WTB am I doing wrong? Bleeding the brakes on an old GM

Posting here to get a bit more exposure, but I'll link the build thread too. I also know we just had a thread on bleeding brakes. 

1965 buick skylark, recently swapped in front disks. New correct brake master and prop valve for disk front drum rear no power assist. New calipers up front, new wheel cylinders in the back. All soft lines new. Many hard lines new. All wheels get plenty of fluid flow from the master when the pedal is pumped and the bleeder open. 

There are 6 bleeders total. 2 on the master, one at each wheel. I've bled the piss out of all 6 bleeders, and am getting no more air out of any of them. Yet the pedal still sucks. There is resistance but I can push it to the floor with my foot if I jam on it. There is clearly air somewhere. 

My method is to open a bleeder with a hose attached (going into a bottle with some fluid in it), pump the pedal slowly 5-10 times, check fluid level in bottle and master, continue if air move to next wheel if none. I've tried putting some suction on the bleeders, and I get air bubbles but I think it is from around the threads. I have a motive power bleeder but not the adapter to connect to the flat top of the GM master. Gravity bleeding moves fluid from all bleeders except the 2 on the master. 

What the berk am I doing wrong? What should I try to make this right? I have bled brakes many times many different ways and it is normally a 15-30 minute job for me. I'm hours into this with not much improvement. I have a strong feeling the air is inside the master and I don't know how to get it out. 

you, my friend, have a bad master cylinder right out of the box.   you're not compressing air, your piston seals aren't maintaining seal at higher pressure.   it happens.  time to get a new MC.

hmmm, just typing this out is helping. I think i'll try putting grease on the threads of the bleeders. Maybe air is being sucked back in past the threads on the final pedal stroke. Even though air isn't coming out in the next stroke I guess it could still happen. 

The two bleeders on the master are the ones that really suck fluid back in when you release the pedal. 

AngryCorvair said:

you, my friend, have a bad master cylinder right out of the box.   you're not compressing air, your piston seals aren't maintaining seal at higher pressure.   it happens.  time to get a new MC.

that would make me feel better, for sure!

edit, also, how do you know this?

Calipers on the correct sides?

Robbie said:

AngryCorvair said:

you, my friend, have a bad master cylinder right out of the box.   you're not compressing air, your piston seals aren't maintaining seal at higher pressure.   it happens.  time to get a new MC.

that would make me feel better, for sure!

edit, also, how do you know this?

because your bleeding at the corners isn't getting air out, yet your pedal goes to the floor when you really stand on it.

but if you think you're sucking air back into the MC when you bleed it, just open those bleeders and let it gravity bleed.  best to have a length of clear plastic tubing over the bleeder, with the free end up.  the clear plastic tubing serves 2 purposes:  1. it lets you see the fluid and any air bubbles as they exit the bleeder and rise up the tube, and 2. it keeps the brake fluid from dribbling all over that side of your engine compartment.

after you do this, if the pedal will still go to the floor, i'm keeping my money on bad MC right out of the box.   i've had several reman MC's that were E36 M3.  mostly A1 Cardone brand.

Furious_E said:

Calipers on the correct sides?

yep, bleeders are up!

Alternatively, does it stop fine?  Some systems just suck and don't feel even remotely confidence inspiring, even when bled properly.  Example, non-hydroboost GMT400s.

I see a few things.

Was the master bench bled? In a vice while tapping it? Did you avoid bottoming the piston and damaging the seals?

When pushing fluid through the system and bleeding at each wheel "pumping" tends to suck fluid or air back in the bleeder. Open bleeder, press pedal ONCE and hold,  close bleeder, release pedal, then keep repeating until no bubbles. Don't forget to check master & add fluid as needed.

Depending on caliper piston size and piston size of the new master, the original manual brake pedal for 4 wheel drums may not be the correct ratio for the disc/drum combo. You may need to move the clevis mounting location. If the original clevis was higher on the pedal (near the pedal pivot point) than the disc application requires the pedal would press easily with a long travel.

¯\_(ツ)_/¯ said:

Alternatively, does it stop fine?  Some systems just suck and don't feel even remotely confidence inspiring, even when bled properly.  Example, non-hydroboost GMT400s.

I haven't tried to drive it yet, because I know the pedal should not get all the way to the floor. Even if the pedal isn't confidence inspiring it should stop north of the floor. 

Also this car has very powerful 'idle drive' meaning you need a lot of brake pressure just when shifting from park to reverse. So I'd rather not even try that shift without being a bit more confident in the brakes!

NOT A TA said:

I see a few things.

Was the master bench bled? In a vice while tapping it? Did you avoid bottoming the piston and damaging the seals?

When pushing fluid through the system and bleeding at each wheel "pumping" tends to suck fluid or air back in the bleeder. Open bleeder, press pedal ONCE and hold,  close bleeder, release pedal, then keep repeating until no bubbles. Don't forget to check master & add fluid as needed.

Depending on caliper piston size and piston size of the new master, the original manual brake pedal for 4 wheel drums may not be the correct ratio for the disc/drum combo. You may need to move the clevis mounting location. If the original clevis was higher on the pedal (near the pedal pivot point) than the disc application requires the pedal would press easily with a long travel.

I did not bench bleed the master. I know about the process, but this master did not come with the little bench bleeding kit (like the loop hoses or the output plugs) so I didn't do it. I thought that I could just use the two bleeders on the master once everything was installed to get the air out of the master. I dunno about bottoming the master. I have pushed the pedal all the way to the floor of the car but I really hope that doesn't bottom the master (that would either mean horrible design or I have the wrong master). 

Unfortunately as much as my wife loves working on cars with me, I have not yet tried the 2 man bleeding. I usually need it on clutches but have never yet needed 2 people for brakes. I can watch the lines on the driver's side however as I slowly pump the pedal and the fluid doesn't really back up when releasing the pedal. As I mentioned above however the two bleeders on the master DO suck a lot of fluid back in when the pedal is released. I could probably try the 2 man method. 

There are two holes on the pedal for the clevis pin. One for power brakes and one for manual brakes as I understand. I'll double check but I didn't intend to change it. 

New master, I wouldn't worry about having damaged seals by pushing the pedal down.

Have you adjusted the drum brakes? If the shoes aren't making contact with the drums pretty quickly in their travel you can get a soft spongy pedal that sinks to the floor because the wheel cylinders are taking up the extra fluid.

AngryCorvair said:

you, my friend, have a bad master cylinder right out of the box.   you're not compressing air, your piston seals aren't maintaining seal at higher pressure.   it happens.  time to get a new MC.

Was thinking the same thing, testing the MC with plugged outputs would confirm.

Here's another one - look at the flares on the ports on the new Master Cylinder. When I replaced the MC on my Courier, the MC was fine, but because the flares on the ports (bolt on) were different, I could never get air all the way out.. Pic for example.

dculberson makes a very important point I forgot to mention about the drums being properly adjusted.

I'd remove the master & bench bleed with the hoses. You can buy a cheap kit to do it at a local advancepepzone. Probably didn't bottom master since you didn't bench bleed. Be sure to tap the master bench bleeding.

I manually bleed using a wood stick to hold pedal if I'm working alone. Takes more time than two person but works the same. Loosen bleeder, press pedal, install stick (cut to length) between steering wheel & pedal, tighten bleeder, remove stick. Been doing it for at least 40 years.

If discs were only offered including power assist you may need to calculate the correct pedal ratio for manual disc application based on the caliper piston size and master piston size & then change clevis mounting point (or master piston size) unless you plan to add assist.  I don't have the math skills, so I have others figure it out for me as the need arises when I'm building cars for people.

Only pic I found quickly, haha. Also serves as trunk prop rod for my Firebird. I have several sticks marked for various cars of my own, customer builds I give them the stick I make for their car.

[URL=https://s240.photobucket.com/user/NOTATA/media/Firebird/MVC-017F.jpg.html][/URL]

dculberson said:

New master, I wouldn't worry about having damaged seals by pushing the pedal down.

Have you adjusted the drum brakes? If the shoes aren't making contact with the drums pretty quickly in their travel you can get a soft spongy pedal that sinks to the floor because the wheel cylinders are taking up the extra fluid.

I’d start here. Even with no air, poorly adjusted drum brakes in the rear will cause a low pedal and poor feel. 

Additionally, if they are way out of adjustment, it can combine with the action of the mechanical proportioning/safety valve causing poor feel and long travel. 

drum brakes are adjusted to the point where they turn by hand but the shoes are juuuuuuust starting to engage. ie it is very difficult to remove the drum without a hammer. Does that seem right?

I hadn't originally done that but it was mentioned in my build thread. So good call everyone. 

In reply to NOT A TA :

ha! great call on the stick. I'm already using a stick just to reduce the need to get into and out of the car 100 times, but I hadn't thought about bracing it against the steering wheel. 

In reply to classicJackets :

Interesting - I'm pretty sure all my flares are the same, but I can double check. 

re: clevis hole

To my knowledge no disks were offered in 1965. It was only 4 drums, and only a single reservoir master. The option was power or not. 

I'm going to a dual reservoir master from a non-power assisted car that did have disk/drum setup (1967 skylark), but I think these master cylinders from GM stuff of the era are all highly interchangeable as long as you get the setup that matches your car (power or not and drum/drum, disk/drum, disk/disk). 

This was basically all in the front disk conversion kit that I got. I just looked at rock auto and it shows the single res 1965 master has a bore of 1 inch and the dual res 1967 master also has a bore of 1 inch. I don't think a size mismatch is the issue here. 

a bench bleed kit like this is not a bad idea, I should probably have one:

https://www.amazon.com/Dorman-13911-Master-Cylinder-Bleeder/dp/B001SG8ZC0/ref=asc_df_B001SG8ZC0/?tag=hyprod-20&linkCode=df0&hvadid=312064691975&hvpos=1o2&hvnetw=g&hvrand=15727882473205915641&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9021588&hvtargid=pla-435726495565&psc=1

so here's a question - what's the performance difference between bench bleeding in a vice and bench bleeding in the car? 

ie if I hook up the return tubes to go right from the master outputs back into the reservoirs, then I should just be able to pump the pedal until its all clear and that would be the same as bench bleeding correct? 

That kit works fine for occasional use. I'd switch to clear tubing.

In a vice you can bleed with the master level where in many cars they're tilted up. You can tap the master to release bubbles while moving the piston in a vice. You can tilt up in front and pump a couple times, then tilt up in back a couple times in a vice. You may have a longer piston stroke in a vice than the pedal travel in the car will provide. Don't pump like a mad man, just slow steady strokes.

In reply to Robbie :

yep, NOT A TA nailed it.

Robbie said:

In reply to NOT A TA :

ha! great call on the stick. I'm already using a stick just to reduce the need to get into and out of the car 100 times, but I hadn't thought about bracing it against the steering wheel. 

Rather than a stick, I use the jack handle from the floor jack. Wedge it between the brake pedal and the seat. 

I recently replaced the master on my car and had a similar problem where the brake pedal was soft and bleeding only got me so far. I jammed the jack handle in there and left it overnight. Bled the next morning and saw lots of air bubbles being spit out. End result was much better!

ymmv

You absolutely need something applying pressure to the brake pedal when cracking the bleeders loose. I tried to one-man my Jetta for a couple sessions before I enlisted my daughter to work the pedal. I got so much air out of one line and it made a huge difference in pedal feel.