‘81 lost brakes..help!
Thread Starter
7th Gear
Joined: Jul 2018
Posts: 7
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‘81 lost brakes..help!
Driving down the beach today in stop and go traffic and all of a sudden my brake pedal goes to the floor, the brake light comes on, and I don’t slow down! Lucky I was able to downshift and slow down enough to get off the road. Check the master cylinder, plenty of fluid, I see no leaks under the car either. After getting a tow home I decide to start diving in and now the brake pedal works like nothing is wrong. Any suggestions? Is there a way to rule out certain components along the line so I’m not throwing parts at it? Any helps appreciated
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
Normally this would be a classic master cyl issue. But because it repaired itself and the Proportioning Valve tripped the dashlight on, I would suspect a caliper in the rear. Sometimes they don't give up a drop of fluid on the floor at first, but are leaking internally (piston seals).
To isolate the master from issues, you can make up two short pieces of ready made brakeline with one end closed off. (the front & rear ports are different dia & TPI)
Install those test lines in place of the brake lines. If the brake pedal is firm then you know the MC is ok and you can move on to another area. Unfortunately, this introduces air into the system and will have to be bled. Prop Valves seldom go bad. Keep pumping the pedal and watch for dampness on one of the rims.
To isolate the master from issues, you can make up two short pieces of ready made brakeline with one end closed off. (the front & rear ports are different dia & TPI)
Install those test lines in place of the brake lines. If the brake pedal is firm then you know the MC is ok and you can move on to another area. Unfortunately, this introduces air into the system and will have to be bled. Prop Valves seldom go bad. Keep pumping the pedal and watch for dampness on one of the rims.
2026 Loser of the Year
Joined: Sep 2013
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From: New Or-leens Loo-z-anna
Did you notice that the brakes were beginning to feel/act differently in the recent past? If so, how did they feel.....soft pedal?.......hard pedal?......low pedal? This info may help members narrow down your problem.
Thread Starter
7th Gear
Joined: Jul 2018
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I’ve only owned the car a week, but I’d say the brakes have felt pretty good. Now that you say something about the rear calipers it has me thinking, I started hearing a small squeak when I braked heavy but was going to wait to have a look see until the next oil change. I also smelled a faint brake smell from the rear when I pulled over today waiting for the tow.
Melting Slicks
Joined: Jun 2011
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The leaks are slow and usually get mixed in with brake dust and at most you might see a wet spot on the wheel after a week or so of sitting. This has been going on for a while and expect you also have rotor run out and air is easily pumped into the caliper with poor piston seals.
You may need to remove the brake pads and check each piston to find the leaks. As for fixing it self I think the proportional valve most likely reset , but it will happen again.
Try this. Car off and pump the brakes. How many pumps to get a solid brake. Then apply pressure to see if the pedal slowly goes to the floor or holds the position.
Thread Starter
7th Gear
Joined: Jul 2018
Posts: 7
Likes: 0
The leaks are slow and usually get mixed in with brake dust and at most you might see a wet spot on the wheel after a week or so of sitting. This has been going on for a while and expect you also have rotor run out and air is easily pumped into the caliper with poor piston seals.
You may need to remove the brake pads and check each piston to find the leaks. As for fixing it self I think the proportional valve most likely reset , but it will happen again.
Try this. Car off and pump the brakes. How many pumps to get a solid brake. Then apply pressure to see if the pedal slowly goes to the floor or holds the position.
You may need to remove the brake pads and check each piston to find the leaks. As for fixing it self I think the proportional valve most likely reset , but it will happen again.
Try this. Car off and pump the brakes. How many pumps to get a solid brake. Then apply pressure to see if the pedal slowly goes to the floor or holds the position.
Just out of curiosity why would this affect the front brakes as well? I realize it’s a closed, pressurized system-but the front brakes have their own line from the MC?
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
Yes, the MC has a front brakeline but it goes to the proportioning valve first, then is divided to left front / right front calipers. Off the Prop Valve is a single line that covers both rears after going through a distribution block..
