HRBrat Posted February 21, 2021 Share Posted February 21, 2021 I'm having some braking issues with my 87 Brat and hoping for some help with diagnosis. The problems started a couple months ago with the left front caliper sticking closed. I got a rebuild kit, took apart the caliper, found some corrosion in the cylinder and buildup of crud on the piston. Cleaned both up with a wire wheel, replaced seals, and put it back on the car. I put new pads on both sides while i was at it. Bled the system but couldn't get the pedal to feel firm. After extensive bleeding of master cylinder and all four corners the pedal could still go most of the way to the floor. If i pump it two or three times it firms up and can lock the wheels in braking, but after a few seconds it seems to lose pressure and the next push will go most of the way to the floor again. I don't see any leaking fluid, and i haven't had to add any to the reservoir, but obviously i haven't done any real driving to see levels go down slowly. Pedal was totally firm without any issues before i did the caliper rebuild. I've bled a full large bottle of fluid through it, and i'm not getting any bubbles. Could this be from the seals in the master cylinder failing? If not that, what else could it be? Thanks for any input! Quote Link to comment Share on other sites More sharing options...
Dee2 Posted February 21, 2021 Share Posted February 21, 2021 1 hour ago, HRBrat said: Pedal was totally firm without any issues before i did the caliper rebuild. It's unlikely the master cylinder was affected by the repair work. Getting air out of the system can be a bi*ch. Don't ask me how I know. Bleeding system is best done with two people. 1 Quote Link to comment Share on other sites More sharing options...
HRBrat Posted February 21, 2021 Author Share Posted February 21, 2021 It definitely acts like there's air in it. I actually got a new caliper and tried that on it as well, but the pedal feels totally the same. I only do the two person bleeding method, and i've put way more fluid through it than i ever have before or on any other car. It comes out clean and clear, and other than the first few pumps after changing the caliper there haven't been any bubbles. After all of that I gave up and had the local subaru-focused mechanic look at it. They thought it was air too and pumped a ton of fluid through it without any change. They think it's the master cylinder, but they don't have access to parts for it. It kinda feels like just an assumption that it must be the MC on their part, but i don't have any other good explanation. Could the brake booster somehow do this? I hear a small puff of air somewhere centrally around the intake manifold area when the pedal is pushed to the floor. i haven't been able to figure out exactly where it is, but possibly related to the vacuum line to the booster? It seems like even if there was a problem with the booster though it shouldn't make the pedal soft... Quote Link to comment Share on other sites More sharing options...
88SubGL Posted February 21, 2021 Share Posted February 21, 2021 I haven’t heard of this on a Subaru, but I had a master cylinder go bad on my ‘85 Nissan truck. I couldn’t see fluid coming from any where, but I kept having to add small amounts of fluid every now and again. After good amount of time doing this, I started having a problem with the brake booster. The booster felt almost nonexistent. Long story short, I was loosing fluid into the booster it’s self. Couldn’t see it from the outside. The master was bad. Ended up replacing both the booster and the master cylinder and it’s worked great ever since. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted February 21, 2021 Share Posted February 21, 2021 1. Needs bled. I hear it’s been bled a lot - but it’s hard to tell without having done it myself. I’ve seen a number of times when a system is opened like that that they’ll need more than a 32 ounce bottle to get all the air out. Like 2 32 ounces. Not those little useless bottles. if it hasn’t run 60 ounces straight of proper bleeding I wouldn’t rule this out 2. If it’s got any rust the rear lines can leak above the gas tank and you won’t see it for awhile. The rust migrates through layered rust just soaking it and if it drips it hits the top of the gas tank with gobs of dust that soaks it up. Takes awhile to get enough build up to flow over the edge and finally be visible. But I don’t know if you’re in a rusty area Subaru master cylinders fail so rarely that I wouldn’t assume it this early. The one time I swore up and down it had to be a master cylinder i replaced it and same symptoms. It ended up being rust like I described above 1 Quote Link to comment Share on other sites More sharing options...
Ionstorm66 Posted February 22, 2021 Share Posted February 22, 2021 (edited) When a master cylinder fails internally its just like a failed cylinder/caliper, you can push the pedal and it gets hard. Then if you keep holding down it will slowly bleed to the floor. This rarely happens because water is heavier than brake fluid, so the water works its way down into the cylinders/calipers. Easy check for air is if the pedal gets hard, but never stiff. You can keep pushing and pushing, the pedal will keep going. With no air, you can flex the firewall before you can get the pedal to the ground. So much so its a common mod on Subaru to brace the master cylinder to the strut. If you have a hill holder it can be a royal pain to bleed. Have to work the clutch while bleeding. I have a pressure bleeder and it still takes a while. You have to do a crisscross: front right, rear left, front left, rear right if I recall Edited February 22, 2021 by Ionstorm66 Quote Link to comment Share on other sites More sharing options...
HRBrat Posted February 22, 2021 Author Share Posted February 22, 2021 Thanks all, I did the criss cross pattern as described in the Muir book. I did a full 32oz bottle. Not sure how much the shop put through it, but they said it was a ton. I feel like a leak it should initially feel firm when i push but then slowly go to the floor. This is the opposite. Initial push or two go almost to the floor, but after a couple of quick pumps its totally firm and feels like normal. This also came on very suddenly. Didn't have any of this issue before the caliper change and the brakes have always been solid. I'm lucky enough to live in the Northwest where salt hasn't been a thing until last year. The Brat is actually an Alaska vehicle that spent most of it's existence in Fairbanks before coming down this way about five years ago. It's got basically no rust. I'll poke around for bad lines, but it doesn't seem likely to me. In the event that it could be the master cylinder, does anyone know where to get one or a rebuild kit? Quote Link to comment Share on other sites More sharing options...
Dee2 Posted February 22, 2021 Share Posted February 22, 2021 (edited) 8 minutes ago, HRBrat said: In the event that it could be the master cylinder, does anyone know where to get one or a rebuild kit? Rockauto has some replacements units https://www.rockauto.com/en/catalog/subaru,1987,brat,1.8l+h4,1267769,brake/wheel+hub,master+cylinder,1836 Edited February 22, 2021 by Dee2 add link Quote Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted February 22, 2021 Share Posted February 22, 2021 (edited) no brake fluid disappearing or dripping? is this model like some later ones where corroded hardlines might let bf 'pool' on top of the fuel tank or something? Edited February 22, 2021 by 1 Lucky Texan 1 Quote Link to comment Share on other sites More sharing options...
idosubaru Posted February 22, 2021 Share Posted February 22, 2021 You are spot on - If it’s rust free then it’s not probably rust related. Quote Link to comment Share on other sites More sharing options...
HRBrat Posted February 22, 2021 Author Share Posted February 22, 2021 Thanks again! Sadly the RockAuto listing is one of those phantom ones that looks available in the list but as soon as you put it in your cart it says the part isn't available. I was able to find a rebuild kit for sale from SummitRacing. Not much out of pocket to give it a try at least. Quote Link to comment Share on other sites More sharing options...
Rampage Posted February 22, 2021 Share Posted February 22, 2021 1 hour ago, HRBrat said: I was able to find a rebuild kit for sale from SummitRacing. It looks like that kit will take a month for delivery. There are some master cylinders listed here. Quote Link to comment Share on other sites More sharing options...
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