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  1. #1
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    My pre-1988 brakes tutorial to end all tutorials - c900

    I have used a 1986 C900 as a daily driver for around six years now. It was only recently that I got to the bottom of the issues I've been having with the front brakes. As many of you know from the Saabsite tutorials and angry grumblings from friends, these front calipers serve as handbrake and service-brake, using a handbrake that acts on the disk through the caliper itself. To a technician not familiar with the calipers, they can look very strange.

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    But they are quite simple, and the handbrake's performance need only be tested in-car to prove its worth to a skeptic. Because it acts on the front brakes, the handbrake can still provide up to 50% of the car’s normal stopping power in the event of a total brake failure. By comparison, a rear-handbrake system only gives about 20% of the power, while de-stabilizing the car when used in an emergency. The fact is, when in good repair, the front handbrake works a lot better than a rear handbrake!

    A certain amount of basic knowledge is necessary to work on these calipers. This knowledge is, more-or-less, applied by the Bentley repair manual. I am providing the equivalent for those who do not have access to this large book. But I’m also providing a lot of other, more specialized information that even the so-called “pros” do not have. It is the result of six years of c900 ownership, three different front-brake problems, two rebuilds, and four sets of calipers.

    I hope someone gets some use out of it.

    Difficulty: 2.5/5

    Tools Required:
    -19mm socket, probably a deep one
    -Breaker bar
    -Pliers of some kind
    -Large, flat screwdriver
    -Torx driver to remove rotor (this is in your toolkit in the trunk if you don't have one)
    -Coat hanger or piece of wire to hang caliper from suspension spring

    Parts Required:
    -Caliper grease
    -Caliper seals, possibly
    -Possibly o-rings for the lever hole
    -Dot-4 brake fluid, possibly
    -Possibly pads

    Torques:
    -Front caliper to swivel member: 81-96 ft-lbs
    -Wheel lug nuts: 66-81 ft-lbs
    A word on removing and re-installing calipers to insure safety-
    Both on front and rear calipers, between the caliper and bolt heads, there is a so-called "locking plate". This thing is just a sheet of metal with two holes:
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    But it's very important. This plate's ends should be bent over to rest against the flat sides of the two caliper bolts. Failure to do so could result in your caliper bolts coming loose and the caliper falling off. I've been in a car when this happened. It's very dangerous, because it could cause the affected wheel to entirely lock up, resulting in a loss of control. If you find that your car does not have locking plates, make some out of sheet metal with a tin snips or similar. They are essential to your safety. When re-installing calipers, be sure to bend the locking plate's ends over the bolt flats once again, to ensure that the bolts will not come loose.

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    Last edited by euromobile900; 16 August 2011 at 16:19.
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  2. #2
    Sam Carlson
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Problem 1: The Sticky Handbrake

    When I bought my car, I was warned not to apply the handbrake, or it would stick on and get very hot. If the cable is free in its housing (it usually is) you probably have a seized handbrake lever on the caliper. The handbrake lever is the metal piece, which you can see close-up in this photo, that the handbrake cable pulls to apply the brake.

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    This sticky-handbrake fix will require jacking up the car (either with jack and jackstands or with your spare-tire jack) and taking a front wheel off.

    The fabled Bentley manual says nothing about how to tear down the calipers and un-stick this lever. The Saabsite and Townsend might have told you that the only cure is to buy new calipers, but they are wrong. Un-sticking this lever is something I can do in about an hour. If it's your first time, you might take two.

    Step 1. Remove caliper from car
    Unscrew the two mounting bolts on the back. They are 19mm, same as the lug nuts. There may or may not be a "locking plate" between them and the caliper body, so take care of this as I mentioned in the first post of this thread.
    You can hang the caliper from the front spring using a coat hanger or other wire, so it doesn't dangle and damage the brake hose.

    Step 2. Remove the caliper yoke from the caliper.
    Some like to remove the rotor and then re-mount the caliper, figuring that the car is a good place to work on the caliper, because it’s bolted on sturdily. This is easy enough to do, just take off the two countersunk-screws (either Torx or Phillips) that hold the rotor on, then whack the rotor a few times with a soft mallet and off it comes. The rotor needs to be out of the way. Then remove the pads by taking out the retaining U-clip using a hammer and punch. Remove the handbrake cable from the yoke. This requires taking off a circlip, which is usually defeated with a screwdriver.
    Then, you're going to need to pound the yoke out of the caliper. You should wiggle the handbrake lever as you do so. Its shaft needs to come out of its hole, as you can see here.

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    Pound gently, and it should come off, pulling the handbrake lever out with it. The lever’s spring will be released, so you should remove it earlier. A funny arched wire will also fall out. Set these things aside.

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    Now the caliper should look like this:

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    As you can see, it’s just a big cylinder with two pistons, one in either end. The handbrake mechanism pushes these two apart via a complex jacking mechanism I’ll explain in my next post, below. For this simple fix, you won’t need to go into it.

    Step 3. Clean-N-Grease
    Clean up the lever's pivot shaft. Look in the hole in the back of the caliper piston. See where the lever goes in? Squirt some caliper slide grease in this hole. Don't be shy now you've got it apart! Be generous!
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    Clean off the lever's pivot using solvent and a scouring pad or similar. God knows it's rusty or corroded or gummed up.

    Also, clean the caliper yoke slide tracks using a file or similar. Not too aggressively, just touch them up.
    Extra credit consists of prying the O-rings (there are 2) out of the lever's pivot hole and replacing them with new from the hardware store.

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    Step 4. Reassemble!
    Insert the lever (without its spring) back into the greasy hole. Marvel at how silky smooth it is to turn. Now squeeze the pistons together while operating the lever (might need a clamp or some channel lock pliers to do this), to make sure the lever pushes the pistons out of the cylinder a bit. If not, you’ll need to go deeper. See my next post in this thread.
    Take it back out, and insert it with the yoke and arched wire at the same time, so it’s just like it was before you took it apart.

    Put in the pads, their retaining pins, and their anti-rattle clips as they were before. Hopefully you won't need to wind in the piston, but if you do, go for it. Everything should fit just fine.

    Step 5. Install on the car!
    If you didn’t take the caliper hose off, you don't need to bleed the brakes or anything. Just put the caliper on the car again, torque the mounting bolts up to spec, FOLD OVER THE LOCKING PLATE, and away you go!

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    Last edited by euromobile900; 16 August 2011 at 16:14.
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  3. #3
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Going Deeper

    If your handbrake mechanism is still stuck, or won’t adjust, you will need to take the calipers further apart. This requires a new seal kit. Also if your calipers are leaking, you can likely just take them apart and re-seal (see my post about piston wear before deciding you can re-seal to stop a leak).

    First step is to pull the pistons out of the caliper. Remove the dust boots and their wire clips first. Usually I find that levering on the lip of the piston with a screwdriver works best for removal, but sometimes I push the whole piston assembly out one side instead.

    In either case, you’re left with a cylinder:

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    And pistons. Without the cylinder, the inside of the caliper piston assembly looks like this:

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    You can see the screw between the two pistons. This screw is part of the self-adjusting mechanism. As you screw the piston in to make room for new brake pads, you are basically screwing it on this threaded rod.

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    On re-assembly, it is imperative that the rod’s little black sheet metal guide be hooked on the roll-pin sticking out of the larger piston.

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    Inside the large piston lies the handbrake mechanism itself. To get this apart, you may have to destroy things, because the pistons are press-fit together with a paper gasket. But usually you don’t need to take it apart; just fill this area with liberal amounts of grease. Once again, I recommend not disassembling the handbrake mechanism within the piston. But I've included the photo of what it looks like to satisfy curious minds.

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    Basically, the lever shaft uses a caming action to turn the disc with the flat-side in the picture with respect to the piston bottom so that the ball bearings (3) cannot sit in their holes anymore, because their holes will not be lined up. As they roll out of their holes, they exert a jacking force between the two pistons. It’s a neat device that rarely has problems. Unfortunately, everything else does.

    Now that you've got all this apart, you can wire-brush the inside of the cylinder (NOT THE PISTONS!) and renew the seals. Be sure to lube them with some brake fluid or Castrol red rubber grease (avail. only in UK) before reassembly. On reassembly, be sure to align the screw rod's black metal thing with the roll-pin on the piston, or else your handbrake auto-adjustment will not work.

    If you find that the piston sliding surface has the slightest bit of rust, you will need to junk that piston. Piston faces can have rust, piston insides can have rust, but no rust can exist on the sliding surface. You cannot hone them or polish them. Just throw them out if they're rusty. Outer pistons (the ones with the the four holes for turning) can be exchanged left to right, but inner pistons (the ones with the slot and lever-hole) cannot. This might be a reason to buy rebuilt calipers, or go to a junkyard and take apart every old-style caliper you see to find the good pistons. Don't nick them, don't score them, don't drop them, and don't use them if they're rusty on the sliding surfaces! Even a small bit of rust like this (picture taken from a rear brake) on the piston's sliding surface can cause a stuck caliper:
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    Last edited by euromobile900; 16 August 2011 at 05:51.
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  4. #4
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Problem 2: Loose Yokes

    Perhaps the second-most common complaint with these calipers is a loud clunk when backing up and braking. This is the dreaded Loose Sliding Yoke. When a yoke is loose, it can slide out of alignment, moving part of the pad closer to part of the disk. The brakes may squeak and chatter, as well as juddering.

    With the brakes on the car, you can check for loose yokes by raising car, taking off wheel, and levering with a screwdriver like so:

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    I do NOT recommend buying rebuilt calipers to cure this. Rebuilds are almost always made from "cores" which people threw away after deciding they are no good. While rebuilds do come with guaranteed-good pistons, the bodies and yokes generally get little more than a sandblast and respray. Here's a picture of a newly "rebuilt" caliper, showing how much play it has between yoke and slide:
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    It's disgusting.
    Some rebuilt units may come with a shim to correct the loose yoke problem. These lack durability at best, and at worst they are timebombs waiting to disintegrate as you descend a mountain pass. If they don’t come with shims, chances are they already have loose yokes.

    So, how do you fix them? Well, you first need to get the caliper sliding surface within tolerance. Here's a picture of a bad sliding surface, from a rebuilt caliper:
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    Edges are rounded, and the surface has paint on it.
    It should look more like this:
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    Good, sharp edges and no paint. If you have slides that look like the bad picture, take a file to them, get them square, and then follow the instructions below.

    Welding the yokes
    First, take the caliper apart and file the slide square. Then bring it and the yoke to a local welder and explain to him that you want the yoke built up. Or DIY if you can weld. In either case, weld on the plate-steel of the yoke, because the cast-iron of the caliper cylinder is too porous and will distort or maybe even crack.

    The yoke can be worn in two ways. Obviously it can be worn to create vertical play, but some yokes get worn laterally as well:
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    Both wears need to be corrected with weld.
    Just explain to the welder what you want it to do, and how the yoke has to slide. He/she will do a fine job and it will probably cost you less than a set of rebuilt calipers anyway! My local guy said he'd do it for $10 a side.

    After you've got this done, you should be good for another 100,000 miles. Stick some grease on the caliper sliding yokes every time you have the wheels off, and they'll last even longer.

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  5. #5
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Problem 3: Brake Judder

    So you're driving down the road, you put on the brakes, and you get massive vibration, a pulsation in the pedal, or a combination of both. This can be caused by any of several culprits. The first is a simple warped rotor. The cure is simple: replace or resurface the rotor. A bit more on replacement rotors later. However, the culprit could also be a bent wheel hub. These are cast, but they can bend a little bit. A machinist with a lathe ought to be able to turn a wheel hub back into plane. If not, you can get a wheel hub from a junkyard, but bear in mind, cars with vented disks (turbos mostly, also the 1987 S) have hubs with different offset than those with solid disks. You will be unable to swap between them.

    The culprit I have found to be most common is actually a side-effect of smart design. The OEM rotors were designed to have two small reductions in diameter, to ease the fitment of new brake pads, as seen in the below photo. The bottom rotor in the photo is an original genuine SAAB:

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    As you can see, there's a slight reduction in diameter that the edge of the pads overhangs. These divots make it easy to slide the pads out, because the pads won't be catching on the usual rust-lip of the rotor, but they tend to catch the pads on their way around, producing a judder that can be very violent at high speed, or very noisy at low speed. You can see from this close-up, where the divot starts there is a band of glazed rotor (darker metal), which I assume makes the problem worse.

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    If your rotor divots are causing this problem, you will likely have glazing like this too. You may find that rust on the rotor surface actually makes the problem disappear until you’ve braked once or twice, so the judder is only apparent after longer drives. Ironically, you may also find that getting the rotors resurfaced fixes the problem. This is only because it takes away the glazing.

    The cure is to replace with some rotors like the ones in the top of the first picture in this post. OEM rotors are obviously no good, and so are Brembo rotors. Raybestos PG or Napa brand should do you fine. They’ve done me well! The bottom line is, you want a generic part, not a super fancy OEM one, but you want quality too. It’s a difficult balance but Raybestos and Napa are trusted brands this side of the pond, and they have been running fine for me. Then, if you need to replace the pads, just file off the rust on the edge, turn the rotor to the right spot, and slide them out as normal. No big deal.

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  6. #6
    Sam Carlson
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Performance Modifications

    The best, most cost-effective, easiest performance mod consists of doing the above to get your existing brakes working right. The following mods are much harder, require guesswork, and are not well-tested. Mod at your own risk!

    So your brakes are operational. They're working well, but you still want more. You clearly need to mod. Some would change to the later, rear-handbrake setup, and use front calipers from a 9000, but if you want to ice-race with those old square-seat soccerball wheels, that's not gonna be possible. Also, you can't run Incas, Shelby Minilites, or the infamous Manholes with a new-style lug pattern. Therefore, this post is a collection of everything I know about modding the pre-1988 brakes for performance.

    Switch to vented
    First thing you can do is to add vented rotors. To do this, you need, AT MINIMUM, caliper yokes, wheel hubs, and of course the rotors. The hubs for vented differ from those for non-vented, in terms of dish or offset. These need to be pressed in and out, so you may be better off just changing the whole swivel member and ball joints. Once that's done, you will need to mount the discs, and then the calipers with different yokes, and you'll be set. I did this to my car in about 3 days, with numerous problems and setbacks, so you should be able to do it comfortably in that amount of time.

    Racing calipers
    If you've got vented rotors and still want more power, there are a few options people have tried. The first is to use some aftermarket Wilwood Superlite calipers. I don't approve of this. Wilwood calipers are for racing. They work well under demanding conditions, but they are not really meant for daily driving, as they have no dust boots. In fact, the decision not to use dust boots is a trade-off. Dust boots often melt under extremely high-heat conditions, which is why racing calipers don't use them. Unlike regular-use calipers, racing calipers don't age gracefully, and I don't know how they cope with sitting and not being used, especially in wet or wintry conditions. After searching some Honda forums, I found numerous references to Wilwood calipers on daily drivers lasting only a year between full rebuilds, and some posts describing calipers randomly blowing seals on the track. It sounds like a bad trade-off to me.

    Rallyists argue that, since the Wilwood units withstand a rally, they must be able to withstand daily use, but I believe they are usually rebuilt shortly afterward, and closely watched throughout--not the kind of care a daily driver's brakes are going to receive. That said, these provide amazing stopping power, so if you want good brakes for your race-build, non-street-legal 900 or 99, these are for you. Here are some pictures of a Wilwood setup.

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    I believe they don't work with Inca wheels (possibly also not with Soccerballs), and they require some spacers to get the caliper offset right, as you can see in the first picture. As you can see, even this guy doesn't have the offset quite right, but that's likely because he wanted as much wheel clearance as possible.

    A durable, more cost-effective mod

    Legend has it that FRONT calipers from a 1990 Subaru Loyale will work on the rear. These also have front-handbrake, so you'll be effectively doing a rear-handbrake conversion without changing the axle or knuckles. Legend also has it that the four-piston calipers from a mid-1980s Toyota 4x4 pickup. I know that the calipers from a 1986 V6 4wd pickup will definitely work, so you just need to cross-reference with that in mind and then go to a junkyard to see what you can find. You will need to re-drill the caliper holes larger than original. I don't know about wheel-fit with these.

    If you want higher-performing set of calipers, these are your options. All use stock disks, and you'll need to change the proportioning valve even if you only change the front calipers, and definitely if you change the rears. Changing the proportioning involves disassembly of the master cylinder and adjusting a pin, but I don't know the specifics. You can also buy an aftermarket proportioning valve, but then you'd have to re-route your lines and not have diagonally-split brakes anymore, and that would be silly.

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    Last edited by euromobile900; 16 August 2011 at 17:29.
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  7. #7
    Edward G
    Saab Enthusiast
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    Saab(s)
    T5.5 84 900T8
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    Euro, I have a torn dust boot on my front brake caliper, the calipers are not leaking to the best of my knowledge. If I buy rebuild kits will I be able to rebuild, or is it likely there is rust there? if it's not leaking now but I pull it apart and there's rust does that mean by rebuild will be destined to fail and leak within a short space of time? I thought new seals would seal better over the rust than old seals?

    Cheers for any insight.

    I flushed the fluid completely a year ago with high quality stuff. I'm ordering seal kits now. Can I replace the dust boot without replacing the main seals - Basically what I'm asking is if my calipers aren't leaking and I just have a torn dust boot, am I better off to replace the seals or leave as be.?!

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  8. #8
    Sam Carlson
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Quote Originally Posted by s900t8v View Post
    Euro, I have a torn dust boot on my front brake caliper, the calipers are not leaking to the best of my knowledge. If I buy rebuild kits will I be able to rebuild, or is it likely there is rust there? if it's not leaking now but I pull it apart and there's rust does that mean by rebuild will be destined to fail and leak within a short space of time? I thought new seals would seal better over the rust than old seals?
    If they aren't leaking, and aren't sticking, there is likely no rust. Rebuilding a caliper that isn't sticking or leaking will likely not hurt things, but it won't do you any good either. I'm always in favor of leaving things alone if they work right. You can tell if a caliper is sticking by turning the wheel by hand with the car raised and in neutral. You should be able to turn it without a terrible lot of force. Also look for uneven wear on the brake pads. If one brake pad is much thinner than its mate, you know you have a stuck caliper and it is time for a rebuild. Rusted pistons usually stick before they leak, and a car that gets daily use and regular brake-fluid changes is unlikely to develop rusted pistons. Replace the dust-boot, sure, but other than that, leave them be. You can replace just the dust boot without replacing the main seals, if you like. You'll need to remove the pads, but I've put dust-boots on without even removing the caliper from the steering swivel member! Save those seal kits for when you need them!

    If you do rebuild a caliper, you may find that the piston is covered in a hazy rust-colored coating. Don't panic! Lots of times, this is just a surface deposit, much like a rusty ring in a toilet bowl that runs off of well-water. Just get a kitchen scouring pad and some solvent and gently scrub until the rust coloration is gone. The rust you should worry about is pitting and other changes in surface texture.

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  9. #9
    Edward G
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    T5.5 84 900T8
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    Quote Originally Posted by euromobile900 View Post
    If they aren't leaking, and aren't sticking, there is likely no rust. Rebuilding a caliper that isn't sticking or leaking will likely not hurt things, but it won't do you any good either. I'm always in favor of leaving things alone if they work right. You can tell if a caliper is sticking by turning the wheel by hand with the car raised and in neutral. You should be able to turn it without a terrible lot of force. Also look for uneven wear on the brake pads. If one brake pad is much thinner than its mate, you know you have a stuck caliper and it is time for a rebuild. Rusted pistons usually stick before they leak, and a car that gets daily use and regular brake-fluid changes is unlikely to develop rusted pistons. Replace the dust-boot, sure, but other than that, leave them be. You can replace just the dust boot without replacing the main seals, if you like. You'll need to remove the pads, but I've put dust-boots on without even removing the caliper from the steering swivel member! Save those seal kits for when you need them!

    If you do rebuild a caliper, you may find that the piston is covered in a hazy rust-colored coating. Don't panic! Lots of times, this is just a surface deposit, much like a rusty ring in a toilet bowl that runs off of well-water. Just get a kitchen scouring pad and some solvent and gently scrub until the rust coloration is gone. The rust you should worry about is pitting and other changes in surface texture.
    calipers are sticking, both front ones are, but not too badly, in terms of sticking I mean the pads are wearing unevenly. I think I will pull them down and clean but not change the seals, I will replace the dust boots on both as they are old and cracked.

    I will clean up the calipers really well and reinstall them. I need to rebleed as I think there may be some air in my lines, pedal is a bit soft.


    Thanks mate

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  10. #10
    Sam Carlson
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    If they are sticking, REBUILD! You haven't got much to lose if they are sticking. The pistons may not be rusted. I have had many calipers stick just because of gum and gunk on the piston, too. Let me know if you need a new piston or two--I have a whole box.

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