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How to check brake booster for function.

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73clint View Drop Down
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    Posted: 11-February-2015 at 7:54AM
73 Gran torino 400m automatic.I tried bleeding the brakes and there is alot of air in the brakes after pumping for an hour.There are no visible leaks and the booster check valve and hose is brand new.

How do I check the brake booster on this car or what else can I check? car was sitting for a few months but if im correct that should not be the cause for air in the system should it?

Brake is soft and goes all the way to the floor.

Disc brakes in front and drums in the rear.

Car stops only a little while running.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Regul8r Quote  Post ReplyReply Direct Link To This Post Posted: 11-February-2015 at 9:03AM
The booster has nothing to do with air in the system.
Bleeding and still air... may still have air in the master.
Did you bench bleex the master?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mcford Quote  Post ReplyReply Direct Link To This Post Posted: 11-February-2015 at 9:34AM
X2 on bench bleeding the master.  not doing this results in having a royal PITA bleeding the brakes on the car.
Mike
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 11-February-2015 at 10:52AM
a savvy roadside repair kinda guy showed me how to swap a master w/o 'bleeding' anything
 
it starts with tweeking each line from the master upward as you disconnect them to keep the fluid from running out, then you swap the masters old for new & do the bench bleed on the car using the brake pedal rather than on a bench with a vice. now reconnect the lines quickly as you can, slightly re-forming them to not be pointing downward into the master so that any air at the flare doesn't migrate upwards into the line
 
with the lines reconnected absolutely do not step on the brake pedal! 
 
just barely touch the brake pedal with your baby toe to manipulate the air at the flair back up through the master reservoir, it's like a 1/16" pedal movement. doing the roadside repair thing he'd have a 2nd driver / helper to watch & verify the bubbles stopped coming up out of the reservoir
 
when your confident there's no more air bubbles coming up out of the valving in the master you can check the pedal
 
IT WORKS I tell ya!
 
not long after he showed me the process I did it on my own car,
about 5 minutes, excellent pedal & I never bled a line on the car after that
 
especially trick if you know the bleeders ain't gonna open Wink
 
 


Edited by Rockatansky - 11-February-2015 at 10:55AM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75GranMan Quote  Post ReplyReply Direct Link To This Post Posted: 11-February-2015 at 1:43PM
Pumping the pedal results in aeration of the fluid. what your actually doing is trying to compress the air in the system. when bleeding  you should open the bleeder furthest from the master cylinder (RR), have an assistant in a single stroke push the pedal slowly towards the floor, when the pedal reaches the floor, you should confirm the pedal is held to the floor while you close the bleeder screw. you can bleed this wheel several times before moving to the LR. then RF then LF. you may have to repeat this sequence 2 or 3 times to confirm all the air is removed. If the master is already mounted to the car it doesn't make much sense to bench bleed it. although it can be done. a dry master will just take much longer to bleed through the bleeder screws then to bench bled. If you bleed the system several times and aren't positive that all the air is removed. you're probably drawing air into the system from somewhere in the system from either the master itself or possibly a line flare that isn't completely sealed. If air is leaking in, fluid will leak out. On any hydraulic brake repair after bleeding the system, I always start the vehicle and use a brake pedal depressor to hold the pedal down towards the floor after I depress the pedal with my foot. starting the vehicle on a power brake car lets the vacuum assist the pedal towards the floor. shut the engine down and inspect all the leak points of the system. If no leaks are found after 10 or 15 minutes of assisted pedal pressure, you should be good to go. If you can't achieve a hard pedal with the engine off after bleeding you probably have faulty master cylinder or a severe mechanical concern (brake adjustment)( incorrect part)( pushrod adjustment) ect. A simple pedal depressor can be made from a length of 1/2 copper pie and a 1/2 or 13mm wrench., slide the box end of the wrench over the pipe. depress the pedal with on end of the pipe and slide the wrench towards the front of the drivers seat, wedging the wrench against the seat to hold pressure on the pedal, easy peasy lemon sqeezey.
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Tighten it down until it snaps and then back it off a half turn!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 11-February-2015 at 3:28PM
if you just changed mastercyliner it should eventually bleed out, but if most of the whole system was dry then there will be air pockets everywhere and can take a while, when bleeding them after 3 or 4 strokes, check the fluid level in the mastercylinder! if it gets low enough to suck any air it will pump that new air down along the system and you'll be bleeding forever Angry just check every few times and if it's half way down top off the fluid and continue bleeding. maybe get it bled the best you can, make sure everything is tight and fill the fluid, let it sit for a while or over night (to let any aerated micro bubbles condense into a few larger air pockets) then try rebleeding again the next day and that should help
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bata747-8 Quote  Post ReplyReply Direct Link To This Post Posted: 12-February-2015 at 11:07AM
I recommend bench bleeding the master, then a good bleed of all four wheel.

I am a manual 2-person bleed guy. Never liked the speed bleeders, handi-vacs and other stuff.

Unless anyone's knows of a good more professional bleeder system? Compressed air is available, so that is not a hindrance.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SirDan89 Quote  Post ReplyReply Direct Link To This Post Posted: 13-February-2015 at 3:05PM
I always bleed by myself a good 75% of the time gravity bleeding works perfect, crack the bleeder and let it drip. Simple and easy but, when that fails I move on to another method which always works, It will bleed lines that even are run higher than the master cylinder which always get huge air pockets. Its cheap and easy too, you might even already have all the parts to make it.

You just need a jar or a bottle of some sort that holds fluid and a piece of hose that fits over the bleeder. put enough fluid in your jar/bottle so you can stick the hose in and not have it above the fluid. Take your hose stick it on your bleeder and then stick the other end in the jar. Crack your bleeder and pump your pedal slowly. Watch your fluid level as it drops fast this way. Pump it a few times and close the bleeder.

Works every time I get something hard to bleed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73clint Quote  Post ReplyReply Direct Link To This Post Posted: 14-February-2015 at 5:02PM
new update,

So I bought a new remanufactured master cylinder and bench bled it just fine,then i threw it on the car so i could bleed the brakes.

I turned the car on to move it into position and when i pressed on the brake pedal the car slowly droped rpms and shuts off.

If the car is idling the car is fine but when the brake is pressed then it just dies. the check valve and hose is brand new and it did not do this with the old master cylinder so what gives?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 14-February-2015 at 6:01PM
check the rear of the mastercylinder were it meets the booster there is a rubber part of the booster that seals the vacuum inside the booster, maybe the new master cylinder is slightly different and not sealing? or the booster is bad??? did it do that with the old mastercylinder?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73clint Quote  Post ReplyReply Direct Link To This Post Posted: 14-February-2015 at 7:05PM
the seal looks good and the same measurements,the pedal still goes to the floor because I have not bled the rest of the breaks but it did not do this until I replaced the master cylinder,no visible leaks.

Edited by 73clint - 14-February-2015 at 7:10PM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 14-February-2015 at 8:25PM
does it idle ok, until you hit the brakes? just pushing the pedal once does it die? or after several repeated times on the pedal? what if you push on it only to about half way to the floor and keep it there just once? (like a normal stop at a stop sign?)
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77 CELICA CUSTOM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73clint Quote  Post ReplyReply Direct Link To This Post Posted: 14-February-2015 at 8:46PM
the car dies fine but if I push the brake half way or all the way down just once the car starts dropping rpms until it dies.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 14-February-2015 at 8:55PM
kinda sounds like the booster is leaking vacuum either behind the master cylinder or around the brake pedal rod inside???   anyone else have any ideas on this?
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90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75GranMan Quote  Post ReplyReply Direct Link To This Post Posted: 15-February-2015 at 2:22AM
start the car. let it run for a minute or two, actually just running for a split second will do...but you wouldn't want to foul the plugs running it for such a short time. Shut the engine down while sitting in the drivers seat don't step on the brake pedal, you might want to shut the window so you can hear if you have a vacuum leak. if you don't hear a leak inside the car. now go out to the booster and pull the vacuum check valve out of the booster, you should have a vacuum rush when you pull the valve out. if there was vacuum in the booster, then it is statically ok. if you don't have vacuum then either the check valve or booster is faulty. my guess would be, you have a massive leak in the booster providing you have no base engine concerns and have strong engine vacuum at idle. if you had good vacuum when you pulled the check valve out. reinstall check valve, now restart to build vacuum again, shut engine down. Depress the pedal about 1 1/2" and listen for a vacuum rush noise an abnormally vacuum noise also indicates a bad booster. proper booster vacuum should allow for about 2 brake pedal depress and releases with the engine off,( Brake on and off immediately).
John 75Gran Torino 4spd
Tighten it down until it snaps and then back it off a half turn!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75GranMan Quote  Post ReplyReply Direct Link To This Post Posted: 15-February-2015 at 2:31AM
Forgot to mention, If no obvious leaks were heard at 1 1/2" then press to 2 1/2" and so forth. you shouldn't hear an obvious leak. If it stalls the engine, It's a big problem 
John 75Gran Torino 4spd
Tighten it down until it snaps and then back it off a half turn!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73clint Quote  Post ReplyReply Direct Link To This Post Posted: 15-February-2015 at 6:17PM
so I put the new master cylinder back on and changed the check valve to the old one and now it doesn't shut off but it still bogs down alittle.then I turned on the engine,let it ran for a minute and shut it off,could not hear a leak from inside then went outside and disconnected the check valve and there was no vacum rush from the booster so what now?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 15-February-2015 at 6:40PM
do you have a mighty-vac brake bleeder? i'm thinking if you used an adapter to fit from the mighty-vac hose to the booster with out the check valve and pumped it to see if you got vacuum or a leak. if your pedal is going way down to the floor as in air in the brake lines, you may get a slight bog of the motor.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75GranMan Quote  Post ReplyReply Direct Link To This Post Posted: 16-February-2015 at 12:47PM
The check valve should hold vacuum in the booster after the engine is shut down. take the valve out and suck on the manifold side of the valve, you should be able to suck through the valve but not blow through it, turn the valve around and you should be able to blow through the booster side but not suck through it. If the valve is ok, then there's an issue with the booster. with the engine running and everything hooked up. take a length of vacuum hose and stick it in your ear, take the other end and follow possible leak points of the booster: where the master bolts up / crimp flange/ around the check valve and grommet/ inside the car by the booster pushrod. If the check valve is good, your gonna hear a vacuum leak somewhere! ( if you had no vacuum rush when the valve was pulled out of the booster) don't hold the length of vacuum line so close to the  leak source that you suck your ear drum out! If the leak is around the master/booster joint, check the rubber seal that is around the booster rod. Did it get damaged torn  somehow? If it's ok, try bolting the old master back up, and listen to hear if it doesn't leak with the old master bolted up. I assume you has good engine vacuum? ( around 18in at idle)
John 75Gran Torino 4spd
Tighten it down until it snaps and then back it off a half turn!
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