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Discussion Starter #1
I remember learning about brakes in auto shop in high school...however, that was almost 40 years ago and although I understand basics, I don't remember much!

So...I have a basic question. Can brake bleeding ruin a master cylinder on a new Jeep?

I have a new Recon and had a shop install a Rock Krawler 2.5" Max Travel Lift that includes new braided steel brake lines. Part of the install obviously includes bleeding the brake lines.

I was having fun in the San Juan Mountains of Colorado last week, until I was making a downhill switchback turn, with a 1000' dropoff, and my brake pedal faded to the floor. No, the brakes weren't hot.

I hadn't noticed it before, but this was only my second day offroad with the new Jeep. When I pressed the pedal, I got braking, but then the pedal faded to the floor. I suspected air in the system and asked the shop that installed the lift to rebleed the brakes. They rebled the system and said they saw no air.

The pedal still faded to the floor after the rebleed; however, I was now on level ground and it didn't seem as bad. I took it to the Jeep dealer to have them check it. They say I have a bad master cylinder. The new one is on order and we haven't discussed warranty.

I just want to be armed with as much information as possible if Jeep says the damage was caused by the shop that installed the lift/new brake lines. I hope it doesn't come to a finger pointing match. As I mentioned, I didn't notice any issues until the second day offroad, so maybe it was just a coincidence.

edit: I should add that on the previous day, I went up and down four 12,000' passes in about 2 hours. On the last two passes, it was raining and muddy, so I used Hill Descent Control for the first time. I didn't realize that the HDC uses ABS in addition to engine braking and when I got to the bottom of the fourth pass, the brakes were overheated - I had never touched them coming downhill. FWIW, I live in Colorado and have driven over countless high passes, both on and offroad, so I'm usually very aware of braking technique coming downhill. Probably a dumb question, but could overheated brakes cause any issues with the master cylinder?

TIA
 

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I am def no expert, but with the heat generated by the brakes does get transferred to the fluid at some point. And not sure on how a master cyl is constructed, just wondering outloud if hot fluid may mess with the MC.

We go to Estes and the RMNP quite often and when the Trail Ridge road is open we hit it every time. That is the time I get to slap stick the auto trans. I have seen a couple of people that only use the brakes and seen some smoke coming from then after the get the vehicle to stop from faded brakes. There was one, where one wheel was spewing fluid from a ruptured line/seal.

Oh yeah, Pikes Peak was fun.
 

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If the break fluid is overheated beyond a certain point it won't recover and would need to be changed. But, that won't cause the problem you're describing.
 

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It's possible that the shop didn't bleed the system properly or well.
I'd do it myself or ask the dealer to check/do it first before going after a master cylinder.
 

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Discussion Starter #5
It's possible that the shop didn't bleed the system properly or well.
I'd do it myself or ask the dealer to check/do it first before going after a master cylinder.

I've read that the ABS system needs a scan tool to cycle it while bleeding to get any air out of that part of the system. I did ask the service rep at my dealership to have the tech look into this. I'm not sure if they did or not, however, they diagnosed the problem as a faulty master cylinder.

Still wondering if bleeding the brakes improperly can cause a problem with the master cylinder.
 

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I've read that the ABS system needs a scan tool to cycle it while bleeding to get any air out of that part of the system. I did ask the service rep at my dealership to have the tech look into this. I'm not sure if they did or not, however, they diagnosed the problem as a faulty master cylinder.

Still wondering if bleeding the brakes improperly can cause a problem with the master cylinder.
I don't think it could cause a problem per se with the master cylinder. But it could leave air in the line somewhere.
The other thing is that they may have mixed different types of brake fluid by mistake and that could bugger the MC badly. Like DOT-3 with DOT-5; that does not work out well...
 

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Discussion Starter #7
I don't think it could cause a problem per se with the master cylinder. But it could leave air in the line somewhere.
The other thing is that they may have mixed different types of brake fluid by mistake and that could bugger the MC badly. Like DOT-3 with DOT-5; that does not work out well...
Good info...thanks! When I had the brakes rebled at the shop that installed the lift/brake lines, they told me the tech heard some hissing when applying the brakes. I tried hard to hear it in my garage later, with my wife operating the brakes, but could not.

They also mentioned they use a "pressure bleeder." I've read those are attached to the master cylinder for the bleeding procedure. I can't find any info on that method damaging the master cylinder, but it seems like a possibility...
 

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As Leadnut points out, if the brake fluid has been boiled then it must be bleed out. Usually just bleeding each front caliper will do this.

You do not need the scan tool to bleed the ABS. A pressure bleed is good, but you can manually bleed the system fairly easily. Just make sure you have the correct technique - open bleed nipple, assistant pressure brakes to floor, close bleed nipple, the assistant releases brakes. Repeat about 25 times for the rears and 15 times for the fronts to get all fluid changed.

bobkbusch, time to start bleeding your own brakes. At least then you'll know what is going on. You only need a plastic tube, jar and 11mm wrench.
 

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Good info...thanks! When I had the brakes rebled at the shop that installed the lift/brake lines, they told me the tech heard some hissing when applying the brakes. I tried hard to hear it in my garage later, with my wife operating the brakes, but could not.

They also mentioned they use a "pressure bleeder." I've read those are attached to the master cylinder for the bleeding procedure. I can't find any info on that method damaging the master cylinder, but it seems like a possibility...
Pressure bleeding will not hurt or damage the master cylinder. I have been using this method for 20 years now. The only issue with it is making sure there is always fluid in the MC. I normally flush my brakes on a yearly bases and have never had a soft pedal using this procedure.

Now it is not hard to over heat stock brakes on our Jeep. I did it earlier this year having some fun coming down a twisty road in northern CA. Got the brakes so hot that by the time I got to the bottom I did not have any brakes. FYI, I had no idea when I started that run that I would smoke the brakes but I was pushing the Jeep to the limits to access just what the limits where when it came to handling. No issues with handling in my mind but it did uncover a weakness in the brakes.

Now back to your issue. All brake fluid will have some amount of water in it. Even new brake fluid right out of the bottle, though it will be a really small amount. Anyway if you boil the brake fluid the water turns to steam and your pedal goes to the floor. Once this is has happened you will always have a soft pedal until you flush the system completely.

If you are hard on brakes like I am it pays to invest in a brake bleeder systems like the following:

https://www.motiveproducts.com/collections/domestic-bleeder-kits/products/chrysler-dodge-mopar-bleeder

This is a one person job and is not at all hard to do. You can follow their instruction or use the dry method that I use and many others, a lot less messy. Again if you are hard on the brakes also upgrade the brake fluid you use. I swap between ATE Super Blue and Motul RBF 600. It made it really easy having 2 different colors when flushing the system but Super Blue is not longer sold in the US and I am still looking for a second fluid.
 

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I haven't pressure-bled since high school. I use a Mityvac.
Mityvac Brake and Clutch Bleeding Equipment

To speed it up I use a syringe to suck out most of the glick from the MC first, add clean fluid, start bleeding from the farthest caliper away. Suck that juice 'til it runs clear and bubble-free.

If your tech heard hissing there could be a hole somewhere in the lines. And that would be your problem.

Also, not a bad idea to replace lines every 4 or 5 years or after a significant heating of the fluid. DOT-3 is hydrophilic and will inevitably absorb water. Water heats, expands, swells your lines, makes them more pliable under load (hence the popularity of steel braided lines).
 

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I swap between ATE Super Blue and Motul RBF 600. It made it really easy having 2 different colors when flushing the system but Super Blue is not longer sold in the US and I am still looking for a second fluid.
I use Endless RF-650 in my Audi. It is highly recommended for high stress driving, albeit a little pricey. I haven't had any issues with the Jeep using normal non-racing brake fluid. Going downhill I will keep it in lower gears or on dirt put it in 4-Lo so I don't need to use the brakes much.

Brake fluid
 

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I haven't pressure-bled since high school. I use a Mityvac.
Mityvac Brake and Clutch Bleeding Equipment

To speed it up I use a syringe to suck out most of the glick from the MC first, add clean fluid, start bleeding from the farthest caliper away. Suck that juice 'til it runs clear and bubble-free.

If your tech heard hissing there could be a hole somewhere in the lines. And that would be your problem.

Also, not a bad idea to replace lines every 4 or 5 years or after a significant heating of the fluid. DOT-3 is hydrophilic and will inevitably absorb water. Water heats, expands, swells your lines, makes them more pliable under load (hence the popularity of steel braided lines).
That is the way I use to do it. It is so much easier with the Motive bleeder. But what ever works is good.
 

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I use Endless RF-650 in my Audi. It is highly recommended for high stress driving, albeit a little pricey. I haven't had any issues with the Jeep using normal non-racing brake fluid. Going downhill I will keep it in lower gears or on dirt put it in 4-Lo so I don't need to use the brakes much.

Brake fluid
If you where following me down that mountain that day and keeping up gears alone wouldn't cut it. I hung the rear end more than a few time and even manage a couple of 4 wheel drifts. I think it is more fun seeing how far I could push the Jeep than any of my racing days in cars design for the application.
 

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If you where following me down that mountain that day and keeping up gears alone wouldn't cut it. I hung the rear end more than a few time and even manage a couple of 4 wheel drifts. I think it is more fun seeing how far I could push the Jeep than any of my racing days in cars design for the application.
We used to do that in high school, my buddy had a 70 Olds Cutlass and I had a 72 Camara. We would watch the Duke Boys and Jim Rockford then go out and practiced the "moves" on the country dirt roads. My days of racing and wrecking cars ended in my 20s, by that time I had wrecked quite a few cars and nearly gotten killed several times. Better to leave the casino with what I had then to keep on betting until the house wins big time.

These days the Jeep it's more about birdwatching, photography, camping, shooting, and sightseeing. I have an Audi that I spool up every so often when I want more excitement.
 

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It sounds to me like the master cylinder is bad, or there is a leak in the system. The pedal shouldn't go to the floor, ever. Overheated fluid needs to be changed out, but even if the fluid was bad the pedal still shouldn't go to the floor.

Not knowing how they bled the brakes is the wildcard here. If they did a 2 man bleed and had an assistant pushing the pedal and releasing it while the second person opened and closed the bleeder can ruin a master cylinder. If the person stepping on the brake allows the brake pedal to go all the way to the floor in some instances the master can be ruined. It is best to put a block under the brake pedal when doing a 2 man bleed to limit the travel, not to allow the pedal to go all the way to the floor.
 

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Discussion Starter #16
It sounds to me like the master cylinder is bad, or there is a leak in the system. The pedal shouldn't go to the floor, ever. Overheated fluid needs to be changed out, but even if the fluid was bad the pedal still shouldn't go to the floor.

Not knowing how they bled the brakes is the wildcard here. If they did a 2 man bleed and had an assistant pushing the pedal and releasing it while the second person opened and closed the bleeder can ruin a master cylinder. If the person stepping on the brake allows the brake pedal to go all the way to the floor in some instances the master can be ruined. It is best to put a block under the brake pedal when doing a 2 man bleed to limit the travel, not to allow the pedal to go all the way to the floor.
Thank you! I don't know how the bleed was performed, they claim it was a "pressure bleeder," but this is very useful information. If you don't mind, how does this "ruin" a master cylinder? Does it deform a seal?
 

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Thank you! I don't know how the bleed was performed, they claim it was a "pressure bleeder," but this is very useful information. If you don't mind, how does this "ruin" a master cylinder? Does it deform a seal?
For lack of a better term, yes. It doesn't always happen, but can and does. A block of wood, or something else under the brake to limit the travel is always a good idea.
 

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It sounds to me like the master cylinder is bad, or there is a leak in the system. The pedal shouldn't go to the floor, ever. Overheated fluid needs to be changed out, but even if the fluid was bad the pedal still shouldn't go to the floor.

Not knowing how they bled the brakes is the wildcard here. If they did a 2 man bleed and had an assistant pushing the pedal and releasing it while the second person opened and closed the bleeder can ruin a master cylinder. If the person stepping on the brake allows the brake pedal to go all the way to the floor in some instances the master can be ruined. It is best to put a block under the brake pedal when doing a 2 man bleed to limit the travel, not to allow the pedal to go all the way to the floor.
If you boil the brake fluid the pedal will go to the floor, no question about it.
 

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If you boil the brake fluid the pedal will go to the floor, no question about it.
True. I should have read the OP's post better. He said this early on:

[I was having fun in the San Juan Mountains of Colorado last week, until I was making a downhill switchback turn, with a 1000' dropoff, and my brake pedal faded to the floor. No, the brakes weren't hot.]

If they weren't hot to the touch the fluid didn't boil. Later on in his post he probably fried the fluid, and glazed or burnt the brakes too. My bad.

Either way the fluid should be flushed out, if the problem persists look for a leak, no leak I'd probably replace the master cylinder.
 
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