Some odd brake issues.

Chris_Red_V8 · Jun 17, 2007

As usual for one of my "bleep! whats wrong?" threads, format is setup, sympton, diagnosis

Setup:
Front - Cobra calipers, 13" vented/slotted rotors, Hawk HPS, Stoptech stainless lines. No uneven wear or glazing

Rear - GT calipers, modded GT brackets, Cobra endplates, cobra 11.65 rotors, oem cobra pads, stock lines, new abs rings and sensors. No uneven wear. New parking brake cables.

Stock MC/Booster
ABS
Fluid flushed and bled yesterday.

Symptoms: Pedal is mushy, even after a bleed/complete flush (although I had a shop do the work, so I should check under the cap and also bleed a bit out myself to check for air and color, because it still feels like air in the system.

The pedal is firmer, but braking response is slow, and right before it comes to a stop, the pedal drops in a good bit in pressure and height (good bit being noticeably wrong). All the hardware seems to be secured, although one of the clips on the rear calipers seems to be bent a bit, the caliper has even wear on its rotor and pads, however. hoses are all ok, and no leaks in the system. Another interesting issue is that now when braking the parking brake light comes on. The parking brake was just repaired with new lines, and the handle is firm when you lift immediately, but I don't believe its dragging.

I thought about just getting all new hardware for the fronts and rears (just service hardware like anti-rattle clips, slide pins and etc), and having the shop rebleed the system, but just seems like this setup should perform much better than it does.

BlownFiveLiter · Jun 17, 2007

A mushy/spongy pedal is a good indicator that there's still some air trapped in the system. It could also be from bad brake fluid, but you should definitely have a very firm pedal. I just swapped to Cobra fronts within the past few weeks and the pedal seemed almost hard at first, even with the brake booster. Took some getting used to for sure.

poboys 94 · Jun 17, 2007

I would take it back to the shop or find a shop that has a brake flush machine cause it sounds like you got air trapped somewhere. When I was wrenching we had a neat machine that had 4 see thru plastic hoses and attached to the bleeder screws and it would suck all the air/dirty fluid out as new fluid was being added in the master and simply watched the hoses. Also make sure the metering valve in the combination valve isnt sticking, a few slight taps with a small hammer has done the trick for me.

go-stang5.0 · Jun 18, 2007

I agree sounds like air in the system still. Ask them how they bled the system...did they pump out all the old stuff (dry system) or did they keep the MC full by adding fresh brake fluid when it got low. Depending on how they did it...there could be air in the proportioning valve (light hammoer taps as mentiuoned before works). Also, there may be air in your ABS HCU (hydraulic control unit)...once air gets in there simple bleeding wont get it out. You have to hook up a scan tool and tell the cpu/ABS to cycle the HCU to get the air out of it. I have heard of someone driving and braking really hard to lock up the wheels so that the ABS kicks on to get the hcu pumping to remove the air from it...then bleed till the air comes out. But that may or may not be true...and its useless if you cant get the brakes to lock up because theres so much air in there. Plus its pretty unsafe. But yea if the shop bled the system ask them how they did it and tell them to check these things because it seems there doing bad work and you shouldent have to fix a problem they caused.

Aslo when you brake and the brake light comes on: Its either the hand brake is on/loose connection there...or (more likely) your MC is low on fluid (that also causes the light to come on). If the MC is low but not super low on fluid, the light will come on when you brake because all the fluid in there rushes to the front of the resovior tripping the light. When you let off the brake pedal and the fluid goes back to its normal "flat" level in the MC the light turns off.

So there you go....

94-302-vert · Jun 18, 2007

I question the master cylinder and/or the booster since you are saying the pedal drops right bwfore the car actually stops...

go-stang5.0 · Jun 18, 2007

Oh I missed that part. Yea even if theres air in the sys. the pedal shouldent drop to the floor. I dont know hw this could be a booster issue. All that would do is make the pedal really hard right, since there will be no assist? I agree with the mastercylinder part tho....you may want to inspect that.

WHITE94COBRA · Jun 18, 2007

When you put the new lines on did you let it gravity feed the new lines? What I mean is hook up the new line on top, leave the bottom off the caliper and let gravity draw fluid through the new line. once the line starts to drip hook it up to the caliper. Now loosen the bleeder valve on the caliper and let it gravity feed until the caliper gets a couple drips comming out. Do the same process on the opposite side, now bleed your brakes like normal, you should only get a tiny bit of air comming out. Now from this point I like to use a hand pump, get a buddy to keep the resoviour full and pump all the old fluid out until it starts comming out clean and new, this will ensure you have clean new fluid as well as no air. Do this process on all four corners. It takes alot of time and even more brake fluid but it also ensures you have clean fluid with no air.
Also if it's a bad master cylinder your pedal will feel soft but not to the floor, I would look more into the air in the lines, however you can never rule out the master, its a quick easy check. If you need help checking that I have an easy way to do it.

Chris_Red_V8 · Jun 18, 2007

WHITE94COBRA said:
When you put the new lines on did you let it gravity feed the new lines? What I mean is hook up the new line on top, leave the bottom off the caliper and let gravity draw fluid through the new line. once the line starts to drip hook it up to the caliper. Now loosen the bleeder valve on the caliper and let it gravity feed until the caliper gets a couple drips comming out. Do the same process on the opposite side, now bleed your brakes like normal, you should only get a tiny bit of air comming out. Now from this point I like to use a hand pump, get a buddy to keep the resoviour full and pump all the old fluid out until it starts comming out clean and new, this will ensure you have clean new fluid as well as no air. Do this process on all four corners. It takes alot of time and even more brake fluid but it also ensures you have clean fluid with no air.
Also if it's a bad master cylinder your pedal will feel soft but not to the floor, I would look more into the air in the lines, however you can never rule out the master, its a quick easy check. If you need help checking that I have an easy way to do it.

How do you check the master cylinder?

It was machine bled, but I checked the MS resivior, almost dry . How they missed that when flushing it I don't know. Refilling it took care of some of the spongyness, but I'm sure there's air in it again. No more pedal dropping and no more dash light.

I am getting an alignment done at Firestone and they offered to do a multipoint check on it for free, so I'll have something on paper to take back to the shop that did the flush.

WHITE94COBRA · Jun 19, 2007

To check the master cylinder, the easy way is to loosen one brake line from the master, put your vaccuume bleeder directly on right there, pull some vaccuume, you should see some fluid right away, if not that proportioning valve is bad, now with the vaccuume still on but no vaccuume being pulled, push the brakes slowly a few times, the fluid should push into the vaccuume line and once the pedal is released it should go back. Follow this procedure on all lines, only two comming off the master. I fabbed up my owm master lines that go to the vaccuume, but i'm pretty sure there is a way to do it without a vaccuume, I have seen mechanics putting a finger over the hole and feeling for pressure, or lack there of.

Chris_Red_V8 said:
How do you check the master cylinder?

It was machine bled, but I checked the MS resivior, almost dry . How they missed that when flushing it I don't know. Refilling it took care of some of the spongyness, but I'm sure there's air in it again. No more pedal dropping and no more dash light.

I am getting an alignment done at Firestone and they offered to do a multipoint check on it for free, so I'll have something on paper to take back to the shop that did the flush.

Chris_Red_V8 · Jun 23, 2007

The pedal really doesn't hit the floor, it stays within a half inch of when it feels normal. However, still, right before a stop, the pedal pressure comes and goes. The pedal feels better all the way from 60-5mph, but from 5mph to a stop, the pedal "pops" and drops resistance variably. The car still stops, but It doesn't feel right at all. Almost feels the same as if a hose was cut, only for that moment. I've checked all bolts, hoses, lines, and I can't find anything.

Had a brake inspection at Firestone (waste of my time, they just measured the pads and rotors, and checked for glaze, which they came back with 30% wear fronts, 25% wear backs, very even with no odd wear).

I need to rebleed the system, but how do I force the abs pump to cycle? If there's air in the system, I bet its there.

GTA_V6_Mustang · Jun 25, 2007

Ok a dropping brake pedal after application, especially when your stopped could indicate the cup seals in the master cylinder primary or secondary pistons are going south on you.

poboys 94 · Jun 25, 2007

Try taking the master off the booster and check to see if there is fluid between them, you dont have to take the lines off of the master to do this just slide it forward enough to run your finger back there and check. When they leak bad enough youll see fluid running down the booster without even having to disconnect the master. If its wet then the master is bad. Make sure you wipe off any excess fluid you might have spilled before you do this.

Chris_Red_V8 · Jun 26, 2007

Had it at another recommended brake shop (shop #3) to test the master (since I don't have any way of working on it at my new condo), and they couldn't find anything wrong with the braking system. However, the pedal feel to me is still too soft and completely unacceptable. I guess I'll have to find somewhere to work on the car myself and break out the motive powerbleeder.

When I do that, where are these lines/ports I'm supposed to crack on the master to bleed it? Also, is there any way for me to cycle my abs system while bleeding?

They did, however, mention all the noise my suspension makes, which isn't normal. I do have a lot of creaking, but I believed it to be bushings that are dry. However, I think now I need to troubleshoot that. I'll be making a new thread to see if there issues there could be related.

They said that what I'm feeling in the pedal right before a stop had to be part of the suspension moving, however, right before a stop, what's moving? the vehicle isn't transferring much weight (in daily driving, I'm very good about letting up on the brake as I come to a stop progressively).

94-302-vert · Jun 26, 2007

Give us a signature so we know your mods.. As you ask more questions this becomes more valuable...

With that being said rubber bushings go bad (dry out and crack) poly bushings need lube to be quiet...

Have you tried changing to a new brake pad?

go-stang5.0 · Jun 26, 2007

You have to hook up a scan tool to cycle the abs HCU. I have never done this so I dont know the steps but the ECC conncetor is on the passenger side by the firewall. I'm sure a shop will be able to do this for you.

Chris_Red_V8 · Jun 26, 2007

94-302-vert said:
Give us a signature so we know your mods.. As you ask more questions this becomes more valuable...

With that being said rubber bushings go bad (dry out and crack) poly bushings need lube to be quiet...

Have you tried changing to a new brake pad?

Here's my car's front end:

AGR steering rack (brand new)
MM tie-rod kit (brand new)
MM alum rack bushings (brand new)
03 cobra a-arms with saleen/MM delrin/aluminum bushings (1.5 year)
steeda x2 balljoints (1.5 year)
Cobra brakes up front (3 years on calipers and rotors and brackets)
Hawk HPS pads (1 year, 30% worn) (tried the oem pads as well, they're 20% worn)
MM/stoptech lines (1 year)
poly swaybar mounts and endlinks (properly sized) (1 yr)
04 Cobra HT Bilstein struts, HR Race springs (3 yrs)
MM caster camber plates (3 yrs)

Some odd brake issues.

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