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Bled Brakes... came back a few days later and no pedal at all??


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#1 benny

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Posted 06 July 2013 - 10:34 PM

Hi All,


Helping a friend out with his project. Rears have been updated to r31 units everything else is factory. Bled the brakes up the other day and had a reasonable pedal(didn't road test but felt firm) went out today after finishing the clutch off and no brakes at all, pedal just goes to the floor. Have checked for fluid on the ground/leaks and cant see anything. Ideas? Master is new also.


Benny



#2 zzzzed

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Posted 06 July 2013 - 10:49 PM

Air lock?

#3 benny

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Posted 06 July 2013 - 11:22 PM

air still in the lines? perhaps.... bled it quite thoroughly though.

#4 dat2kman

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Posted 07 July 2013 - 09:08 AM

Unscrew caps on master cylinders, let us know what, or what isn't , in there.

Peel back carpet inside footwell. Any mousture?
Possibly master has crapped a seal, and leaked it all back into the Vac unit.

#5 RLY240

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Posted 07 July 2013 - 10:50 AM

Did you bleed the master cylinder?

#6 nizm0zed

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Posted 07 July 2013 - 11:50 AM

Possibly master has crapped a seal, and leaked it all back into the Vac unit.


Thats what i'd be thinking too...
Also, has it been sitting for a few days leaking onto a porous ground surface? even concrete is porous.
If so, it could have leaked out enough fluid via line fittings ect (look at the connections to the rear calipers you just changed) and soaked into the ground. Would only leave a stain but not necessarily a wet patch.
Did you use new flare fittings on the lines or the existing ones when you changed the calipers over?
Do the flare fittings match the calipers?

#7 benny

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Posted 07 July 2013 - 07:16 PM

Unscrew caps on master cylinders, let us know what, or what isn't , in there.

Peel back carpet inside footwell. Any mousture?
Possibly master has crapped a seal, and leaked it all back into the Vac unit.



fluid levels in master havent moved/changed.


Did you bleed the master cylinder?



now that I think about it i didn't bleed the master just the callipers. could this be the issue?


Thats what i'd be thinking too...
Also, has it been sitting for a few days leaking onto a porous ground surface? even concrete is porous.
If so, it could have leaked out enough fluid via line fittings ect (look at the connections to the rear calipers you just changed) and soaked into the ground. Would only leave a stain but not necessarily a wet patch.
Did you use new flare fittings on the lines or the existing ones when you changed the calipers over?
Do the flare fittings match the calipers?



Im 99% sure that there were no marks on the ground but will double check the actual callipers. Used old/existing flare fittings which im 99% sure are correct for the R31 calliper.

#8 Zedman240®

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Posted 08 July 2013 - 08:45 PM

Always bleed the master first then caliper furthest and work to the caliper / drum with the shortest line. IIRC

#9 benny

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Posted 15 July 2013 - 02:42 PM

UPDATE!!! bled the master (didn't seem to expel any air) had a firm pedal again. under vacuum it lost pedal again. there is a hose running from the booster straight to the rear of the efi manifold. Is there ment to be something inline? Ideas?

#10 dazzed

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Posted 15 July 2013 - 06:20 PM

UPDATE!!! bled the master (didn't seem to expel any air) had a firm pedal again. under vacuum it lost pedal again. there is a hose running from the booster straight to the rear of the efi manifold. Is there ment to be something inline? Ideas?

depending on the position of the rear callipers the callipers could be mounted on the wrong side with the bleeder valves at the lower part allowing a air pocket in the top of the piston if the callipers are mounted at the top in line with strut you will have to take the calliper off to bleed it .if thats not the problem you said a new master cylinder was fitted if the push rod in the booster came out upon removal of the master  cylinder the compression rubber in the booster may have fallen into the bottom of the booster and you wont be able to retrieve it unless you split the booster or get another rubber from another booster and just leave the lost one in there it wont do anything, other than the push rod length in the booster is too long which means wrong master cylinder and if thats the case the the brake lines around wrong way fronts going to back an vice versa, I get this all the time Ben

#11 dazzed

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Posted 15 July 2013 - 06:26 PM

UPDATE!!! bled the master (didn't seem to expel any air) had a firm pedal again. under vacuum it lost pedal again. there is a hose running from the booster straight to the rear of the efi manifold. Is there ment to be something inline? Ideas?

there is a one way valve in line to stop vacuum leaking off but even if it wasnt there it would cause the pedal to sink but check make sure it is there as it should be. the valve is in line near the rh w.w washer jet, oh yeah what car is this we are talking about ?

#12 benny

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Posted 15 July 2013 - 07:29 PM

hey daz.... thanks for the reply.


it is missing the check valve but I was under the impression it shouldn't need it?? callipers are mounted at 9 o' clock so shouldn't have issues with bleeding. I didn't replace the master, im thinking at the moment that this is the best bet? Any gurus feel like coming over and having a look over the w/e??

#13 Wayne G

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Posted 17 July 2013 - 05:01 PM

did you bleed the fronts too?  sounds like possibly a bad master, by-passing internally, therefore no external leak or fluid loss.  line clamp to isolate all of the callipers and see what the pedal feels like and if it stays the same after a period of time.  with all four callipers isolated from bled master, the pedal should be at the top and rock hard.  just my 2c worth.

#14 benny

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Posted 17 July 2013 - 05:58 PM


did you bleed the fronts too?  sounds like possibly a bad master, by-passing internally, therefore no external leak or fluid loss.  line clamp to isolate all of the callipers and see what the pedal feels like and if it stays the same after a period of time.  with all four callipers isolated from bled master, the pedal should be at the top and rock hard.  just my 2c worth.


I will try this over the weekend and post back... thanks wayne

#15 benny

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Posted 18 August 2013 - 05:03 PM

STILL STRUGGLING!!


I rebled the rears todays by removing them an got a bit more air out. The problem still remains though..... can press the brake and it will seem to build up pressure, as soon as i stop pumping it loses pressure again?? Any more ideas??

#16 benny

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Posted 18 August 2013 - 05:58 PM

I should also note im able to pump up the pedal when car is off then once started the pedal sinks..... from what I've ready its most likely the master?? maybe still air in the lines?? i didnt rebleed the front today?

#17 Lurch ™

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Posted 18 August 2013 - 06:09 PM

Was the MC rebuilt?

I had similar symptoms & realized I had the accidentally reversed an O-ring in the MC.

#18 MaygZ

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Posted 18 August 2013 - 06:17 PM

Benny Boy,

are you losing fluid?  Are the master cylinder levels going down? 

If the answer is yes, then you have an external leak.  Find it and fix it.  It could be anywhere in the system so after checking the likely spots (all the pistons, back of the master cylinder - into the vac unit) then check along all the lines and any pressure switches.

If the answer is no (to lowering levels) then you have an internal leak.  These are nearly always in the master cylinder where a cup has folded or split.  This allows any pressure built up to leak back into the non-pressured side of the system.  The only way to fix it is to remove it and replace the cups.

With regard to the one-way valve in the manifold vacuum line from the manifold to the booster:  the valve allows a constant vacuum to be maintained in the booster.  Obviously manifold vacuum changes (quite a lot) depending on engine rpm and throttle opening.  Without this valve your braking assistance will change a lot through the rev range (with a wide open throttle - stuck open or just wanting to dab them to balance the car) you will have no boost.  They are a pretty universal thing so you should be able to source one from any vehicle that has a similar sized booster.  They are easy to check - blow through one way - no blow through the other.

MaygZ


#19 benny

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Posted 18 August 2013 - 06:37 PM

Benny Boy,

are you losing fluid?  Are the master cylinder levels going down? 

If the answer is yes, then you have an external leak.  Find it and fix it.  It could be anywhere in the system so after checking the likely spots (all the pistons, back of the master cylinder - into the vac unit) then check along all the lines and any pressure switches.

If the answer is no (to lowering levels) then you have an internal leak.  These are nearly always in the master cylinder where a cup has folded or split.  This allows any pressure built up to leak back into the non-pressured side of the system.  The only way to fix it is to remove it and replace the cups.

With regard to the one-way valve in the manifold vacuum line from the manifold to the booster:  the valve allows a constant vacuum to be maintained in the booster.  Obviously manifold vacuum changes (quite a lot) depending on engine rpm and throttle opening.  Without this valve your braking assistance will change a lot through the rev range (with a wide open throttle - stuck open or just wanting to dab them to balance the car) you will have no boost.  They are a pretty universal thing so you should be able to source one from any vehicle that has a similar sized booster.  They are easy to check - blow through one way - no blow through the other.

MaygZ



Was the MC rebuilt?[font=Verdana][font=Verdana]I had similar symptoms & realized I had the accidentally reversed an O-ring in the MC.[font=Verdana][font=Verdana]




I think the MC is new but not 100% sure.... fluid levels aren't changing and went over everything again and nipped everything up ( i found that the right hand front in the distribution block was leaking and not nipped up correctly but haven't bled the fronts again since). I have added the check valve and issue remains the same. I will try bleed the fronts up again but i dont think thats the issue.


One last thing worth noting since the interior is all back in the BRAKE light in the centre facia is lit which i think is pressure related in the distro-block?


I pulled the master off the booster and checked for leaks... there were none.


did i mention i freakin hate brakes :o

#20 MaygZ

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Posted 18 August 2013 - 06:48 PM

The fact that the master is new or just rebuilt doesn't mean the fault is not in there.  If for example the pedal was pushed all the way to the floor (during the initial bleeding process) before the it was allowed to fill with fluid the friction could have easily turned a cup.  Or if the initial bleed was a violent affair with severe and extreme pumping of the pedal (and I have seen very competent mechanics do just that) then same thing.

I will say it again - if the fluid levels are not changing - you have an internal leak!

MaygZ




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