Bleedin' brakes!! Arrghhhh!!!

[markcro]

4 months later and my GT6 still sits up on axle stands with no brakes. I tested the new master cylinder as suggested above and it seems fine. Bleed it more and still nothing. >:(
But as it happens, a chap on the SXOC has just rebuilt his calipers and is experiencing the exact same problems. He went through all the same process of elimination and nothing. As a last ditch attempt he pumped the rebuilt brake pistons out one at a time, but not letting them pop out of the caliper, and then pushed them all the way back in. He went trough each of the pistons this way. Then rebled the brakes. And bingo- perfect solid brakes!
He reckons that one of the seals was not settled right and while not allowing fluid to leak out, but was letting air to be sucked in. Moving the pistons in and out forced the seals to settle and seal properly.
I haven't anything to loose so on Sunday I will give this ago! Fingers crossed!!!  ;)

[rotoflex]

I had a recent inability to get all the air out after a brake rebuild.  

Seeking help from a friend, who does thing methodically & in order, he had me stand on the brake, then he loosened the union of one of the brake pipes to the master cylinder to let it squirt out (into a rag stuffed all around & under the master cylinder, so as to keep brake fluid off the paint), then he tightened the pipe union at the MC again, let the brake pedal up, repeated a couple of times, then did the same with the pipe for the other circuit where it was attached to the master cylinder.  

Solved & no need to go further:  the air bubble was somehow trapped in the MC & had not been evacuated in my previous bleeding attempts that had runabout a quart of brake fluid through.

[markcro]

But did you have any brake pressure at all?  I think I'm beyond that- 1.5 litres of fluid, then replaced the master cylinder and another 2 litres of fluid and still nothing- pedal straight to the floor........ :'( >:( :X

[markcro]

Just home after going back over the brakes and moving the pistons in and out. And still no pressure whatsoever!  >:( :'( :B
I've put the covers on her and she can sit there until next year. Fu<k it, I've enough jobs to be doing on my SX that I'll get on with.

One last thought. The guy on the SXOC with the same symptoms believed that his caliper itself was not sealing. That the join between the two halves were allowing air in but no fluid out. He replaced the full caliper and his problem was solved.
Now thinking back, I did drop one of the calipers on the ground as I was rebuilding them. Has anyone heard of this as an issue?

At this point I'm sick of the whole thing.  :'(

[junkuser]

"Now thinking back, I did drop one of the calipers on the ground as I was rebuilding them. Has anyone heard of this as an issue?"

Very unlikely that this would cause a problem.

Unfortunately sounds like there is still air in he system somewhere, so time to get someone to help you if you are sure everything is assembled correctly.

[nang]

For the price of a couple of new rear wheel cylinders, if they were mine, I'd replace them if they were the originals. One less thing to worry about.  ;D
Tony.

[markcro]

I feel better after a sleep- less frustrated with this job that I expected to have finished in April.  :-/
I've passed about 40 quids worth of fluid through the system at this stage between the original and now the brand new master cylinder. The system would have to be nothing but air as there is still zero brake pedal pressure.  :(

None of the brake pistons front or rear are leaking which is the headwrecking part. I'll go back to basics and take off and disassemble the calipers all over again- bugger!  :X
Nothing worse that covering the same ground over and over again. Failing this I will brankrupt myself and start replacing everything with new. I'm thinking now that I should have just bought new calipers to begin with as the cost of rebuilding these two would have nearly paid for one brand new one. Not to mention the time saved.  :'(

It's a beautiful sunny day today- perfect for a drive. :(  But I don't even want to look at the little b1tch for at least a few weeks.  ;)

Yes I might just replace the rear cylinders as well. In for a penny in for a pound... :(

Cheers guys

[BrendanD]

When I get to this point I get it towed to a reliable classics friendly garage and say 'fix it please'.
Funnily, they usually do.....

[Spider]

Try clamping the flexible brake hoses in turn and pressing brake pedal to ascertain which corner of the car is the cause of the problem. It does not take much of an air bubble to make the pedal go all the way to the floor. I bleed some brakes with one of the callipers demounted from the wheel and had the same symptoms, it was not until I had the bleed nipple at the highest point that the air was removed and I got some feel back in the brake pedal.

[jaybee]

Please don't think I'm asking the obvious, but your problem might be straightforward and you're not seeing it. For example, a friend of mine had a similar problem, and finally he noticed he fitted the calipers wrong way round (left caliper on right hub, and vice-versa). The bleed nipples were at the bottom of the caliper instead of the top!
Firstly, you don't say if your brakes are single line, or dual circuit (tandem master cylinder). I assume because you have a servo, theyr'e single line, and so they should bleed easily. Here are 2 strategies you can try.
1. Gravity bleeding - fill the master cylinder, and have someone keeping an eye on it and top it up. Open all 4 bleed nipples and allow gravity to do the rest. When clear fluid (no bubbles) comes from any bleed nipple, close it. When all 4 are done, try the pedal. You can fit short sections of clear plastic tube to the bleed nipples whilst bleeding if you don't want fluid running down your calipers or brake backplates.
2. Pressure bleeding - buy a kit (I have a Gunsons, it's good!). Make sure the kit has a lid that fits your master cylinder. if not, order one from the manufacturer. Fill the reservoir of the kit as well as you master cylinder reservoir. Follow the instructions to pressurise the bleeder, and off you go!
I have found that brakes can be very successfully bled at VERY low pressure (I have used a spare tyre at only a few PSI as the pressure source, and I once used an inflated car inner tube - and it worked perfectly.
No need to run your engine, or to pump the pedal in either of the above methods. Good luck!

[markcro]

Cheers Spider and Jaybee, all suggestions are welcome and appreciated. And as you say it is very easy to over look the obvious when frustration sets it.
- I removed and rebuilt the calipers one at a time so they are on the right way around.
- A few people suggested getting one of those pressure bleeding kits. Are they not messy as in getting fluid all around the reservoir? I just have an image of it squirting fluid everywhere and messing up my newly painted bulk head. I may get one as if they are that easy to use then great! I also like the gravity idea! I'll try that. Where is the best place to pick up clear tubing?

I haven't looked at the car since. Couldn't bring myself to in case I burnt it out instead!  ;) But I plan to go out to it on Sat and work a few hours into the night and see what I find.

Thanks again guys.  :)

[Davemate]

Try holding down the pedal and at the same time push the caliper pistons back as far as they will go and the same with the rear cylinders.
Make sure the fluid in the master does not overlow and remember to refill before you lift the pedal.
I have done this sort of thing on a few cars that refuse to bleed up.
It's a way of reverse bleeding the system,you may have air trpped in a place that it won't shift from going one way  it it might move if it's blasted from the other direction
It is a two person operation unless you a way of holding down the pedal

Hope that makes sence !

[firebobby]

I read somewhere about reverse bleeding brakes using a pressure system from the extremities back to the master,as Dave points out :)

[jaybee]

You can use windscreen washer tubing, because its only a temporary fitment. You can also use a jar at each wheel with a smidge of brake fluid in the bottom of it, and put the ends of the clear tubes into the fluid. You can then see very easily when the fluid is free of bubbles. You will, of course, need 4 jars, and you will have to put spacers (wood blocks?) under them to get the height correct for the ends of the tubes. A bit of messing around to set the job up, but well worth the effort usually.

If you use a pressure bleeder like the Gunsons, it has its own reservoir. If you empty the reservoir by bleeding any remaining fluid in it through the vehicle brake system, it won't cause any fluid spillage when you disconnect everything. I think Halfords used to sell these at one time, and they are still popular, so I'm sure they are available on the internet.

[nang]

I usually work alone.
Here's a pic of my "2nd person" to hold the clutch/brake pedal down when bleeding. Been used on a lot of different cars, hence the many different holes.  8)
Tony.

[markcro]

Yesterday I went back to the car after not even setting eyes on the car in weeks as I'm fed up and had stuff to do on my Nissan for a track day etc. Anyway thanks to some of the suggestions above I think that I have isolated at least the corner where the problem is:

- The brake pedal goes straight to the floor.
-But with the driver side front brake hose clamped the pedal goes solid about 2 inches off the floor. So this rules out the new master cylinder as the issue and would point to the driver side front caliper.  (solid at 2inches off the carpet- does this still sound a little far??? Although I haven't bled the system properly since the last disconnecting and reconnect of pipe unions)

So with the above logic I have removed the brake caliper and striped it down again. Before stripping it I noted that there is absolutely no leaks what soever. I striped it down and the brand new seals and pistons that I put in look 100% perfect. So I'm back to scratching my head again as the caliper looks perfect but if my logic is right then the clamping the hose does points to this corner.............
I will put it all back together again and see what happens. But even if it does fix it it doesn't give me total confidence as will this happen again? I wouldn't want this to happen when I am coming to the end of a motorway!

I measure one of the old pistons and it is 54mm dead on. The new pistons are 53.96mm. The 0.04mm would hardly make any difference? And if it did then surely fluid would be leaking?! That is what gets me, there is no fluid leaking anywhere......... :-/ :B

[thebrookster]

Three possible things spring to mind then, you either have air in the calliper, calliper is leaking or the hose is expanding.

How old are the flexible hoses (I am being lazy, so I apologise if you have mentioned this already)? An old rubber hose loses it's structure somewhat, and turns into  a balloon if you are not careful.

I assume the piston sizes are diameters, and no I would not have thought that would make any difference to the pedal, only effect it would have would be leaking fluid which you have already ascertained it is not doing, so unlikely.

So, check the hose for condition and ensure you are completely bled when you re-assemble.

Cheers,

Phil

P.S Having now gone back and read the thread start to finish, my gut feeling strongly says check the flexible brake hoses. If they have not been replaced recently do them anyway, rubber does die so I now class this as a routine replacement part tbh.

[markcro]

Cheers Phil. Yes God knows how old the rubber hoses are but they look to be in good condition. I have a set of Goodrich braided hosing sitting in a box for the last 3 years which I have never gotten around to fitting, so this is the perfect opportunity.
As said above on one of my posts, one of the guys on the Nissan site had the exact same problem and he reckoned that the caliper itself was leaking, but allowing air in but no fluid out. And he ended up just replacing the whole caliper and the problem was fixed. Not sure if I but the leaky caliper without it leaking fluid out, as the fluid it so runny that it would have to get out somewhere. Anyway, I'll soldier on. I am getting this f**$%^^% car on the road before winter comes. This issue has totally wasted the summer.

[markcro]

So today with the help of  friend we confirmed the issue is with the front right hand side caliper. The hose is fine.

- Fully bled all four corners today and the brake pedal still goes to the floor...
- Clamp the drivers side front brake hose and the pedal goes solid about 2 inches off the floor. Release the clamp and the pedal dives straight into the carpet.
- Removed caliper and rebuild it, but the exact same as above....


Now this is where it gets very strange and neither of us could explain it as it just doesn't make sense!! :o

- Clamp one piston in the caliper and let the other piston move out until it locks against the disk, the brake pedal goes firm.
- Clamp the other piston and do the same, the pedal goes firm.

But the both pistons move out until they hit the disk and the pedal goes to the floor!!! WTF?!?!?!

Clamp either piston and I can get brake pressure, but allow both pistons to move and no brake pressure... why?! It doesn't make sense!

So come Monday I am ordering a new caliper as I'm sick of this issue.

[junkuser]

Not likely, but are the pistons being retracted by the dust seals on that caliper?
Just sounds as though the volume of fluid required to move the pistons sufficiently exceeds the stroke volume of the master cylinder.
Are the dust covers in the same positions on both front calipers?
Are the front calipers of the same design on both sides as there were different designs of dust seals.
Would really be nice to understand what is happening.

[thescrapman]

You shouldn't be getting 2 inches of pedal travel with the suspect caliper clamped off, you should probably only have inch travel maximum with everything connected, so even when you change the caliper you still have a problem.

Cheeers

Colin

[JohnD]

Good diagnostics, Mark!
But they could point to the master cylinder.   Limiting the movement of one piston will limit the movement of the master cylinder piston.  Allow both to move and the M/c piston may go beyond a point at which it seals.
Have you done anything to the M/c?
Have you tried the same diagnostics to the opposite caliper?  If the same happens, then the M/c is the common factor.

John

[markcro]

Thanks for the replies.

- I left the dust seals off the caliper so that I could inspect for any slight seepage around the cylinders. There is no seepage or leaks. So the dust seals aren't a factor in effecting the cylnder movement.
The calipers are original to the car so are the same on both side and in fact looked like they had never been removed from the car in near 40 years! A total bugger to remove!

- When I clamp the passenger side caliper it has no effect on the pedal travel at all. The pedal will bury itself in the carpet straight away, so no effect at all.
In contrast the pedal goes firm as soon as you clamp the drivers side.

- interesting theory on the stroke of the master cylinder, one I had not considered. I actually hoped that the master cylinder would never ever have to be touched again as I replaced it with a brand new one and painted the bulk head while I had all of the master cylinders out of the way..... my lovely paint will be messed up taking the MC off.. :-(

But this makes me question is there is a issue with the MC at all?
- I replaced the original MC with a brand new one when this problem originally occured. It made no difference but at least I have a brand new MC. Is this new one faulty just as the old one that came off must have been?
-If the issue is with the MC along the lines of it's stroke and not flowing enough fluid (hadn't thought of that!), but then how come it can flow enough fluid for the passenger side and firm up when the driver side is clamped. But won't firm up with the passenger side clamped?

So my options are now:
- Replace the driver side caliper with a brand new one.
0r first
- Rebuild the original master cylinder, remove the brand new one (ruining my lovely fresh paint :-( ) and fit the original again. But what are the chances of the original MC going just as I rebuilt the brakes and the the brand new being faulty too?

A very strange and time wasting problem. Frustrated and perplexed!!


Can someone press their brake pedal with their hand as hard as they can and tell me roughly the distance from the carpet that it goes solid? This will give me a rough guide. Mine goes firm about 2 or 3 inches off the carpet with the driver caliper clamped off.

Thank!

[markcro]

I forgot to add the most confusing part- if I clamp both pistons the pedal dives into the carpet..... :D

So to recap:

- no clamps- pedal digs into carpet.
- brake hose clamped - pedal goes firm
- Clamp one piston or the other in the caliper and the pedal goes firm.
- Clamp both pistons in the caliper and the pedal goes straight into the carpet


:D

[JohnD]

That it doesn't matter which piston you clamp, or that clamping the hose makes it go firm, makes it more likely to be a caliper problem. That you have a new M/cylinder makes it less likely (though not impossible!) that is culprit!

I just read back to the start - you rebuild both calipers.  In my book a new problem is always due to what you last did to the car.   Your diagnostics point to that caliper, so rebuild that caliper again, before getting new.   There must be something in the split between the two pistons - O-rings between the halves??? - to cause this, that hasn't gone in right.
JOhn