Bleeding Brake Mystery.
Discussion
I have just replaced the brake servo, master cylinder and rear slave cylinders on my S2 Vixen. The old master cylinder still worked but as I was doing the rest and the master cylinder was probably original except for new seals some 32 years ago it seemed worth changing. I also had a front calliper which kept seizing when the car was laid up for a while which I was going to free up and check once I had brake pressure.
When it was back together and full of brake fluid I did a quick bleed and managed to free one of the seized cylinders. However I could not get enough pressure to free the other one, so went round doing a proper brake bleed.
Until now I have never had any problems bleeding brakes. (The first job I ever had to do on a car of my own was to bleed the brakes some 40 years ago). So I went round initially the simple one man way (Tube in jam jar, open bleed screw, run round and gently pump pedal 2 or 3 times, run back and close bleed screw & check for bubbles in tube. Invariable 2 goes per wheel is plenty). The rears were fine but the front callipers kept being full of air. I therefore elicited the help of my beautiful assistant to do it the professional way (Open valve, press pedal, close valve, release pedal). Still rears fine but the front callipers just kept blowing air bubbles and not getting any less.
Totally confused as I cannot understand where the air is coming from. I have checked everywhere for brake fluid leaks and can’t see any. The air is more that you would get in the system as a continuous stream of bubbles keep coming out. The fluid in the reservoir goes down a bit but not as much as if it was pumping continuous fluid.
So I guess the air must be getting in from the master cylinder but I can’t understand how unless it is assembled back to front or all the seals have been left out or something strange (They are not particularly complex items)
So anyway I then put back my old master cylinder and after a couple of pumps it was all fine. So I sent back the master cylinder as faulty and requested a replacement. I the mean time I managed to free the other calliper cylinder which was totally rusted up so I fitted a new calliper.
I have now got the replacement master cylinder and this time I even pre filled it before putting it on the car. Initially I did a gravity feed on the front callipers and this seemed to work very well with clear bubble free fluid flowing. However the brakes were still a bit spongey so I again did a thorough bleed of all 4 corners with my patient assistant but again at the front callipers kept getting a continuous stream of bubbles. Giving up in despair, there was a reasonable amount of pedal pressure so I thought I’d let it settle overnight. The next day no brakes at all.
So I’m totally baffled. Could it be another duff master cylinder (TRW) or am I losing the plot?
When it was back together and full of brake fluid I did a quick bleed and managed to free one of the seized cylinders. However I could not get enough pressure to free the other one, so went round doing a proper brake bleed.
Until now I have never had any problems bleeding brakes. (The first job I ever had to do on a car of my own was to bleed the brakes some 40 years ago). So I went round initially the simple one man way (Tube in jam jar, open bleed screw, run round and gently pump pedal 2 or 3 times, run back and close bleed screw & check for bubbles in tube. Invariable 2 goes per wheel is plenty). The rears were fine but the front callipers kept being full of air. I therefore elicited the help of my beautiful assistant to do it the professional way (Open valve, press pedal, close valve, release pedal). Still rears fine but the front callipers just kept blowing air bubbles and not getting any less.
Totally confused as I cannot understand where the air is coming from. I have checked everywhere for brake fluid leaks and can’t see any. The air is more that you would get in the system as a continuous stream of bubbles keep coming out. The fluid in the reservoir goes down a bit but not as much as if it was pumping continuous fluid.
So I guess the air must be getting in from the master cylinder but I can’t understand how unless it is assembled back to front or all the seals have been left out or something strange (They are not particularly complex items)
So anyway I then put back my old master cylinder and after a couple of pumps it was all fine. So I sent back the master cylinder as faulty and requested a replacement. I the mean time I managed to free the other calliper cylinder which was totally rusted up so I fitted a new calliper.
I have now got the replacement master cylinder and this time I even pre filled it before putting it on the car. Initially I did a gravity feed on the front callipers and this seemed to work very well with clear bubble free fluid flowing. However the brakes were still a bit spongey so I again did a thorough bleed of all 4 corners with my patient assistant but again at the front callipers kept getting a continuous stream of bubbles. Giving up in despair, there was a reasonable amount of pedal pressure so I thought I’d let it settle overnight. The next day no brakes at all.
So I’m totally baffled. Could it be another duff master cylinder (TRW) or am I losing the plot?
GAjon said:
Right, I'm gonna say it, you may tell me to p
s off for suggesting this, but you won't be the first, are the calipers upside down?
I know someone, someone who had done loads of brakes who did it, John someone he was called.!
I wondered about that. Also the PDF is a known culprit for this and TRGB do a conversion to omit it but it's odd that it's cured by the m/c changes off for suggesting this, but you won't be the first, are the calipers upside down?I know someone, someone who had done loads of brakes who did it, John someone he was called.!
Yup I'm sure it is all the right way round and not upside down 
.
Normal bleeding problems would be air stuck in an awkward high point but that would leave the brakes spongy but without air coming out.
One curious thisg is that when I press the brake pedal there is a curious speak/ croaking sound that I hadn't noticed before. Not sure if it is the master cylinder or the new servo and forgot to take note when I out the old master cylinder back on.
. Normal bleeding problems would be air stuck in an awkward high point but that would leave the brakes spongy but without air coming out.
One curious thisg is that when I press the brake pedal there is a curious speak/ croaking sound that I hadn't noticed before. Not sure if it is the master cylinder or the new servo and forgot to take note when I out the old master cylinder back on.
Direct in line servo. There were no fluid leaks on the servo end of the master cylinder.
Only thing I can think to try next is to disconnect the outlet and fit a straight plastic hose into a jam jar. Then get someone to press the pedal. Need to buy some more brake fluid first as already wasted a couple of litres.
After that it is to take the master cylinder apart which I was reluctant to do on a new unit.
Only thing I can think to try next is to disconnect the outlet and fit a straight plastic hose into a jam jar. Then get someone to press the pedal. Need to buy some more brake fluid first as already wasted a couple of litres.
After that it is to take the master cylinder apart which I was reluctant to do on a new unit.
Is the PDWA still in the circuit?
Personally I would always omit this hateful bit of kit. MK4 Cortina 3 line grilling master cylinders are also the way to make an improvement.
If you don't use an easy bleed then the alternative is to buy a vacuum bleeder. Both bits of equipment give far better fluid bleeding that just pumping the pedal and opening the nipple.
N.
Personally I would always omit this hateful bit of kit. MK4 Cortina 3 line grilling master cylinders are also the way to make an improvement.
If you don't use an easy bleed then the alternative is to buy a vacuum bleeder. Both bits of equipment give far better fluid bleeding that just pumping the pedal and opening the nipple.
N.
Edited by Dollyman1850 on Sunday 27th November 16:07
Have you tried bleeding your way down the system, i.e master, any inline unions then caliper? I've clamped flexis to do this in the past.
I've never actually used a pressure bleed type of kit but I know lots of poeple have good results, big difference is that you get a much greater movement of fluid & hence more ability to move the fluid and air rather than just feeding fluid around the bubbles!
I've had situations on motorbikes where I've had to unbolt the caliper & hang it above the master to bleed the air out!
Other questions / thoughts...is the pipe fitting for the front circuit actually pinching up corrctly when it's tightened (i.e not just bottoming out on th thread)? I've had that issue on some fittings which are thresded to the end - there are a few variations.
The port in the res through to the master port is clear & there is nothing which could be working like a 1 way valve (and pulling a hefty vacuum in the system on the pedal release)?
It's also worth thinking about bleeding the fronts first as pressure in the rears could be limiting your ability to purge air from the fronts (pressure bleeding would get around this).
Some can be utter pigs...I remeber putting the best part of a gallon of fluid through a Renault 11 & it achieved nothing other than raising my blood pressure & coating the floor in patches of brake fluid.
Stew.
I've never actually used a pressure bleed type of kit but I know lots of poeple have good results, big difference is that you get a much greater movement of fluid & hence more ability to move the fluid and air rather than just feeding fluid around the bubbles!
I've had situations on motorbikes where I've had to unbolt the caliper & hang it above the master to bleed the air out!
Other questions / thoughts...is the pipe fitting for the front circuit actually pinching up corrctly when it's tightened (i.e not just bottoming out on th thread)? I've had that issue on some fittings which are thresded to the end - there are a few variations.
The port in the res through to the master port is clear & there is nothing which could be working like a 1 way valve (and pulling a hefty vacuum in the system on the pedal release)?
It's also worth thinking about bleeding the fronts first as pressure in the rears could be limiting your ability to purge air from the fronts (pressure bleeding would get around this).
Some can be utter pigs...I remeber putting the best part of a gallon of fluid through a Renault 11 & it achieved nothing other than raising my blood pressure & coating the floor in patches of brake fluid.
Stew.
Update on the brake master cylinder. Still baffled and no idea what is going on.
I took off the new master cylinder againand stripped it down to see if there were any obvious faults. All looked fine , all the right parts in the right order. So reassembled, filled and bled it on the bench and refitted to the car. I then gave all the connectors that I had disturbed an extra tweak to make sure they were sealed.
Went to bleed the brakes and still the same problem. Air continuously pumps out of the front brakes ( Far too much to b e in the system - it must be getting pulled in somewhere) and also notices that when the pedal is pumped that air bubbles also rise in tto the reservoir from the cylinder whuich is just wrong.
I then stripped down my old cylinder and gave it a good clean. (The bore is showing signs of its age but nothing fundamental). Filled and bled it and put it on the car. Not a single bubble rose into the reservoir however much I pumped trhe pedal, and I had all 4 wheels bled and clear in 10 minutes. The brakes are not brilliant (Probably need new pads) but she has just passed the MOT so can't be that bad.
So I'm still none the wiser on why the new master cylinder doesn't work. I stripped it down again for a closer look and still can't see anything obviously wrong.
If I get any answers I'll post an update.
I took off the new master cylinder againand stripped it down to see if there were any obvious faults. All looked fine , all the right parts in the right order. So reassembled, filled and bled it on the bench and refitted to the car. I then gave all the connectors that I had disturbed an extra tweak to make sure they were sealed.
Went to bleed the brakes and still the same problem. Air continuously pumps out of the front brakes ( Far too much to b e in the system - it must be getting pulled in somewhere) and also notices that when the pedal is pumped that air bubbles also rise in tto the reservoir from the cylinder whuich is just wrong.
I then stripped down my old cylinder and gave it a good clean. (The bore is showing signs of its age but nothing fundamental). Filled and bled it and put it on the car. Not a single bubble rose into the reservoir however much I pumped trhe pedal, and I had all 4 wheels bled and clear in 10 minutes. The brakes are not brilliant (Probably need new pads) but she has just passed the MOT so can't be that bad.
So I'm still none the wiser on why the new master cylinder doesn't work. I stripped it down again for a closer look and still can't see anything obviously wrong.
If I get any answers I'll post an update.
I had a similar problem last winter after mine dumped a pool of fluid under a back wheel. I replaced both rear slave cylinders and then couldn't build up any pressure when I was bleeding.
The master cylinder reservoir has a large rear section and a much smaller section at the front which is completely seperate from the rear. With the main rear section full of fuid the front section was empty. I filled it with fluid through the 1/4" gap bled the brakes and it is now fine.
I haven't a clue why it did it or whether it indicates a problem but the brakes are now better than ever and I haven't had a problem since.
Mark
The master cylinder reservoir has a large rear section and a much smaller section at the front which is completely seperate from the rear. With the main rear section full of fuid the front section was empty. I filled it with fluid through the 1/4" gap bled the brakes and it is now fine.
I haven't a clue why it did it or whether it indicates a problem but the brakes are now better than ever and I haven't had a problem since.
Mark
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