Urgent: Air/Hissing brake pedal after bleeding and installing stainless lines

[ewrjontan]

So after spending a year replacing my clutch, all bushings and suspension, starter, etc with no issues, I finally ran into a problem while attempting to install my stainless brake lines. Purchased some cheap-o flare nut wrenches and ended up rounding the rear lines. I was able to install the line in the rear driver side (hard line to caliper) and both front lines. Unfortunately, I will just have to live with my rubber lines on the rear passenger side until I want to fork out money for new hardlines.

Anyways, I didn't do anything prior to installing the lines; just undid them and let the fluid leak out and replaced them. By the way, the brakes were working perfectly fine prior to this. When I went to bleed the brakes I noticed that my reservoir was empty.

Did not think anything of it. So bled the brakes with my Motiv power bleeder. Everything went well until I ran out of brake fluid. The reservoir was full but my power bleeder was dry (though plenty of fluid in the lines) so I think that was fine. Anyways, wanted to bleed the clutch as well and ended up throwing in some half empty containers (but opened a few months ago) of brake fluid in my bleeder and pumped it through. Bled a full liter and half or so through the calipers and beat the crap out of them with a mallet; seemed to get most if not all of the air out.

Long story short, my clutch pedal feels perfectly fine but my brake pedal makes an air/hissing sound when I press on it. After searching, everything I am seeing is that my brake booster is $%^&. I hope this is not the case, could it potentially be due to the fact that I put old brake fluid in the system which probably has water in it? I am super pissed at myself for doing it but figured I could run it for a bit while breaking in my clutch; did not want to wait since I can't find Motul RBF600 locally.

Any ideas? How much of a pain is it to install a new brake booster?

[TostitoBandito]

I can tell you that it's not the fluid. What you're describing has nothing to do with the quality of the fluid. You could've flushed with old used fluid and it still shouldn't cause any weird noises like that.

I'm no expert, but if you're hearing a hissing it seems like there may be air in the master cylinder. This can happen if you allow your fluid level to drop too low, as you described happening prior to you bleeding (reservoir empty). Either that, or you have a leak someplace, though if that were the case you'd have a puddle of brake fluid.

[ewrjontan]

How can I get the air out of the master cylinder then?

[AJLM34A]

I let my brake system go completely dry when I rebuilt my calipers and replaced my lines. I used a Motive brake bleeder and still had a soft pedal when done. All I had to do is gravity bleed the system one corner at a time, then rebleed with the Motive and pedal was fine.

[nick325xit 5spd]

Hissing is the brake booster.

[tjm3]

First, you're aware that when you do some brake line work you should use some sort of pedal depressor to push the brake pedal down about 1/2-3/4 inch? That pushes the seals past the compensation port in the master cyl so the fluid won't leak out.

Second, is the hissing coming from the master or the brake booster. The booster always makes noises just like that. That's the way they work.

Third, the clutch and brake system are all separate components. The only thing they share is access to the brake fluid reservoir and you'll notice the tap for the clutch master is about halfway up the side of the fluid resorvoir. Why is that? It's really no surprise that the clutch works and the brakes don't after using the same fluid in both.

It's not the SS lines and it's probably not the booster either. Test the booster. Engine off, pump the brake about 5 or 6 times to vent the residual vacuum and keep the pedal down on the last pump. Start the engine with the pedal depressed and if the booster is good it'll pull the pedal even further towards the floor. Of course, this assumes it wasn't on the floor to begin with or that a bad seal in the master allowed fluid to fill up the booster.

If there's air trapped in the master cyl then do a little research on how to get it out. Vacuum type master cyl bench bleeders are best but there's other ways.

[ewrjontan]

I let my brake system go completely dry when I rebuilt my calipers and replaced my lines. I used a Motive brake bleeder and still had a soft pedal when done. All I had to do is gravity bleed the system one corner at a time, then rebleed with the Motive and pedal was fine.

How long did you gravity bleed for?

First, you're aware that when you do some brake line work you should use some sort of pedal depressor to push the brake pedal down about 1/2-3/4 inch? That pushes the seals past the compensation port in the master cyl so the fluid won't leak out.

Second, is the hissing coming from the master or the brake booster. The booster always makes noises just like that. That's the way they work.

Third, the clutch and brake system are all separate components. The only thing they share is access to the brake fluid reservoir and you'll notice the tap for the clutch master is about halfway up the side of the fluid resorvoir. Why is that? It's really no surprise that the clutch works and the brakes don't after using the same fluid in both.

It's not the SS lines and it's probably not the booster either. Test the booster. Engine off, pump the brake about 5 or 6 times to vent the residual vacuum and keep the pedal down on the last pump. Start the engine with the pedal depressed and if the booster is good it'll pull the pedal even further towards the floor. Of course, this assumes it wasn't on the floor to begin with or that a bad seal in the master allowed fluid to fill up the booster.

If there's air trapped in the master cyl then do a little research on how to get it out. Vacuum type master cyl bench bleeders are best but there's other ways.

Thanks for the info. I wish I would have known to push the pedal in but all of the DIY's and youtube videos that I found never mentioned anything about things to do PRIOR to removing the lines :/ Seems to be my master cylinder then. I am seeing a lot of info about clutch master cylinders but very little about the brake mc (specifically pertaining to the e36 platform). Is there any way to bleed the mc with it still in the car? Other than gravity bleed like mentioned above?


I guess I am going to try this:

https://www.youtube.com/watch?v=oi4BnNA3Ep4

[AJLM34A]

How long did you gravity bleed for?

Not too long, about 20 seconds each caliper. I was by myself, if I had someone to help I would have had them slowly push the pedal after I opened the bleeder instead of the pump several times then open bleeder. One thing that helps is to bleed into a clear container with a few inches of clean brake fluid and tube all the way to the bottom. It will allow you to see air bubbles better.

[TostitoBandito]

Don't worry too much about the pedal, it's only to slow fluid leaking out your hoses/fittings while they're disconnected. I accomplished the same thing by vise-gripping my old rubber hoses while I was off rebuilding the calipers. Even without the pedal pressed, I didn't drip too much fluid on myself while changing them. Another trick which I did use was to plastic wrap the top of the brake fluid reservoir and seal it up. If air can't get in then it makes it more difficult for the fluid to drain.

[tjm3]

... I accomplished the same thing by vise-gripping my old rubber hoses while I was off rebuilding the calipers. Even without the pedal pressed, I didn't drip too much fluid on myself while changing them. Another trick which I did use was to plastic wrap the top of the brake fluid reservoir and seal it up. If air can't get in then it makes it more difficult for the fluid to drain.

The first is guaranteed to damage the inside of the hose that's supposed to contain upwards of 1500-2500psi brake fluid pressure. Not a smart idea, and if you do this with SS lines with the teflon liner then smart is just a vague concept.

All of the reservoirs used in the last 40 years are made airtight in the fluid chamber. Otherwise your brake fluid would get trashed in about an hour on a humid day. Look up 'hygroscopic' . Also, ever notice the little neoprene/vinyl bellows under the caps? Guess what that's for?

Unfortunately, people are using this forum and it's information as a 'how-to-do-it' source where it's more relevant to use it as 'don't-do-it-this-way' info like they should instead.

[hc1001]

When i have to remove a caliper, i remove it with the line and plug the hardline with a rubber cap. I have a whole bunch of different ones i found laying around that came with parts like my stoptech BBK, clutch slave cylinder, etc...

And yea, just dont open the reservoir so the system remains closed.

I also use vise grips on the hard to break/rounded hardline fittings.

[TostitoBandito]

The first is guaranteed to damage the inside of the hose that's supposed to contain upwards of 1500-2500psi brake fluid pressure. Not a smart idea, and if you do this with SS lines with the teflon liner then smart is just a vague concept.

Why exactly should I care about damaging my OLD brake lines? The ones being replaced with steel? Sorry if I wasn't clear about that. Obviously you don't want to clamp any brake line you intend on using.

[ewrjontan]

Ok so I am lost. I ended up trying to bleed the MC from in the car (as shown in this video https://www.youtube.com/watch?v=oi4BnNA3Ep4) and re-bled the calipers. Seemed to work a little bit...the hissing noise was gone but the pedal was not holding pressure; if I press the brakes the pedal slowly goes down more. From what I am reading, it sounds like there is an internal leak in my master cylinder. Does that sound right? I ended up pulling it off to see if I can just bench bleed it before buying a new one but I am super confused as to how you bench bleed.

In all of the videos I have seen, people fill the reservoir, run some hoses from the two brake line holes back into the reservoir. Then you pump. However, the cylinder has three ports on it. If I were to bench bleed as described, am I supposed to plug the reservoir holes then?

I also read that you can submerge the MC in brake fluid and just pump until no more bubbles come out. Sounds good. However, either way I do this...how the heck do you prevent air from getting back into the MC when installing? Once you remove the MC from the tub of brake fluid...won't all of the fluid just leak right out? How the heck can you not re-introduce air back into it?

Does it sound like I have a leak and should I just go ahead and grab a new one?

Also how the heck would my MC just kick the bucket just from running it dry? It's not like I pumped the brakes with it dry. Once I got done installing my lines I fill the reservoir and bled the calipers. I'm so mad that I have yet again wasted more expensive brake fluid just to install stainless lines :/

[AJLM34A]

If your brake system worked fine before you installed new brake lines, I would focus on air in the system. There is a post within the last few months about the bleeder valve on the abs pump and being able to get all the air out that way.

Put everything back together, focus on 1 corner at a time. Buy several quarts of DOT 3 fluid and get someone to help you bleed the old ways; either pump several times and hold, or you open the bleeder, have them slowly push the pedal down while you have the tube in a clear container with 3" of fluid in it. With a good LED light watch for bubbles, then you close the bleeder; repeat until there is no more bubbles, then move to another caliper.

[ewrjontan]

Don't you mean Dot 4? Well, I just went ahead and bought a remanufactured master. Hope fully that works. In regards to bleeding it though...bench bleed, submerge it?? How do I prevent leaks? Even if I cap it, once I try to install the lines, isn't the fluid going to seep out and take in air? Or will the fluid seeping out prevent air from coming in?

[ewrjontan]

So, the best way to bleed the cylinder? Do I just submerge it in fluid, cap it off, then get the lines back on? I figure I will just follow this (at 2:35) if no one else chimes in.

https://www.youtube.com/watch?v=Uz4OwuUGVOA

Also, with the master cylinder having been disconnected...do I need to worry at all about the ABS pump? I don't want to go on breaking even more shit

[BrianJ]

I’d recommend bench bleeding. Kit will come with plugs. Here’s a good tutorial. https://youtu.be/7rImn6nJ4Dw

And for god’s sake....don’t listen to Scotty Kilmer. Annoying as hell.

[ewrjontan]

Probably one of the better videos I have seen. I still don't understand though, when you remove the fittings to connect your brake lines, wouldn't you end up introducing air into the system?

[BrianJ]

It’ll leak as you install the lines. But the loss is minimal. Watch the reservoir as you reinstall the lines to ensure it doesn’t run dry.

[TostitoBandito]

Yeah, you won't lose more than a couple ounces unless you really take forever. Just do one line at a time and check the reservoir after each to make sure there's fluid in it. Any air from the new empty lines will be purged once you bleed all four corners.

[ewrjontan]

Installed the new master (without bench bleeding) and still had a sinking pedal. Ended up squirting some soap/water on my lines to check for leaks. Ended up finding a slight leak with one of my master cylinder fittings and tightened up the rest of my lines. Re-bled the traditional way with a friend and brakes work fine now.


Curious if my old master cylinder was actually bad or not :/