Mushy Brakes - mystery???

CL65 Captain

CL65 Captain

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Joined
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I have a mystery....

Car has mushy brakes, I mean real mushy. Not talking about pad bite. Pedal travel is 3+ inches before I even get pressure (almost to the bottom of pedal travel), and pumping them does not bring up pressure.

Here is what I have tried.

New pads (OEM).
Inspected calipers for leaks including the piston seals - bone dry.
Inspected Dali SS lines and no leaks - bone dry.
New Master Cylinder (OEM).
Complete flush of the hydraulic fluid - and bleed, bleed, bleed.
Removed my Speedbleeders and vacuum bled all calipers with OEM bleed screws.
Removed, cleaned and regreassed all the caliper slide pins.

I have bled, both manually and by vacuum - several times and there are no more air bubbles - NONE. I flushed 6 32oz bottles of fluid through the system to make sure.

I went out and exercised the ABS and then re-bled the system - no air.

The only thing I haven't tried is changing out the Dali SS lines, but they aren't leaking as they are dry and if they were leaking they would also let air in and the system is bleeding with no air bubbles at all now. As well, I would think that a leak would cause an "open" system and pedal pressure would not hold and would decrease - it doesn't.

The pedal holds pressure. With the car off, you can pump them up firm. Turn the car on it drops about 1/2" like normal. However, when you drive there is WAY too much pedal travel and it feels real mushy with all braking force coming at almost the end of the pedal travel. It holds pressure, so there doesn't seem to be a leak. Yes, I know that NSXs have a little travel at the beginning - I've own this car for 5+ years. However, this is ALOT of travel and definitely not even close to normal.

And yes, I know... bleed. I did and did and did and believe me after pushing 6 large bottles of fluid through - it's bled.

I am at my wits end with this. The only thing I haven't tried is replacing the Dali SS lines - but I can't see that being the issue. I hate to spend $100 to replace SS lines with new SS lines for nothing. I am going to try and take them apart at the caliper and inspect them. However, the process of elimination leaves the lines as the only thing I haven't replaced yet.

???????????????????? :confused:
 
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What fluid are you using? I tried a performance brake fluid (Motul) and my pedal felt mushy afterwards. I bled the system a few times and still no improvement. Finally, I bled all the Motul out, put in fresh Honda brake fluid and the pedal pressure came right back. I'm done with aftermarket brake fluid. Having tracked my former NSX (not my current one yet) many times, Honda fluid works the best for me.
 
Vytas said:
What fluid are you using? I tried a performance brake fluid (Motul) and my pedal felt mushy afterwards. I bled the system a few times and still no improvement. Finally, I bled all the Motul out, put in fresh Honda brake fluid and the pedal pressure came right back. I'm done with aftermarket brake fluid. Having tracked my former NSX (not my current one yet) many times, Honda fluid works the best for me.
Click to expand...

Yea, Honda fluid is not an option. The car is tracked often.

I was running ATE Blue and flushed with cheap Autozone Dot 4. I am waiting for more ATE Blue. The results were the same with both fluids. Fluid may have a very small effect, but not the dramatic effect that I am experiencing.

The more I think about it, the more I think it might be my SS brake lines. I change pads often and sometimes at the track. Let's say I haven't always hung the calipers up by a wire when changing pads (usually I can set the fronts on top of my giant Dali air deflectors) and I am sure they have been stretched a time or ten. :redface: Perhaps, over the course of the last two years they have been on the car - 20+ pad swaps, they have been stretched a bit. Only one way to find out - new SOS lines.
 
just as a data point - my car with stock calipers (but big rotors), motul 600, ss lines, and hawk pads has excellent pedal feel, the best i've felt on any car i've driven. when i ran hp+ f/r during street use it was the same cold or hot, with ht10 up front it's a tad soft when cold but firms up nicely once heat is added.
 
Check to see if the distance from the brake pedal to the floor is the recommended 8.58 inches. If it's more than that you can make the adjustments to correct it. My point being is that maybe you have too much pedal travel before your master is being engaged. There are no leaks, the booster and check valve seem to be working as they should and the system is properly bled. You've got me stumped. I've never had a brake line swell on me so if that's it, it seems it would be very unusual. Good Luck and let us know.
 
Check anything that can mess up the alignment with the rotor and the caliper. It doesn't take much at all!

For example a bad wheel bearing, lose caliper mount or something fractured.

Possibly something (debris, pebble, imperfection) on one of the hubs that is causing the rotor to be eccentric in relation to the caliper.

You might even try put the car on a rack and turning the tires to see which one causes the mush.

good luck

Drew
 
Ya know, I seem to recall running into a similar problem back when I used to wrench for a living. Stuck bias/proportioning valve comes to mind but it was so long ago(20+ years ago) I can't be sure. Don't have an NSX service manual yet to look at but it might be something you might want to look into.
 
or simply the o-rings are beginning to leak by- you don't get enaugh pressure with the car off but once you turn it on and power assist comes on then the fluid passes by. how old is your master cylinder?

my bad- i see it you changed it.
 
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swerve said:
or simply the o-rings are beginning to leak by- you don't get enaugh pressure with the car off but once you turn it on and power assist comes on then the fluid passes by. how old is your master cylinder?
Click to expand...

First post says it's a new oem master cylinder. I am running Motul w/ my Brembo setup and no issues. I don't think it's the brake fluid nor the bleeding. Go with the lines. Sounds like they've been through a lot anyway so wouldn't hurt to replace them as preventive maintenance/safety.

Jeff
 
After you replace the brake lines, you can also try moderately tapping the calipers with a rubber mallet when you're bleeding to hopefully "jiggle" and release any small air bubbles around the piston/s.

I'm not sure if that technique helped me a lot when I deleted my ABS, but my pedal is rock solid and has been recommended on here before.
 
A terminology issue to discuss first. There are the metal "fixed in place" brake lines, and then there are the flexible rubber brake hoses that go from the calipers to the body, where they attach to the metal brake lines.

Those flexible hoses can weaken internally then balloon out under pressure.

Are the "Dali SS Lines" the flexible hoses? I haven't seen their product, but to flex their interior most likely is rubber (or a flexible synthetic), with the SS protecting the lines from abrasion and rupturing.

I just had the opposite problem on one of my cars. A metal clamp, that completely surrounds a 2" section of hose and anchors the hose at mid point, rusted internally. The net result is it choked off the hose so no pressure got to the caliper. But the pedal was nice and firm.:biggrin:
(I cut apart the old hose out of curiousity to find out what what blocking it. I had never run across a blocked line or hose before.)

It would not take much ballooning to cause your problem. Perhaps you can have someone push on the pedal while you wrap your hand around each hose and check for any ballooning.

I hope this helps, and good luck. Problems like this can be quite frustrating!:eek::eek:
 
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ftuhy said:
A terminology issue to discuss first. There are the metal "fixed in place" brake lines, and then there are the flexible rubber brake hoses that go from the calipers to the body, where they attach to the metal brake lines.

Those flexible hoses can weaken internally then balloon out under pressure.

Are the "Dali SS Lines" the flexible hoses? I haven't seen their product, but to flex their interior must still be rubber, with the SS preventing the lines from abrasion and rupturing.

I just had the opposite problem on one of my cars. A metal clamp, that completely surrounds a 2" section of hose and anchors the hose at mid point, rusted internally. The net result is it choked off the hose so no pressure got to the caliper. But the pedal was nice and firm.:biggrin:
(I cut apart the old hose out of curiousity to find out what what blocking it. I had never run across a blocked line or hose before.)

It would not take much ballooning to cause your problem. Perhaps you can have someone push on the pedal while you wrap your hand around each hose and check for any ballooning.

Good luck. Problems like this can be quite frustrating!:eek::eek:
Click to expand...

Yes the Dali lines are the soft lines that run from the hard line to the caliper. They are rubber lines with a stainless steel braded exterior and clear vinyl sleeve on top of that.

I just ordered a new set and will see if that fixes the problem.
 
That's a really strange problem. Though, I don't see how much the SS lines can swell with the steel braiding? If you have a firm pedal without power assist and a mushy pedal with it, it sure sounds like a master cylinder issue, as swerve said. Maybe you got a bad new cylinder? Makes me wonder about my new clutch master and slave... :frown:
 
Honcho said:
That's a really strange problem. Though, I don't see how much the SS lines can swell with the steel braiding? If you have a firm pedal without power assist and a mushy pedal with it, it sure sounds like a master cylinder issue, as swerve said. Maybe you got a bad new cylinder? Makes me wonder about my new clutch master and slave... :frown:
Click to expand...


No, if the master was bad it would loose pressure at the bottom of the pedal travel. Same, if I had a leak. It holds pressure fine.

I think the problem may lie when I was not careful over the years when changing pads (often) and maybe stretched them. If you stretch a rubber hose enough it might have some elasticity allowing them to balloon. Usually air in the line will cause the same symptoms that I am experiencing with one exception - when you pump the brakes, the pressure comes back up. If the line is ballooning, then each time I pump the brake, it balloons out absorbing the hydraulic compression - causing a mushy feel. Will find out next week when the new lines arrive.
 
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CL65 Captain said:
No, if the master was bad it would loose pressure at the bottom of the pedal travel. Same, if I had a leak. It holds pressure fine.

I think the problem may lie when I was not careful over the years when changing pads (often) and maybe stretched them. If you stretch a rubber hose enough it might have some elasticity allowing them to balloon. Usually air in the line will cause the same symptoms that I am experiencing with one exception - when you pump the brakes, the pressure comes back up. If the line is ballooning, then each time I pump the brake, it balloons out absorbing the hydraulic compression - causing a mushy feel. Will find out next week when the new lines arrive.
Click to expand...

Does car pull when brakes are applied ?
 
Just a wild guesses here, but on my Subaru the master cylinder needs to be bled seperately if it runs dry. There is a whole different process to do this, one which normal bleeds at the caliper wouldn't fix. Also the ABS system on the STI requires a seperate bleed. Just ignore me if none of this is relevant to the NSX, but I bet you'd try witchcraft if you thought it would help at this point.

Did you ever had a good pedal with the new master cylinder?

Be careful about removing play from the brake pedal. I over did it once and the pads dragged when they got hot (on track)-- then they got really, really, really hot and ruined the rotors.
 
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nsx2tall said:
Just a wild guesses here, but on my Subaru the master cylinder needs to be bled seperately if it runs dry. There is a whole different process to do this, one which normal bleeds at the caliper wouldn't fix. Also the ABS system on the STI requires a seperate bleed. Just ignore me if none of this is relevant to the NSX, but I bet you'd try witchcraft if you thought it would help at this point.

Did you ever had a good pedal with the new master cylinder?

Be careful about removing play from the brake pedal. I over did it once and the pads dragged when they got hot (on track)-- then they got really, really, really hot and ruined the rotors.
Click to expand...

I bench bled the master before install. ABS on 97+ is not a separate system like the early models - it self bleeds anyway and is working since I purposedly went out and activated it a few times.
 
Just throwing this out there as it seems you've already tried everything else...

At one of our 12hr enduro races a few years ago, the brakes suddenly went mushy as well. Bled the system, didn't fix the problem.

Long story short, it ended up being BAD shims - the thin medal piece that sits behind the pads that usually cause squeeling if you don't apply anti-squeek compound on them.

We removed them completely and it fixed the problem.
 
C-speed said:
Just throwing this out there as it seems you've already tried everything else...

At one of our 12hr enduro races a few years ago, the brakes suddenly went mushy as well. Bled the system, didn't fix the problem.

Long story short, it ended up being BAD shims - the thin medal piece that sits behind the pads that usually cause squeeling if you don't apply anti-squeek compound on them.

We removed them completely and it fixed the problem.
Click to expand...

Not running shims. :)

New brake lines should be here next week ~ the only thing yet I haven't tried.
 
CL65 Captain said:
Not running shims. :)

New brake lines should be here next week ~ the only thing yet I haven't tried.
Click to expand...

I highly doubt brake lines would cause the symptoms you're having - you would have seen obvious signs of damage... ie: swelling, leaking.

Have you checked for a seized caliper piston?
 
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CL65 Captain said:
yep. Pulled off all the calipers. All pistons retracted and extended back when I changed my track pads back to new OEM pads.
Click to expand...

Ok.. but you did physically check their movement with everything installed? ie: have someone pump the brakes and you physically put your hand on the caliper/slider and look and see if the caliper is flexing/pads are biting.

You may discover something by doing that as the calipers may appear fine on the bench. One caliper may not be reacting/moving... Stuck piston(s), bad prop valve, debris/blockage in one of the lines leading to the caliper, stuck slider(s), bad MC, etc etc.

Also, dumb question, but I've seen it done before.. you do have the calipers installed on the correct side right? ie: bleed nipple on the TOP side?
 
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