Squishy Brakes

[SoCalDMC12]

Hi Folks,

Wondering if I can solicit some advice:

Lately, I've noticed that my brake pedal is real squishy. At first I thought I was just not use to driving my Delorean any more (only drive it once every 1-2 weeks because of school, though that's gonna change soon). But now I feel there's definitely a problem.

I brought it to a local mechanic who, after BARELY driving it in his parking lot, said that it was a bad master cylinder. Plausible, I suppose, but I'm wondering if it could be anything else (i.e. perhaps an air bubble in the lines).

Thoughts?

- Geoff

[opethmike]

Is the master cylinder original? If so, I agree with the mechanic. The rubber inside of it is simply not going to last 35 years.

Take off the access panel, and look for signs of external leakage. It is also possible for it to leak internally. In either event, if it is original - replace.

[SoCalDMC12]

Is the master cylinder original? If so, I agree with the mechanic. The rubber inside of it is simply not going to last 35 years.

Take off the access panel, and look for signs of external leakage. It is also possible for it to leak internally. In either event, if it is original - replace.

Probably original... I never replaced it in my 12 years of ownership. Is this an easy DIY job, or best left to the pros?

[Jonathan]

I agree with the likely assessment that it's the brake master cylinder.

Is it an easy DIY job?

My own take on our cars is that nothing we work on is particularly "easy" or simple for that matter.

Where does it rank on the pain in the rump scale? Probably somewhere in the middle between changing your air filter and changing your TABs.

Would you consider changing out your own water pump? It's of similar complexity to that job. Not all that hard to access and you need to refill the fluid and purge out air from the system before calling it finished.

It's less difficult than changing out a fuel accumulator. but more difficult than changing out a coolant reservoir.

[opethmike]

If you are familiar with the concept of bench-bleeding, and purging air from your brake lines, you are good to go on doing it. If you are not, pay someone to do it, this is your safety after all.

Though, I will politely disagree with Jonathan, as I think these cars are cake-easy to work on.

[SoCalDMC12]

If you are familiar with the concept of bench-bleeding, and purging air from your brake lines, you are good to go on doing it. If you are not, pay someone to do it, this is your safety after all.

Though, I will politely disagree with Jonathan, as I think these cars are cake-easy to work on.

About the most complex thing that I've done is change out my alternator. Since brakes are rather "mission critical", will probably just leave it to the pros.

[opethmike]

Definitely the right call if someone hasn't walked you through it before. Not worth learning by trial and error with brakes!

[Jonathan]

Good call on the safety aspect and letting someone else handle the work. There are easier, and less crucial, things to do yourself if that's your comfort level.

The jury is out on what is easy or simple on these cars. To me anyway. A function of how other stuff in life is going I suppose. If you are coming up aces in all the other areas in life, the proverbial chip leader, then yea, most things on the car are a piece of cake and wouldn't frazzle you much doing them. If you're on the other end of that spectrum though, you might just use something frustrating on our cars like a rusty bolt or tight work area to snap and go ape-shit with a sledgehammer on the car or whatever else might be close by.

[opethmike]

Good call on the safety aspect and letting someone else handle the work. There are easier, and less crucial, things to do yourself if that's your comfort level.

The jury is out on what is easy or simple on these cars. To me anyway. A function of how other stuff in life is going I suppose. If you are coming up aces in all the other areas in life, the proverbial chip leader, then yea, most things on the car are a piece of cake and wouldn't frazzle you much doing them. If you're on the other end of that spectrum though, you might just use something frustrating on our cars like a rusty bolt or tight work area to snap and go ape-shit with a sledgehammer on the car or whatever else might be close by.

To be fair, I have a pet gorilla that I've trained to turn wrenches for when I encounter rusty ones.

[opethmike]

His name is Pickles.

[David T]

While it is possible it is a bad master cylinder it can also be a bad hose. If they are original they should also (all four) be replaced too. If the brake fluid is dark and nasty looking figure on rebuilding all 4 calipers too. Most brake problems can be avoided by flushing and replacing the brake fluid every other year. If you have a 5-speed do the clutch at the same time. Again, if that fluid is also dark and nasty figure on doing the master and slave cylinders. While doing that, if you still have the plastic hose, time to replace it with the S/S braided one.

[Andrew]

The level of difficulty of replacing a master cylinder depends greatly upon the condition of the car (i.e. rust). If the lines are seized to the master removing them can be considerably difficult. If you embark on this job yourself, invest in a good flare wrench. Do not muscle the lines off! Tap the wrench with a hammer to break the line nuts free.

Proper bench bleeding is also important. Even after bench bleeding, the full system should be bleed to purge any excess air. Like the master cylinder lines, the bleeders may open up with little effort, or they may be seized. With regard to the bleeders, a 6 point box wrench is strongly advised. Like the master lines, tap the wrench with a hammer, don't muscle them off.

I've had success using a MAPP gas torch to carefully heat the bleeders. However, if you go that route, always make sure to take the necessary precautions (like a water hose at the ready!) And don't heat the bleeders so much that you melt anything. In contrast, I would not heat the lines to the master due to their close proximity to the master cylinder reservoir.

[DMCMW Dave]

The only things that can cause squishy brakes are air in the lines, or a bad master. The only way to get air in the lines is to improperly bleed the system after repair, it generally doesn't happen all by itself.

Bad calipers either stick (i.e. no brake action but a stiff pedal) or leak (usually painfully obvious - messy).

Bad hoses, if plugged, will cause the brakes to hang/drag, or leak. Will not cause squishy brakes.

Bench bleeding is over- rated. Pressure bleeder is all you need.

[Jonathan]

A pet gorilla named Pickles that turns wrenches for you?! Sheesh, I'm gonna have to get my trunk monkey back into training!

https://www.youtube.com/watch?v=hq0mUxRKHQY&list=PLoxADsZ9YforxtjWODy3Kz_8JjLH-Nxp7

[SoCalDMC12]

While it is possible it is a bad master cylinder it can also be a bad hose. If they are original they should also (all four) be replaced too. If the brake fluid is dark and nasty looking figure on rebuilding all 4 calipers too. Most brake problems can be avoided by flushing and replacing the brake fluid every other year. If you have a 5-speed do the clutch at the same time. Again, if that fluid is also dark and nasty figure on doing the master and slave cylinders. While doing that, if you still have the plastic hose, time to replace it with the S/S braided one.

Fluid looked nice and clean, but still gonna have it done by the pros. Just seems safer to me. I do want to get more familiar with the mechanical bits of my car, but for something as important as brakes... seems better to leave it to people more knowledgable than i until I build up more mechanical acumen.

[David T]

[QUOTE=DMCMW Dave;223509]The only things that can cause squishy brakes are air in the lines, or a bad master. The only way to get air in the lines is to improperly bleed the system after repair, it generally doesn't happen all by itself.

Bad calipers either stick (i.e. no brake action but a stiff pedal) or leak (usually painfully obvious - messy).

Bad hoses, if plugged, will cause the brakes to hang/drag, or leak. Will not cause squishy brakes.

Bench bleeding is over- rated. Pressure bleeder is all you need./QUOTE]

I have to disagree with you on this one. A bad hose, one that swells as you step on the brakes, will, indeed, cause a "squishy" pedal. Like a balloon, it grows and swells, absorbing all of the pressure. Once you take your foot off the pedal it shrinks back down to normal and looks fine.

[DMCMW Dave]

I have to disagree with you on this one. A bad hose, one that swells as you step on the brakes, will, indeed, cause a "squishy" pedal. Like a balloon, it grows and swells, absorbing all of the pressure. Once you take your foot off the pedal it shrinks back down to normal and looks fine.

I've never seen a brake hose do that. Ever. In fact, I don't think I've ever even seen one leak. I suppose anything is possible but the odds are really against this being the problem on this guys car.

The only thing I've ever seen happen to brake line hoses is breaking down or plugging internally and "going check-valve".

The steel lines will rust through, but that's not squishy, the pedal goes to the floor and you find puddles.

[Bitsyncmaster]

I've never seen a brake hose do that. Ever. In fact, I don't think I've ever even seen one leak. I suppose anything is possible but the odds are really against this being the problem on this guys car.

The only thing I've ever seen happen to brake line hoses is breaking down or plugging internally and "going check-valve".


I've had both front brake hoses on my 2005 Malibu "going check-valve". Nothing else wrong with the brakes just the brakes dragging and the rim so hot you could not touch it. I cut the old hoses to see the plug. It was just the inside of the hose breaking down. You could feel it pull to the bad side and know you lost engine power somehow. Don't think you would even know if a rear brake hose did that except for the smell when you get out of the car.

[David T]

If you put your hand on a hose when someone steps on the brakes you will feel it stiffen and grow in diameter. When they break down they can "go check valve" or they grow an anuyerism, a bubble where a section of the hose pops out like a balloon. It doesn't leak but it absorbs all of the pressure and the pedal goes to the floor. When you release the pedal it shrinks back down and looks normal. This happens because the braiding inside the hose fails and can't contain the pressure. When it "goes check valve" the lining inside comes loose and the pressure gets "behind" it and prevents the pressure from getting back to the master cylinder to be released. Either failure mode is BAD and that is why you do not use brake hoses when they are 30 years old. The lines molded into the side of the hose are there for a reason. It is a good visual indication of the hose being twisted. If you install a brake hose and twist it, you will cause it to fail quickly. The braided S/S hoses don't have that marker so you have to be careful not to put a twist into it when you install it. The reason the pedal will feel much firmer with the braided S/S hoses is because the outer braid prevents it from expanding as much so you don't lose as much pressure so the pedal feels harder and higher. They still have rubber inside so they can also fail like a check valve eventually.