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brake master cylinder ST1


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#1 st184a

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Posted 09 September 2016 - 05:56 AM

hi i recently  bight a 184 coupe,the brakes were a bit dodgey ,''was told needed brake pads and new rotors not thick enough for a machine.had that done , now its looking like master cyl is dodgy  as has full firm pedal but if let foot off brake and put foot back on go near to the floor, dose that seem like master cylinder ,  and the fluid had full flush bleed  and how do u get the bloody nut off the stud on master  cylinder  that's closest to inner guard and the bottom one  not much room to work lol cheers guysa



#2 ausjd2703

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Posted 09 September 2016 - 10:00 AM

best way imo to test a master is to "pinch" all four flexible brake lines. vice grips work but be careful not to pierce or crush the line.

start the car with all four lines pinched, if pedal is firm and doesnt slowly drop then it is not the master. if it drops then its the master.

 

worn pads can cause a spongy pedal, due to the slide pins and single piston calipers the pads taper, this is a source of spongyness in some instances.

 

if your master tests good the release the four clamps one by one, if the pdeal gets suddenly worse then thats the corner you are having issues with.

 

i am assuming you have properly bled the system and bench bled the master.


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ADM ST185 running Gen 3 3SGTE with GTX2867, Haltech PS1000, Racepak dash, Wilwood 330mm four piston fronts. work CR Kais 17-8. full 3" exhaust. FMIC.


#3 st184a

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Posted 09 September 2016 - 03:27 PM

Hi front and rear pads where changed ,rotors machined slide pins were checked make sure move freely and caliper pistons allso move freely ,,complete fluid flush and bleed till no more air ,near ltr fluid was pumped through it ,im not sure what yiu mean by bench bled the master cyl il try the pinching rubber hose just have get couple more claps

#4 Dvsone

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Posted 15 September 2016 - 06:17 PM

You need to bench bleed the master when you install a new one. If you have just done pads and rotors this should be fine. I'd say follow ausjd's advice and test the master amd lines to each wheel to determin where the problem lies. Generally a spongy pedal will indicate air in the system somewhere...

#5 st184a

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Posted 16 September 2016 - 11:24 AM

Im not sure what your refering to bench bleed master cyl guys first time ive heard it ,DVSone the brakes arnt spungy ,on the brake test for rego check it passed fine i asked him how brakes felt as thought air in line said no they fine or wouldnt pass the foot brake pressue test , but its when you lift your foot off the brake then reapply the brake the pedal sinks to allmost the floor ,let brakes off again has firm pressue brakes ok ,let foot off reapply pedal sinkes again ,there no sign of spoungy brakes even when pedal sinks to floor its still firm but its likr not enough pressure in the line for brakes to come to firm stop, allso when car is in park or standing still with motor running and you pressing the brake dose same but you hear the motor dropping rpm each time pressing brake pedal its been sugested its the brake booster , either way i had look at removing the master cyl a friend gave me a new master cyl he never used incase my cyl needs replaceing it looks like a night mare to get to the 2 lower nuts i tryed to reach around to nut closest to the shocky tower just to see if could get it n no way could get close to it sorry its bit long reply but hopefully this explains it a bit better whats happaning cheerz guys

#6 st184a

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Posted 16 September 2016 - 11:26 AM

Will be doing the clamp line test this weekend just to be sure got get couple more clamps

#7 Dvsone

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Posted 17 September 2016 - 08:43 AM

Ok cool. It could be booster related but i would be leaning more towards the master cylinder being the culprit. The clamp test will tell us more but also check all vaccum lines on the intake manifold and around the booster.

As for changing the master if that is the problem it is a bit of a hard job to get to but with 3/8 wobble extensions, uni joints and stubby spanners it can be done without too much trouble.
When fitting the new master cylinder you should always bench bleed it first which involves placing the master cylinder in a vice or something, fill up the reservoir with fluid while blocking the ports on the master cylinder. Then you need to push the plunger on the master cylinder in and out to create pressure and while holding the plunger in release one port to allow the air to come out, block the port again and repeat the process. It is basically the same principle as pressure bleeding the brakes but done on the bench to remove any air from the master before fitting it to the car.

My explinations are a bit poor but hopefully this helps a bit




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