I wonder if anyone can help I have had some issues with my breaks for some time….. At the time of the last MOT the brake pedal was quite hard and when pushed the brakes came on with a jolt, the pedal then stayed down until you pulled it back with a foot underneath. I took the front callipers off and cleaned the pistons etc, after replacing them and bleeding the brakes they seems to work fine. (It passed the MOT) However, after a couple of weeks of not using the van the brakes started to do the same, jolting on and the pedal staying down. I then replaced the front callipers expecting them to work fine but the problem although better is still there, when you brake the brakes are better but there is still a slightly had push to get over and then the brakes are fine. The pedal still does not return properly although it is not as bad. If the brakes have been pressed the servo tries to take over on deceleration unless you pull it all the way to the top. Looking at the servo it is the original I think although the mounting bracket has been re-welded so perhaps it has been replaced. (I assume it was fitted with the servo from new, it is a 1979 van conversion 2.0 twin carb). Finally when looking at the master cylinder there is a small pin hole underneath near to where it joins the servo and this seemed to be weeping some brake fluid when I bled the system but is not anymore. I think perhaps it needs a new servo and master cylinder but I want to ensure I am replacing the correct parts. I have not checked but could the servo have a blocked breather pipe. Thanks.
I think your looking at the master cylinder. There is very little to go wrong with a servo except the diaphragm. And that usually only leave you with a heavy peddle. However If brakes are locking on you need to work backwards. If the pistons don't move back then try loosening the brake pipe to them. If they do then work along the pipe work. It could be a flexi brake hose that's not flexing like it use to. Finally you'll get back to the master cylinder. If undoing it from the servo it frees up then it's here. Make sure the peddle can travel back freely. If it does then it won't e the servo. Have you had any work done to the front beam?? We had one in with a badly adjusted actuating rod that following a front beam. A few turns on the adjuster nuts and all was good again.
An easy thing to check is that there's a small (about 1mm) amount of free play in the master cylinder pushrod. You'll see the threaded adjustment bit on the pushrod. If it's too tight, the m/c cylinder piston never travels fully back, uncovering the internal valves, so the brakes may not release fully.
What Snotty says, or the return spring on your brake pedal has snapped, or the brake pedal shaft is seizing because it needs cleaning and greasing. Sounds like the latter to me - needs a hard push then ok then won't return...
Thanks for the replies. I am aware that servos are normally quite reliable and then don’t tend to offer as much assistance if not functioning correctly but I wondered if this could be linked to the problem. I forgot to mention that I have already checked the callipers and they are brand new, I have also replaced the copper pipes and flexi hoses. I have replaced the return spring and striped, cleaned and greased the whole mechanism. I have also checked the pedal mechanism for play and there is a few mm when the brakes are not depressed. As stated in the original post the problem seemed to disappear after I cleaned the original callipers and replaced the pipes, when it returned I then replaced the callipers but the problem is still there. I will have to strip the master cylinder and the servo to check, could the return spring in the master cylinder be broken? Thanks.
