SpyderD

I've always had problems with the soft brakes in my car. The brakes travel to the floor, although I can pump them up at times. With a strong cam in the car I know there isn't much vacuum to operate the brakes, but I don't think that's the problem.

So this weekend I tried to bleed the brakes, rear brakes first. With my wife pumping the pedals I couldn't get a constant flow of fluid out of the bleeder valves. I followed prescribed methods - attache tube to valve, pump a few times, keep peddle depressed, open valve, close valve when pedal released. Fluid would come out with the pedal depressed, then actually appear to get sucked back into the calliper after a second while the pedal was still depressed. I tried all four valves - same results. Had my wife pump like crazy, still not able to bleed.

Previous owner replaced brake booster, master cylinder, brake pads, some other brake work possibly a couple years ago. Could it be a bad master cyclinder? Brakes have sucked since I got the car and I did try to bleed the brakes about a year ago with the same results before I turned the car in for an extended engine rebuild. Brakes seem to be getting worse.

blunsford

Low vacuum won't cause that problem.

The way you described bleeding the brakes is wrong. You close the bleeder valve while the pedal is being held down to the floor. You don't release the pedal from the floor until AFTER the bleeder valve is closed.

SpyderD

no, no, no. I close the valve when the peddle is still depressed. It blows out brake fluid and then sucks it back in after a second WHILE THE PEDDLE IS STILL DEPRESSED.

theandies

First, bleed the master cylinder then start with the right rear caliper and work your way around the car to the left front caliper. Sequence should be rt rear, left rear, rt front, left front. You may have "gook" (technical term) in the lines that are clogging the bleeder. If you can't get good flow after the above steps the I suggest flushing the system and starting with all new fluid. You may also want to look at your flex lines. If they are old then they may need replacing because the rubber gets old and when you apply your brakes they may be expanding causing a spongy pedal. It sounds like a full brake system inspection is in order. Vette brakes can be a pain so take you time and look at everything. The next time I have to do mine I am going to get one of those brake bleeder pumps to help me (my wife thinks its boring sitting in the car pumping the pedal).
Good luck

PRNDL

Sorry to change the subject, but is it just me that has the word "travel" highlited as a link? Is it some friggin spybot on my computer or is it something the original poster put into his post? I have been getting a ton of popups lately and have run some antispyware programs several times... :mad
MJ

foundvettelifeisgood

MJ--My travel is not highlighted.

SpyderD--I suspect it relates to the booster. :smash:

SpyderD

OK I'm getting some flush out of it after about an hour of working on it. Not a constant flow, some of it is still getting sucked back in and there is always a gap of air in the clear tube I am using between the fluid getting pumped out of the caliper and the jar and fluid I have in the cup that the clear tube leads to (I am making sure no air gets sucked back in). I'm having my wife pump it up ten times and hold it before I open the vavles, bubbles are poping out. After about an hour of pumping between calipers I got maybe 2 cups out (I now owe my wife a bunch of dinners out for her efforts) and the fluid comes out clear. Maybe this is exactly what is supposed to happen? What a pain!

Should I take the master cylinder out and "bench bleed" it? I do not get any bulge in the flexible brake line when pumping, it looks like it was replaced by the previous owner. foundvettelifeisgood - The booster was also replaced (looks like a rebuilt unit). Now I can understand a bad booster effecting the power brakes but not causing the brakes to bleed back in with the peddle down. Can you explain? I thought boosters were fairly full proof.

bmizell

I have a 74/350 that was doing the same thing. I went through a couple of gallons of brake fulid, replaced the calipers. the master cylinder and all of the rubber flex lines. including 75% of the seel lines. I later found out that the C3's have a bad habit of allowing air to escape into the system if your rear wheel bearing are out of tolerance. I am currently installing an upgrade O ring seal package which allows more seal area than the typical lip seals.along with new cross drilled rotors. While I am at it I am also rebuilding the rear suspension. One thing just leads to another.

SpyderD

bmizell - you mean rotor run out? That's a possiblity, the trailing arm bushings need to be replaced, the car has about 90,000 miles on it, I have no doubt the bearings need to be replaced.
but would this cause the inability to get a good bleed on the brakes?

I do have an update - This afternoon I tried the front brakes and got a good bleed, poured out like crazy.

Well I put all the wheels on so I will be able to tell tommorrow if the half a&&d bleeding job I was able to do on the rear firmed up the brakes or not.

GTR1999

Sounds like rear brake system is pumping air. You have to check the rotor runout and get it under .003" if you're going to keep a steady firm pedal. Use the indicator to check the bearings for end play, should be under .003" also.
Do a search of the archive on rear bearings,brakes,bleeding problems- there should be a LOT of info there.
gary

GDaina

His problem is getting a steady flow of fluid from the rears...rotor run out won't hinder the flow of fluid. Do you have a air compressor? Get a power bleeder, use no more than 5# air pressure. If you don't have those, I would consider taking it to a shop and have them power bleed the rears....assuming your rotor runnout is within specs.

You can make a power bleeder....use a spare MC cover and attach an air chuck fitting, or use a flat 1/8" piece of metal, lay a healthy 1/4" bead of silicone to seal against the MC...seal the hole with silicone...clamp the flat metal with C-clamps. If you use this set up, you will have to replenish the MC with fluid once the baby jar is half full with fluid.

gliot1

I had the same problem until I bled in the proper sequence. Most cars you bleed longest line to shortest. Not so on a C3 Corvette. Check the shop manaul. Off of the top of my head I believe its Left rear, right rear, Left front right front. I bled until I was blue in the face and could not get a hard pedal. After I followed the proper sequence it firmed up immediately. Awhile back someone posted the technical expalanation of this, but I can't reacall it.

carriljc

I'm going to make one of these today. I'm tired of struggling with bleeding...besides it looks like fun to make.
http://www.bmw-m.net/TechProc/bleeder.htm

SpyderD

Sequence in Haynes manual says LR RR. But I checked out a bunch of posts here and almost everyone says do it RR (furthest away) then LR. So now I am confused. I tried RR LR.

I have a vacuum guage, do you think I can rig that up to be a bleeder pump? It can pull out fluid from the valve I guess.

Mack

Left rear IS., L.R. OS., R.R. IS., R.R. OS., Left Front, Right Front. Exact opposite of a normal car.

72GACRZR

Is this related to the propotioning valve? If it's stuck to one side, it could be cutting off the rears.

MN-Brent

I gravity bled mine with no success and then I did pump and hold and got a super solid pedal (even better than my 98 Blazer).

I used this sequence: RR inner, RR outer, LR inner, LR outer, RF, LF.

During bleeding, you are having fluid pump out and then back in with your clear hose attached to the bleeder with the pedal firmly pushed down??

EDIT: When you bleed the brakes, have the clear hose moving upward from the bleeder so the bleeder remains covered in fluid in the tube or no air is touching the bleeder metal.

Usually if you have an air leak anywhere (when your bleeding the brakes), you would have a fluid leak also (not talking about air pumping calipers while driving). If you have no fluid leaks, I would start looking at the Master Cylinder (MC) and replace it if in doubt, its cheap. It has been stated that these are sometimes bad out of the box.

I would also double check how your wife is holding down the pedal.

Also you are not susposed to let the pedal travel all the way to the floor as this stresses the seals in the MC. Have your wife pump and hold and only let out smaller amounts of fluid, so the pedal doesn't max out its travel.

These brakes are not that difficult to manage.

PS: get the O-ring caliper pistons and dont leave home without em'

Good luck.
Brent...


[Modified by MN-Brent, 10:44 PM 10/20/2003]

70Stingray454

Just recently replaced all four calipers and master cylinder one of my cars. Day after being done headed for cruising on coast. When I hit Mississippi no brakes. Went to Chevy dealer had them check brakes, they bled them. Two days later returnibg home lost brakes again. Brought it back to shop, put new master cylinder and compression(proportion) valve component. Gravity bled brakes. No trouble since. May want to check it out.

SpyderD

OK my brakes are still bad so I am going to pop the rear wheels again this weekend, bleed them in the proper sequence, and see what happens. I also think I didn't have the rear end raised high enough (over the rest of the brake lines). Raising them higher would in theory help the air flow out right?

Then if that doesn't work I will start replacing parts - first m/c, then proportioning valve, then rear calipers (O rings sleeved calipers).

(edit) MN-Brent - I have indeed had that pedal all the way to the floor (almost pushed it through the floor board last weekend returning from the Vette Expo) to help it to stop, and I am sure my wife did the same thing while pumping the brakes. Maybe I should replace the m/c first.




[Modified by SpyderD, 2:10 PM 10/21/2003]