[Asheahan01]

Hi all, I need some help with my brakes.

My '83 Spider Veloce lost it's brakes while driving today. The pressure slowly went down until I couldn't brake at all (over the course of ~5 miles or 10 minutes of backroad driving). I puttered into work using my parking brake.

The brake pedal regained it's stiffness for a short time while sitting in the parking lot. Continuous pumping revealed air bubbles coming up through the rear of the fluid reservoir when letting off of the break. A buddy held the reservoir down tight and I pumped the brakes again with fewer bubbles coming through. Also, there were no leaks until after securing the reservoir down with a pipe clamp, at which point the bubbles nearly stopped, but fluid very slowly dripped down from the middle of the master cylinder where it meets the booster(? idk the big round thing's name) after pumping the pedal hard.

Our hypothesis: the rear O-ring on the fluid reservoir has dry rotted and needs to be replaced. I've heard of replacing these, but I genuinely have no idea how to get the reservoir off of the car without breaking it! Is there a way to remove the brake fluid reservoir without taking off/replacing the whole master brake cylinder? Any other suggestions for where I should check?

 

[Andrew]

They rot in the air and ozone and heat. You pry the reservoir off with a big screwdriver or pry bar. If the seals are perished it should come out readily. You can get new seals by themselves, but if they're that old I'd sure question the state of the brake MC. And you're going to need to bleed, most likely, so replace?
Andrew

 

[Asheahan01]

They rot in the air and ozone and heat. You pry the reservoir off with a big screwdriver or pry bar. If the seals are perished it should come out readily. You can get new seals by themselves, but if they're that old I'd sure question the state of the brake MC. And you're going to need to bleed, most likely, so replace?
Andrew

Thanks Andrew! I've found the grommets on Centerline for $17, so i'll definitely try those first. I have heard of kits to replace the internal o-rings. Do you know where I could find one of those? The kit on centerline only shows boxes, so I'm not sure what I'm getting if I ordered that one.

 

[Andrew]

That's totally different. The rubbers on top are on the gravity side, sealing the reservoir to the master cylinder. The o-rings inside, you're rebuilding the master cylinder. If you haven't done it before I wouldn't start now. I'd buy a new MC, install, bleed. Watch out for the o-ring on the end of the MC that seals the vacuum into the booster. And look in the booster for any fluid, having maybe leaked out of the MC into it.
Bleed afterwards. You know how to do all this?
Andrew

 

[Asheahan01]

Okay. I do know how to do all of it except for looking inside the booster (I assume I look through where the MC is?) Attached are some images (sorry for the blur, but you guys understand). Would finding an o-ring to replace the seal at the booster be an option? I also think the rubbers on top are bad because the brake reservoir wiggles pretty easily compared to the new trans fluid reservoir.

 

[Asheahan01]

Note that the zip-tie is not permanent, but it did seal the system by putting pressure on the reservoir, thus it allowed me to drive home

 

[bianchi2]

Okay. I do know how to do all of it except for looking inside the booster (I assume I look through where the MC is?) Attached are some images (sorry for the blur, but you guys understand). Would finding an o-ring to replace the seal at the booster be an option? I also think the rubbers on top are bad because the brake reservoir wiggles pretty easily compared to the new trans fluid reservoir.
View attachment 1697359 View attachment 1697360

the photos are why on things that can rust, and are importand.. i give it a 2 quick shots of black spray paint.. keeps the rust off the parts, and keep any rust from migrating into the threads

 

[Asheahan01]

Hi all,
Brake master cylinder replacement went well, but bleeding is a pain. I emptied the old fluid out of the lines when I replaced the MC. don’t have any special tools, and for whatever reason I am unable to get fluid to any calipers except the front drivers side. Can someone please send some instructions? Everything I’ve tried from experience and YouTube has not helped. Stumped.

 

[Gubi]

Bleed at the master. Fill the reservoir and crack open the three line fittings (just loosen until the tube is loose, no need to remove them fully). When you get steady fluid out off each one, close it up. Then you should be able to bleed at the wheels.

 

[Asheahan01]

Should I pump the MC with the lines open? I’ve been doing this: crack lines, push pedal and hold, close lines, release pedal and repeat

 

[Gubi]

I've never had to. I just leave them open until I get fluid out with the pedal up.

Once that's done you can gravity bleed to make your life easier. Just open the bleeders at the wheels and let it sit until you're getting fluid out of them, then close. Keep the reservoir filled while you do this. This'll fill the lines and make the final bleed with the pedal faster and easier.

Honestly a Motive pressure bleeder makes the job infinitely easier and I'd recommend one if you plan on doing this again.

 

[Asheahan01]

Alright. I’ve been at it for about 5 hours now so I’m gonna pack it for today. My stomach’s calling, lol. I’ll be working on it again on Saturday. Thank you very much for the advice!

 

[Gubi]

I’ve found that, when I get stuck, if I walk away and come back to it later or the next day, things usually go much better.

I’m pretty certain you’ve just got air in the MC. LF wheel feeds from the bottom of the MC so that’s why that one is getting fluid. Just loosen the other two and let them self bleed, then gravity bleed for a bit and it should all start magically working.

 

[Asheahan01]

Agreed, getting the air out is always tricky. For my case, the “self bleed” means letting fluid run through the two ports on the side of the MC without pushing the pedal, correct?

I might try jacking the side with the brake fittings up to get the air to travel out, too. I used this on a friend’s radiator once because his driveway was slanted… hmm. I’ll keep the thread updated.

 

[Gubi]

Yes, just open the ports and don't push the pedal: make sure it is all the way up. No need to jack up that side: if you look at the MC you'll see that the side ports connect to the top center of the cylinder bore. The air will come out fine with the car level. Then let it gravity bleed a bit to fill the lines to the calipers.

 

[Asheahan01]

Yes, just open the ports and don't push the pedal: make sure it is all the way up. No need to jack up that side: if you look at the MC you'll see that the side ports connect to the top center of the cylinder bore. The air will come out fine with the car level. Then let it gravity bleed a bit to fill the lines to the calipers.

Got it, thanks!

 

[Asheahan01]

Still no luck. I even tried putting a small vacuum on the passenger rear caliper and couldn’t pull any fluid through. I’m gonna try bench bleeding the MC inside of the car, but another question I have for that is this: once I bleed it and reattach the brake lines, how will I get fluid into the return line? Won’t it just re-introduce air into the system if I attach it without fluid inside?

 

[Gubi]

Okay, that's weird. So what exactly happened: you opened the ports on the master with a full reservoir and no fluid came out? Or fluid came out at the master but you're still not getting any to the wheels?

Is it possible your booster pin is misadjusted? If that's too long it could be pushing on the MC piston to the point where the openings to the reservoir are blocked. Usually you can just swap the MC without having to adjust that, but maybe the new MC is made differently?

Long shot but I don't really have any other brilliant ideas. Maybe loosen the MC at the booster, pull it slightly away, and see if that makes a difference?

I bleed it and reattach the brake lines, how will I get fluid into the return line? Won’t it just re-introduce air into the system if I attach it without fluid inside?

Not sure what you mean by "return line"? There isn't a return line, there's just the three brake lines: one for each front wheel and one serving both rear wheels.

 

[Asheahan01]

Fluid came out of the MC, but not at the calipers. How steady is a steady amount, because I was getting a steady but slow drip from the MC, but not enough to form a single stream. Also, if I’m just getting drips, how do I get more out? I do have a bleeding kit but it only has one correct fitting.

I decided to take the brake fluid and lines out of the MC and restart. I didn’t adjust the pin when removing the old cylinder, and I made sure they matched before putting the new one on. I’ll check that again though.

Not sure what you mean by "return line"? There isn't a return line, there's just the three brake lines: one for each front wheel and one serving both rear wheels.

Typo: I meant rear line, not return, sorry.

update: I took the rear line off just now And no fluid came out. The reservoir has fluid in it on that side still

 

[Gubi]

That doesn't seem right at all. Pull the MC away from the booster, see if you get flow.