MikeKey

Hey guys, I'm a little out of my league. And not getting to far trying to search the forums. Seems most brake issues I keep getting when searching are related to people bleeding the brakes.

Ok, my brake lines where recently replaced by the PO along with the Calipers. The booster also looks fairly new.

I've had the car for not almost a month now, and about a week ago the rear calipers started squealing. Popped off the rear tires, noticed that they've replaced all the rotors on the car with the exception of the rear passenger side. (other sides are slotted, where rear passenger looks stock, with what look like stock pads, WTF?)

Anyways, I cleaned them, they've been kind of quite, but not really.

Not sure if this above info is important, but onto my big issue.

Today I drove to work, like normal. Parked the car, level ground. Put my cover on. Worked 8hrs came outside, got in the car. Started her and as I was exciting the parking space, immediately noticed my peddle going all the way to the floor.

Just earlier today the peddle was tight and firm, like a proper peddle should be.

Feels like the brake booster is out. I've got brakes, but now I have to mash those things all the way to the floor.

I've never experienced a mechanical failure with a parked car, usually always happens to me while moving.

I popped the hood and checked the visibile vacuum lines, all seem good.

I'm out of my league at the moment, the most brake experience I have is with rotors and pads.

Before I tow her to a shop, I thought I'd ask if anyone has any suggestions on what I should examine or look for that might point me towards the culprit.

BTAL

What's the fluid level in each master cylinder reservoir?

MikeKey

I'm going to go ahead and bleed the brakes tomorrow as that seems to be the #1 first recommendation I see on some of the threads with similar accounts of what happened to me.

http://forums.corvetteforum.com/c3-t...e-failure.html

MikeKey

Both reservoirs are full.

Roughrider

What happened to me with a '78 Vette I used to own was a sudden loss of braking...and I was able to let the car coast to a stop thankfully.

My problem turned out to be a caliper seal...it wasn't leaking but sucking air in. No amount of bleeding the air would have cured it. The caliper was rebuilt and no more problem.

If you want to check the master cylinder, pull the large vacuum line off it...the engine rpm's should increase. If the rpm's stay the same, you have a bad booster due to an internal vacuum leak. Even then, you should have manual braking...more difficult but should work.

MikeKey

Ok, in park with engine running, the RPM's increased when I removed the main vacuum line as you described.

Also, while in park with engine running, the peddle goes straight to the floor.

With the engine cut-off the peddle is fairly firm.

mrvette

Classic example of crappy booster, I suggest you buy a Hydro Boost, runs of the power steering pump , and fuggetaboutit....

MikeKey

Well I see BTAL converted to Hydro Boost and now my interest is peeked. No vacuum sounds like a win to me.

my 76 ray

In my experience, a faulty booster usually results in a hard pedal because there is no power assist. You could have a bad master cylinder.

Easy Mike

Boosters seldom fail. You need to question why one of the original rotors was not replaced. Sounds to me like that particular corner was been a problem before you got the car.

79L48

Agreed. And if it isn't a problem with that one rotor/caliper, than it is likely a failure of the master cylinder. It can still be full but not be working as the seal at the back will blow and there will be little fluid transfer when you push the pedal. If you pump the pedal with the car off and it refuses to stiffen at all, look at the master cylinder. Easy fix. If it isn't new, replace it anyway.

Mike Ward

Hard pedal with engine running, bad booster. Hard pedal with engine off, normal. Pedal going to floor is never the fault of the booster. Beware of advice from people with fuzzy wigs.

MikeKey

Something is goofy because today it's working (building pressure). Tomorrow I'll bleed the system and pay close attention to that one screw ball caliper.

xCCTer

MikeKey

Oh, btw Thanks guys. I'll get her figured out.

PeteZO6

With three new rotors, I'd be concerned about why the fourth was not replaced, but more importantly, were the rotors that were replaced checked and corrected for runnout. Chevrolet riveted the rotors to the hubs for an important reason, so the rotors could be machined with practically zero runnout. The rigidly mounted calipers in this design require a true rotor, if there is any runnout, the oscillation generated as the rotors turn will cause the caliper pistons to pump air into the calipers.

Do a search on this, and you'll find plenty of information (and pros & cons too, so you'll have to sift through some mindless chatter) on how to measure and correct excessive runnout on your car.

FatRatShark

A friend of mine, his 68 camaro did the samething we rebleed the system and replaced the master cylinder just in case. problem cured. so take your pick of what you want to replace. caliper? mastercylinder? or bleed system?. I say do all, can never be to careful with these classic cars.

boeing46

I agree with this but it could be many things. I really doubt the booster is the problem. Just because a master cylinder is new means nothing. I have gotten several bad ones. Be careful whatever you do and do your testing in a safe place.

mwm1993

had very similar symptoms in my 80 last year. the pedal would feel good if the car sat for a few days but the pedal would get to the floor if I pushed it for a minute. Replaced master cylinder and bled and haven't had any problems since

mrvette

MY direct A TO B comparison, without touching the brake lines one bit, proved the point,.....the only thing replaced was the HB/booster....

once the air was outta the p/s lines, and booster, the car actually has driven GREAT for over 5 years now....HB works, vacuum sux....

believe me, I fought this crap for years, and I have this car since '95 now, and always had a 4" soft pedal even at bottom of the stroke,

I did it specifically the way I did to be comparing apples to apples not oranges, NO brake lines were touched one damn bit, just the booster...

so all you guys loving on old crappy booster designs need learn a new trick....