Installed a new OEM master cylinder back in January and have had zero issues until last week when I noticed dripping coming from the underside "valve" of the MC. Any ideas on causes other than a faulty MC? It has gotten worse over the past week and now losing quite a bit of fluid each day. Appreciate any thoughts.

 

There's a rubber grommet that the plastic reservoir sits in, make sure it is firmly seated (pushing downward). Also, it could be coming from a line on the opposite side, check for properly tightness. Or, unfortunately, got a poorly rebuilt assembly.

 

So there ended up being the smallest, little trickle of brake fluid coming out of one the lines attached to the master cylinder. Couldn't see it with my eye. Line just needed a little tightening. I'm a relieved idiot!

 

Don't be embarrassed! We've all been there, in one way or another. Just celebrate that you found the problem with an easy fix before investing more time and money chasing solutions unrelated to the problem.

Unfortunately there was anxiety. Fortunately anxiety does not come with a cash cost.

 

I think I'm going to have this emblazoned on my family crest.

 

Much like the upper control arm bushes are the Achille's heel of the BMW E28, master cylinders seem to be a common weak spot on these trucks. All three of my drivers lose fluid at the master reservoir seal, and have a blinking BRAKE light in the cluster because they're tripping the level sensor on hills, again. Pretty much every Disco I've ever seen has a master cylinder that looks like it came up from the Titanic. Do RRs have this problem too? Is there any upgrade path there?

 

P38 RR’s have a completely different system. It is a pressure system instead of vacuum.

 

Ok, I'm guessing it's a hydroboost system that replaces a vacuum booster. I could certainly be wrong but I don't think the method of boost would matter to the hydraulics. BMW did the same thing in its older models but the master cylinder and the rest of the hydraulic circuit were the same in cars with hydroboost or vacuum boost. I was wondering if there was a scenario similar to the situation with the LR blocks, where RRs had superior parts, and if there was a crossover that could be used in the Discos. And by the way, some consider hydroboost to be the second Achille's heel in the E28 and there are guys who tear out the hydroboost and convert their cars back to vacuum boost, which is pretty simple in the E28 since that chassis came with either system depending on which engine you had. The brake components themselves are the same for either style booster. And, in the "answer to the question not asked" department, the larger master cylinders, calipers, and rotors from the 7 series cars are a direct bolt up to the E28 chassis and a very common upgrade to cars that are nearly 1000lbs lighter. Anyway, I digress. The masters in our Discos are a mess and I'd love to know if there was a better option. Even an upgraded seal would probably do wonders.

 

Usually the aftermarket design MC's are pretty robust as far as seals are concerned vs the OEM units especially for the reservoir seals.