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?
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.
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 thought about the seals but yes it is the right way round. I did take photos just to check
I think it it has PDWA. I sat think because it has a block that looks like a PDWA but it has no switch. I did wonder whether any possible PDWA failure modes could introduce air into the system but can't think of any. It would also have to be some type of double fault since the old master cylinder works.
Brakes usable with the old master cylinder . i.e. it did pass the MOT. but sure they used to be better. No air comes out when bleeding so suspect the old pads as it did seem to improve the more I drove it.
Interesting point about the free play on the servo. I wasn't aware it was adjustable. Will have a look in the morning.
Interesting point about the free play on the servo. I wasn't aware it was adjustable. Will have a look in the morning.
spent most of last night coming up with a theory why incorrect pushrod adjustment could come up with the symptoms I'm having. Has myself totally convinced this would give me the answer.
Checked it today and the adjustment is fine. aaaaagh.
I've now had more than enough of brake fluid for this year. Will now give it a rest over Christmas and see if next year brings any new ideas. ( maybe if i filled it with rum sauce it might work better)
Checked it today and the adjustment is fine. aaaaagh.
I've now had more than enough of brake fluid for this year. Will now give it a rest over Christmas and see if next year brings any new ideas. ( maybe if i filled it with rum sauce it might work better
)Couldn't resist another play today even though I should have been helping get ready for Christmas.
Took both master cylinders apart and compared the dimensions of the pistons etc. Both identical. Only difference I could see was the new master cylinder had new looking seals as would be expected.
Then assembled the new one again. Filled it with fluid on the bench with clear plastic pipes from the outlets back into the reservoir (under the fluid). Pumped the piston until all the air was out and the plastic pipes were full of clear fluid. So far so good and I was tempted to put it back on the car and try again. Then noticed that pumping the piston I could get air bubbles to come up into the main reservoir. No on every pump or even consistent with the length of pump but still fairly frequently. Carried on long enough to be clear it was more than just trapped air. This was one of the symptons I had noticed on the car which didn't happen on the old master cylinder.
I then swapped the tipping valves. Did the same again and this time once it was fully bled I could not get air to rise into the reservoir.
So the tipping valve is a possible suspect. Altrhough they look identical the only noticable difference is that the spring is a bit stronger on the new one.
Still not conclusive until :
1) I can repeat it a few times in case it is an assembly coincidence
2) I can prove it is not just masking another problem.
Anyway now definitely sick of brake fluid everywhere.
Merry Christmas and thanks for all the sugestions so far
Took both master cylinders apart and compared the dimensions of the pistons etc. Both identical. Only difference I could see was the new master cylinder had new looking seals as would be expected.
Then assembled the new one again. Filled it with fluid on the bench with clear plastic pipes from the outlets back into the reservoir (under the fluid). Pumped the piston until all the air was out and the plastic pipes were full of clear fluid. So far so good and I was tempted to put it back on the car and try again. Then noticed that pumping the piston I could get air bubbles to come up into the main reservoir. No on every pump or even consistent with the length of pump but still fairly frequently. Carried on long enough to be clear it was more than just trapped air. This was one of the symptons I had noticed on the car which didn't happen on the old master cylinder.
I then swapped the tipping valves. Did the same again and this time once it was fully bled I could not get air to rise into the reservoir.
So the tipping valve is a possible suspect. Altrhough they look identical the only noticable difference is that the spring is a bit stronger on the new one.
Still not conclusive until :
1) I can repeat it a few times in case it is an assembly coincidence
2) I can prove it is not just masking another problem.
Anyway now definitely sick of brake fluid everywhere.
Merry Christmas and thanks for all the sugestions so far
Finally seem to have got the brakes sorted (delayed by Christmas, bad cold and holiday).
In the end after trying numerous combinations of bits from the old cylinder and the new I concluded that the only option was to try some new seals. I got a set of new seals and tripper valve from Rimmers, popped them all in and hey presto it worked fine. Put it on the car and bled the brakes without any problem without any fancy kit or helper (as it should be).
I had intended to change the seals one at a time to see which one was the problem but by then I was so hacked off I just changed them all. (I would have changed them all in the end anyway).
The only thing I can conclude is that there was a problem with the primary seal even though it was "new" and looked OK. (the tipping valve or other seals shouldn't physically be able to let air in) Maybe uit had been stood in stores for years and the seals degraded???. I'll get on to the supplier for comment.
In the end after trying numerous combinations of bits from the old cylinder and the new I concluded that the only option was to try some new seals. I got a set of new seals and tripper valve from Rimmers, popped them all in and hey presto it worked fine. Put it on the car and bled the brakes without any problem without any fancy kit or helper (as it should be).
I had intended to change the seals one at a time to see which one was the problem but by then I was so hacked off I just changed them all. (I would have changed them all in the end anyway).
The only thing I can conclude is that there was a problem with the primary seal even though it was "new" and looked OK. (the tipping valve or other seals shouldn't physically be able to let air in) Maybe uit had been stood in stores for years and the seals degraded???. I'll get on to the supplier for comment.
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