Help: brake issues
10-03-2018, 12:16 PM
#1
Help: brake issues
My 997.2 seems to have reduced brake performance recently. Car takes a lot longer to stop from even low speeds. Pedal feel keeps changing between soft and mushy on first pump to normal after a few pumps. Brake bleeding has been done multiple times both manual with one person inside pumping the brakes and with the motive pressure bleeder as well. Fluid is new.
Front and rear brake pads are new (hawk ceramics) and rotors are oem Porsche resurfaced recently when the pads were changed. Rotor is above the minimum thickness. No steering wheel vibrations on braking.
I do notice the abs getting engaged even when braking from 60-30 mph.
we checked the vacuum pump and lines going to the brake booster. No obvious leaks. Vacuum pump has no leak or corrosion on the outside.
could it be the abs control module or master cylinder? Cannot be brake booster as pedal is not brick hard and no hissing sounds. I don’t mind changing out master cylinder but the abs module is quite expensive to change on a whim. Any way to really diagnose this issue?
no codes either when scanned with durametric. The Indy is stumped as to what it could be. Any suggestions on what we could try next?
Front and rear brake pads are new (hawk ceramics) and rotors are oem Porsche resurfaced recently when the pads were changed. Rotor is above the minimum thickness. No steering wheel vibrations on braking.
I do notice the abs getting engaged even when braking from 60-30 mph.
we checked the vacuum pump and lines going to the brake booster. No obvious leaks. Vacuum pump has no leak or corrosion on the outside.
could it be the abs control module or master cylinder? Cannot be brake booster as pedal is not brick hard and no hissing sounds. I don’t mind changing out master cylinder but the abs module is quite expensive to change on a whim. Any way to really diagnose this issue?
no codes either when scanned with durametric. The Indy is stumped as to what it could be. Any suggestions on what we could try next?
10-03-2018, 02:01 PM
#2
Rennlist Member
First ask what was done when bleeding the last time they worked. Was the reservoir bled too low? If so, air gets into the system affecting the ABS system and gives a mushy feel as you describe. A full empty of the system, flush and refill is the next thing to do, to level set and make sure the booster, ABS module or master cylinder aren't malfunctioning. Do the cheap stuff first, then work up from there. When air gets into these systems, it can be very tricky to get out, and the symptoms are as you describe. May take a couple of bleed dry/flush and fill cycles.
10-03-2018, 02:37 PM
#3
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My understanding is that if the reservoir was bled too low, resulting in air getting into the system, you must do several hard brake applications that engage the ABS. The issue being air that gets stuck in the ABS system, and the only way to release it is to engage the ABS.
I found this out when I bled mine too low. I did several ABS engaging stops, re-bled, and everything was fine after that. And note that "re-bled" meant flushing fluid through 3-4 times. I re-flushed until I got zero air out of any caliper. Note that since all fluid in the system was new, I was capturing an re-using the same fluid.
I found this out when I bled mine too low. I did several ABS engaging stops, re-bled, and everything was fine after that. And note that "re-bled" meant flushing fluid through 3-4 times. I re-flushed until I got zero air out of any caliper. Note that since all fluid in the system was new, I was capturing an re-using the same fluid.
10-03-2018, 02:58 PM
#4
Rennlist Member
I know it won't impact pedal feel too much, but have the rotors been resurfaced at the time you swapped pads, and are the pads different this time? The Hawk Ceramic low dust pads require a lot more pressure than OEM and perform better when warm (but not hot). Have they been bedded in?
10-03-2018, 03:27 PM
#5
The reservoir level never went too low, I made sure to monitor it closely through the whole process numerous times. Air in the abs lines is still possible. Will try bleeding it again by activating the abs pump using dirametric or piwis if I can get one.
yes rotors were resurfaced when I changed the pads, it was oem Porsche pads (textar)in there before. I followed hawks bed in process.
yes rotors were resurfaced when I changed the pads, it was oem Porsche pads (textar)in there before. I followed hawks bed in process.
10-04-2018, 08:06 AM
#6
RL Community Team
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Were the brakes fine before the brake work or was the brake work done to try and resolve the same issue?
10-04-2018, 11:47 AM
#7
The brakes always felt Weak since I got the car used. When the brakes reached the stage when car could no longer come to a quick stop, I replaced the pads, rear pads had crack marks on them. The rotors also had some pad marks on them in one spot which I assume happened when I left the car parked for a few weeks and maybe some water got on it. That’s why they were resurfaced.
Will try cycling the abs pump bleed method next.
Will try cycling the abs pump bleed method next.
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11-16-2018, 01:33 AM
#8
Update, using a piwis activated the abs pump to bleed the brakes again. Problem still persists.
We have ruled out air in lines, brake fluid, master cylinder, brake booster, pads and rotors.
no fluid or vacuum leaks anywhere in the system.
next up is to check all the caliper pistons and seals. Abs module is not throwing any codes and the Indy could not really find any issue with it. Unless it’s some strange problem with the module which is not throwing a code. Also can’t just swap and check another abs module from another 997 as they are programmed to the vin.
We have ruled out air in lines, brake fluid, master cylinder, brake booster, pads and rotors.
no fluid or vacuum leaks anywhere in the system.
next up is to check all the caliper pistons and seals. Abs module is not throwing any codes and the Indy could not really find any issue with it. Unless it’s some strange problem with the module which is not throwing a code. Also can’t just swap and check another abs module from another 997 as they are programmed to the vin.
11-16-2018, 01:59 AM
#9
RL Community Team
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Going back to your first post, you said you could feel the ABS module engaging even from stops from 60-30 MPH. Does that happen on all the stops and maybe why the brakes feel week, because when you try to modulate them normally, the ABS kicks in and prevents that. If so, I'm thinking one of your wheel speed sensors may have gone bad and is falsely telling the system you have wheel lock-up which is engaging the ABS. You seem to have looked into everything else, but I didn't see that mentioned.
11-16-2018, 12:52 PM
#10
Forgot to mention that I did remove and visually inspect all 4 wheel speed sensors. They did not have any dirt or grime on them or any visible damage. No error codes relating to the wheel speed sensors . I did not check the ohms with a voltmeter, I will probably try to do that next when inspecting the brake pistons and seals.
yes the abs does engage at low speeds only if you press the pedal a bit firmer than normal pedal pressure.
yes the abs does engage at low speeds only if you press the pedal a bit firmer than normal pedal pressure.
11-16-2018, 01:07 PM
#11
RL Community Team
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If you go out and do a drive with some fairly hard braking, like enough to activate the ABS system, it would be interesting to know what your rotor temperatures are (infrared thermometer) and compare LF to RF and LR to RR. If the calipers are sticking, only a couple of the wheels might be getting actual brake pressure, which would then make those wheels lock sooner and trip the ABS. You might feel reduced braking effectiveness since you're only using half the stopping power of the car and the wheels with that stopping power are locking early because they're getting a lot more braking force than the other wheels. Carefully inspect the hard brake lines for any kinks, like if someone did a brake job without properly loosening the fasteners and actually bent the hard metal lines or left the calipers hanging from them unsupported, which may have kinked them.
11-16-2018, 09:15 PM
#12
Rennlist Member
I had the hawk ceramic and thought they were garbage. Mushy and no bite. I bet that it’s your master cylinder. Replace with a gt3 master cylinder. Can find one for about 250 online and an Indy can replace it.
11-16-2018, 11:10 PM
#13
I had swapped out the master cylinder and booster with another used set (same part number) a while back when the issues started. It did not improve the braking.
the gt3 master cylinder will not improve braking distances, it will just make the pedal feel firmer if I’m not mistaken.
Just to rule out a bad set of pads,I have new ferodo ds2500 on order. it should be here next week. Keeping my fingers crossed. I don’t mind changing pads,rotors,master cylinder or wheel speed sensors.
Replacing abs module even with a used one is a hassle as it needs to be programmed etc to the car so really hoping I don’t Have to go there.
the gt3 master cylinder will not improve braking distances, it will just make the pedal feel firmer if I’m not mistaken.
Just to rule out a bad set of pads,I have new ferodo ds2500 on order. it should be here next week. Keeping my fingers crossed. I don’t mind changing pads,rotors,master cylinder or wheel speed sensors.
Replacing abs module even with a used one is a hassle as it needs to be programmed etc to the car so really hoping I don’t Have to go there.
Last edited by Presto; 11-19-2018 at 02:15 AM.
11-24-2018, 06:13 AM
#15
As my ferodo ds2500 are expected to be delivered tomorrow, I started removing the hawk ceramics I had on the car. I immediately noticed the rear pads are very glazed and almost glass like. Just the rear and only the pads. Pad wear is almost minimal due to the low mileage on them. Rotor looks fine.
i know high heat causes pads to glaze but these pads have not seen any track or aggressive driving. About 200 miles of normal commute with light braking.
so now I need to figure out why the pads glazed over. The wheel did rotate freely when I installed the pads, I know the pads touch the rotor slightly even when not braking, how do I determine how much they need to touch?
Maybe the caliper piston is not retracting completely? I inspected the pistons, I can move them with my fingers and none seem to be ‘sticking’
could a large rotor run out cause the pads to get glazed as well? The rotors were resurfaced once before, I don’t have a run out gauge but usually a large variance causes brake vibrations atleast for the front wheels. Maybe in the rear it’s less noticeable?
i know high heat causes pads to glaze but these pads have not seen any track or aggressive driving. About 200 miles of normal commute with light braking.
so now I need to figure out why the pads glazed over. The wheel did rotate freely when I installed the pads, I know the pads touch the rotor slightly even when not braking, how do I determine how much they need to touch?
Maybe the caliper piston is not retracting completely? I inspected the pistons, I can move them with my fingers and none seem to be ‘sticking’
could a large rotor run out cause the pads to get glazed as well? The rotors were resurfaced once before, I don’t have a run out gauge but usually a large variance causes brake vibrations atleast for the front wheels. Maybe in the rear it’s less noticeable?