    Work boots to keep it on the ground or vice

Method and type of grip/leverage explained on the photo. Try to turn the piston first to break rust. Start with penetrant, then WD40 to wobble/spin it out.

Jaguar XJS Brakes with pistons and calliper fused (massive corrosion).

If the groove and flange (required to hold piston’s rubber boot sealed) is gone – consider your brake calliper dead. Alternatively rebuild those each summer or invest in custom made 316 stainless steel or titanium brake pistons.
If the flange is still there:
1.    Buy 10pack of 3/8 UNF hydraulic grease nipples (as per example photos - rear inboard brake callipers only)
2.    Cheapest, most discounted grease (borrow from Jaguar Lover) and a grease gun.
3.    Butane torch / MAPP torch
4.    Pack of left hand cobalt dills from your must-have toolbox – laying close to you, just in case…

Start from removing the bleed screws, also bridge pipe unions if you’re rebuilding rear callipers:
-    Give it a slap with a hammer in the areas corresponding with threaded locations.
-    Spray those with Liquid Wrench and leave for a while
-    Don’t try to unscrew it on cold – you will round the heads. Do it only with use of gas torch, MAPP is my choice, gives quicker thermal expansion. Heat the entire area, not only the screws/unions
-    During a nice reddish glow – try to unscrew it.
-    If the head snaps – grind it flat with Dremel/angle grinder, grab your cobalt drills, start from small diameter, then go higher and higher. When approaching the 3/8” diameter or getting too close of the calliper’s wall off-centre it’s time to use left-hand drills. If you don’t have them, use diamond Dremel burr or milling cutter. Go slightly into the threaded wall in two opposite places to split what’s left from screw/union. Now dig it out. Use small pin punch or broken drill. My choice – CNC end mill and cordless drill.  You can damage the threads slightly but not massively Don’t go too deep – the threads are located only in the central length of the bleed screws / unions.

Now get the bastard pistons out:
-    screw in grease nipples everywhere – it will also function as a blanking cap
-    attach grease gun
-    pump the grease gun until you will hear loud BANG!!!!! Avoid being hit by piston bits ricocheting from the ceiling.
-    you must be an absolute oaf to believe that: grease is gas-like compressive and it will catapult the piston like your BSA air rifle or tear it apart (LEAVE NOW)
-    repeat with next half of brake calliper
-    for front brake calliper - you will find that some of the pistons will come out quicker. You will have to use your brain/imagination and ratchet straps, piece of wood or your wife’s heavyweight stockings to prevent this. And yes, you will have to do it before splitting,