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FAQ: Master Brake Cylinder rebuild

Thu Jun 16, 2005 6:45 pm

ST165 Master Brake Cylinder Rebuild

Not sure how many of you have done this, but I didn't find any info on it, and after a search I saw a few other people who had replaced their master cylinders. Not sure how different it is for a 185 but I'm guessing it's fairly similar. I had actually bought another master cylinder off of someone because I didn't want to screw this up, but since I already had the kit and my old MC, thought I may as well give it a shot.

Reason for doing this:
165 brake cylinder from Conicelli: $237.61
Piston kit from Conicelli: $47.29

I got the part number for this kit from a local Toyota dealer, though I see Conicelli also has a Master Cylinder Repair Kit for $55.31 also, not sure what's included in that (maybe the piston kit + reservoir?). The part # I ordered was 04493-20170.

Here's the brake cylinder laid out, along with the piston kit.

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This is what's contained in the kit. On top is the #2 piston, then the spring for it, then the #1 piston and spring. Then a few misc. parts (for the life of me, I could not find anywhere to put that hairpin or the two larger copper washers. Whoops!). It also came with a (not pictured) screwdriver condom, to protect the inner "sarface" of the cylinder. Believe it or not, those were the only instructions included with this kit.

Step one is to remove this screw and pull off the reservoir

This one's kinda tricky. I didn't have all my tools with me and ended up using a pair of pliers and a bent paperclip to get this guy off, but a pair of needlenose pliers should do the job just fine. Be careful, though, because if it's not fully drained (even though I thought mine was), you'll end up with your hands covered in brake fluid. If I were doing it again, I would put something through the hole on top, where the reservoir mounts, to hold piston #1 in place while I removed the screw. Especially since once I did get the clip off, it went flying about 3 feet away.

Piston #1 should pull right out now.

Next, you need to remove the (10mm) bolt that's on the bottom. Under this bolt is that small metal rod that was in the kit, and that's holding piston #2 in.

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What you'll do here is hold the entire thing upright (the way it would be mounted in the car) and push in on the end of piston #2 with a screwdriver. The pin that was hiding under the bolt should fall out once there's no pressure on it.

Don't forget to use your screwdriver condom!

After that, the second piston should come right out relatively easily.

Here is the old stuff (top) and the new stuff (bottom). Honestly I'm not 100% sure that this brake cylinder needed a rebuild (replacing it didn't end up fixing my problem anyway) but it's good experience at least :) This is also a really good time to give everything a good cleaning. I try to clean every part I take off/work on with the AllTrac. With a car this old, it's a losing battle, but at least some of it will look decent.

Now, reassembly is a snap. Slide Piston #2 back into the cylinder (spring end first), while it's set upside-down. Then, as you push in with the screwdriver (plus protective tubing), you should be able to put the pin into the hole and, it should fall right into place. You'll probably need to turn the screwdriver to line up the holes for it. Once it's in, put the new bottom bolt and copper washer on to keep the rod in place

Now piston #1 goes back in, and I used the same technique as before, inserting something into the hole on top (be sure it's not something that would scrape the interior walls of the cylinder) to hold the compressed piston in place, while I put the clip back in. Then just pop the reservoir back on, replace the screw (for some reason you don't get a new one of those) and you're back in business.

All in all, it's a pretty easy job, so if you're planning to replace your master cylinder, this shouldn't add much time onto the project and would save you a lot of money.
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Fri Jun 17, 2005 12:57 am

Good read indeed! So have you noticed any difference in brake feel?

Fri Jun 17, 2005 1:51 pm

in this particular case, no :P that's the real kicker. I actually replaced my brake cylinder last weekend with a slightly used one, and this was a rebuild of the one I pulled off. I'm convinced I'm getting air in my lines from somewhere though, because it worked like crazy the first time I drove it after replacing the cylinder and bleeding the brakes. But driving later that night I noticed I was having to pump the brakes again, so I'm thinking the brake cylinder wasn't the problem.
I never knew entirely how one worked, and when I opened up the kit and just saw a bunch of crazy parts and nonsensical instructions, it was a bit intimidating at first. So when I had the kit and the extra cylinder lying around, I figured what the hell :)

Fri Jun 17, 2005 2:46 pm

how are your wheel bearings? another member was having to pump his brakes after replacing everything and it turned out that one of his wheel bearings was going out and the slop was pushing the piston on the caliper back in too far, thus needing to pump the brake to push it back to where it needed to be. Just a thought really.

Fri Jun 17, 2005 2:58 pm

I actually remember reading that, and the previous owner (only had the Trac for a few months) had replaced bearings on one side but not the other. On my first trip out after replacing the brake cyl. the brakes were good and hard, super responsive, but would need almost a full pump before they started to grab after I made a hard left turn. So I'm thinking the bearings are bad (wouldn't a rotor that's been milled too far do the same thing also? haven't checked to see if the rotors have been turned or not but was planning on picking some brembos up eventually anyway), but then that evening and the next day the brakes were super spongy and needed 2-3 pumps to get up to decent stopping power, so I'm guessing it's a combination of the two.

Tonight I'm going to replace the bleeder screws and put some teflon tape on them this time to make sure they have a really good seal and no air can get in there, and check all the lines/calipers for any sort of leak. Failing that, any other ideas? I'm pretty sure the bearings are bad, but that's kind of a secondary problem in addition to what feels like a good amount of air in the lines.

Thanks for the input :) Before I read that thread, I never would have considered bearings for a brake problem.
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