Welcome to the Corvette Forums at the Corvette Action Center!

Bleeding brakes on my '81. Pro tips anyone?

Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
After discovering the brake fluid in my vette was at least 6 years old, and seeing that it was no longer clear, I decided I wanted to change the brake fluid out. The method I was going to use was gravity bleed through the rear calipers first, but making sure the fluid never got empty at the M/C. I got the brake fluid to flow out, but after a while, it completely stopped flowing. I did NOT pump up the brakes or disconnect the filter at the booster, so I'm guessing that was my problem....

Anyways, I broke off the outer bleeder at the right rear, so I replaced the caliper (after spending HOURS trying to extract the bleeder). Obviously now the brake light is on and the pedal goes to the floor. However, I cannot bleed the rear brakes at all. I get equal amounts of air and fluid coming out the back. I have drawn an entire large bottle of fluid through the rear brakes, but I'm sucking air in somewhere. It's driving me absolutely nuts. The fluid is clear at the M/C, and I haven't let it get dry. I have a mityvac hand vacuum pump that holds vacuum, but when I open the bleeder screw just a quarter turn, fluid and air are coming out. So air is coming in from somewhere. I have read and researched this for HOURS. I tried the grease trick where I coated all the connections; bleeder, hose, hose connections, but still I am sucking in air. What about Teflon tape around the bleeder screw threads? The front of the vette is slightly higher than the rear (if that matters; my jack stands are slightly uneven in height). Is there some trick or tip anyone has before I pull my hair out and get it towed to a shop? Should I get a helper to depress the brake pedal and try to bleed that way? I'm at wits end. Thanks for all replies.

-Tatortot
 

bill81vette

Moderator
Joined
Jan 17, 2004
Messages
4,316
Location
Troy,NY
Corvette
1981 dark blue metallic
'Your sucking air from somewhere'...the only thing that has changed is the caliper...
I would not use teflon tape on the bleeders
is the bleeder line tight???
have you tried to make the vette level when you bleed the calipers???
I would take the caliper off and pressurize it on a bench to make sure its sealed..
otherwise call the vendor and see if they have another replacement.
good luck!!
 

Antz81

Well-known member
Joined
Dec 21, 2013
Messages
936
Location
Auckland, New Zealand
Corvette
1981 4 speed
Had the same problem bleeding mine. Bleeding the brakes by getting someone to depress the brake pedal solved the problem.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
First thing to do is not use vacuum bleeding on C2/C3 disc brakes. The piston seals were not designed to seal against a vacuum and they will leak air when a vacuum is applied.

To bleed, the best way is to use a pressure bleeder.

Second best is to foot bleed. Start by jacking the back up high and removing the tires. Fill the master then open all four bleeders on the rear calipers. Close each when it starts to weep brake fluid. Now open the bleeders on the front calipers. Leave them open until they week fluid. All the time, keep the master full.

Once you have fluid at all six bleeders, then put your assistant i the car. Tell them to smoothly and slowly stroke the pedal three times and hold. When you open the bleeder, have them push with modest speed, not smash the pedal to the floor. As they push you need to close the fitting just before they bottom the pedal.

First bleed the master either by opening the bleders, if it has them, or by cracking the brake pipe fittings.

Now, go do the calipers. Start with the inside bleeder on the LR. Go LR-I, LR-O, RR-I, RR-O, RF and then LF.

Best fluid value is Valvoline Synthetic in quarts.

Good luck.
 

GTR1999

Well-known member
Joined
Sep 4, 2003
Messages
1,146
Location
New Haven CT
Corvette
1969,1972,1975
Hib listed very good advice above. Good idea to clean out the old brake fluid too.

What I do is to check the rotor runout and bearing play, if those are really out of spec and you're using lip seal calipers then you're going to have air in the system in short order.

With the rotor runout under 005" ( I set them to 000-0025) make sure the rotors are clean and scuff them with 100 grit paper or a DA.
If you broke the front calipers away from the hose then you're going to need a new copper washer for them. It goes between the caliper and hose. If the hoses are more then 7-10 years old check them good, they close up just your arteries do with fatty foods. It could get so bad it will close off and lock the brakes on.

Once the rotors and hoses are good, new pads if used in place, then you can bleed the system. If the MC was not broken loose or run dry you shouldn't have to bleed it but if so I like to bench bleed them and install back on the car. I use good ole DOT3 brake fluid and like it as long as you watch it like you have. It will absorb moisture and become acidic over time. For I used the 2 person method of bleeding and have had great success with it. Now I use a motive bleeder and really like it. Once I changed the way it clamps on the MC the system will be pressurized and you can watch the gauge to see if it drops before opening a bleeder. If it does then there is a leak somewhere you have to find and repair before going any further. Once you're sure there are no leaks I go to the RR and bleed both sides, then go to the LR and do the same. I use a clean vinyl tube on the bleeder into a clear glass jar with clean BF in it. Once the bleeder is opened look for bubbles and dark fluid. Close once you see it go clear without bubbles. Do the other bleeder the same and then the other caliper the same. Then I move on to the fronts and do the RF & LF. The nice thing about the Motive is it will hold about a qt of new fluid and keep the MC from going too low. There should be enough BF in it to do one wheel set.

The bleeders are tapered seat so you don't need any sealant on them and don't want to risk system contamination. If the bleeder is frozen in place chances are the sear is damaged and sometimes a new bleeder won't work or seal.

Properly set up with runout, bearing set point, pads and bleeding the brakes will work as good as any new car today. They were good systems starting in '65 the problem was when mechanics starting working on them without understanding the way they function compared to the other cars of the period.
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
Fantastic replies from all. You guys are absolutely correct in that the Mity-Vac is a waste of time. I had my girlfriend pump the brakes as I bled and it got MUCH better. The brake light even went out. However, the pedal still goes to the floor. It stops, but it can be better. I bled each bleeder at least a dozen times, starting at the RR inner, then outer, then LR inner, then outer. , but every time I cracked the bleeder, tiny (I mean minuscule) bubbles came out. It doesn't matter how much I bled them, they just kept coming. Any thoughts on why that is? I'll jack the rear up higher in a couple of days and try bleeding again.

A quick question: per the shop manual, it says to first crack the bleeders, THEN apply the brake pedal. Is this correct? Or should the brake pedal be applied first, THEN the bleeder be opened? Thanks!

-Tatortot
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
I don't care too much about what the manual says as far as "cracking" the bleeders.

Have your assistant pump the pedal slowly three times and hold. Open the bleeder. As she nears bottoming pedal close the bleeder. Have her release the pedal. Wait 3 seconds then pump three times again and so on and so forth until you get no air. Also, parts of the insides of those calipers can trap air due to surface tension. On the last pedal pumping session, I give each caliper a good knock with a plastic hammer to dislodge any bubbles.

If you still are getting air, given the master cylinder is in good condition, then I'd say your calipers are shot and either need to be replaced or have the bores sleeved then all new seals installed. Them them apart and inspect the bores. If you see any pits or corrosion, scrap or sleeve the calipers. pits and corrosion cannot be repaired with honing.
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
Thanks for the info, Hib. I will do just as you said. Thanks!

-Tatortot


I don't care too much about what the manual says as far as "cracking" the bleeders.

Have your assistant pump the pedal slowly three times and hold. Open the bleeder. As she nears bottoming pedal close the bleeder. Have her release the pedal. Wait 3 seconds then pump three times again and so on and so forth until you get no air. Also, parts of the insides of those calipers can trap air due to surface tension. On the last pedal pumping session, I give each caliper a good knock with a plastic hammer to dislodge any bubbles.

If you still are getting air, given the master cylinder is in good condition, then I'd say your calipers are shot and either need to be replaced or have the bores sleeved then all new seals installed. Them them apart and inspect the bores. If you see any pits or corrosion, scrap or sleeve the calipers. pits and corrosion cannot be repaired with honing.
 

dougelam

Well-known member
Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
Hi stingray, are you able to to send a pic of the caliper on the car that you replaced?


Sent from my SM-T530NU using Tapatalk
 

Antz81

Well-known member
Joined
Dec 21, 2013
Messages
936
Location
Auckland, New Zealand
Corvette
1981 4 speed
While we are on the subject of bleeding brakes. I've had the hard line that connects to my left rear caliper out for a few weeks now (flexible line still in in place), while I replaced the wheel bearing (What a fun job that was, had to make a new shim to get the play in the bearing right. now sitting at about 0.003" using a 0.148" shim (0.003" bigger than is supplied in the kits).
Manual says if it was disconnected at the wheel then only that wheel needs to be bleed.
What do you guys think? I'm inclined to think that I should bleed both wheels since air could easily traveled up into the main line over that time.
 

dougelam

Well-known member
Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
If you removed the line and did not push on the pistons then there is no need to bleed anything!
If you were to look at the hole before you put the line back on you would have seen the fluid just inside.
As you were screwing the line back on I'm sure it gravity bled itself as you tightened it up.
If you are unsure about this bleed away ☺

Sent from my SM-T530NU using Tapatalk
 

dougelam

Well-known member
Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
Nice, paint or bare?

Sent from my SM-N920P using Tapatalk
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
I assume paint, as the brake clean I sprayed on it clouded the finish ;LOL


-Tatortot
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
Here's a picture of the new caliper. You can see what the brake cleaner did....

20160319_210448002_iOS_zpshbnjfglx.jpg
 

GTR1999

Well-known member
Joined
Sep 4, 2003
Messages
1,146
Location
New Haven CT
Corvette
1969,1972,1975
Here's a picture of the new caliper. You can see what the brake cleaner did....

20160319_210448002_iOS_zpshbnjfglx.jpg

I see the rotor is held on now by the lug nuts so you will want to check the run out closely. You want it under 005" thru 360*. Also I see an empty bracket for the brake hose. There should be a horseshow clip there to hold the rubber hose in place. There should be a steel caliper line from the hose to the caliper.
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
GTR1999,

The horseshoe clip is there, holding the rubber hose, but is not visible at that angle. The e-brake clip has sheered off, and apparently that isn't the first time. It looks like somebody welded in a replacement and that broke too! But when I pull the E-brake the car stops so I know it's working, at least on one wheel :L

Thanks for all the replies. She's up and running again and braking great.

-Tatortot


I see the rotor is held on now by the lug nuts so you will want to check the run out closely. You want it under 005" thru 360*. Also I see an empty bracket for the brake hose. There should be a horseshow clip there to hold the rubber hose in place. There should be a steel caliper line from the hose to the caliper.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
I always pay close attention to brake how-to threads because of the safety issues.

If you removed the line and did not push on the pistons then there is no need to bleed anything!
If you were to look at the hole before you put the line back on you would have seen the fluid just inside.
As you were screwing the line back on I'm sure it gravity bled itself as you tightened it up.
If you are unsure about this bleed away ☺

Sent from my SM-T530NU using Tapatalk

I'm sorry but the above is very bad information.

Anytime you open up the brake hydraulics to the atmosphere, you need to bleed the brakes. The statement that "...it gravity bled (sic) itself as you tightened it up." is completely inaccurate.

In fact, the only air that will "gravity bleed" will be air above the fitting in question. Any air below the fitting, and there will be some, will not gravity bleed.

Admittedly, we're likely talking the difference between a somewhat "soft" pedal and a "hard" pedal rather than no brakes and a hard pedal, but brakes are both a performance and safety issue.

So, if you open the brake hydraulics to atmosphere bleed the darn brakes! And there is another reason for bleeding brakes after opening up the system. Brake fluid absorbs moisture. Any moisture content reduces the fluid's boiling point and you want to avoid that as the lower the boiling point, the sooner you boil the fluild and, when that happens, the pedal goes really soft.

If you want to read good information about the C2/C3 disc brake system, look no farther than right here on the CAC.

Big Block From Hell Series | Part 12 - Most of everything you'd ever want to know about 65-'82 Brake Service - CorvetteActionCenter.com
Big Block From Hell Series | Part 13 - The rest of everything you'd ever want to know about 65-'82 Brake Service - CorvetteActionCenter.com
 

dougelam

Well-known member
Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
I'm sorry hib but your link to brake service states "gravity is simple and effective" where do you get "completely inaccurate" from that?
Maybe you better stick to researching stupid shit like valve stem clearance and the miniscule differences in fluids that at the end of the day No one cares

Sent from my SM-T530NU using Tapatalk
 

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors

Dealers:

MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Parts/Accessories:

Vetteskins

Advertise with the Corvette Action Center!

Double Your Chances!

Partners

Top Bottom