circuswings

Full fluid change when I had the SS lines put in. No change in brake feel - still mushy.

Does anyone know how to isolate the issue to the MC or brake booster - any tests I can do to see if there's internal leakage in the MC or a bad vacuum line to the booster?

Bill Dearborn

If you are driving on the street DOT3 fluid is fine. If you are driving on the track you want a fluid with a high (550+ degree) dry boiling point that is flushed through the system no more than 10 days before the event. That can be a DOT 3 or 4 depending on the manufacturer.

What Z06 model do you have? Yes most dealers have pressure bleeders as they reduce the time and manpower to do the bleeding. However, two person pump and hold bleeding works just as well Gravity bleeding works well unless they are doing the Tech II ABS bleed procedure which more than likely works best with some sort of vacuum or pressure being applied through a tool or pumping the pedal.

When you installed the brake lines did the master cylinder reservoir go dry? If so it is possible air got in the brake pressure modulator valve and the ABS Automated bleed with the Tech II might need to be done.

Bill

ralphsmithiii

My Z is the 2LZ model. I didn't put new lines in myself just new rotors and pad-lets. When I got my first oil change (since owning the car 2 years ago) the dealership told me my car was in mint condition for being an 07 with 36k on the clock. Their only recommendation was to have the brake fluid changed as they said there was metallic material in it(?). At first, it seemed like a quick way for them to get another $99 out of me so I passed.

Now, 16K miles later and a new set of rotors/pads I'm sure the fluid is overdue. However, I have a feeling that there's air in the abs system somewhere or the abs sensors or module is bad although it doesn't show in the DIC. My reasoning behind it is that about a month after I bought the car, I replaced the entire stereo system and my battery went dead due to have it disconnected for several days. I went to push start the car and when the tried to start, it bucked for a second and never fired up. Shortly after I jumped it with cables but noticed an ABS module warning in the DIC that was on (maybe something about replacing or servicing it). I immediately shut the car down and let it sit for 5 minutes. Started it back up and no more ABS warning.

However, I never noticed any difference in the braking after but I think that's because I never really had to brake hard during the next several months and didn't drive it much. So, I'm now wondering if during that short bucking of trying to push start the car if something was damaged electronically or if somehow air got into the system when I jammed the brakes on to stop the car from rolling although the car never really fired up.

Although I don't mind spending the time to gravity bleed it myself, I'm thinking it may just be more cost effective and less time consuming to have the same dealership who changes the oil change the fluid and test the system.

circuswings

Possibly worth nothing - when I'm at a stop, if I repeatedly press the brake pedal it gets progressively mushier. Relatively quickly so. I've never experienced this in any other car. Does this point towards any particular component?

DSteck

Just as an update... After replacing the master cylinder, there has been no improvement. I'm at a loss because everything in the vehicle is new.

Dr.Ron

Finally after 3 years!! lol Just kidding!

I really hope you get it sorted out....Since you changed every thing already, maybe it IS a vacuum issue of some sort.

For reference, I had Motul fluid put in to replace the stock fluid at a friend's shop, and we used a tech 2....Afterwards, the car felt better, but I was slightly underwhelmed. 2011 Carbon Edition Z06.

Fast forward to last weekend,and I did another swap with my Motive bleeder and Motul fluid. When I took the car out and did some hard stops from 35-40mph to 5mph, I literally got nauseous to the point I had to stop doing it from the g-forces I was experiencing during the braking....That never happened before...And the ABS was activating almost every time also. I have better braking than ever now!

Ron

0Anthony @ LGMotorsports

I'm taking the short road here....so forgive me if I missed something.


Cliff notes.
-car has stainless lines
-new master
-9000 bottles of fluid through it
-no leaks
-big cam


Have you checked the booster itself? Also with that, made sure there is no vac. leak with it? Not sure what you are pulling for vac. but that can effect it, but they typically get a hard pedal with that and not much stopping power.

How much abuse have the calipers been through? Even the C6Z if the calipers have been pushed hard enough you can get flex in the caliper itself and generally it will never get a good pedal again until the calipers have been replaced.

Is there a leak at the caliper piston seals?

What brake pads? I know this sounds stupid but there is a compressibility factor with the pads. Also if they have some sort 'sound insulator' that can play a role in giving some negative feed back.

Bill Dearborn

I lost track of this thread until Anthony brought it back up. Based on this comment it looks like at the time of the post you hadn't had the brakes bled with while using the Tech 2 to run the valves in the BPMV. Since you didn't install the brake lines yourself you can't be sure air didn't get into the BPMV while they were off the car. Having fought getting new stainless lines screwed onto the ends of the hard brake lines at each corner of my car I know what can happen when you get frustrated with things that aren't working like they should and lose track of the amount of fluid that is draining past your hands and onto the floor.

Push starting the car won't damage anything in the ABS unless you do some serious physical damage to the car which would be very obvious.

Have you resolved the issue yet?

Bill

DSteck

Admittedly the booster has not been replaced. It could be an issue, but with the engine off, if you pump up the pedal and hold your foot down, you can depress it to the stop eventually.

I have 50kPa at idle and 62kPa in gear. I've had Z06s with 72-74kPa at idle that still have a good pedal.

I had the calipers rebuilt when they were powder coated. This issue has existed since before then. I run two piece rotors with Coleman rings and Carbotech pads (521s or something like that).

If the booster was leaking, I could see having a hard pedal. The problem is I never get a hard pedal though. It's very soft (enough that I can hit the mechanical stop with ease while engine is running), and there really isn't any feedback from the brakes. When they were first installed, I went out and did about thirty 60-10 braking events, slowly increasing the pedal effort. If I get them hot, they'll get some feedback. Something isn't right though. The braking ability is nowhere near what it was when the car was new. It'll still trigger the ABS, but it used to do it immediately if I slammed on the brakes.

I'm going to try a couple more ABS bleeds. After that, I may just roll a hand grenade under the car.

Bill Dearborn

Are you using any heat shields between the pads and the caliper pistons? I put some titanium heat shields between the rear caliper pistons and the pads and had the problem you are describing. Did all sorts of things trying to resolve it. When I finally pulled the shields out the problem went away.

Bill

DSteck

No. They are the pads as they come out of the box

0Anthony @ LGMotorsports

Which is one major reason I don't like using them. The only time we had to resort to anything like that was at Long Beach...but never on the rears, it was always the fronts as they see the most heat and the most abuse.

That leads into part of what I was getting into with the pad compressibility. A pad itself can be softer or harder, and in some cases you can feel that back in the pedal, others you might not. Now when you go and stack something in there like a Ti shim they typically are not 100% flat against the piston and the pads so they take up some room and just like pad knock back it will give you a soft pedal.

If you absolutely have to use them to keep it from burning the brakes up, not much you can do but other than that, I try to stay away from it.

Any dirt or anything behind the rotor hat that might not let it sit flat against the wheel bearing and cause the rotor to rock or move around?


As for pushing the pedal all the way down, Any stock car if you push long enough you can hit the stop...or I have been able to on all the Vette's I have owned when the engine is off. If you keep pumping it should keep moving the pedal up though.

Bill Dearborn

I assume you mean you didn't add any aftermarket shields or spacers between the pads and the pistons. Pads as they come out of the box could be said when shields or spacers are used.

Bill

DSteck

No spacers, shields, or unicorn blood.

0Anthony @ LGMotorsports

Well that's the problem right there...no unicorn blood.

avizandum

Chasing the same symptoms as OP. I do have Ti shields. Did you modify and keep them, or ditch them altogether?

Update: Twenty minute job to get an inch of pedal back and free!

circuswings

Seemed like this was solved by fixing a leak between the TB and the intake manifold. Needed to bring revs up a bit to get some initial brake pressure but it's been fine driving around.

Autocrossed the car last weekend and would have intermittent braking issues. Issues were on braking sections into hairpins where I'd pretty much be briefly WOT to near redline and then hard on the brakes. Basically seemed like after going WOT I had to wait a bit to get back on the brakes. Maybe a vacuum issue related to going from WOT to off throttle? Car has a big cam, heads, intake manifold. Also running a 335/30-18 square tire setup.

Coach62

I've got some extra that I'll make you a great deal on, friends and family rates here.