92 loyale, 4wd, spfi.

The brakes have been somewhat week over the last yr or so. Peddle travel when braking was long and would only start to slow/stop the car at the last 30% of peddle travel. Was getting pretty tired of it so I decided to see how well it would actually stop the car or if it would even lock up the tires at all.

 

So I pushed on it pretty hard then it felt like something blew and peddle go to the floor. The odd part is I cant find any fluid leaking, master cylinder is still full????????????????????? I pushed on it enough trying to find the leak it should have been empty by now. getting alot of air noise coming from the master cylinder area. If the booster is blown I wouldnt think it would act like this. didnt see any rips in the boot under the fill cap either.

 

Any ideas on where to start, maybe try bleeding them and see what happens.

 

Thanks

Could be the master cylinder, an internal leak (pure speculation here). A good test after you bleed the brakes is to have the engine running (for vacuum boost), and apply moderate pressure to the brake pedal. If the pedal slowly moves towards the floor, it's a bad MC.

+1

This happened in my 1998 Mitsubishi once.

 

I had everything done, new drilled and slotted brake rotors, pads, rebuilt calipers, new master cylinder, dot-4 fluid...

 

Was great for first 2 weeks, then in Oregon City I went to hit the brakes when a guy slammed on his and rear-ended him. They asked what happened and when I gave symptoms they said that my MC failed, probably due to an internal leak which could've come from the warehouse or poor installation.

Could be the master cylinder, an internal leak (pure speculation here). A good test after you bleed the brakes is to have the engine running (for vacuum boost), and apply moderate pressure to the brake pedal. If the pedal slowly moves towards the floor, it's a bad MC.

 

My first thoughts as well. The seals were probably getting weak, when you slammed on it, might have been enough to throw them over the edge.

sure sounds like MC lost it's marbles.

 

although - a very small leak can reduce to unusable pressure yet take awhile to be spotted. a blown piston seal in the caliper can bleed fluid into the dust boots and prevent fluid from being seen or loosing much from the reservoir. or the lines above the crossmember can have the very beginnings of a pin hole leak due to rust, but take awhile to collect and hit the ground, and they are prone to rust there.

I put a new master cylinder in a little over a yr ago:mad:

was parts store master cylinder if that matters much.

 

When I was bench bleeding it I remember it beeing hard to push esp more then 1/2 way had to lean into it to get it to travel the whole way. Maybe a bad part.

possible. hard to say...kind of a roll of the dice. i thought the same thing when i replaced a master cylinder about a year ago.....replaced it again....still pedal to the floor. ended up being the rear lines rusted.

 

i've never seen it, but i've heard of brake hoses failing in such a way that they "expand" like a big bubble so the fluid doesn't move. doesn't sound likely, but i have seen them do the opposite and collapse and act like a valve, locking the brakes.

 

two-ish questions:

 

why did you install a master cylinder last year and did it 100% resolve the issue?

 

how many miles since installing the new master cylinder?

The car sat for awhile and a mech. said it needed replaced. I couldnt remember what the brakes felt like before, so I replaced it, they felt better but wanst sure if they were 100%

 

around 10,000 miles ago

MC or fluid loss somewhere.

 

keep pounding that pedal to exacerbate any possible fluid leak. it'll be caused by rust, so additional pressure is going to blow it out sooner or later or cause enough fluid loss to eventually be noticeable in the reservoir or on the ground/piston area.

 

if you lived in the rust belt the rust/leak issue becomes more probable than less likely non-rust areas.

 

what does it do if you pump the pedal really fast like 3 or 4 times in a row - does it build any pressure at all - or all pumps identical?

 

good luck cookie, hope you nail it, off for the night.

Ill try pumping fast and see if any presure builds.

 

There is allot of noise coming from the MC area makes me think its shot.