Rear Caliper Overhaul on the SVO
By Mike Fleming
The rear brake calipers on the SVO are certainly a mysterious part of the car. It’s probably the parking brake and self-adjusting mechanism that confuses most people and strikes fear in their hearts when someone speaks of overhauling the calipers. In fact, some may tremble when thinking about repairing any caliper. In this article we’ll disassemble, clean, inspect, paint, and re-assemble the rear brake calipers on an SVO. or “How to go from this (left) to this (right) in three [or so] easy steps.” Grab your tools and let’s get started.
Have a look at the line drawing to the left showing an exploded view of a caliper and its internals (courtesy of Ford’s Chassis Service Manual, Brake Section). Those part names are the ones we will use here.
The thing that looks like a stretchy rubber seal that’s on the outside of the piston and caliper is the Boot. It keeps brake dust and road grime from entering the clean areas of the piston and caliper bore. This part is contained in the overhaul kit, Napa #979, Caliper Kit.
The thing that pushes on the pads, with the brake fluid behind it is called a piston. The piston, on the fluid side, has a parking brake adjuster mechanism inside it. So the piston is often referred to as the Piston and Adjuster and is serviced as a unit only – do not try to remove the adjuster from the piston unless you have a replacement piston available. Note the piston in the rear caliper has the empty cup end going into the caliper whereas the typical front caliper piston has the flat end going into the caliper, to reduce the amount of fluid needed in the caliper.
Next comes the Piston Seal, another part of the 979 kit. It fits inside the caliper bore and seals the fluid area from the outside world.
Then comes the Caliper Housing which holds the Bleed Screw (and cap), and mounts to a bracket on the axle via two Allen-head Caliper Locating Pins to the caliper mounting bracket (not shown).
Inside the caliper, from the rear, goes the Parking Brake Thrust Screw and Seal (part of 979 kit – the seal). An Anti-Rotating Pin to prevent the thrust screw from rotating, but allows it to move in-out.
Three balls separate the thrust screw from the Parking Brake Operating Shaft. The Thrust Bearing pushes on the operating shaft by the End Retainer. The retainer has an o-ring seal to the caliper housing and a seal to the operating shaft (both o-ring and seal are in the 979 kit). The Parking Brake Operating Shaft and the Parking Brake Thrust Screw each have three cam-step recesses so when rotated next to each other, with the steel balls in place, they separate in distance, thus pushing the piston outwards (towards the pads).
Lastly is the Actuating Lever that connects to the parking brake cable and a Bolt to hold the lever to the parking brake operating shaft. The operating shaft is splined and the lever has an internal spline to match – it goes on in one of three positions, so we’re safe in not needing to mark it before removal. The levers are labelled LH and RH; the thrust screws and operating shafts are sided and labelled. Piston/adjusters are the same for both sides.
Replacement Caliper Locating Pins, the Allen-head ones, are available in pairs (a caliper worth, via Napa #82579, Caliper Bolt (left)). Also worth getting is Napa #82574, Caliper hardware Kit, one per caliper (right). These kits are still available from NAPA, as are bleeder screws, pistons, etc: <click here>
First off, look over how things are mounted to know how to put it all back together. But before we take anything off, let’s remove all the old brake fluid from the Master Cylinder and pump fresh fluid through each rear caliper bleed screw until it comes out clear. Since we’re rebuilding the rear calipers it wouldn’t make much sense to put them back on to then pump dirty fluid through them, right? Once fresh fluid is coming out each bleed screw, I disconnect and plug the center flex hose from the hard line at the chassis rail and cap the hard line to keep them from dripping. Then suck the rest of the fluid from the hard lines and calipers with the vacuum tool.
Pick whichever caliper you want to start with and disconnect the parking brake cable from the lever (pull retainer and pin). Then disconnect the brake hose from the hard line, leaving the hose attached to the caliper. Remember there will still be some brake fluid dripping from the hose, but not much if you’ve followed procedure. Keep it off the paint and out of your eyes.
Remove the caliper pins using a 7mm Allen wrench (they only go to 30-40 Ft-Lbs). These pins should have that silicone grease on them so be careful how you handle the pins coming out.
Mount the caliper into a vice so you can see the piston. The caliper body is cast iron (and heavy!) so it won’t break easily. It’s nice to have a small pan to catch any remaining brake fluid. Unthread the piston anti-clockwise, taking it out. I use a hefty pair of needle-nose pliers (not the electronic kind!) and there are all sorts of special tools to unthread pistons. When it comes free of the adjuster, it will flop around, maybe still held by the dust boot. Pull it out by hand and catch any remaining fluid in a pan. Remove and discard the dust boot and piston seal. I use a pointed brass thingie to get the seal out (right).Warning: It is gonna be cruddy in there (left).
Remove the flex hose and bleed screw from the caliper body. You’ll need to source new, soft copper washers or soften the old ones. Replace aluminum washers with copper ones.
On the rear of the caliper (parking brake lever side), remove the 13mm hex bolt from the parking brake operating shaft and remove the lever and seal. The levers are thoughtfully labeled (L and R) so we don’t mix them up.
Using either a very large adjustable open end wrench or a real 1-5/16 inch socket, loosen the end retainer. It's tightened to about 90 ft-Lbs, so make sure the caliper is securely mounted. I highly recommend using the proper socket. Once it's loosened, it'll turn out by hand (right). Note it has an o-ring seal near the outside (also in kit 979). Don't drop or loose any of the steel balls – there should be three.
Note that this section of the caliper doesn’t use brake fluid and there shouldn’t be any in here. It’s all lubed by the silicone brake grease, same stuff you’d use to lube the spark plug boots. If you don’t have lots of it, go get some (left) - ~$4 at your local Ford dealer for a large tube. Referring to Figure1.jpg above, remove and set aside the End Retainer, Thrust Bearing, Parking Brake Operating Shaft and the three steel balls (right). A magnet-on-a-stick helps here. Note all of these parts have silicone grease on them so handle carefully and maybe keep some paper towels handy to keep it from getting on everything.
Remove the parking brake thrust screw from the rear of the caliper housing (left-left). Note the seal that separates the silicone–grease-lubed area from the brake fluid area (left). Using the magnet-on-a-stick, remove and store the Anti-Rotation Pin (right).
Clean everything and discard all the parts that are being replaced: seals, bolts, pins, etc. Match up the outgoing parts with the new ones to make sure you have everything needed to put things all back together. I used my walnut-shell blaster to clean the assorted pieces of the calipers then had several of the parts powder coated. So clean everything to remove all silicone grease, brake fluid, and any assorted road grime. Inspect for rust and corrosion – repair or replace as needed.
Now is a good time to test the piston adjusters to see that they’re working correctly. Place the piston, adjuster end up, into a soft-faced vice (maybe with some cardboard pieces to keep from scratching the piston). Mark the inner adjuster with a marking pen so you can observe rotation. Thread the Parking Brake Thrust Screw about 5 full turns into the piston adjuster. (left) Using a pair of levers or flat blade screwdrives, raise the adjuster away from the piston until it stops, about ¼”. Note that the adjuster will come straight up inside the piston (right). As you release the thrust screw, notice that the adjuster rotates. Repeat these two steps – lift and release (a bit different from lift and separate) – to see the adjuster move around inside the piston (<- left). When there is some clearance in the pads to the rotor, and the brake pedal is depressed, the piston moves outwards towards the pads and rotors, and when released the adjuster rotates the piston on the thrust screw taking up the clearance. If the adjuster doesn’t move properly or freely, replace the piston assembly.
Now that we have all the parts cleaned and ready to assemble (right), let’s getstarted (getfresh beer) . Use some fresh brake fluid and some clean q-tips and wet the inside of the piston bore in the caliper. Be sure to wet the seal groove. Then wet all sides of the new piston seal and install it into the groove (left-left). Install the dust boot into the groove in the piston bore (left).
Now comes the fun part – installing the piston into the dust boot. Wet the inside of the new boot and outside of the piston with brake fluid and finangle them together. The boot is much smaller than the piston and needs to be stretched to a large diameter to fit over the bottom of the piston. It’s a job that is easier to do with the fingers of a 3-year-old and 5 hands. If you choose to use pulling tools or feeler blades to open the boot, be very careful to not pull the boot out of the bore groove or tear it. Once the piston is inserted into the boot (left), manually push the piston fully into the bore to seat the outer lip of the boot on the piston (right). If the piston won’t go fully into the bore by hand, take it apart again and get the bore and piston clean this time.
The piston from the rear of the caliper looks like this (left-left). Fill up the piston center with fresh brake fluid to the top of the adjuster threads then install the o-ring seal ontothe Parking Brake Thrust Screw (left) and wet the seal with fresh brake fluid. Note this seal separates the pressurzed brake fluid system from the parking brake mechanism. Also note that once the caliper is mounted, there is no way to bleed the caliper to get air out of the center of the piston, hence the reason why we fill it now. Not too much or you’ll need that pan again.
Now thread in the Parking Brake Thrust Screw and rotate it clockwise using a ¼” allen wrench until it bottoms into the bore at the back of the caliper (left). Rotate to align the cutout for the Anti-Rotation Pin. Add some Silicone grease to each of the three depressions and the pin hole and then install the pin and the three steel balls (right).
Install the o-ring and shaft seal into the End Retainer. Add some grease to the inside of the End Retainer (left). Install the Thrust Bearing (right), a little more grease and then the Parking Brake Operating Shaft. Lube the outer seal area in the caliper housing and the seal and o-ring in the End Retainer and plop the assembly into the backside of the caliper - the Parking Brake Operating Shaft will fall inwards onto the steel balls (left). Securely grab the caliper housing in a vice and tighten the End Retainer, 1-5/16 inch hex, to 75-95 Ft-Lbs (right). Make sure the caliper is securely mounted in the vice, the shaft seal stays in the End Retainer, and the splined shaft end of the operating shaft still turn easily during and after the tightening process.
Position the Actuating Lever over the splined shaft so its end is away from the bleed screw at the bottom of the caliper (left). Apply a dab of Loctite 222 or 242 (light strength, blue stuff) and tighten to 16-22 Ft-Lbs.
Install the new Insulators and lube then with silicone grease (right). Insert the Allen head Caliper Pins into the insulators. Remember to torque those pins to 30-40 Ft-Lbs when you re-install the caliper onto the pads and bracket on the axle. When you’re installing the rear rotors, don’t forget that they’re directional. When installed the top of the fins will point rearwards.
Install the brake hose using new copper washers and tighten the hollow bolt to 10-15 Ft-Lbs. Clean and install the Bleed Screw and tighten to 5 Ft-Lbs.
With the caliper(s) back on the car, connect the brake lines and pump some fresh fluid through each caliper, then use your normal bleeding process (note the left rear is the longest distance from the master cylinder). Be sure to not let the master cylinder run empty or the bleeding process takes so much longer. Here’s a tool I use to keep the MC resevoir from running empty. Lastly, check for leaks at all brake line connections that were disturbed and from the calipers themselves.
Pump the brake pedal about 50 times from full up, to about 20 Lbs of pressure. This should bring the piston adjusters out enough to allow the parking brake to work. If you can still slide the calipers side-to-side by hand more than about 1/16 inch, then they’re still too loose – gimme another 20 and test again.
Lastly pull up on the parking brake handle and see that it holds the rear rotors or wheels from turning. The adjustment is beneath the coin tray, under the parking brake handle (13mm hex nut). I manage to get my car to have the rear wheels spin easily at 2 clicks and hold at 6. YMMV.