Faulty Brake Hoses (Allows fluid to flow forward under brake pedal pressure but not to return.)
The above comment explains one reason brakes may either 'stick -on', drag or worst case scenario, lock!
The caliper in the photos is for an MGB but fitted to my ZB Magnette. Both front hoses illustrate blockage and failure to return fluid to the master cyl.
Method: The caliper was held in a vice and 2 small sash clamps used to retract the pistons. Exposed piston edges were cleaned and lubricated with brake assembly lube (gel) before being retracted.
With both pistons clamped and pressure applied to the clamps fluid would not exit the open end of the brake hose. With one clamp removed and the other tightened progressively the free piston would move out from its housing. This was then reversed for the other piston. No fluid exited from the open ended hose.
A clamp was placed on each piston again. Pressure applied. No movement occurred. No fluid exited the open end of the brake hose.
The same process was repeated (as above) but this time the bleeder valve was opened. Fluid exited and the pistons moved inside their respective housings.
* Note the TIG wire inserted into the brake hose...I was unable to pass it fully through!
* Both front hoses were faulty yet appear perfectly fine externally.
This is PS side refurbished and fitted with stainless braided lines.
A quiet couple of weeks but this is now planned in, I will feedback once I change the hoses, fluid and degunk everything then will see where get to
Quite happy to replace the servo but as its exchange and needs to come off as do a lot of parts around it I will test the easy bits first to gauge the results.
As it is exclusively a front brake issue I am not sure in my mind its the servo as that would affect the rear wheels too but I am open minded, it needs doing so will get done. Brakes are a non skimp especially on a car of this size and weight.
Not in a mad rush slowly slowly and methodical works for me! Pragmatic approach. I have many projects auto and non auto but keen to get it moving and enjoy the majesty!
In the interim we've had the opportunity to really challenge the car and the history and it is a very nice vehicle indeed with amazing history so despite the issue we are very pleased with it indeed. It feels cherished but useable not a concours air bubble car and it will be driven / enjoyed.
We have fed the leather and that has responded very well, was feeling dry and beginning to crack now feels supple again, rear backrest stitching needs a repair but otherwise good interior and all but the clock and the dreaded overdrive working. That's a job for later
We are building a list of to do's most of which are protective rather than repairs, Dinitrol here we come
On top of the hoses we will be testing the calipers as I've had this before myself, they are available rebuilt so am happy to change them should that be needed. Discs look new but are a bit blue after being cooked, will be repacking the hubs to replace the grease that boiled out. The car travelled very minimal distance so hopeful we can salvage some of the parts at least
It was slightly more than just an experiment...I needed to refurbish the front brakes on my ZB Magnette (modified many moons ago to a boosted twin circuit system with discs up front.
Before you decide to rebuild/change-over the front calipers focus on replacing both front brake hoses first. The MGB calipers on my Magnette weren't locked to the extent your P5s front brakes were but the car would not roll forward even on an incline. Simply changing the hoses for new freed the calipers of residual pressure.
When you get around to doing this first fully retract both caliper pistons (a sizeable quantity of fluid will displace back the the master cyl so ensure it doesn't overflow.) Clean and then smear some brake assembly lube around the outside perimeter of the caliper piston when the pads are removed before retracting the pistons. This should free them up if they're sticking.
* As only the front brakes locked on your car that should discount the compensating port in the master cyl being blocked or obscured by swollen seals, dirt or grit?
I have bought new flexi hoses and intend to fit them soon
I bumped into a Rover P6 restorer at my sons college evening (!) and thought id get some free advice, definitely the servo 100% in his experience, he does P5 as well. He foolishly wore a logo shirt so was fair game...
Plan to tackle that soon and send away for refurb, does anyone stock these non exchange? if so I cant find one!