midnight mechanic

I re did my brakes. They worked but the pedal was hard, as in it really took allot of force from my thigh to brake.

The gal at o'reilly's said that I have a collapsed brake line. Now how can a brake line collapse when they are either at normal ambient pressure or under high pressure if the brake pedal is pushed?

The real problem was I had a loose vac hose going to that huge thing connected to the master cylinder (thanks to miti-vac).

So is the "collapsed brake line" a bunch of bullshit??

Kaaarl12a

iTrader: (6)

Only way to colapse one is bending/ physically pinching it. Brake system pressures are extremely high no way to colapse them under normal circumstances.

Vierte

iTrader: (2)

Yea.... there are a lot of people that work at autoparts stores that haven't the slightest clue. Please always take their recommendations with a grain of salt. A guy from advance auto try to sell me a timing belt for the Rx-7 once.

The huge thing is a brake booster. It uses vacuum to a increase the applied braking force.

jgrewe

iTrader: (1)

Rubber brake lines can deteriorate from the inside and cause the exact problem you describe. I had a dragging caliper on my wife's minivan a few years ago that ended up being a line issue. Under the pressure of applying the brakes the fluid would move through it, barely. Release the pedal and the line would hold the pressure for a while. I thought is was a caliper problem and replaced it.

When trying to bleed the system I couldn't get a lot of fluid to flow out freely. The older guy I used to share a shop with mentioned the rubber line(that looke fine to me on the outside). Replace the rubber line; Problem solved.

So, a lot of autoparts store counter people may not know how many cylinders a 454 has(yes a girl asked me that when I wa trying to buy spark plugs) but sometimes they have a clue.

t_g_farrell

iTrader: (1)

No vacuum == hard to press pedal, no doubt. Collapsed line my a$$! Clogged line, maybe.

Ignore counter folks, they mean well but often have no valid context for your problem.

rx7lives

Get a set of these guys from either Mazdatrix or RB for $94.50. They fit perfectly.



They make a great difference in feel not to mention longevity and then you don't have to listen to the 'master' mechanics' at the parts place.

j9fd3s

iTrader: (3)

+1. very common on German cars. the hose acts like a check valve.

gerald m

I wouldn't say collapse is the right word but I have also seen this problem more than once . What happens is the multi layered rubber line ( never the metal lines ) has separates inside and instead of the fluid going down the center of the line it will follow between two layers of rubber and webbing building up excess pressure and cause a problem like you describe either when applying or when releasing like jgrewe has mentioned. That said it should only effect the brake where the rubber line has failed not all 4 wheels .( not very often but it does happen ) so I wouldn't totally discredit the parts person . Most of the time when a brake booster fails you can still get enough action to apply the brakes . Gerald m.

Rob XX 7

iTrader: (8)

when you have one do it while driving and the caliper basically locks up you will believe it can happen

regardless its good practice to swap those lines out due to age, they are a wear item

misterstyx69

iTrader: (142)

You got that hose on Backwards.
There is a one way check valve in it.
If you put that hose on wrong you brakes will be hard as a rock.
Take the hose off,flip it and put it back on.
Then POST.

sommmatt

iTrader: (2)

That's braided steel around a flex hose of similar construction. They can fail the same way, and you can't identify any potential failures until there is fluid coming through the steel.

Flex hoses fail. Collapse is a term that exists for explaining to customers. Ultimately fluid no longer transfers effectively, and no one ever cuts the flex hoses open to learn the true reason why.

Most of the time the fluid transfers to the caliper or wheel cylinder to lock the brakes, but will not release. If you suspect this and have a wheel that will not turn, crack the bleeder open for that wheel. If hydraulic pressure is released, the flex hose is suspect of failure.

midnight mechanic

the brake hoses were swapped out around 2005 because they were cracked and 22 years old.

and that big assed thing connected to the master cylinder, ya, brake booster, that's what I meant.

rx7lives

I didn't say thy couldn't fail but as they are ensconced inside an SS shell, they're less likely to decompose due to fuel/oil saturating them.

They do make a big difference in feel.

What is on the inside of an aircraft rated SS part?

RotorMotorDriver

iTrader: (1)

Not entirely true. These chemicals can and do soak through the braid plenty easy. They are more resistant to abrasion from rubbing on things.
This is true. The braid holds the hose from expanding under pressure
Depends on application. Some have nylon, teflon, etc. Not all are rubber.

~T.J.

rx7lives

Well. in my over thirty five years of driving,owning numerous 7's the closest I ever came to a hose collapsing and that was a hose that had a complete failure (not an RX-7). After my heart started beating again, I could see it leaking from the back left hose. I made it home with the front brakes but it's usually the backs that provide the pedal feel. After the rears were out of the picture, I had to almost go to the floor to stop while having one hand on the emergency brake lever.

If you're going to buy new rubber brake hoses and for an over twenty year vehicle you should, consider the SS ones. They do hold up, last time I pulled a wheel, the lines looked new. That's not saying what your saying is impossible but the SS lines are better, yes?

I also have an SS clutch line.

Finally, I seem to remember that when I looked into the lines before I installed them, it didn't look like rubber. However, Mazdatrix doesn't say anything unusual is in the SS brake lines so I assume it's rubber. I've got a bearing to replace so I'll see if I can straighten the line and point one end at the sun while looking at the other to see if I can determine what it's made of.

In fact, I'll send Mazdatrix an email and ask.

rx7lives

I asked Mazdatrix and this is their answer:
The hose inside is Teflon. It holds more pressure without expanding than a rubber line.