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I, like a lot of other people, almost drove myself to drink trying to get a reasonably high, firm pedal in my C3. My buddy and I spent hours and hours bleeding, adjusting, bleeding some more, replacing the proportioning valve, bleeding some more, you get the idea.
I finally ended up with a decent sort of pedal that got the car through a French safety check so I could register it here, but I still didn't think it was right. Sometimes, sitting and waiting for something, idling in drive, the pedal would sink even a little bit further. It wasn't good enough.
Then I had an inspiration, or maybe a crazy idea. Bubbles don't want to go down in a fluid, they want to go up. (Observe your beer). Yet, when bleeding the brakes, we are forcing the fluid from the highest point in the system to the lowest, trying to force air bubbles to go down. I decided to bleed the brakes backwards, from the callipers to the master cylinder. I thought this would also have the added advantage of taking any last bits of air out of the master cylinder because the compensating port is the highest place in the system.
So, I cut the hose on my trusty pressure bleeder, cobbled up a smaller plastic tube to fit into it and then removed the rear Wilwood calliper. Looking at this picture, I have no idea how Wilwood thinks all the air is going to come out of these things while they are mounted. I put a block of wood between the pads and used bungee cords to hold the calliper up.
I then hooked the bleeder hose to the bottom fitting, pressurised the tank and opened the bottom bleeder to let the fluid in. I had removed some fluid from the master cylinder and had my wife watching for bubbles. Sure enough, she said that a few very small bubbles came out and then stopped. I then opened the top bleeder on the calliper and got some bubbles there too. Every so often, I'd go and remove some fluid from the master, and to make a long story short, did all four corners. I did leave the front callipers in place, there was no reason to remove them. I don't know how much more air came out of the system and up through the master because my wife abandoned me due to boredom.
But, I can tell you, this car has never had a pedal like this. It's quite high, firm, and predictable. It seems like when there was air in the system, the brakes were either on or off like a switch, either not stopping the car or throwing me through the windshield. They are now literally perfect.
If you think I'm nuts, fine, but the fact of the matter is, it worked.
You can do a similar thing with the MC on the car. Very simple. Raise the back of the car up as high as you can get it, lower the front. This makes the MC tip front edge lower than the back. Check with a level. Now take the lid off of the MC, "slowly" push the pedal, have someone watch the reservoir for bubbles. This forces the air up against the seals then out the MC reservoir. This will release the bit of air in the MC that is so hard to get out. And you are correct, no matter how many ways you try, you can't push bubbles down in fluid unless it's in a small tube. (MC Caliper)
You can also get a similar effect with the rear calipers. Raise the front of the car, lower the rear as much as you can. This makes the rear calipers at a higher angle so the air can escape up and out. Bleed the rears normally. Kind of the same as you did.
Nothing crazy here. I have pushed brake fluid backwards many, many times on Harley's. works the treat.
I'm not surprised its been done before, there's probably no such thing as a new idea. I just didn't know anybody who had.
Is there a particular reason why its easier to bleed Harleys this way?
I'm not surprised its been done before, there's probably no such thing as a new idea. I just didn't know anybody who had.
Is there a particular reason why its easier to bleed Harleys this way?
My Harley calipers can be impossible to bleed. The front caliper master cylinder is at the top of the handle bars. If the front wheel has left and right calipers and a T-fitting connecting them to the handle bar master cylinder the problem is doubled. That is why we bleed the calipers by forcing the fluid up to the master cylinder.
THEN....there is the Rear caliper master cylinder which is located at the "right-foot" brake pedal on the lowest part of the Harley frame. It is easier to bleed because the caliper is higher than the rear master cylinder (go figure)'. All Harleys may not have a problem with bleeding the calipers.
you bleed the system backwards every time you push the pistons back into the bores on any calipers to replace the pads. or wheel cylinders. what you are NOT bleeding is any air already in the calipers. the bleeder is at the top of the caliper for this purpose. the fluid line is always lower. the downhill bleeding thing is not really an issue as the whole time it is going downhill it is inside a thin brake line and air has no ability to bypass the fluid pushing it to stay on the uphill side of the line.
Last edited by derekderek; Jun 17, 2021 at 12:08 PM.
We bleed Harley front brakes from the bottom up for the simple reason that air wants to go up. pushing fluid from the bottom up makes short work pushing the air out of the master instead of the other way around.
I, like a lot of other people, almost drove myself to drink trying to get a reasonably high, firm pedal in my C3. My buddy and I spent hours and hours bleeding, adjusting, bleeding some more, replacing the proportioning valve, bleeding some more, you get the idea.
I finally ended up with a decent sort of pedal that got the car through a French safety check so I could register it here, but I still didn't think it was right. Sometimes, sitting and waiting for something, idling in drive, the pedal would sink even a little bit further. It wasn't good enough.
Then I had an inspiration, or maybe a crazy idea. Bubbles don't want to go down in a fluid, they want to go up. (Observe your beer). Yet, when bleeding the brakes, we are forcing the fluid from the highest point in the system to the lowest, trying to force air bubbles to go down. I decided to bleed the brakes backwards, from the callipers to the master cylinder. I thought this would also have the added advantage of taking any last bits of air out of the master cylinder because the compensating port is the highest place in the system.
So, I cut the hose on my trusty pressure bleeder, cobbled up a smaller plastic tube to fit into it and then removed the rear Wilwood calliper. Looking at this picture, I have no idea how Wilwood thinks all the air is going to come out of these things while they are mounted. I put a block of wood between the pads and used bungee cords to hold the calliper up.
I then hooked the bleeder hose to the bottom fitting, pressurised the tank and opened the bottom bleeder to let the fluid in. I had removed some fluid from the master cylinder and had my wife watching for bubbles. Sure enough, she said that a few very small bubbles came out and then stopped. I then opened the top bleeder on the calliper and got some bubbles there too. Every so often, I'd go and remove some fluid from the master, and to make a long story short, did all four corners. I did leave the front callipers in place, there was no reason to remove them. I don't know how much more air came out of the system and up through the master because my wife abandoned me due to boredom.
But, I can tell you, this car has never had a pedal like this. It's quite high, firm, and predictable. It seems like when there was air in the system, the brakes were either on or off like a switch, either not stopping the car or throwing me through the windshield. They are now literally perfect.
If you think I'm nuts, fine, but the fact of the matter is, it worked.
This is what I do, less work to get the last bit of air from a MC.
you bleed the system backwards every time you push the pistons back into the bores on any calipers to replace the pads. or wheel cylinders. what you are NOT bleeding is any air already in the calipers. the bleeder is at the top of the caliper for this purpose. the fluid line is always lower. the downhill bleeding thing is not really an issue as the whole time it is going downhill it is inside a thin brake line and air has no ability to bypass the fluid pushing it to stay on the uphill side of the line.
I see your point. All I know is that after doing this, I went from an iffy brake pedal to one that was probably as good as its going to get. So, something worked.
Interesting thought. One issue is that you need to suck the excess out of the M/C as needed. Not sure you could get all the air out of that valving in the M/C.
If that method was "better". it would have been the chosen approach for the last 100+ years. But...it isn't.
Interesting thought. One issue is that you need to suck the excess out of the M/C as needed. Not sure you could get all the air out of that valving in the M/C.
If that method was "better". it would have been the chosen approach for the last 100+ years. But...it isn't.
I think there's a couple of reasons why it's not too popular.
It's messy. Next time I would take the bleeder screws out and put teflon tape on the threads to prevent seepage.
It's more difficult. You have to have a pressure bleeder and adapt the tube coming from it to something that will fit tightly over the bleeder. You also have to go to the front of the car regularly to syringe the accumulating fluid out of the MC reservoir and squirt it into something else.
I think you're right, for 98% of the cars out there, this method isn't better because it isn't necessary, but the air problems in these brakes is legendary. I tried everything possible five times each over the course of weeks. As I said before, all I can tell you is it worked.
I think there's a couple of reasons why it's not too popular.
It's messy. Next time I would take the bleeder screws out and put teflon tape on the threads to prevent seepage.
It's more difficult. You have to have a pressure bleeder and adapt the tube coming from it to something that will fit tightly over the bleeder. You also have to go to the front of the car regularly to syringe the accumulating fluid out of the MC reservoir and squirt it into something else.
I think you're right, for 98% of the cars out there, this method isn't better because it isn't necessary, but the air problems in these brakes is legendary. I tried everything possible five times each over the course of weeks. As I said before, all I can tell you is it worked.
While this worked for you its more work than required. Factory calipers are a little easier than using wilwood calipers. Wilwood rear calipers don't bleed while mounted the first time. They need to be removed and bleed the first time.
But C3 brake bleeding isn't difficult but takes time. So if the system has been opened this is the procedure I have used successfully for many years.
I use my car for road course track days so the brakes must be 100% or nothing.
Here is the setup at the MC. I connect my air compressor to the MC to apply ~ 30 PSI. If you apply lower pressure it doesn't work as well requiring more time between bleeding each caliper.
1. Fill the MC and mount the pressure system.
2 Next clamp the brake pads to push the caliper pistons fully into the caliper.
3. Apply ~ 30 PSI at the MC and bleed the caliper via the bleed screws until you get no air. I use a 6ft clear plastic tube connected to the bleed screws to assist with how much fluid I can bleed before the MC runs out of fluid. ( !!! important to not let the MC fluid go dry !!! ) but if you do let it go dry repeat the process bleeding the MC while on the car. You don't need to bench bleed the MC.
to determine fluid amount I remove the plastic tubing and introduce air into the tube and bleed until the air pushes out the 6ft line. The longest line (rear passenger caliper) requires about 4 full bleeds of the air bubble on a 6ft line. Note the MC gets low after about 3 6ft line bleeds.
so re-fill the MC as required.
4. Then with pressure still being applied release the clamps from the brake pads allowing the pistons to release using the pressure at the MC.
5. Repeat this to fill each caliper.
Now that the system is full with fluid we can now start the final bleeding procedure.
1. Start at the MC before doing anything else.
This is the procedure I use the bleed the MC. It has always found air in the MC.
Watch the 2 video's in the linked post to see why this works and its by design. Also when I have soft brakes usually 90% of the time bleeding the MC has fixed the problem.
Important to note this is not done just 1 time. After a empty system I have repeated this process 3 days in a row to get all the air from the MC.
Once the MC is clear of air then I start to bleed each caliper again.
2. again clamp the brake pads to push the piston into the caliper
3. apply ~ 30 PSI at the MC
4. bleed each bleed screw until no air or min 1 complete fluid exchange for the line.
5. with pressure still applied at the MC release the clamps for the brake pads. Watch the pads push and apply against the rotors. On the front you should notice that you cannot rotate the rotors since the pressure at the MC is applying the brakes.
6. Release the pressure at the MC and re-fill as required.
To reduce the amount of fluid used I capture the bleed fluid into a clean jar and re-use.
Once I am happy with no air I bleed using new fluid.
How you apply pressure at the MC varies from motive products to a modified version I what I do, doesn't matter just get ~ 30 psi at the MC. This will push the fluid quickly.
Last edited by cagotzmann; Jun 19, 2021 at 10:11 AM.
While this worked for you its more work than required. Factory calipers are a little easier than using wilwood calipers. Wilwood rear calipers don't bleed while mounted the first time. They need to be removed and bleed the first time.
But C3 brake bleeding isn't difficult but takes time. So if the system has been opened this is the procedure I have used successfully for many years.
I use my car for road course track days so the brakes must be 100% or nothing.
Here is the setup at the MC. I connect my air compressor to the MC to apply ~ 30 PSI. If you apply lower pressure it doesn't work as well requiring more time between bleeding each caliper.
1. Fill the MC and mount the pressure system.
2 Next clamp the brake pads to push the caliper pistons fully into the caliper.
3. Apply ~ 30 PSI at the MC and bleed the caliper via the bleed screws until you get no air. I use a 6ft clear plastic tube connected to the bleed screws to assist with how much fluid I can bleed before the MC runs out of fluid. ( !!! important to not let the MC fluid go dry !!! ) but if you do let it go dry repeat the process bleeding the MC while on the car. You don't need to bench bleed the MC.
to determine fluid amount I remove the plastic tubing and introduce air into the tube and bleed until the air pushes out the 6ft line. The longest line (rear passenger caliper) requires about 4 full bleeds of the air bubble on a 6ft line. Note the MC gets low after about 3 6ft line bleeds.
so re-fill the MC as required.
4. Then with pressure still being applied release the clamps from the brake pads allowing the pistons to release using the pressure at the MC.
5. Repeat this to fill each caliper.
Now that the system is full with fluid we can now start the final bleeding procedure.
1. Start at the MC before doing anything else.
This is the procedure I use the bleed the MC. It has always found air in the MC.
Watch the 2 video's in the linked post to see why this works and its by design. Also when I have soft brakes usually 90% of the time bleeding the MC has fixed the problem.
Important to note this is not done just 1 time. After a empty system I have repeated this process 3 days in a row to get all the air from the MC.
Once the MC is clear of air then I start to bleed each caliper again.
2. again clamp the brake pads to push the piston into the caliper
3. apply ~ 30 PSI at the MC
4. bleed each bleed screw until no air or min 1 complete fluid exchange for the line.
5. with pressure still applied at the MC release the clamps for the brake pads. Watch the pads push and apply against the rotors. On the front you should notice that you cannot rotate the rotors since the pressure at the MC is applying the brakes.
6. Release the pressure at the MC and re-fill as required.
To reduce the amount of fluid used I capture the bleed fluid into a clean jar and re-use.
Once I am happy with no air I bleed using new fluid.
How you apply pressure at the MC varies from motive products to a modified version I what I do, doesn't matter just get ~ 30 psi at the MC. This will push the fluid quickly.
Ah, that's interesting. I had the pressure in my bleeder at about 12 PSI, nowhere near as high as you're using. That may be the difference.
Thanks.
Nice process...and likely important for road race vehicles. Lots more trouble than using a wrench, tubing and a bottle with a 'friend' working the brake.
Crazy Backwards Bleeding Idea
