|12-21-2018 11:57 AM|
|johnsongrass1||I take stuff apart all the time just to see how it works. Usually learn something like I shouldn't have cause it won't go back together.|
|12-21-2018 11:53 AM|
|12-21-2018 09:14 AM|
|12-21-2018 07:39 AM|
|lmsport||the mid-eighties to about 90 model f-bodies were campaigned for bad calipers....people with auto trans never use their e-brake which means the ratchet mechanism in the rear calipers never gets exercised which is how the calipers adjust themselves as the pads wear. GM replaced the calipers with units that had coated parts in the ratchet.|
|12-21-2018 05:08 AM|
Somehow it alway's goes back to the basics. This thread reminds me not to over think a problem and look at all the standard parts first.
Glad you found and corrected the issue.
|12-20-2018 07:14 PM|
I think it's fixed. The issue appears to be a simple problem that I have never encountered for the mere reason that everytime we, son and I, jump into a new project we always put new brake hydraulics on every wheel end and I change every brake line, hard and soft. This GTA is not mine nor my son's, and it's a rust free unit which is unlike most all of the rust belt beauties that we usually build/work on. So I ***/u/me that there wouldn't be a corrosion issue.
I pulled off the rear calipers and found the sliding sleeves that ride on the o-ring were rusted and not sliding. The passenger side was not moving at all and the driver side was better, but not moving properly. The result is that the pads were too far from the rotor after the brakes were released causing an excess amount of fluid needed to have them engage the rotor. This caused the brake light from the combination valve switch and no rear brakes on the 1st pump. A couple of minutes with a scotch roloc disc and a little caliper grease was needed.
Tony's post about panic pushing of the pedal and Olnolan's video put me onto it. And lmsport's last post describing the excessive bias was what got me thinking. When I was 'panic stop' pushing the pedal with no light and good rear brakes the light bulb went off in my head. Only took me a week or so - hehe.
Thanks for the help everyone - it was entertaining, educational and interesting - at least to me lol.
Tomorrow it's supposed to rain in monsoon fashion - 3" or so - and be in the 50-60 degree range. Which should do it for a temporary cleaning of the salt off the roads. Perhaps I can get in a couple more burnouts and brake tests.
Thanks - Jim
|12-20-2018 05:20 PM|
|lmsport||brake light means big pressure difference, if no air in system then the master is not putting out the correct pressures. do you have access to brake pressure gauges, we use them for race cars to get an idea on brake bias.|
|12-20-2018 08:17 AM|
Did you watch the proportioning valve video? They show it and explain it. It's just a threaded plastic plug with a nipple on the end.
|12-19-2018 07:03 PM|
Forgot to mention that it still, repeat still, is only letting the brake pedal travel with 3-4 inches of the floor when bleeding the rears - the pedal will not go to the floor when bleeding the rears. Maybe this is normal for 4 wheel disc as I'm usually working on a disc/drum setup.
|12-19-2018 06:57 PM|
A brief synopsis : brakes worked great for a little over a year until this last spring. The front brake hoses were holding the front brakes on(original hoses). Changed hoses, pads and calipers and all was well - drove less than 200 miles. This fall the brake light would come on occasionally and has gradually worsened to the description in the title including the brake light on at the same time as the 1st pump.
I had one suspect steel line on the left rear, so I changed it tonight - no difference and identical complaints. Two things - I did as Tony described - stab the pedal very hard. When that is done the brakes work fine and no brake light. I'm testing this on jack stands with the motor off, the motor running, and the motor running in gear. Normal brake application in all three states results in brake light and no rear brakes until pumped up.
My son was manning the brake pedal this evening and he mentioned that pumping the brakes quickly is difficult because the pedal doesn't return quickly as compared to everything else he drives.
The only parts that haven't been changed are the rear calipers and the booster. From my understanding of booster function I don't see how this could be possibly caused by the booster. Nor do I see how it could be a caliper or calipers causing this.
I'm open to all suggestions. Ole Nolan - describe the proportioning valve centering locking mechanism to bleed the brakes. I could remove the switch and jam something in the slot to hold it in place while bleeding, but geesh, I've never heard of anything like that.
|12-19-2018 07:23 AM|
Is this a new setup?
Has it worked properly in the past?
|12-19-2018 07:21 AM|
It could be the combination valve is going off-center while you're bleeding the brakes, it happens sometimes. Get one of the centering plugs and use while bleeding.
|12-17-2018 08:07 PM|
Yes to the pedal but it also tells you that the MC is moving and returning fluid.
Binding is possible. So is a loose wheel bearing or a caliper rocking around or a flexing caliper mount.
Sometimes the pedal will feel hard because the piston is bound up and a release of the pedal relaxes the bind enough to retract the piston further than it needs so the next time it take two or more pumps to move the piston enough. Keep in mind the pads are always rubbing the rotor on a disc brake so the piston only need to move 1/16" to apply enough pressure on the pad/rotor contact.
At $20 each, I'd change them and dress the caliper brackets if your are at all in doubt.
|12-17-2018 07:37 PM|
Also, I tore apart the original m/c. There was nothing wrong with it, much like the proportioning valve. I'm onto rigging up my pressure gauge in different locations to the rears. I need to make a piece of NiCopp line that I can hook to a bubble flare union. I can see a visit to the parts store in the near future.
Any chance I could have a caliper binding causing this? Both rear calipers are originals from '90 but it's a Florida car with less than 80k for what that might be worth.
|12-17-2018 07:17 PM|
|johnsongrass1||You could try too attach the lines together and see what happens before going through all the work of replacing the MC again.|
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