My brake bleeding notes
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Le Mans Master
Joined: Jun 2019
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From: Loveland
My brake bleeding notes
For 1968 only. My brakes are now better than they have ever been. Solid pedal that engages at the very top. Hallelujah! Here are a few observations. When I removed the MC I found it was installed with washers between the MC and the firewall. I had to check the assembly manual to see if this was correct,,, it was not. This moved the MC forward a bit. This made the pedal have to move just a bit farther to start the braking. Inside the bore there are little orifices up into the reservoirs, the seals need to move past these before any brake pressure starts. I removed the washers. My pedal starts braking much earlier than is did before.
I have bench bled the MC before but I found something new, for me. As you push in on the plunger it compresses the first spring and you feel some resistance. I thought this was the end of the stroke. I found that it will press farther in when the second spring compresses. Knowing this will help a lot when bench bleeding. As I pushed farther in I was able to get more air out of the MC. Air bubbles will come out of the hoses, and even more out of the small holes into the reservoirs. After bleeding the MC, level, in the vice, I tilted it a bit forward and then backwards. I was able to get even more bubbles out as it was tilted. Two BS wives tails. First I keep hearing not to push the plunger all the way in because it will tear or flip the seals. BS! This is only true in OLD rusty POS MC's, it has nothing to do with a new shinny MC bore. The plunger has a limiting rod and a spring so it doesn't compress to far. Second,,,, keep the MC level when bleeding. Air in the bore will ALWAYS be at the top of the bore. You can never push the seals far enough in to zero out the air/fluid space. Just pure physics! When you tilt it just a bit the air will move up against the seals, then when you push to bleed it, the air will find the little holes up and out of the reservoir. Air will never push down and out, only up and out. There are seals pushing forwards and backwards, so tilting it both ways help force the air up and out.
After installing the MC I bled the brakes with my new Motive bleeder. I was surprised I didn't get any air bubbles from any of the bleeders. I used more than a quart of fluid. But my brakes are very solid now.
Just so you can breathe again,,, I rebuilt and reinstalled the "brake light warning switch". Trust me,,,, it isn't a proportioning valve, metering valve, ETC. It's only function is to light up the brake warning light, when the front or back brakes fail. It doesn't shut off any fluid, it doesn't meter anything, it doesn't proportion anything, it's not adjustable. Even with the heavy duty brakes, that were offered in 1968, it was the same. Your 68 could have very easily been modified by "bubba" but that doesn't make it correct. It may be better, but not original. Not that I really care about originality. I see many of these switches for sale. They even call it all sorts of things, but that doesn't make it so either.
Whew!
Two other notes: At some point you have to remove the MC bleeder kit fittings. If you do it after installing the MC on the car, fluid will leak out and air might seep in. While still on the bench I put the MC cap on and installed the short lines and block onto the MC. Also,, With the MC installed, rear of the car up, the MC checked with a bullet level and tilting front lower, I took the cap off and pushed the pedal in slowly, I got lots of air out of the reservoir holes. This was just after I carefully bench bled it. Not sure why or where the bubbles came from. This technique is documented on YouTube. You can also get a hard pedal.
I have bench bled the MC before but I found something new, for me. As you push in on the plunger it compresses the first spring and you feel some resistance. I thought this was the end of the stroke. I found that it will press farther in when the second spring compresses. Knowing this will help a lot when bench bleeding. As I pushed farther in I was able to get more air out of the MC. Air bubbles will come out of the hoses, and even more out of the small holes into the reservoirs. After bleeding the MC, level, in the vice, I tilted it a bit forward and then backwards. I was able to get even more bubbles out as it was tilted. Two BS wives tails. First I keep hearing not to push the plunger all the way in because it will tear or flip the seals. BS! This is only true in OLD rusty POS MC's, it has nothing to do with a new shinny MC bore. The plunger has a limiting rod and a spring so it doesn't compress to far. Second,,,, keep the MC level when bleeding. Air in the bore will ALWAYS be at the top of the bore. You can never push the seals far enough in to zero out the air/fluid space. Just pure physics! When you tilt it just a bit the air will move up against the seals, then when you push to bleed it, the air will find the little holes up and out of the reservoir. Air will never push down and out, only up and out. There are seals pushing forwards and backwards, so tilting it both ways help force the air up and out.
After installing the MC I bled the brakes with my new Motive bleeder. I was surprised I didn't get any air bubbles from any of the bleeders. I used more than a quart of fluid. But my brakes are very solid now.
Just so you can breathe again,,, I rebuilt and reinstalled the "brake light warning switch". Trust me,,,, it isn't a proportioning valve, metering valve, ETC. It's only function is to light up the brake warning light, when the front or back brakes fail. It doesn't shut off any fluid, it doesn't meter anything, it doesn't proportion anything, it's not adjustable. Even with the heavy duty brakes, that were offered in 1968, it was the same. Your 68 could have very easily been modified by "bubba" but that doesn't make it correct. It may be better, but not original. Not that I really care about originality. I see many of these switches for sale. They even call it all sorts of things, but that doesn't make it so either.
Whew!
Two other notes: At some point you have to remove the MC bleeder kit fittings. If you do it after installing the MC on the car, fluid will leak out and air might seep in. While still on the bench I put the MC cap on and installed the short lines and block onto the MC. Also,, With the MC installed, rear of the car up, the MC checked with a bullet level and tilting front lower, I took the cap off and pushed the pedal in slowly, I got lots of air out of the reservoir holes. This was just after I carefully bench bled it. Not sure why or where the bubbles came from. This technique is documented on YouTube. You can also get a hard pedal.
Last edited by kodpkd; Mar 20, 2021 at 09:55 AM.
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