Bleeding brakes - it's getting worse!
Discussion
So I changed my rear calipers over last night (so they are the right way up) and bled the brakes again. I started at the rear passenger, then rear drivers, then front passenger then front drivers.
I have a vacuum tester I have been using to pull through brake fluid until bubbles stop and then (with the line full of fluid into the collector) give the pedal a few pushes to double check clear fluid is coming through. I did this at each corner and topped up the brake reservoir a couple of times during each corner to keep it near full.
Last time I took my car out the brakes were spongy but they stopped me OK from about 20-30mph. I just tried my car again and didn't make it off my drive. The brake pedal goes to the floor with little resistance and the car rolls freely.
What have I done wrong?
I was sure I had done everything correct and I pulled over a liter of fresh 5.1 through. I don't understand how they could have gotten so bad, I am beginning to wish I had just left them spongy so I could have at least driven it slowly to a garage.
If I miss the MOT slot tomorrow I doubt I will be making it to Burghley in a Cerbera.
I have a vacuum tester I have been using to pull through brake fluid until bubbles stop and then (with the line full of fluid into the collector) give the pedal a few pushes to double check clear fluid is coming through. I did this at each corner and topped up the brake reservoir a couple of times during each corner to keep it near full.
Last time I took my car out the brakes were spongy but they stopped me OK from about 20-30mph. I just tried my car again and didn't make it off my drive. The brake pedal goes to the floor with little resistance and the car rolls freely.
What have I done wrong?
I was sure I had done everything correct and I pulled over a liter of fresh 5.1 through. I don't understand how they could have gotten so bad, I am beginning to wish I had just left them spongy so I could have at least driven it slowly to a garage.
If I miss the MOT slot tomorrow I doubt I will be making it to Burghley in a Cerbera.
Odd question, but when pumping the pedal have you stroked the master cylinder all the way? Sometimes, and it very much depends on the quality of the parts, stroking the master cylinder beyond its usual travel can run the seals over "new" material which can be rougher, damaging the seals slightly. It may be worth cracking a nipple open again and having a helper prove the master cylinder is actually pumping?
I was trying not to push the brake pedal all the way down when giving a few pushes after vacuuming out the air bubbles as I know this can cause problems. It could be the master cylinder but I hope not.
If I crack open a bleed nipple again and push the brake pedal down will it still push brake fluid out if the master cylinder has failed?
If I crack open a bleed nipple again and push the brake pedal down will it still push brake fluid out if the master cylinder has failed?
TimJM said:
I was trying not to push the brake pedal all the way down when giving a few pushes after vacuuming out the air bubbles as I know this can cause problems. It could be the master cylinder but I hope not.
If I crack open a bleed nipple again and push the brake pedal down will it still push brake fluid out if the master cylinder has failed?
It may, but it should be a very positive squirt/stop squirting if the master is in good order and it's been bled properly. As Tanguero says though, maybe try old fashioned pedal pump bleeding? I've used pressure once but otherwise have always just done it the old fashioned way - i.e. I've never used vacuum so I wasn't aware of that potential issue above.If I crack open a bleed nipple again and push the brake pedal down will it still push brake fluid out if the master cylinder has failed?
ETA: There should also be a very sharp increase in pedal weight when the nipple is closed mid-pump if all is in order.
I'm not a Cerbera specialist, but i had the same problems on my T350. Even my mechanic (not particularly knowledgeable on TVR specific questions) couldn't find the fault.
My car has the Sierra Cosworth rear calipers, which seem to be prone to oxygen getting trapped, if the cylinder isn't wound back all the way. Found this info here on PH, but can't remember exactly where.
So my mechanic used this special tool to wind back both cylinders on the rear brakes and indeed more air bubbled out! The improvement in braking force was massive. All the required values were achieved during brake testing. The brake pedal feels still a bit spongy, though. So still not perfect in my eyes. I guess i have to repeat the sequence once again.
My car has the Sierra Cosworth rear calipers, which seem to be prone to oxygen getting trapped, if the cylinder isn't wound back all the way. Found this info here on PH, but can't remember exactly where.
So my mechanic used this special tool to wind back both cylinders on the rear brakes and indeed more air bubbled out! The improvement in braking force was massive. All the required values were achieved during brake testing. The brake pedal feels still a bit spongy, though. So still not perfect in my eyes. I guess i have to repeat the sequence once again.
Was just going to ask if you bleed both nipples on each caliper as that caught me out a few years ago.
I do in board nips first then out board.
I work from the furthest caliper from the master cylinder back towards it as well as do you.
It might be worth getting a hand and lifting the calipers high and upright to bleed them, I have never had any issues except me being a numpty after having the whole system drained and pipe work replaced.
I do in board nips first then out board.
I work from the furthest caliper from the master cylinder back towards it as well as do you.
It might be worth getting a hand and lifting the calipers high and upright to bleed them, I have never had any issues except me being a numpty after having the whole system drained and pipe work replaced.
Edited by scotty_d on Wednesday 9th April 15:13
To get maximum flow through a caliper and bleed nipple definitely use the 2 man/woman method.
First, clamp off the flexys to the 3 calipers FURTHEST from the master cylinder. Use proper clamps or vice grips but do not squash them too hard.
Now open the inner bleed nipple on the front driver's side caliper a good half turn. Tell the pusher to press the pedal hard and fast 5 times then hold down. Close the nipple then let the pedal up slowly. Open and press down etc until no air bubbles present. Then do the outer one - open, press down to the floor, close, up, etc.
Now clamp it off.
Then do the other front the same way and clamp off afterwards. Go to the back driver's side and repeat the process, clamping off and finish at the passenger rear.
Don't forget to remove all the clamps after!!!
This method of clamping ensures all the pressure goes to the nipple you are opening and the higher pressure usually ensures all air is expelled. If the master seals have partly turned this method sometimes helps to re-seat them.
First, clamp off the flexys to the 3 calipers FURTHEST from the master cylinder. Use proper clamps or vice grips but do not squash them too hard.
Now open the inner bleed nipple on the front driver's side caliper a good half turn. Tell the pusher to press the pedal hard and fast 5 times then hold down. Close the nipple then let the pedal up slowly. Open and press down etc until no air bubbles present. Then do the outer one - open, press down to the floor, close, up, etc.
Now clamp it off.
Then do the other front the same way and clamp off afterwards. Go to the back driver's side and repeat the process, clamping off and finish at the passenger rear.
Don't forget to remove all the clamps after!!!
This method of clamping ensures all the pressure goes to the nipple you are opening and the higher pressure usually ensures all air is expelled. If the master seals have partly turned this method sometimes helps to re-seat them.
My rears were fine using one of those one man easy bleed kits, a pipe with a non-return valve in, but the fronts were a right pain I just didn't get any fluid through at all. So I gave up & when for a cupper but left the hose attached to the loosened off nipple, when I came back some time later there was fluid dripping all down the caliper. So I did the same for the other side, then had to do the two person method on my own by wedging the pedal down, eventually that got all the air out, but it took at least half a day.
Success!
The two person method works. I started again in the same order (furthest to closest) with my helper (wife) the rears had no air at all. As soon as I loosened both the inner and outer nipples fluid flowed through. We gave them a few peddle pushes and just fluid on all four rear bleed nipples but the pedal was still going to the floor with little resistance.
Then we did the fronts. The passenger inner first and again just fluid came through but my wife said the pedal was starting to firm up. We finished up doing the outer then drivers side inner and outer and agin just fluid - not even a bubble. However, the pedal was getting firmer and firmer.
By the time we finished the pedal was rock hard and could only be pressed a small amount. I took it for a quick "round the block" and the brakes work. The pedal has softened slightly as you would expect but if you press it hard you do stop quickly.
I will see how it is in the morning just in case there is some sort of slow leak somewhere but for now all is looking good.
The only thing I don't understand is that no air came out and the fluid coming through was the new fluid but yet the brakes have gone from zero resistance to me being able to lock the wheels up on my driveway from about 5-10mph.
Looks like the MOT could be on for tomorrow. I just tested the basics (lights, horn, wipers) and they all work so fingers crossed.
The two person method works. I started again in the same order (furthest to closest) with my helper (wife) the rears had no air at all. As soon as I loosened both the inner and outer nipples fluid flowed through. We gave them a few peddle pushes and just fluid on all four rear bleed nipples but the pedal was still going to the floor with little resistance.
Then we did the fronts. The passenger inner first and again just fluid came through but my wife said the pedal was starting to firm up. We finished up doing the outer then drivers side inner and outer and agin just fluid - not even a bubble. However, the pedal was getting firmer and firmer.
By the time we finished the pedal was rock hard and could only be pressed a small amount. I took it for a quick "round the block" and the brakes work. The pedal has softened slightly as you would expect but if you press it hard you do stop quickly.
I will see how it is in the morning just in case there is some sort of slow leak somewhere but for now all is looking good.
The only thing I don't understand is that no air came out and the fluid coming through was the new fluid but yet the brakes have gone from zero resistance to me being able to lock the wheels up on my driveway from about 5-10mph.
Looks like the MOT could be on for tomorrow. I just tested the basics (lights, horn, wipers) and they all work so fingers crossed.
N7GTX said:
To get maximum flow through a caliper and bleed nipple definitely use the 2 man/woman method.
Glad you have it all sorted, and this is another vote for the GF method of bleeding brakes (and clutch). I have complete confidence in my GF being able to pedal when needed and report if there's an issue. She's used to the difference between cars as well, even though she rarely drives. I admit I've never tried using a pressure bleeder, but I'm not the least be tempted.I don't know anyone that has had any success with the vacuum bleeders, they seam to draw in too much air around the bleed nipples. I pressure bled my braking system when rebuilding my braking system and although difficult to seal on the reservoir bled very easily, the clutch was done the old fashioned method with a rather unwilling helper!
I agree, lots of air can be drawn in by the threads on the bleed nipples, especially if the threads are worn. This can give the impression of lots of air in the system. Bit of Ptfe on the threads can help.
Also with the master keep the fluid level up. With it having two fluid compartments it's easy to run dry on the front brakes as the rear compartment is hard to see.
Also with the master keep the fluid level up. With it having two fluid compartments it's easy to run dry on the front brakes as the rear compartment is hard to see.
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