Hi all, Have had all 4 brake calipers overhauled and now refitted to the car but I can't get the brakes to bleed properly despite several goes at bleeding all 4. The original brake failure was caused by a sticking calliper boiling the fluid but once freed off and cooled down the brakes were ok to drive home. So the master cylinder was working ok at that point. I'm wondering if the pedal going to the floor when I had the problem and subsequently when bleeding the system has damaged the seals in the master cylinder? Is changing the mc a simple diy job? The workshop manual shows a clearance, with adjusting nut, inside the servo but does not say how to adjust it. Thanks for any thoughts / advice! Chris.
Be sure to bleed the master cylinder otherwise you can cycle gallons of fluid through the system and never get it properly bled. I had the same problem and as soon as I bench bled the master cylinder the problem went away and the system bled perfectly.
It is very rarely the master that is the culprit when fault finding on the Dino's brake system. As Rob mentioned above the master must be bled very thoroughly and so must the brake proportional valve. Have a read through this: https://www.ferrarichat.com/forum/threads/santa-came-early-this-year-with-00504.388966/page-9 Best Peter
Thanks Rob and Peter, great advice which will no doubt sort the problem. I think I'm going to take a look inside the master cylinder too, as the pedal travelling to the floor may have damaged the seals. Seasons Greetings from England! Chris.
During normal usage the travel of the pistons in the master cylinder is very small, so corrosion starts to appear in the bore of the cylinder where the seals don't go. When there is a leak in the system or you need to bleed the system, pushing the pedal down causes the pistons to move through the corroded area, damaging the seals. It is much better to use a pressure bleeder or vacuum bleeder so you are not pushing the seals through the corroded area. It sounds like it is time for a master cylinder rebuild, and possibly a re-sleeve of bore of the master cylinder casting.
Thanks Brian, yes it makes sense to overhaul the m/c at the same time as the calipers even though it was operating fine, as I've likely caused damage to the seals. A couple of years ago on my other 246 the m/c failed and the mechanic who looked after it (also a 246 owner) said that within the previous few weeks his had also failed and he just had to do another local 246 too! At the time he said not worth rebuilding, just buy a new one. However, I find new items are often not to the same quality standard so I think I will get it re-sleeved and new innards - unless you advise otherwise?
It is better to rebuild the original master, even if it needs re-sleeving. The reproduction brake masters have all sort of quality issues.
Thanks Brian, I will do that and also get my original other one rebuilt at the same time - glad I kept it! The last thing you need is to be worrying about the braking system! These quality issues on repro items seem to be affecting all classic cars these days.
Why not check if you have an issue first? If worried; Open up the master and check the seals and the seal bore. If no pitting / corrosion and seals are okay assemble it again, save your money and be happy. I have often heard about the issue with damaging the seals when bottoming out the pedal, but I have never seen the issue in the real world. But I have often seen pitting and corrosion half way down the stroke in the cylinder and this will cause leaks past the piston seals.
Good point Peter but I think there will be problems in there. The pedal feel has a "step" on the way down and there was a lot of contamination in the brake fluid. All the issues I've had with the car so far have been as a result of very little use over the last 35 years. Anyway, we will take a look and see what we find.
