Disco 1 Disco 1 abs brake troubleshooting. UPDATED

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123asd said:
Many thanks for your thoughts. If the master cylinder is at fault why does it seem to behave without the servo? Is there a rebuild kit suitable for the abs master cylinder?
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you apply less pressure on the cylinder push rod and so seals, a new cylinder is better
 
discool said:
The theory was that air would still be trapped in the longest pipes if bleeding was started on the short pipes first,
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maybe if the longest pipes were not bled at all but as long as all the pipes are well bled no air should be trapped in there no matter in which order you bleed them... that LR sequence has other more complicated explanation which has to do more with safety but it's too long for me to write it in english... as about the OP's problem i have serious doubts it's about air in the system, my first suspect is the servo unit
 
sierrafery said:
maybe if the longest pipes were not bled at all but as long as all the pipes are well bled no air should be trapped in there no matter in which order you bleed them... that LR sequence has other more complicated explanation which has to do more with safety but it's too long for me to write it in english... as about the OP's problem i have serious doubts it's about air in the system, my first suspect is the servo unit
Click to expand...


Many thanks, would your suspected fault be amenable to repair with the rebuild kit or replacement?

Cash is tight and i am keen to try and avoid replacing too many expensive components.
 
sierrafery said:
maybe if the longest pipes were not bled at all but as long as all the pipes are well bled no air should be trapped in there no matter in which order you bleed them... that LR sequence has other more complicated explanation which has to do more with safety but it's too long for me to write it in english... as about the OP's problem i have serious doubts it's about air in the system, my first suspect is the servo unit
Click to expand...
im not sure of your thinking ,how can a servo make a pedal sink underfoot ,that has to be air ,passing seal or ballooning flexi
 
I dont know anything about a servo unit repair kit... when it comes about brakes aka safety i'm always biting the bullet and fit new genuine parts though the master cylinder being suspect too better start with that cos it's cheap and even if you'll have to get a servo too never regret that you have a renewed braking system
 
jamesmartin said:
im not sure of your thinking ,how can a servo make a pedal sink underfoot ,that has to be air ,passing seal or ballooning flexi
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My thoughts also, but having had no bubbles of any significant nature in 3l of brake fluid flushed through since i got the thing a balooning flexi would quite potentially fit the bill.
 
123asd said:
My thoughts also, but having had no bubbles of any significant nature in 3l of brake fluid flushed through since i got the thing a balooning flexi would quite potentially fit the bill.
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get someone to pump the pedal and see if you have fluid splashing in the resevoir
 
jamesmartin said:
im not sure of your thinking ,how can a servo make a pedal sink underfoot ,that has to be air ,passing seal or ballooning flexi
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my thinking is based on the following description cos there is a possibility to be an internal leak and when vacuum is applied the pushrod to travel forward without pressure to the brakes to be fully released... possibility which is in that fault chart as well IMO a master cylinder seal leak should be noticeable without servo assistance too...though i sustain my purple signature

D1 brake servo.jpg
 
sierrafery said:
my thinking is based on the following description cos there is a possibility to be an internal leak and when vacuum is applied the pushrod to travel forward without pressure to the brakes to be fully released... IMO a master cylinder seal leak should be noticeable without servo assistance too...though i sustain my purple signature

View attachment 121589
Click to expand...
brake fluid cant be compressed it would have to have air or a leaking seal for the pedal to sink whatever pressure the servo applied, you cant push the pedal without the push rod moving into the master cylinder
 
i think id start with the master cylinder, another thing you can do is clamp each flexi one at a time and see if clamping each has the same effect
 
123asd said:
Master cylinder ordered.

Any tips for avoiding getting air in the abs unit whilst fitting it?
Click to expand...
you cant avoid it just bleed at each inlet and outlet by slackening the fittings pressing pedal and hold till fittings retightened the let pedal up repeat till clear fluid appears then repeat the same at the calipers
 
So chaps, new master cylinder fitted and it is much better. Interestingly it was a non abs master cylinder fitted.

Still some air in the thing by the feel of it but i will try and hunt it down on monday. With a swift pump i can now get the abs to activate going downhill so hopefully that will push the air into the more easily bleedable parts.

Some other issues arose on the trip, see new thread if you could kindly guide me.
 
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