MadPhil

Hi all,
I've been reading this forum for a while but this is my first post so I'd just like to say a big HI :D and I hope one day soon my vette could be up near the standard of some of those on this site.. :thumbs:
(Oh and I am in New Zealand if there are any other Kiwi's reading this)

Coming back to the reason for posting.
My front right Caliper was leaking from the piston seals. So I decided it was time to do some maintainence and do all the brake seals. I mean the car is getting near 30 yrs old. So pulled the calipers off, gave them all a good clean and wash, replaced the seals. Bought a new Master Cylinder and replaced all the brake fluid and bleed the system.
Sitting in the shed had awesome brakes, pedal was nice and firm. Took it for a run and the pedal goes right to the floor, but the car stops. So maybe there was some air in the system somewhere.
Got out the Haynes manual and bleed the system as per the book, and we even used a vaccum bleeder to make sure there was no air in the lines.

Once again awesome brakes when sitting in the shed. Start the engine, and the pedal goes to the floor. :confused:
So we tested the brake booster with a vaccum guage and it was working fine.
Turn the car off and the pedal is firm, start the car and the pedal goes soft. :confused:

We blocked off the lines going to the front calipers and everything is perfect. So there can't be any problems with the rears.

My father looked at them the other day and reckons that when the engine is running 2 of the pistons in the front right caliper are returning further than normal. (Yes we know this shouldn't be possible).

Basically that was just a long spel to ask, has anyone had similar troubles or can think of something else we should be checking.

Thanks heaps for any thoughts on the subject.
MadPhil

Jvette73

Did you bench bleed the master before putting it on? It can be forever trying to get the air out if you dont first bencj bleed the master before installing. Also do your rear calipers have 2 or 3 bleeders. If it has 3, then ignore the lower bleeder on the outside half. It should be plugged. I had trouble gravity bleeding mine with the lower bleeder since it was letting air back in as fluid dripped out. The gravity bleed method worked good for me once I foillowed the correct sequence and ignored the lower outside bleeder on the rears. Just remove the master cap, fill the resovior, loosen the first bleeder and let it run till the master is half empty. Fill the master and let it run some more. Dot it twice for each bleeder while following the correct sequence. Again, ignore the bottom outside bleeder in the rear and bench bleed the master before starting. This is what finally worked for me.

Oh and welcome aboard :cheers: :smash:


[Modified by Jvette73, 5:40 PM 3/25/2003]

77Dream

:iagree: I had a heck of a time bleeding the brakes when I did mine, It took a long time to get it right. I would think there was no air in the lines, but sure enough, there was.

I would drive a little and use the brakes allot, then go home and bleed them. Had to do this several times before I finally got all the air out.

wayne_69_427

Always start bleeding the wheels from the r/r then l/r then r/f and l/f. The air is most likely in the longest line or furtherest wheel from the master cylinder.

joe73vette

BTW, if you didn't bleed the master you can get most of the air out by partially depressing the pedal and releasing about 100 times (it doesn't take that long). The little air pocket will clear out eventually.

Also, are you sure the rod between the power booster and master cyl is the same length as with the old master cyl?

Joe

Rockn-Roll

I think some of the problems people have with vette brakes is that the rear calipers have two bleeders, and they both need to be bled one at a time. Also, I find people trying different methods and not really knowing which method will work. My solution was to purchase a Brake Inspection and Repair manual from the State Bureau of Automotive Repair...you can find them listed in your local telphone directory under the government sections. Most manuals are around $50 and well worth it. You will be able to understand the brake system better, and to learn the proper method for testing and bleeding brake systems. If you don't feel the need to purchase the book, then read the rest of my post to find out what I learned from the book:

According to the Bureau of Automotive Repair (BAR) brake inspection & repair manual the only bleeding method that will detect all leaks and bleed the system at the same time is to slide the box end of a combination wrench onto a bleeder, attach a clear hose to the bleeder valve, other end into a clear 1/2 fluid ounze bottle, open bleeder valve about 1/8 to 1/4 turn, (run engine at idle for power brakes) pump brakes with bleeder open while watching hose until clear bubble-free fluid exits then retighten bleeder, refill master cylinder every 20 pumps. Do this in order of RRI, RRO, LRI, LRO, RF, LF. Repeat this cycle once to be sure all air is out of the system and that no air is getting in.

If you keep getting air bubbles out of a bleeder then there is a leak somewhere, usually it's the caliper and replacing or rebuilding it fixes it. Holes in the system can be small enough to let air in, but not leak fluid which is why pumping is best because it will cause a vacuum in the system when letting up off the brakes, while providing the desired pressure to properly bleed the system.

This method is best because it activates the system the way it will be used thus detecting any problems that may occur while using the brakes on the road (except warped rotors which you find out upon test driving).

I think brakes are important, and if you can't get them bled properly then try to find a mechanic that will talk to you...see if they will let you read their BAR brake inspection & repair manual...they are required to have it at their site if they have the BAR Brake Inspection Station sign out front. Sometimes visiting when they are getting off with a 6-pack helps loosen their tonque...when I was the on-duty mechanic at a Chevron station I woulda spilled my guts for a beer...or was that spilling my guts after too many beers? Oh well, you get my point.

Jvette73

As per my Haynes manual the correct sequence is not as was listed in above responses. Its strange to me as well but the manual lists the sequence as left rear inner, left rear outer, right rear inner, right rear outer, right front, left front. This goes against to common belief of beginning with the longest line, nevertheless, its what the Haynes manual says and has been verified to me by several other forum members in the past. Another trick I learned through the forum members, which I used last time as well during my gravity bleeding, is to tap on the caliper with a hammer to help dis-lodge trapped air bubbles in the calipers as the fluid flows out.

MadPhil

Hi all.

Thanks heaps for all your input. Its great to have people that are willing to take the time and try to give advise. :hurray:

On closer inspection 2 of the 4 pistons in the front right caliper (when the engine is running) were returning further back into the housing. So when we stood on the brakes it was taking more oil to push them out that fraction further which is why the pedal went to the floor.

Why were the going back in to far you ask (well maybe). We had put the rubber boot on those pistons upside down (compare to the others).
The rubber of the boot was quite firm so when it was upside down the extra force, combined with the vibration of the engine running must have been allowing the piston to return to far.
I know it probably sounds really stupid, but that seems to be what the problem was. We fliped the boot over and they didn't creep back into the housing. Unfortunatly with pulling the caliper apart so many times we must have accidently put a nick in the O Ring seal between the 2 caliper halfs. So its now leaking out of there. But new replacements are on the way so hopefully soon (once it stops raining) I'll be out :steering: once again. :cool:

Which is good because over the next couple of nights I have to spend some time going over the race car. The the season end coming up no doubt it will take some hits.

Anyway thanks again for all your help and insights.
MadPhil