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No brakes or brakes sticking??


Robos911

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Just refitted the brakes after adjusting the handbrake. I had to bleed the rear and now the front are stuck on??? After releasing some fluid to free them off, it takes about 10 pumps of the pedal before any bite. Its was all working before i took it apart, any ideas?

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10 pumps before bite, you must have air in them still, no idea about what happended to the front, unless extreme pumping has somehow manged to push out a sticky piston which is now siezed. I would clamp off 3 corners on the flexi pipe with an appropriate brake line clamp, then try your pedal, if its one pump and rock hard, then clamp that flexi on and try another corner, and keep going until you find the problem corners then rebleed.

Ps you dont need to even touch the rear calipers to do the handbrake...you just adjust through the hole in the disk...then on the cables themselves. 

Edited by Strictly
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13 minutes ago, Strictly said:

10 pumps before bite, you must have air in them still, no idea about what happended to the front, unless extreme pumping has somehow manged to push out a sticky piston which is now siezed. I would clamp off 3 corners on the flexi pipe with an appropriate brake line clamp, then try your pedal, if its one pump and rock hard, then clamp that flexi on and try another corner, and keep going until you find the problem corners then rebleed.

Ps you dont need to even touch the rear calipers to do the handbrake...you just adjust through the hole in the disk...then on the cables themselves. 

Thanks, good idea, the only problem is its braided lines, not sure if i can clamp these🤦‍♂️  
I wasnt very clear above, the handbrake tube wasnt sitting right, i had replaced the cables, all the lines, flexis etc, so it had to come apart.  About the only original bit is the servo. I used a pressure bleed and im wondering if that couldve damaged it? Ive been round bleeding twice and im deffo getting clean new fluid through? Also thought about the bias valve causing the front to lock....

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Ah for braided no i dont clamp

What pressure did you use? 1 bar (15 psi) or less and you will be fine. Sounds like quite a bit of work; Check all lines of course (connections). One trick i have tried in the past, which worked a few times, was all bleed nipples closed, pump the brake pedal say 5 -10 times, then go and quickly open and close one bleed nipple, you may get a gush of air. Its worked for me where the i basically managed to push all the air to the nipple, but of course it could not get past it, until i quickly opened and closed it. 

If the servo is the only original bit, then does that mean the master cylinder was also changed? if so bleed the master cylinder. It may not be air, it may be something else, but i suppose you have to rule that out. 

If you are really stumped in a couple of days then I would do this..... Disconnect the rear brakes at the flexis, put your old flexis  back on and clamp them (or buy 2 x female stop for the line), so that only your front brakes are actually connected to the car, and then see how they feel, if still not right, do the same thing on the rear, add the old flexis and clamp (or disconnect and block the lines), and keep chasing it on to a simpler and simpler system......until you have a nice hard pedal, that pumps up right and stays hard, then work back wards one pair or corner at a time. 

Ive worked on cars for 25 years (hobby and professional) and I still hate hydraulics when it came to problem solving!

 

 

 

 

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It's not uncommon for the master cylinder to leak fluid past the seals. If you haven't replaced this, it could be your problem.

Have you checked to make sure the seals on the front calipers are not leaking after they played up?

What year is your car? No bias valve on an SC although I don't see why it would affect getting a firm pedal either way.

Edited by Phill
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What age / model car ?

Not looked to closely at my P circuits, but just thinking out loud..... With a dual circuit master cylinder, you could have got the second piston stuck in its bore, blocking off its vent to the reservoir.  Having mechanically released pressure to the second circuit, you are now relying on the first piston to pressure both circuits (& it would struggle to pressurise the second circuit).

That would need a master cylinder rebuild or replacement.

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In addition to the above relating to the master cylinder I have also heard quite a few people say that pushing the pedal to the floor during bleeding can cause a problem with seals in the MC.  It seems that normal operation of the pedal movement is in a limited range on the MC but when bleeding if the pedal is pushed to the floor it can causes seal damage because the piston and seal are operated in a range they are not normally used to.  This sounds very logical to me and I now only press the pedal half way down or use a pressure bleeder.  Hope this helps

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29 minutes ago, Ian Comerford said:

In addition to the above relating to the master cylinder I have also heard quite a few people say that pushing the pedal to the floor during bleeding can cause a problem with seals in the MC.  It seems that normal operation of the pedal movement is in a limited range on the MC but when bleeding if the pedal is pushed to the floor it can causes seal damage because the piston and seal are operated in a range they are not normally used to.  This sounds very logical to me and I now only press the pedal half way down or use a pressure bleeder.  Hope this helps

I wrecked a master cylinder many moons ago doing just this. Now I only pressure bleed.

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if you want to confirm its the master cylinder before fitting a new one, as before refit your old flexis, bleed through the callipers then clamp all the flexis off, if the pedal still sinks, bleed the master, then rebleed the calipers and re-clamp the flexis, and the pedel still sinks after that replace the master.

If you have thrown your old flexis away, then either block off the lines, where the flexis attach and then bleed and check, or just fit a new master cylinder. I myself hate "just throwing parts" at something on a hunch, and will always diagnose a fault with a part before replacing it.

I've never wrecked a master cylinder through bleeding, and that in 25 years or so, and something like 200 cars or more. I'm sure it can happen, i've just never had a problem, bleeding either 2 man or 1 man. The only problems I have had where related to the wrong parts being fitted, so the pedel never felt right. 

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