Air in brake system still?

[roger1]

Are the brake lines original? Rear cylinders? There might be a tiny leak and as air gets in your pedal deteriorates.

Like I told Longroof, the rear cylinders are Bendix that I put in back in 2013.
The brake lines are original but they look really good. The car only has 75K on it and never lived anywhere but Texas. No winter or salty conditions at all. No corrosion of any kind anywhere underneath or on the body of the car either.

 

[Mike T]

I replaced the master cylinder in my 65 GTO years ago and even though the numbers for the master cylinder matched my application I ended up with squishy pedal. Long story short, it turned out the piston travel in the new master cylinder was shorter than the one that came off t he car. Brought it back to the parts place and swapped it for another of the same model and it worked just fine.

 

[fleming442]

When I first got my Bonne, I had some problems with the brakes. What I found was that the rear inlet from the reservoir wasn't sealed correctly and it would suck air in. I found it accidentally while removing the cap to put fluid in; the rear was really loose. I forget what exactly the problem was: o-ring or snap ring, but I fixed it and it's been good since. Not saying it is your problem, but worth checking out.

 

[roger1]

I'm thinking pontiacgp is correct that I have a defective master. I haven't tried adjusting the rear brakes yet though.

I've been researching online on getting a power bleeding system. I'm looking at the Motive 0115 as it has the large plate to fit these plastic master reservoirs.

I'm wondering about 2 other things too. One is whether I'm doing anything wrong with my bench bleeding process that could be damaging the master since this is 3 master cylinders in a row on this car I've had issues with. Maybe I shouldn't be clamping the body in my vise.

The other is what master should I try next? My thought was the a new AC Delco would be the best. Now I'm not sure sure.

 

[1KWIKSIX]

I've got the Motive power bleeder and the 1115 large GM adapter.

Works great, just gotta be sure you've got it clamped down with some extra C clamps or it's gonna leak under pressure and spray down your firewall with brake fluid! Ask me how I know. LOL

 

[roger1]

Thanks. I had read some other reports of needing a C clamp for it. I've got a pretty good assortment of them so it shouldn't be a problem.
I did get it ordered this morning. I could get it the fastest with Amazon but it's still looks like Wednesday when I will get it. Since I'm waiting anyway, I put a new Centric master in the order. I think Centric is an OEM supplier so I figured it should be good quality. But then again that's what I thought when I bought the AC Delco too. But, somehow I still feel I might be doing something during the bench bleeding to screw it up since this is 3 masters in a row I've had trouble with.
So, I also bought this to help me bleed the master:
Cardone 10-5000MCB

 

[roger1]

When I first got my Bonne, I had some problems with the brakes. What I found was that the rear inlet from the reservoir wasn't sealed correctly and it would suck air in. I found it accidentally while removing the cap to put fluid in; the rear was really loose. I forget what exactly the problem was: o-ring or snap ring, but I fixed it and it's been good since. Not saying it is your problem, but worth checking out.

I didn't work on the car today but just went out to check this. The plastic reservoir looks fully seated in the body and both lines are tight into the side of the body.

 

[roger1]

I've got the Motive power bleeder and the 1115 large GM adapter.
Works great, just gotta be sure you've got it clamped down with some extra C clamps or it's gonna leak under pressure and spray down your firewall with brake fluid! Ask me how I know. LOL

I just reviewed the order I made yesterday and realized I got mixed up on the numbers and ordered the Motive kit with the smaller plate by mistake. But, I'm going to keep it because I can use it on my other older cars with cast iron reservoirs.
So, I just ordered this Power Probe BA14 adapter for the larger plastic reservoirs that the gbody cars have:

The alignment shop I had bleed the brakes the other day had one this style and it worked really well. It was a BG brand but pretty much the same as this. This is about the same price as buying the Motive 1115 separately would have been and I think I'll like having this one more.

 

[roger1]

Update.
Got my new master cylinder in. I also installed a rear brake cylinder bracket kit. I didn't know about those until recently and realized these are must-have. Made sure the rear brakes were adjusted properly too.

I pressure bled the brakes with my new Motive unit and Power Probe adapter. I put some valves on it so I could totally purge the air from all the tubes before pressuring up the unit. Worked pretty well. Brake fluid kind of comes out of the calipers and cylinders slow but seemed to do the job. I went around the car twice and bled out about 4 oz out of each location both times.

Well, I'm still not happy with the brakes though. I can lock the wheels up on a concrete surface but not on normal asphalt one. Pedal travel just seems too far too. Normal driving feels fine. Stops straight and excessive pedal travel isn't noticed unless it's more of a panic type stop. However, I don't think I have air or anything is malfunctioning. I think I'm just experiencing what people complain about with stock GBody brakes.
I've done lots of reading on the forums and it sounds like there are many, many complaints of this. It's more noticeable to me now than it was before. I've gone to wider and stickier tires than I had before. I'm pretty sure those would be a lot harder to lock up than stock size wheels and tires.

I've read many forum posts about upgrades like going to Blazer or LS1 brakes. I may have to give this thought. I also see that some have gone to using BBody master cylinders and vacuum boosters too. I do wonder that with the Power Stop kit I just put on this car if I could do a master cylinder and maybe a booster upgrade and achieve results I'd like.

I'd appreciate thoughts and advice.

 

[roger1]

Need better braking than what I've got.
Decided this is what I'm going to do:
https://gbodyforum.com/threads/just-made-decision-for-brake-upgrade.69097/

Yup. Wasted some money because I won't be using the new Power Stop calipers and the new master cylinder I just bought. I can re-use my new ceramic pads though.

It's more appropriate that this subject be put in a new thread.
If anyone has any comments, let's continue them in the new thread.
Thanks for all the help so far.