Master cylinder seal going?

[TIMMOS29]

Quick question

Ive done a full brake fluid flush and Disc pad change.

When i press the pedal it is hard then very very very slowly it drops. Is this a sign of a failing MC seal? or after 20 years is this just normal stuff.
I havent lost any fluid.

Tim

 

[Dubbedown]

If pedal feel was fine before then, you may have done something wrong during the flush. Did you pressure bleed or have someone step on the pedal?

 

[Usel]

Dropping pedal is usually air in the system.

 

[Dubbedown]

Dropping pedal is usually air in the system.

He has the opposite issue

 

[Usel]

Dropping pedal is usually air in the system.

He has the opposite issue

"When i press the pedal it is hard then very very very slowly it drops"

When this has happened to me it was air in the system and I had to bleed the system again due to air. Usually described as a dropping or sinking brake pedal.

 

[enuff_zed]

Have you done the abs pump bleed procedure ?

 

[TIMMOS29]

Have you done the abs pump bleed procedure ?

nope

 

[bigwinn]

1000% air in the system

Take it from someone who has had this issue

As the guys say the inpa bleed may now be necessary

How did you do the bleed- what process did you follow?

 

[TIMMOS29]

1000% air in the system

Take it from someone who has had this issue

As the guys say the inpa bleed may now be necessary

How did you do the bleed- what process did you follow?

Hi thanks for help

So wehn i bough the car the discs pads where all rusty but it passed its test no problems, but i noticed that the pedal tended to slowly sink when pressed at lights ( braking is still great)

SO i replaced the discs and pads and did a fluid flush, using a one man bleeding kit and undoing the nipple and pumping until fresh fluid was seen in the pipe and no air bubbles.did this in rotation. brakes are rock hard but it still doesnt hold very well.
I didnt bleed the ABS unit as the resovoir didnt run dry.
I have a Launch 123E that offers ABS bleeding function but to be honest too scared to use it.

 

[enuff_zed]

1000% air in the system

Take it from someone who has had this issue

As the guys say the inpa bleed may now be necessary

How did you do the bleed- what process did you follow?

Hi thanks for help

So wehn i bough the car the discs pads where all rusty but it passed its test no problems, but i noticed that the pedal tended to slowly sink when pressed at lights ( braking is still great)

SO i replaced the discs and pads and did a fluid flush, using a one man bleeding kit and undoing the nipple and pumping until fresh fluid was seen in the pipe and no air bubbles.did this in rotation. brakes are rock hard but it still doesnt hold very well.
I didnt bleed the ABS unit as the resovoir didnt run dry.
I have a Launch 123E that offers ABS bleeding function but to be honest too scared to use it.

Ah, so just to get us back on the right path, the pedal already did that before you changed everything?
I suspect we were working on the theory it was something you did.
So it could be:
1. Seal failed in the master cylinder
2. Air in the ABS pump from something done before you got the car
3. Sticking calliper piston - initially doesn't move, then with more pressure it finally does move and the pedal goes down a bit more.

Does the pedal continue to sink, or move a bit further, then stop?

 

[TIMMOS29]

1000% air in the system

Take it from someone who has had this issue

As the guys say the inpa bleed may now be necessary

How did you do the bleed- what process did you follow?

Hi thanks for help

So wehn i bough the car the discs pads where all rusty but it passed its test no problems, but i noticed that the pedal tended to slowly sink when pressed at lights ( braking is still great)

SO i replaced the discs and pads and did a fluid flush, using a one man bleeding kit and undoing the nipple and pumping until fresh fluid was seen in the pipe and no air bubbles.did this in rotation. brakes are rock hard but it still doesnt hold very well.
I didnt bleed the ABS unit as the resovoir didnt run dry.
I have a Launch 123E that offers ABS bleeding function but to be honest too scared to use it.

Ah, so just to get us back on the right path, the pedal already did that before you changed everything?
I suspect we were working on the theory it was something you did.
So it could be:
1. Seal failed in the master cylinder
2. Air in the ABS pump from something done before you got the car
3. Sticking calliper piston - initially doesn't move, then with more pressure it finally does move and the pedal goes down a bit more.

Does the pedal continue to sink, or move a bit further, then stop?

thanks for the help again.
With the car not started the brake pedal feels hard and sinks very slowly to the floor

I dont seem to be losing any fluid

 

[enuff_zed]

Hi thanks for help

So wehn i bough the car the discs pads where all rusty but it passed its test no problems, but i noticed that the pedal tended to slowly sink when pressed at lights ( braking is still great)

SO i replaced the discs and pads and did a fluid flush, using a one man bleeding kit and undoing the nipple and pumping until fresh fluid was seen in the pipe and no air bubbles.did this in rotation. brakes are rock hard but it still doesnt hold very well.
I didnt bleed the ABS unit as the resovoir didnt run dry.
I have a Launch 123E that offers ABS bleeding function but to be honest too scared to use it.

Ah, so just to get us back on the right path, the pedal already did that before you changed everything?
I suspect we were working on the theory it was something you did.
So it could be:
1. Seal failed in the master cylinder
2. Air in the ABS pump from something done before you got the car
3. Sticking calliper piston - initially doesn't move, then with more pressure it finally does move and the pedal goes down a bit more.

Does the pedal continue to sink, or move a bit further, then stop?

thanks for the help again.
With the car not started the brake pedal feels hard and sinks very slowly to the floor

I dont seem to be losing any fluid

OK, so to start with, do a proper pressure bleed, then follow that up by bleeding the ABS pump. You will need INPA or something similar.
No point in diving in to change stuff until you're certain it is properly bled.

 

[damocell]

What model/engine is this on? This is important as some of the later e85/6 models had a different ABS/DSC pump

I had the same and chased all sorts of things, like MC, etc. In the end, it was the ABS/DSC pump that was the problem. I would bleed the system using ISTA, and the pedal would react like there was air in the system. The pedal also got worse/longer over time, especially after hard braking.

 

[TIMMOS29]

Ah, so just to get us back on the right path, the pedal already did that before you changed everything?
I suspect we were working on the theory it was something you did.
So it could be:
1. Seal failed in the master cylinder
2. Air in the ABS pump from something done before you got the car
3. Sticking calliper piston - initially doesn't move, then with more pressure it finally does move and the pedal goes down a bit more.

Does the pedal continue to sink, or move a bit further, then stop?

thanks for the help again.
With the car not started the brake pedal feels hard and sinks very slowly to the floor

I dont seem to be losing any fluid

OK, so to start with, do a proper pressure bleed, then follow that up by bleeding the ABS pump. You will need INPA or something similar.
No point in diving in to change stuff until you're certain it is properly bled.

Great today bought a pressure bleed kit that relies on pressure from a spare wheel, excellent bit of kit for 20 quid. Used my launch diag machine i got off ebay for 130 quid which has an abs bleed option that works a treat. And seems to of solved the sqishy pedal on braking problem.

 

[enuff_zed]

thanks for the help again.
With the car not started the brake pedal feels hard and sinks very slowly to the floor

I dont seem to be losing any fluid

OK, so to start with, do a proper pressure bleed, then follow that up by bleeding the ABS pump. You will need INPA or something similar.
No point in diving in to change stuff until you're certain it is properly bled.

Great today bought a pressure bleed kit that relies on pressure from a spare wheel, excellent bit of kit for 20 quid. Used my launch diag machine i got off ebay for 130 quid which has an abs bleed option that works a treat. And seems to of solved the sqishy pedal on braking problem.

Hopefully sorted then.