What's the best way to bleed the brakes on a 69?

[Greg L.]

I seem to be having issues with bleed my brakes(I've always hated the brakes on this car).

Booster is original.
All lines and hoses are new.
Calipers are remanufactured from Muskegon Brake
Master Cylinder is a new GM Restoration Parts one.

First I tried to gravity bleed with no luck, then I tried to vacuum bleed starting at the R/R with no luck.

Second, I took the master cylinder off to bench bleed it and it seemed to work. I hooked my vacuum bleeder up to the line connections on it and was able to pull fluid through so it should be okay. Then I hooked the vacuum bleeder up to the R/R caliper and with my thumb over the line where it would connect to the master cylinder I was able to pull vacuum. I also did the same to the F/R caliper and held my thumb over the front line at the master cylinder and could pull a vacuum on the front half too.

Third, I put the master cylinder back on the car and hooked the lines up and then tried to vacuum bleed it again but as before I couldn't pull any fluid from the rear reservoir.

Fourth, scratched my head, had a beer and then came in from the shop before I do something stupid and now I'm sitting here wondering if anyone has any ideas for me?

One point of interest on my bench bleeding.... as I push the piston in I get a small squirt from the front port of the front reservoir but nothing from the front port of the rear reservoir. as I release the piston there is a small "wave" of fluid from the rear port on both reservoirs. Shouldn't the front port of the rear reservoir also give a little squirt as the piston is pushed in? my four wheel disk knowledge is limited to only this car. Did I mention that I've always hated the brakes on this car??

Thanks guys.

[Edward J.]

Re: What's the best way to bleed the brakes on a 69?

Greg, did you use stainless lines on the car?I find there are harder to seal, if so re-check all the fittings crank them a extra turn. there harder to seat. and the same goes for the steel lines with a leak.

If there any fittings that are not sealed it will pull in air each time the pedal is released, which will cause a real problem trying to bleed the brakes.

If the master cylinder is bench bleed properly and then installed it will push fluid each caliper,If the system has a improperly sealed fitting it will pull the air into the system each time the pedal is released.

I don't know if you have used the bleeders with the check valves in them, but its a good one man operation.some of the auto parts store carry them.

[Phil D.]

Re: What's the best way to bleed the brakes on a 69?

I bought one of those mityvac vacuum bleeders and promptly took it back for a refund. I can't imagine how anyone could expect it to work. Sucks air around the threads of the bleed screw. Tried the suggestion of putting grease on the threads and it just sucked the grease and then sucked air again.

On my 69 and on my brother's 72, it seemed to work best to do it the old-fashioned way with a helper in the car to push the pedal to the floor and hold it. On many other cars, I have been able to use the one-man setup of submerging the end of the bleeder tube in a jar of brake fluid, but again, the c3 seems to suck air too easily around the threads of the bleeder screw so that doesn't to be totally reliable.

I've never tried a pressure bleeder. Somewhere online I saw catastrophic pictures of a pressure bleeder malfunction and have been somewhat dubious of the idea, but in principle they should work great. There's instructions on here somewhere how to use a large c-clamp and a block of wood to hold the cap on the mc on instead of the chain that comes with the pressure bleed kit. As long as I can call my brother tho, I'll do it the old fashioned way. Its cheaper.

[Stephen L.]

Re: What's the best way to bleed the brakes on a 69?

Get yourself a helper and bleed the brakes the old fashion way, using pedal pressure. This will reveal any leaks you may have at the fittings etc. Just remember to fill the reservoir often.

[Bill C.]

Re: What's the best way to bleed the brakes on a 69?

the rear brakes are the hardest to work the air out of.

I always gravity bleed...
when bleeding the rear try and get the nose of the car higher than the back (slight upward angle).
When bleeding just set the master cap on top of the master cylinder- do not clamp it down.

1. loosen up one of the lines attaching to the brass block at the rear.
Let gravity bring fluid to that point.
2. tighten the line back up.
3. loosen the r/r inside bleeder screw and allow the fluid to flow out there.

*** I have at this point used the process described above where you put a hose from bleeder screw into a bottle of brake fluid. Then pump the brake pedal sevral times drawing fuild in and pushing out the air. This wil work nicely since there is fluid to push forward (from step #1).

4. then move on to the r/r outer bleeder.

5. repeat #3 and #4 for the left rear.

[Paul J.]

Re: What's the best way to bleed the brakes on a 69?

Greg,

I'm with Stephen. Several people have told me that they have used various bleeders successfully, and I have no reason to doubt them. But we still do it the old fashioned way. It only takes a few minutes, and it's cheaper too.

Paul

P.S. I like Step Four, especially the beer part. It always keeps things in persective for me, and lets me enjoy it as a hobby even with the frustrations.

[Larry M.]

Re: What's the best way to bleed the brakes on a 69?

For most of my car life, I bled brakes the old fashioned way using a helper....period. Always worked.

In recent years, I found that I can use a Mighty-Vac to initially fill the lines and calipers. Then have a helper (generally my unhappy wife) to do the final pressure bleeding by pumping the brake pedal. This combination of vacuun and pressure works well with DOT 3/4 fluid as well as DOT 5, which is harder to bleed since it likes to entrain/entrap air. I have never been able to successfully only vacuum bleed the system....especially when using DOT 5.

The use of the Mighty-Vac does save some time....which minimizes the time the wife sits in the car in the hot/humid garage with a fan on her and pumps the brakes and complains. So it IS worth something.

Maybe I should get the MOTIVE pressure bleeder and save her some aggravation??

Larry

[Rick B.]

Re: What's the best way to bleed the brakes on a 69?

All good points raised here..... I myself have only done it the "old fashioned" way and did so recently. I experienced similar problems to you but did not give up. I have spoken to some real old veterans from brake shops on this subject and for what it is worth they told me that once you replace so many components invariably there will always be massive amounts of air trapped somewhere in the system almost similar to an air lock (but not quite).
I found that perseverence and a rubber mallet ( rap each caliper numerous times periodically to "free" up the air bubbles/locks to move ) will eventually cause small amounts of fluid to appear and then gradually the system bleeds normally as one would expect.

Rick

[Greg L.]

Re: What's the best way to bleed the brakes on a 69?

Thanks guys, I like doing it the old fashon way too but thought I'd try out my vacuum bleeder for once. Plus I'm a one man show right now and I'd like to get them blead this weekend if possible.

The lines are TBW, not stainless. I decided against the stainless because of the problems they have with sealing and bending to fit properly.

Like I mentioned, I can pull vacuum at each caliper bleeder with my thumb over the line where it connects to the master cylinder for the front and rear half of the brake system so I'm thinking that the system should pull fluid through it with just the vacuum bleeder...but maybe not.

I also just noticed that with the master cylinder installed I don't see any "squirt" or "wave" of fluid from the ports in the reservoir when I step on the pedal. It's almost like the piston is already past the compensating port. I have pedal free play but could the rod between the master and booster need to be shortened? I guess it could also be because there is no fluid in the lines for the master cylinder to push against to cause the "squirt and wave" actions. Any thoughts on that?

I rebuilt the entire brake system on my GTO last fall and it was a pain to bleed the entire system too so maybe I just need to work at it a section at a time like I did with it. I'll try try getting fluid back to the bleeder block first and see if that helps.

[Edward J.]

Re: What's the best way to bleed the brakes on a 69?

Greg, don't make any adjustments to the push rod, it should be set from the factory.

Go back and recheck the fittings for tightness and look at them to see if theres any signs of leaks.

Bill- had a good Idea at the rear fitting into brass block - remove and raise the front of car to gravity bleed to the rear. and then open the caliper bleeder- outboard and fill the calipers with a old ketchup bottle and a piece of hose til the fluid comes out the brass block. the fronts are the shortest lines they short not give you to many problems

[Greg L.]

Re: What's the best way to bleed the brakes on a 69?

Thanks Rick. I always thought that pressure or vacuum bleeding was prefered after a complete brake overhaul because it eliminated the "air lock" issue so that's why I'm scratching my head on this one.

Time for round two!

[Terry M.]

Re: What's the best way to bleed the brakes on a 69?

I seem to be having issues with bleed my brakes(I've always hated the brakes on this car).

Booster is original.
All lines and hoses are new.
Calipers are remanufactured from Muskegon Brake
Master Cylinder is a new GM Restoration Parts one.

First I tried to gravity bleed with no luck, then I tried to vacuum bleed starting at the R/R with no luck.

Second, I took the master cylinder off to bench bleed it and it seemed to work. I hooked my vacuum bleeder up to the line connections on it and was able to pull fluid through so it should be okay. Then I hooked the vacuum bleeder up to the R/R caliper and with my thumb over the line where it would connect to the master cylinder I was able to pull vacuum. I also did the same to the F/R caliper and held my thumb over the front line at the master cylinder and could pull a vacuum on the front half too.

Third, I put the master cylinder back on the car and hooked the lines up and then tried to vacuum bleed it again but as before I couldn't pull any fluid from the rear reservoir.

Fourth, scratched my head, had a beer and then came in from the shop before I do something stupid and now I'm sitting here wondering if anyone has any ideas for me?

One point of interest on my bench bleeding.... as I push the piston in I get a small squirt from the front port of the front reservoir but nothing from the front port of the rear reservoir. as I release the piston there is a small "wave" of fluid from the rear port on both reservoirs. Shouldn't the front port of the rear reservoir also give a little squirt as the piston is pushed in? my four wheel disk knowledge is limited to only this car. Did I mention that I've always hated the brakes on this car??

Thanks guys.

When I put DOT5 in my 1970 I found gravity bleeding didn't work when there was air in the lines, and the purpose of bleeding the brakes is to get the air out.

I also found drawing a vacuum at the calipers only pulled the pistons back into the calipers, and wouldn't pull the fluid from the master cylinder. I think some of that may be because the DOT5 is more viscous than mineral based brake fluid.

I had to use pressure to force the fluid to the calipers -- then gravity worked fine.

BTW: The worst brake issue I ever worked on was a 1969 that had the wrong master cylinder. Some one named Bubba put a power brake master on a manual brake car. That was back before we identified the different casting numbers. It resulted in identifying the proper casting numbers, but I had an awful time convincing the owner that the solution to his "poor braking" complaint was another new master cylinder.

[John H.]

Re: What's the best way to bleed the brakes on a 69?

I quit fiddling with gravity-bleeding, vacuum-bleeding, and oddball stuff like the "Phoenix Injector" years ago, when I bought a Motive pressure bleeder; best sixty bucks I ever spent for a tool. Bleeds Corvette disc brakes (from dry) in ten minutes, with no helpers, every time, and you don't have to keep checking the master cylinder.

I use a 6" C-clamp and a piece of 1-1/2" square tubing to hold the adapter on instead of the chain-and-wingnut arrangement that comes with it. Nothing moves brake fluid like pressure.

[Greg L.]

Re: What's the best way to bleed the brakes on a 69?

Success! Thanks guys.

I took each bleeder out and stuck a rubber nipple in it's place to make an air tight seal(too much air was leaking past the bleeder threads as someone had mentioned) then used my vacuum bleeder. I needed to pull about 15 " Hg before anything would flow but once I got it up there it worked very well to get fluid to the calipers. Once fluid was there they blead out normally the old fashion way.

I did however have two leaks with these new lines, one at the rear right and one at the diff pressure switch. I loosened and tightened them a few times and I think I got it but I'll double check later today. If these TBW ones leaked like this I can just imagine what stainless ones are like.

John that's a neat set-up. So how does it work?

Does the air tank that you pump up just have air for the pressure or does it push fluid into the reservoir as well?

What pressure do you pump it up to?

If it pumps fluid into the reservoir then how do you prevent it from spilling fluid when you remove the cover from the master cylinder?

[Larry M.]

Re: What's the best way to bleed the brakes on a 69?

Greg:

Glad you "got er done". The idea of the rubber plugs was excellent.....since these bleeders can pull in a lot of air around the threads as you found out. When I use the Mighty-Vac, I use a quart mason jar as a vacuum reservoir and first pull it down to 15" HG. I pinch off the temporary hose to the bleeder to ensure no air leakage back into the jar. Then I open this hose and the bleeder for the brake set I want to bleed. It normally takes 2-3 times like this to fill up that section of brake line and caliper. But it goes rather quick.

The MOTIVE bleeder John showed uses around 5-10 psig air pressure. You can do it either way....filling the tank with new fluid, or just using the tank to supply the correct pressure to the master cylinder. Some leaks/drips/mess is usually encountered if you use the first option and fill the MOTIVE tank with brake fluid. It is a very neat setup, and recommended/preferrd by many. I just don't do this task enough to buy one and keep it around. The garage is too full as it is.

Larry