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> Brake Pedal Won't Release
sdthomas
post Aug 8 2018, 09:31 AM
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As I was driving home from work yesterday, I noticed my brake pedal seemed to get firmer and firmer. It got the point where just tapping it slightly would engage the brakes, as though there was no more travel in the pedal. When I got home I noticed all four wheels were very hot to the touch so the brakes had clearly not been fully releasing. I let it cool down and checked the pedal and it felt normal but now I'm worried about driving it.

What could cause this?
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Eric_Shea
post Aug 8 2018, 09:42 AM
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Remove the carpet and floorboard and check for fluid in the pan. This would mean a failed/failing master cylinder. When that happens (and just from age) your old nylon bushings can fail. It is probably time for a new MC and Pedal rebuild.
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dr914@autoatlanta.com
post Aug 8 2018, 09:52 AM
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probably bad pedal cluster bushings causing the pedal to stick the brakes to get hot boiling the fluid

QUOTE(sdthomas @ Aug 8 2018, 08:31 AM) *

As I was driving home from work yesterday, I noticed my brake pedal seemed to get firmer and firmer. It got the point where just tapping it slightly would engage the brakes, as though there was no more travel in the pedal. When I got home I noticed all four wheels were very hot to the touch so the brakes had clearly not been fully releasing. I let it cool down and checked the pedal and it felt normal but now I'm worried about driving it.

What could cause this?

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sdthomas
post Aug 9 2018, 06:11 PM
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OK I finally was able to check out the pedal cluster. It was rebuilt about 4 years ago the bushing still looked to be in good shape. No sign of any brake fluid. I drove it around the block and the pedal froze up again. I lifted the front end and could barely turn the wheels. It's as though the MC isn't releasing when pushed in. What's the next step?


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mepstein
post Aug 9 2018, 06:15 PM
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When’s the last time you replaced the MC and soft lines.
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sdthomas
post Aug 9 2018, 06:31 PM
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I haven't replaced the MC since I've had owned (about 5 years). The soft lines were relatively new when I bought it so I suppose are about due for replacement. Is there a way to verify that the MC is the problem?
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porschetub
post Aug 9 2018, 07:14 PM
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QUOTE(sdthomas @ Aug 10 2018, 12:31 PM) *

I haven't replaced the MC since I've had owned (about 5 years). The soft lines were relatively new when I bought it so I suppose are about due for replacement. Is there a way to verify that the MC is the problem?


The soft lines can look fine on the outside and be buggered on the inside,is your master cylinder pushrod returning freely after pushing the pedal in ? is the fluid clean or rusty coloured? whole bunch of stuff to look at,sounds like sticking caliper pistons to me...sure Eric will sort it for you.
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sixnotfour
post Aug 9 2018, 07:22 PM
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make sure you have a bit of free play (rattle) before the pushrod hits the master to tight does just as described
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porschetub
post Aug 9 2018, 11:08 PM
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QUOTE(sixnotfour @ Aug 10 2018, 01:22 PM) *

make sure you have a bit of free play (rattle) before the pushrod hits the master to tight does just as described


Good point hadn't thought of that,I had to do mine as there was too much play.
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mgphoto
post Aug 10 2018, 08:06 AM
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Rear venting clearance to tight, check .004"
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Tbrown4x4
post Aug 10 2018, 08:57 AM
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If all 4 brakes are dragging, the last thing I would suspect is a hose or stuck caliper.

Your brake master cylinder has two rubber cups inside (primary and secondary) that seal inside the bore and build pressure when you push on the brake pedal. Just in front of these cups is a small inlet port. As you use the brakes and heat up the fluid, it expands, and travels back to the reservoir through the ports. If there is not enough pedal free play, these ports can be blocked by the rubber cups. The fluid has no where to go when it expands, and the brakes drag.

The first thing I would check is pedal free play (as suggested above), and make sure the pedal returns to the stop every time.

That said, your master cylinder looks a little crusty. There should be a rubber boot on the end to keep dirt and moisture out. I would suggest replacing it and bleeding the brakes. Might be a good time to replace the hoses too. (Also suggested above.)

I would recommend PMB for all the replacement parts. 914 rubber has a nice M/C for sale as well. I just rebuilt my front calipers, and replaced the M/C and hoses. A little challenging to bleed, but the results are worth it.
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sdthomas
post Aug 10 2018, 11:41 AM
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Thanks for all the advice; it's super helpful. First things first though: how do I free up the brakes? If I just open up a caliper bleeder and let out some fluid will it relieve pressure in the system?
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Spoke
post Aug 10 2018, 11:42 AM
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QUOTE(sdthomas @ Aug 9 2018, 08:11 PM) *
It's as though the MC isn't releasing when pushed in. What's the next step?


So after you drove it and the brake pedal froze up, did you check the free play in the pedal to eliminate it from suspicion? The pedal should be loose before it contacts the plunger on the MC. You can check the free play with your hands as it's more sensitive than pressing with your foot. Was the pedal loose with free play when the brakes were froze?
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wndsrfr
post Aug 10 2018, 07:06 PM
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QUOTE(sdthomas @ Aug 10 2018, 09:41 AM) *

Thanks for all the advice; it's super helpful. First things first though: how do I free up the brakes? If I just open up a caliper bleeder and let out some fluid will it relieve pressure in the system?

It certainly should...and if the wheel won't rotate then it's a stuck caliper piston..
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sdthomas
post Aug 11 2018, 01:11 PM
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The free play goes away once you push on the pedal. I checked it this morning and there was a little play in pedal. But it went away after using the brakes.

I guess at this point I'm wondering if there's a quick fix, or is time to refurbish everything (MC, calipers, lines, rotors) which will put an end to the 'fun car' for the year (IMG:style_emoticons/default/sad.gif)

QUOTE(Spoke @ Aug 10 2018, 10:42 AM) *


So after you drove it and the brake pedal froze up, did you check the free play in the pedal to eliminate it from suspicion? The pedal should be loose before it contacts the plunger on the MC. You can check the free play with your hands as it's more sensitive than pressing with your foot. Was the pedal loose with free play when the brakes were froze?
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KELTY360
post Aug 11 2018, 01:19 PM
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Do it in increments Shawn. Start with the MC; it's a likely culprit and you're going to end up replacing it anyway as part of a more complete process.
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Tbrown4x4
post Aug 11 2018, 01:38 PM
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Agreed. Do the master cylinder first. Not too difficult. The worst part is pushing the supply lines into the grommets. I have a pressure bleeder you can use, if nobody closer does.
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dr914@autoatlanta.com
post Aug 11 2018, 02:08 PM
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I second that


QUOTE(sixnotfour @ Aug 9 2018, 06:22 PM) *

make sure you have a bit of free play (rattle) before the pushrod hits the master to tight does just as described

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mepstein
post Aug 11 2018, 02:29 PM
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I would look at 914rubber’s MC that uses screw in lines.
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steuspeed
post Aug 11 2018, 03:16 PM
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Sounds like MC issue. Maybe just blockage? I did mine last year. Pedal was going to the floor. I bought a 17mm from Pelican Parts. Lots of debate on stock 17mm vs 911 19mm. Be sure to bench bleed before install. I could not get the air out until I used a pressure bleeder. Also, getting the tubes back in the top of the MC is not easy. Could be a trick?
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