This service applies to my 1988 Silver Spur, which is a 20,000 series car (24274). Yours may be completely different.
Before we begin, let's discuss the things that will be accomplished. There are six calipers on the car (two for each of the front two wheels, one for each of the two rear wheels). These will all be rebuilt. There are six flexible brake hoses (one per wheel in the front, two per wheel in the rear). These will all be replaced. The two low pressure hoses from the two mineral oil reservoirs to the pumps will be replaced. Four low pressure hoses at the accumulators will be replaced. Two braided steel high pressure hoses at the accumulators will be replaced. Finally, the system will be bled.
There are no particularly peculiar tools that will be required. Here is a list:
1/2" breaker bar
assortment of SAE size sockets for above rachets, including a 12mm 3/8" socket
3/8" swivel socket extender
extensions for your 3/8" and 1/2" rachets
some type of pick to extract caliper seals/o-rings
7/16" flare wrenches (to fit around brake hose fittings)
air compressor with a blow gun fitting
With these tools, we are ready to begin.
Depressurize the system
There are two procedures to depressurizing the system. The first and easiest is to turn the ignition key to the on position (don't start the car) and slowly depress and release the brake pedal up to 100 times until both brake pressure warning lights are illuminated on the dashboard.
The second, and more appropriate way to depressurize the system is to simply open the bleed screw on each accumulator. There are two accumulators, both accessible at the front of the car, passenger side. One is easily accessible under the bonnet. Simply open the bleed screw (12mm) until the system has bled (you will be able to hear when it is completed). Close the bleed screw.
The second accumulator is slightly more difficult to access. If you have not removed the wheels yet, you can access this by turning the wheels completely to the right. You can access this accumulator bleed screw from in front of the front wheel, and you will need to use a 3/8" extension and the 3/8" swivel (with swivel right next to the 12mm socket). Bleed in the same fashion as the first accumulator. Close the bleed screw. The image below is from above the engine compartment, but access is made through the passenger front wheel well. Although not shown in this image, access is easiest with a swivel just before the socket.
Regardless of which technique you choose, complete the bleeding by opening the rear strut bleed screw and allowing fluid to expel from this bleed screw until flow ceases. You will want to have a tube hooked to the bleed screw before opening it up (unless you cherish a mess). The rear strut bleed screw is just forward of the passenger rear wheel and is accessible without even jacking the car up.
You might have already removed the wheels by now, but if not, raise the car and secure it with jackstands, and remove the wheels (13/16" socket). Please do not work under a car that is held up by a jack only, but instead secure it with jack stands.
As the next step, we want to remove the rear calipers. The order of things to do from here to bleeding the system is not critical, but I chose rear calipers because they looked to be the most difficult job. One more note before we begin removing anything....ensure that all fittings that you will be removing/disconnecting are clean. In fact, I used PB Blaster (which is a super penetrant) on all the fittings to make sure they would be easy to break free (not sure if this was necessary, but I had no problem breaking free the fittings which I assume were last torqued 13 years ago). After allowing the penetrant to soak in, I cleaned most fittings with Brake cleaner, and some of them I then used compressed air to really dry them off and make sure the dirt was gone (but sometimes the air just dislodged dirt from other areas in the vicinity, thus making it dirty again, so I usually skipped this step).
Removing Rear Calipers
There are several fittings on the rear calipers that must be disconnected. The first is actually a bridge pipe from the inside of the caliper to the outside of the caliper. These fittings (as well as ALL the rest of the caliper fittings) are 7/16". After disconnecting these fittings, there is also a mounting point of this pipe to the caliper in order to keep it rigid. Remove this mounting nut (11/32") -- I used a nut driver. Remove the bridge pipe.
One of the fittings on the inside of the caliper, towards the center/bottom, is the lower bleed tube. Disconnect this fitting, and you should also remove the block where this bleed tube leads. The block is where the lower bleed screw is located.
The other two fittings are from hard lines coming along the chassis (originating at the flexible lines we'll be replacing later). You can disconnect these, and I also found it necessary to remove their mounting points from the chassis (3 or 4 points, all 11/32"). This way they'll have a little more flex so you can move them out of the way when it comes time to remove the caliper.
One of those two rigid lines went into an "adapter" at the caliper. This adapter should still be mounted in the caliper and must be removed. It requires a 3/4" open end wrench. I do not understand the logic of this adapter. See the image below of the one I broke, next to the other one which survived. In essence what you have is a rigid line coming into an adapter, and the adapter with the identical thread going into the caliper. Why not just have the rigid line go all the way to the caliper? Why am I searching for logic here?
The next step is to remove the caliper bolts. When I got to this point, I almost panicked, because the head of these bolts look like something I don't have a socket to go on. But in reality, a 12 sided socket (9/16") goes on just fine. These bolts are accessible from the inside of the hub. They were torqued on pretty good, so I used a breaker bar to break them free. You will need an extension in order to reach these bolts. Please take care that the socket is seated properly on the bolts, because it's my guess you don't want to round off the heads of these bolts. There are two of them to remove (see blurry image below).
You're almost ready to remove the caliper. There are two more things in your way.
First, the parking brake. There is a rod going from the lever on the chassis to the mechanism on the lower section of the caliper. You need to remove the cotter pin and the clevis pin on one or both ends of the rod. In retrospect, I would remove both ends and remove the rod altogether...you're going to have to later, and if it's out of the way right now it will be easier to remove the caliper. I also turned the click adjuster on the parking brake mechanism out (counter clockwise) far enough that the pads were more clear of the rotor.
Secondly, if you try to swing the caliper out, you'll notice that one of the points where a hard line fits into the caliper will not clear the bracket on the car. Don't try to force it, it won't come. You need to loosen the hub, but only a little bit. There are four bolts back where you just removed the caliper bolts. The workshop manual says you will have to turn these each approximately 4 revolutions. I used the breaker bar on these (sorry, I don't remember their size). They also required a fair amount of torque to break free, so again ensure that your socket (on the end of an extension) is fully seated on the head of the bolt before trying to loosen. Again, removal is NOT necessary. Simply loosen them enough so that the hub can rock out enough for clearance of that fitting.
Remove the caliper.
You've just done the difficult part. Caliper rebuilding is straightforward and quick....except for the preparation. Preparation is simply cleaning the caliper up. Here is a picture of what mine looked like upon removal:
Remove the brake pads and start cleaning. Clean clean clean. Clean until it's clean. Now it's time to disassemble the caliper. There should be a dust cover on each piston, held on by a clip. These both are part of the rebuild kits. Remove these from all pistons. Now it is time to remove the pistons. On these rear calipers, 3 of the 4 pistons were easy to remove. I put a block of wood inside the piston and found the brake fitting that fed each piston and stuck my air gun from the air compressor on that fitting and "Pop" out comes the piston. This was trivial for the two pistons on the inside of the caliper, and one piston on the outside of the caliper (as well as both pistons on all four front calipers). However, the fourth piston on each of the rear calipers were trouble.
For the outside pistons, there is only one feed (incidentally, this was the feed from that bridge pipe). Once one piston is out, it is not easy to feed compressed air to the second piston on that side. I tried putting the removed piston back in there but air escaped from somewhere. If you try this method, be sure to connect that lower bleed tube back on or else air will simply escape from there freely. After many attempts, my father arrived and began twisting the piston by hand. The more he twisted it back and forth, the easier it was to work it out of its bore. It eventually worked free and out (on both rear pistons). Short of this, if you simply cannot remove a piston, it is possible to break the caliper into two pieces, but that is beyond the scope of this webpage. This would require further replacement of seals/o-rings within the caliper. If you do end up having a problem with a piston, try grabbing it with your fingers on the lip, or with some type of tool on the lip. Under NO CIRCUMSTANCE do you want to grab the actual piston surface (the part that goes into the bore) with anything with more friction than your fingers. You don't want to booger up the sides of the pistons or else you'll have leaks there.
Clean the caliper again, and finish up with compressed air. I also used that air gun in each fitting and in the bridge pipe to blow out any dirt/debris that might have entered. Use a small dental pick to get a hold of the seal inside the bore and remove it. DO NOT booger up the piston bore. Clean again.
Now it's time to reassemble. Put some mineral oil on the seal before installing it, and then also put mineral oil on the piston and the piston bore before you install it. Install the dust covers and clips. You're done!
Note in the picture below the pistons, seals, dust covers, and clips for one rear caliper.
Rear Caliper Installation
Parking brake adjustment could be the subject of another webpage, but I will say one thing since we have the parking brake actuation rod off. The distance between the nut and the other fork should be 2.25" (see image):
Install the parking brake actuation rod on the parking brake mechanism on the caliper before installing the caliper. Believe me, you want to do this first or else you'll never get that clevis pin back in there once the caliper is on the car (actually, I managed to do it successfully on one caliper, but on the other one I couldn't, and I had to remove the caliper all over again). Just put the rod on, and as you slide the caliper back onto the rotor, feed the rod into the hole on the bracket holding the chassis parking brake mechanism (hopefully this will all make sense when looking at the car).
You will have to rock the hub again in order to put the caliper back on. The rest of the installation is reverse of removal. A few things to note: the caliper bolts torque to 80-85 foot pounds, the hub bolts that you had to loosen torque to 60-65 foot pounds, and all fittings torque to 6 foot pounds. Also, as I stated above, parking brake adjustment is a fairly complex subject (if there's enough interest, I'll write a webpage on that). But one thing you'll want to adjust is that clicker adjuster you might have loosened when removing the caliper. You want to tighten it so that you can just barely turn the wheel by hand (when the parking brake is off). You'll probably want to have the wheel on to do this adjustment, although you won't have to have it on tight with lugnuts...just set it on there. Once you have the clicker at this point, loosen it back three clicks.
Install the pads.
Front Brake Caliper Removal/Rebuilding/Installation
This is much simpler than rear calipers. There are two calipers per front wheel, and these are connected by a bridge pipe. This pipe must be removed. Incidentally, on my car, for both front wheels, this bridge pipe was easily disconnected from one caliper, but wouldn't budge out of the other caliper. This is fine. As long as you can remove the calipers, you're fine. There is one fitting coming into the calipers from a hard line, and this must be disconnected. The front caliper has a wear sensor wire coming from the inside pad, and this wire must be disconnected. Each caliper is held on by two caliper bolts. That's it!
To rebuild the caliper, simply follow the instructions above for rebuilding the rear calipers. It is so similar it is not worth repeating here.
Installation of the calipers is reverse of removal. The caliper bolts should torque to 80-85 foot pounds. The leading caliper, inside pad has a wear sensor. Before removing this caliper and pad, note the routing of the wire so you can route it in a similar fashion when reinstalling the caliper. Another thing to note before removing the calipers is where the wire tie holding the brake pad sensor wire is so you can neatly put everything back how it was when you reassemble.
Rear Brake Lines
There are four flexible brake lines in the rear, two per wheel. Follow the rigid lines from the rear calipers forward along the chassis, and you will see two brake lines together.
These fittings again are all 7/16". On each fitting, there is a rigid line where the flexible hose connects. They connect at a bracket, and on the rigid line side of the bracket is a nut on the end of the flexible hose. You can use open end or flared wrenches on these. Please ensure they're clean before breaking them open. There is also a washer there, so be sure to remember where the washer goes. These fittings, when you put the new hoses on, torque only to about 6 foot/pounds. Below is an image of the old and new hoses:
Front Brake Line Installation
There's really not much to say here. Installation of these hoses is trivial. 7/16" fittings, one hose per wheel. Cleanliness is important!
Low Pressure Hoses Under the Hood
There's not much to describe on installation of these hoses other than their location.
There are two at the mineral oil reservoirs. Each of these hoses is also covered in a foam sleeve which should be replaced at this time. Install the sleeve before installing the new hoses. Note below that the hydraulic fluid warning panel will have to be removed before you can access the hose clamps on the reservoir side of these hoses.
There are four hoses right near the accumulators. Two smaller ones are closer to the front of the car and these are held on by hose clamps and are not that difficult to remove/reinstall. The two hoses just behind these are slightly bigger. They go directly to the accumulators. The top accumulator is very easy to access. The lower accumulator is much more difficult to access (you'll need a long stout screwdriver with a relatively narrow slot head). Unfortunately, none of these hose clamps have a hex head, so you have to use the slot head of the screwdriver. You might consider replacing all these hose clamps anyway (I recommend ABA brand hose clamps). Of note is that the hose that goes to the lower accumulator on my car was in very very poor condition. It was definitely time to replace the hose (13 years old, 128,000 miles).
Lastly, you have two high pressure steel braided accumulator hoses. These again are 7/16" fittings. Some of the fittings are easier to get to from the top of the car, others are easier from the bottom. Figure it out. :-)
You're just about done with this entire service. Only thing left is bleeding.
Bleeding the System
With all the items I had worked on in the hydraulic system, I had lost more than a small amount of mineral oil. I don't know if it is recommended procedure, but before I began bleeding the system, I topped up the system. I first put mineral oil in the reservoirs until the fill indicator sleeve was visible in its appropriate spot. I then started the car and allowed it to pressurize. I continued to top off the system until it was full and fully charged.
Next I shut down the car and depressurized the system by loosening both accumulator screws. With both screws loosened, I ran the car at 1500rpm for about a minute (estimated on the RPMs). I shut the car down and closed the accumulator screws.
For brevity, I am enclosing an email I wrote of the rest of the bleeding procedure here:
i) Set up 5 "catchers" for the mineral oil that will be expelled from the bleed screws. One catcher for each wheel, plus one for the g- valve. Each catcher can be a can or one of the stand up ziplock bags. I like it to be clear. You need to put enough mineral oil at the bottom of each catcher that you can immerse the end of a bleed tube into the mineral oil while bleeding.
ii) Put a clear bleed tube on each bleed screw (I bought clear tubing from a plumbing store). There is one bleed screw at each front caliper, two at each rear, and one at the g-valve. There's also one for the struts, but you can use one of the tubes from the rear caliper for that. Ensure the bleed tube is immersed in the mineral oil at the bottom of each catcher.
iii) Open the bleed screws on each of the front calipers and the g-valve (all 7/16"). Depress the brake pedal, start the car and run it at 1000rpm (guesstimate this if you don't have a tach on your car). Allow
mineral oil to flow through the bleed screws into your catcher until ALL THREE bleed points are completely air free. LEAVE THESE OPEN, go back to the passenger rear caliper and open these bleed screws. Now go back to the front calipers and the g- valve and close these bleed screws.
iv) Bleed at the right rear caliper until air free. LEAVE THESE TWO BLEED SCREWS OPEN. Go to the driver side rear caliper, open these bleed screws, then go back to the passenger side ones and close.
v) Bleed at the passenger rear caliper until air free, then close these two. Allow the system to pressurize.
vi) Either load the trunk with weight or do something to activate the leveling system (I jacked up part of the rear suspension). Open the strut bleed screw and allowed to bleed until air free (note that the system is under full pressure on this bleed screw when you open it). Close bleed screw.
Of note is that in this procedure, the system is never closed and allowed to pressurize while bleeding (until the struts). So it's not really as complicated as it sounds if you remember the goal of not allowing the system to pressurize.
Also, it was really easy with four people (one guy in the car, one on either side of the car, and me under the car at the g-valve).
Lastly, make sure you don't run the reservoirs dry.
You're done, congratulations!
Here are just a few more tips that I learned from my job. First off, bleeding is not an easy thing. In fact, when I went for my first test drive, I was disappointed because braking performance was seriously degraded. The car would stop just fine, but what was happening is that under light braking, performance was degraded, and suddenly at some point in heavy braking, the car would finally begin braking hard. As it turns out, there was much air in the system. I tried driving the car for about a week to see if it would settle out, but it didn't. Only after I re-bled the system did it perform properly. There was a LOT of air expelled at the front calipers, with little or none at the rear.Lastly, after you bleed the rear suspension, you might be worried that the rear end appears to be sagging. Don't fret. I've bled my car's hydraulic system twice, and both times this happened. After a very short time, the rear suspension is fine.