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Can I Test the Brake Booster with the engine out
I searched this, but didn't fine anything. I have the motor out, and I want to test the brake booster. Can this be done using a MityVac vacuum pump? Can the vacuum pump be used to make the brake booster function while I bleed the brakes? I hope this is not "the stupid question".
Ben |
no need for it. brakes r bled with engine not running anyway.
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Procedure for Testing Brake Booster with engine off
Thanks for the reply. I am having a very difficult time bleeding my brakes, and I want to ensure the brake booster is functioning properly. I found instructions for "bench testing" a brake booster at the following url:
Vacuum Brake Booster Testing and Diagnosis I hope this helps anyone else that might be looking for the procedure, which could work to test a brake booster at a salvage yard, for example. |
The brake booster is only functioning with the engine running. Have you recently replaced any of your braking components and if so what have you replaced?
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Brake Parts That I Replaced
Background: I parked the car in my garage some 15+ years ago due to a busted/stripped teeth on a stationary gear in the engine. I bought a rebuilt engine that I hope to install soon. The brake system was working fine at that time, aside from needing new pads/shoes.
Now: I replaced most of the brake system, except the hard lines. The master cylinder was frozen, so I replaced it. I bench bled it before it was installed and it was moving fluid and the air bubbles had stopped. It seemed to have bench bled fine. I replaced the shoes, and brake cylinders in the rear; the calipers & pads in the front, and the brake hoses were replaced with S/S hoses. I could not get the system to bleed properly. The pedal would not firm up, and I could not get fluid to move through the system properly. Then, when I could not get the brakes to bleed properly, I installed speed bleeder valves. No change. Then, I tried bleeding them using the MityVac. No change. Then, I replaced the brake booster. No change. So, now I am wondering if the original factory brake booster was working properly all along, or if it was bad but I also got a bad one as a replacement. I understand that the brake system can be bled without the assistance of a functioning brake booster (i.e. without the engine running). But, I want to know it will work when the engine is back in the car and ready for the road. I also wonder if I could have gotten a bad master cylinder. I have never had a problem bleeding brakes like this before, but then again, I see other threads indicating this has been a problem for others as well. I am totally open to suggestions and advice. |
What kind of a pedal are you getting? How much travel before engagement? The pedal will have some free play and these cars are known for a little sponge in the pedal.
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Re: How Much Pedal Are You Getting/Travel Before Engagement?
Originally Posted by mazdaverx713b
(Post 12285723)
What kind of a pedal are you getting? How much travel before engagement? The pedal will have some free play and these cars are known for a little sponge in the pedal.
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What is your brake bleeding procedure. Should be Master bench bled 1st, then RR-LR-RF-LF
If you don't have any fluid leaks under pedal pressure,there is nothing to be gained by tightening things further. Are your rear shoes/hardware installed correctly and adjusted properly? Out of adjustment rear brakes will cause low pedal on any car,even without the bleeding woes you are having It is possible to get a defective part,happens to everyone. Was the master cyl/booster new or reman,brand name,identical to the one it replaced? I don't see your year car listed,do you have left and right calipers in their respective position,if so bleeders will be on top of calipers both side. If not you'll never be able to get all air bled out.. If the above doesn't address the air in system issue,try putting a suitable container under each bleeder and crack all bleeders open and observe steady flow of fluid from each. Close bleeders,top up master cylinder,have an assistant pump pedal SLOWLY 3x and hold and go around in order of RR-LR-RF-LF and release bleeder til pedal on floor,close bleeder before helper lifts to pump again,move to the next. By the time you've bled each in order 1st time you should see a difference in pedal. Go around as many times as necessary to get a full firm pedal,could be 3,4,5x before satisfactory. You need to pump pedal slowly-too fast will aerate/foam the brake fluid introducing more air into system you're trying to bleed out. |
Brake Bleeding Procedure
Originally Posted by gslseforme
(Post 12287642)
what is your brake bleeding procedure. Should be master bench bled 1st, then rr-lr-rf-lf
that is the sequence i used, except my '83 gs does not have a bleeder valve on the LR. if you don't have any fluid leaks under pedal pressure,there is nothing to be gained by tightening things further. i do not have any leaks. are your rear shoes/hardware installed correctly and adjusted properly? Out of adjustment rear brakes will cause low pedal on any car,even without the bleeding woes you are having yes. it is possible to get a defective part,happens to everyone. Was the master cyl/booster new or reman,brand name,identical to the one it replaced? mc is a new ac delco 18m190 professional brake master cylinder assembly which is similar but not exactly the same as mine. The cap is located on one end instead of the center, and the electrical fluid level sensor is there, but in a different location. I have been unable to locate one that is identical. In this case, the photo on the internet was identical, but the part i received was not identical. However, they appeared similar enough that i went ahead and installed it instead of returning it, since i do not know where to get one that is identical. i don't see your year car listed 1983 gs ,do you have left and right calipers in their respective position,if so bleeders will be on top of calipers both side. If not you'll never be able to get all air bled out.. yes. Each is stamped with the appropriate l and r for their location and the hose and bleeders are on the top. if the above doesn't address the air in system issue,try putting a suitable container under each bleeder and crack all bleeders open and observe steady flow of fluid from each. Close bleeders,top up master cylinder,have an assistant pump pedal slowly 3x and hold and go around in order of rr-lr-rf-lf and release bleeder til pedal on floor,close bleeder before helper lifts to pump again,move to the next. By the time you've bled each in order 1st time you should see a difference in pedal. Go around as many times as necessary to get a full firm pedal,could be 3,4,5x before satisfactory. i am considering backing up some; i will remove the master cylinder and bench bleed it again; i will remove the brake booster and re-install the factory unit which was working the last time the car was running... I replaced it because i replaced the master cylinder, and had access to it. I am not certain that the booster rod on the new booster is properly adjusted. I read in a repair manual (not the mazda manual) that mazda used a special tool for adjusting the booster rod. I do not have access to the tool, but my old booster worked when it was last running, and i am pretty sure it was installed at the factory. you need to pump pedal slowly-too fast will aerate/foam the brake fluid introducing more air into system you're trying to bleed out. O.K. |
Will monitor your thread for updates,have a suggestion on how to adjust pushrod freeplay without special tool.
Did replacement m/cyl look identical dimensionally? |
I would appreciate your suggestions on adjusting the push rod free play. I still have all the original parts. I will post photos of both master cylinders.
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Originally Posted by GSLSEforme
(Post 12289434)
Will monitor your thread for updates,have a suggestion on how to adjust pushrod freeplay without special tool.
Did replacement m/cyl look identical dimensionally? https://cimg5.ibsrv.net/gimg/www.rx7...b631a439b3.jpg Currently installed (left side view) shown in photo above https://cimg6.ibsrv.net/gimg/www.rx7...d7207924b2.jpg Replaced (left side view) shown in photo above https://cimg8.ibsrv.net/gimg/www.rx7...4552b70d4e.jpg Currently installed (left side view) shown in photo above https://cimg7.ibsrv.net/gimg/www.rx7...cd1d6547fd.jpg Removed (left side view) shown in photo above The brake fluid sensor from the removed master cyliner does not fit in the currently installed master cylinder, which did not include a sensor. Ben |
The replacement looks more like correct original part than what you took off. Was hoping to see pics of the business end of both to see if depth of master cylinder piston is same or different.
Measure both if you can,maybe pics of both showing back end in detail. When you push brake pedal down by hand do you feel a slight amount of play and then feel resistance of pushing master cylinder piston in,which when you let off returns to same amount of free play at top of travel? |
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