Difficulty bleeding brakes

[nibor17]

Hello everyone,

First, I'm a newbie at working on cars, but part of the reason I bought my 300 was to learn, which I have done a lot of! But still, forgive me for being ignorant!

So, after replacing the rear subframe bushings in my 84 Turbo, I have not been able to successfully bleed the brakes. The job required detaching the soft rear brake lines at the rear crossmember. I had hoped that because the rear of the car was raised about 18 inches into the air, all I would have to do was to bleed the rear brakes of air and top up the fluid.

Before bleeding, pedal was soft and wouldn't get hard with pumping, and there was a fairly quiet wheezing sound coming from (I think) the master cylinder. Could only be heard with hood open and window rolled down. Blamed it all on the massive amount of air in the lines. So, I bled the rear brakes. The pedal was slightly firmer and would build up some firmness, but it slowly depressed under pressure if I didn't keep pumping it.

So I bled all four brakes, and the pedal was slightly firmer after pumping, but still falls under pressure. Went around and bleed all four three more times- no change. Now, it could be that there is still a lot of air in the rear lines, but the bubbles coming out of the bleeder valves are the small, uniform type that I'd expect to see leaking in from the open valve itself, not from the system. Maybe there is sill air in it, but I have gone through about 70 oz of brake fluid. The front brakes have no bubbles at all, but the valves are larger and provide a better seal on my tubing. There are no fluid leaks that I can find anywhere. I initially had my brother pump the brakes while I opened and closed the valves, but I am now using a hand vacuum system.

I tried turning the car on, and the pedal has almost no pressure at all, goes all the way to the floor.

I also still have the wheezing sound coming from the master cylinder. Starting to think it just might be bad. Also, not sure if this might have causes any issues, but while the rear brake lines were off I turned on the car to test something. Could turning on the car with the brake lines open damage anything?

Anybody got any ideas? Do I just need to keep bleeding it? Should I try bleeding the master cylinder? I'm a noob- so I have no idea how to do that! ;-)

I'm pretty much at my wits end with this!!! Thanks for any advice you can give.

[evildky]

The wheezing sound is normal, there is a rubber seal on the inside of the firewall where the pushrod enters the master and asn the pedal is pressed the piston inside the master moves forward drawing air in around that little boot, no cause for alarm.

Starting the car should have had no ill effects.

Toss the vacuum bleeder, they tend to be more trouble than they are worth unless you get a high end kit and even then can be spotty.

Start with the rear, have a friend pump the crap out of the pedal and hold before cracking the valve, notice I said to crack the valve you only want it open enough to let the pressure off than close it immediately. do this a few tomes on each side of the rear until you get NO air bubbles at all! Repeat the process up front. You do the rears first because after the fronts are bled you often don't get enough pedal movement to bleed the rears.Be sure you keep the master filled and don't suck any air into the system, also do NOT recycle the used brake fluid, if it's new fluid you still need to let it sit for a few hours after being pumped out to recycle as it will be charged with air and you'll never get it all bled out.

[nibor17]

Thanks for the information.

Just spent almost 3 hours bleeding all four brakes over and over again. I have a line connected to the bleeder that leads into a bottle with clean fluid above the valve so any bubbles rise up and no air is drawn in. No bubbles out of any of the brakes, but no change in the pedal either. It will get firmer with pumping, but it is still softer than before I pulled the the rear lines apart. When the car is on, the pedal is still very soft, goes all the way to the floor. The brakes do apply, however.

I am fairly confident that all the lines are fine...I only detached the rear lines, didn't touch anything else. Not losing any fluid.

As you can tell, I don't really know what much about brakes. Is there any way that simply disconnecting the rear lines could damage the system? The brakes worked great before I started this project, so I'm sure I'm just doing something wrong, but I've already spent 5 very long hours bleeding them!

Thanks for any additional information you can give, though I'm pretty sure I'm doing something wrong or there is a particularly stubborn air bubble in there somewhere. Got any suggestions to coax it out?

I really appreciate your help!

[evildky]

DO NOT recycle the fluid! Not unless it has had hours to settle. Just because you don't see air in it does not mean that it is not at least partially aerated.

Failure to build pressure means one of 2 things, either you have a pressure leak, if at the wheels it's visible or at the master where it is invisible, the fact that everything worked before you did your work would suggest the master is fine but could still possible be bad. The more likely cause is air in the lines. recycling aerated fluid could very well be causing you to chase your own tail, or there is air int he system you have not managed to get out, sometimes air bubble will get trapped bear a bleeder which is why sometimes you see people banging their calliper with a wrench while bleeding, usually having someone vigorously pump the crap out of the brakes and hold while you crack the valve a few times in rapid succession should get it. I did have a car once, can't remember which car it was, but the bleeder wasn't quite at the top so I pulled the calliper and stuck a block of wood in the calliper to keep the piston from coming out and positioned the caliper so that the bleeder was at the high point.

[nibor17]

Don't worry, I'm not recycling fluid at all, and doing my best to not draw any back in. Wasteful, but it's cheap insurance against problems.

Thanks for the help. I'll tinker with it some more tonight, but I'll probably just get it towed to a shop near me and have them do it. I can admit when I've been defeated! Based on your input, it sure sounds like there is just still a lot of air in the system that I can't get out. My other car needs to go in the shop this weekend to fix the heater, so I need the 300 back to keep me mobile. :-p

Cheers!

[nibor17]

I just ended up driving the car to a shop near me to have the brakes bled. Braking action was fine, but the pedal was very soft and had a lot of play. Really though, I had to get the 300 working because the heat on my other car just went out...the fun never ends. ;-)

Test drive does indicate the advantages of replacing 31 year old rubber rear bushings with polyurethane...handling was noticeably better even at road speeds, and the ride, while being firmer, was also more stable and less bouncy. Improvement on all fronts!

Thanks again for the help, evildky. I've been rearing this forum and ones like it for awhile now and I've gained a lot from them. Glancing around this one, I see you are all over the place helping people and offering opinions. Cheers mate!

[Desert Rat]

I opened this with interest...Just replaced all my bushings this past weekend and went through this myself. I ended up having a siezed rear caliper that wasn't returning to its original position so those had to be replaced as well. The new urethane does make a difference. I also added new shocks, new rear springs, new upper and lower spring pads, new front strut mounts and bearings, Ball joints, and tierod ends.

was quite the job.

[Pitts]

Got the exact same issue actually. Started about 3 weeks ago. However, after a lot of braking, I eventually couldn't pump enough to get any pressure at all. Did a full flush, was fine for a week before it wasn't building any pressure again (one of those moments I'm glad I live in a small town and have a manual). I was suspecting the master cylinder as well. Bought a new one (not remanned) and still got the same result so far (have to pump twice before I get full brake power). Gonna wait it out a few days to see if I have to pump more again. If so and the same happens to you, check the brake booster and it's check valve (plan on doing that tomorrow). It sounds like the best culprit for our situations (or at least mine). If the pressure at the brakes (after 1-2 pumps) stays the same for a week, then I plan to do a through bleed (if one ever existed). I was using a mightyvac hand pump keeping at 1-2" of mercury to bleed my lines (takes some time, but does alright in my opinion. Let me know what your local shop says so I can check that out for my car.

[Pitts]

Well I checked the brake booster check valve (in FSM under brakes, simple and 1 minute to do from start to finish) and the vacuum lines. All were good. Hooked up a vacuum gauge (to where the cruise control vacuum line goes; which I bypassed). Had 17 inches of mercury (it's a unit to measure vacuum Nibor17) at an idle of 1000 rpm (she doesn't like to idle well under 800, lopey from the cam upgrade and the high altitude). When pumping the brakes, I'd lose 2-3 inches of mercury. But only when I was pumping at idle, so it's normal. So the brake booster is ruled out as well.

You can test the brake booster, brake booster check valve, and vacuum lines with a vacuum gauge and carb spray (on a cold engine as it's flammable; or you can use water). Means my only options are a very tiny leak (which I haven't lost any fluid or noticed any spots) or air trapped somewhere. Let me know how your brakes are doing currently since it has been a few days since you took it to a shop for a bleed.

[nibor17]

Sorry for not replying to this with the outcome. Got sidetracked with the holidays!

Turns out the the master cylinder was shot. Replaced it and the problems dissipated. Sadly, now the car has developed electrical issues (probably related to the subzero temps we've been having) an I can't enjoy it. :-p