Front brakes not releasing

[Forkie]

Me again In brief - do these cars have an issue with the caliper pistons not retracting for any other reason than the caliper/ piston being at fault? Went to remove the OSF a couple of evenings ago - went to turn it and dear me it was stiff as .
So wheel off. Inboard half of caliper thick in brake dust, outer not half as bad. Could barely turn hub with wheel off. Really struggled to remove pads. Pads out - hub now free. Could just about move both pistons back home. One pad back in one side, a piece of wood to dummy a worn pad in the other. Gentle brake pressure applied to bring the piston with the dummy in out further - to push the piston back in took considerable effort. Repeated this around 5 times, then swapped over to do the same procedure on the other piston. Exactly the same. So push back number 5 just as hard as the first one. Did not have much hope that anything would be different by that but popped both pads back in anyway ( with both pistons fully home). Spun hub - all good. Applied footbrake - attempted to turn hub - solid again. Great. I would assume the NSF maybe the same. So just as a reminder - all these parts were brand new, but fitted 15 years ago, and done maybe 250 miles. So new calipers, new pads, new discs, braided hoses. Brake system was bled right through as new rear pipes had been fitted last year. So just thought i would ask on here before i start stripping the ' all new brake system' , yet again. The half pistons that emerged on the above exercise looked brand new, no rust or scoring, and no fluid leaks.

[Forkie]

To quote the manual - ' The inner seal ( on the piston) , which is retained in a groove inside the cylinder, prevents fluid leakage and provides a running clearance for the pad irrespective of how worn it is, by moving it back a fraction when the brake pedal is released.'
So, i would assume, that is not happening - would you agree that is the problem, so a reseal of the new calipers is required, or may there be another cause.

[Alec]

Hello Forkie,

brake fluid absorbs water so it is most likely to be corrosion within the caliper. A strip down and reseal if the corrosion is not too bad.
While it is the devil's work to some, I have used silicone brake fluid for decades, which does not absorb water nor require regular replacement.
I am in the process of restoring a car of mine laid up since the late 1990s and none of the calipers were seized, discs front and back.


Alec

[johnnydog]

I had exactly the same symptoms on the front brakes on my PI which had been laid up for a good number of years - application of the footbrake moved the caliper pistons out no problem, but then the brake pads were binding quite severely. A good bit of effort was then needed to get the pistons to retract.
The problem was the front brake flexible hoses. I replaced both fronts and then the problem was solved. The hoses had collapsed internally - foot brake pressure was sufficient to push brake fluid through to the caliper, but when it was released the pressure remained as if the brake pedal was still depressed.
With two new hoses everything returned to normal operation!

[Alec]

Hello Johnny,

that is a possibility but easily checked by opening the bleed screw when trying to retract the piston, if the hose is a problem then the piston will then retract.
He does say however that he has fitted new braided brake hoses, (I assume he means the Goodridge type which do not suffer from the same problems as rubber hoses.)

Alec

[Forkie]

Hi to you both, a couple of interesting points made. Alec, yes i am aware of the water absorbtion, and i did come across your post re the Jaguar whilst having a trawl through some posts on here before posting up.
So regards your initial post, i was kind of hoping that may not apply as the ' new' calipers ( along with all the other new parts) were fitted after coming off the road,, so had never had any fluid through the system until early last year when it finally got sorted. But now thinking on, i suppose the internals of the caliper may well have gained some corrosion over that long period anyway....even in a dry but not heated garage.
And yes Alec, the braided hoses are the Goodridge type.
Am more than slightly miffed as she was booked in for the first show in 15 years this coming Sunday, so that is now scuppered So it would appear then that the ' new ' calipers may well need an overhaul then - it was in my mind, but i suppose i was just hoping for an easy, 5 minute fix - why did i hope for that!!!! I did just have a quick look on CW site, thinking i will just exchange them again for ease - but unfortunately out of stock . This car is a constant reminder of two things - their on - going commitment of time required, and do not let them stand still for long periods of time .....

[Forkie]

Just re-reading your post John , what you describe is exactly what i am having. Could it be possible that the braided hoses are the issue? I know they do not suffer the internal collapse issue, hence why i sourced them - fit and forget ( a bit like fitting new calipers ) - i am almost tempted the next chance i have to do just that - take pads back out, fit the dummy to push piston out a bit further, undo bleed nipple , then go for a push back. So with that in mind, if the piston is still requiring fair effort to retract, the fault lies with the caliper internals. If the piston(s) retract easier, the fault would be the braided hose.....
As an aside, as i have always had this ' lack of top end ' for 18 months, no engine issues found after extensive tests, i now know that i DID have gearbox issues which i always suspected, that is now sorted after a hefty rebuild cost, but still feels ' strangled' - i now wonder if this is the reason - brakes on, right from the start, but maybe progressively worsening over time - right from the start of last year i did wonder about the brakes, but kept feeling the wheels here and there for heat after driving, nothing alarming being felt, and never smelt hot at any time either....but it is now certainly adding up all round. Maybe ....

[johnnydog]

I think doing as Alec suggested is the next thing to check - retracting each piston in turn with the bleed nipple open on that caliper, and seeing if the effort required is less or the same. I'm surprised however that a reconditioned caliper in effect stored without ever having had brake fluid through it should suffer from internal corrosion sufficient to cause this issue, even if the bleed nipple was left 'open' to the atmosphere.
You haven't actually said in so many words, but are both fronts doing the same or is just occurring on one side?
You haven't mentioned (unless I've missed it!) anything about the brake master cylinder. Have you ever stripped it and put new seals in (assuming the bore was good and not pitted of course!)?

[Forkie]

Hi John. Firstly, i had to refer back to my ( many) notes on this car's timeline - obviously it was never planned to take as long as it did , to be off the road. Anyways - the car came off the road in August 2008. According to my notes, the O/S front had its brake overhaul in October of 2008, the N/S 1 month later - November 2008. Both sides within one month of each other. NOS Goodridge flexis fitted ( all 4 corners) , NOS discs, Blackstuff front pads, NOS rear shoes, NOS rear cylinders, new copper pipes to rear, fronts were still good from the splitter under the tunnel - still good today. The Master Cylinder was always suspect - so i had that out and re-sealed it. Piston assembly looked good at the time. Ref the calipers - left as installed - so assume bleed nipple ' up tight'. In other words, thats why im struggling to see where the system has absorbed water,as no brake fluid has passed through. I know i am not going to make the show now, but at the same time i still need to get my head around what the problem is.

[Forkie]

I appologise - i thought i made things clear earlier - the car lives in a boggo standard garage , so can only really get to one side at a time - car needs to be turned around each time to get to the other side, bit of a pain but - at least it is garaged. I just assume at the minute that both sides will be the same, as both sides have had the same treatment. But until i turn the car around i cant really confirm that.