Jaguar Repair: 1984 XJ6 Vanden Plas leaky master cylinder, brake master cylinder, hose clamps

Question
QUESTION: Howard,

  My brake master cylinder was leaking from the grommets under the reservoir, so I replaced the grommets, no change, figured where they sit in the master it was pretty rusty so perhaps a bad seal.  I replaced the master with a rebuild unit, leak is still there but not so bad.  I noticed the reservoir doesn't seem to sit right down on the master even with the pins in.  I checked the reservoir, no cracks or leaks, maybe the spigots on the bottom have worn a bit thin ?  I tried 2 hose clamps to pull the reservoir down tight against the master but it didn't help.  Have you seen this before - should I try some brake grease or just replace the reservoir now ?

  Merry Christmas !

  Steve.

ANSWER: Hi Steve,

Before you replace the reservoir try loosening the cap to see if the vent in the cap is stopped up and from engine compartment heat the fluid is expanding and causing pressure in the reservoir. No harm can come from leaving the cap a little loose just for a test. If that stops the leak, just get a new cap if you can find one.

Also, you can have a fine crack in the reservoir that is not noticeable and fluid running down the plastic is hard to spot. Clean the out side of the reservoir very well and after you note the leakage run a clean dry finger around the reservoir to see if you can find any wet on the outside of the reservoir. I have found leaks in the seam around the front of the top part.

Howard

---------- FOLLOW-UP ----------

QUESTION: Howard,
 
  It leaks as the car sits cold, I can watch it come out from around the master cylinder reservoir mounts just under the reservoir whether the cap is tight or not.  I took it for a short drive and lots came out and leaked on the paper towels underneath.  I really cleaned up the reservoir and the spigots under it, I think the spigots are undersized for the grommets, the front one is about 1/4 inch in diameter, the rear maybe 1/2, they each use a different type of seal, when I put the spigots into them, there is no real pressure required, and no sense a good seal is made.  I think the spigots are undersize due to wear or shrinkage.  Or there is a hidden crack.  Rocking it back and forth can produce leaks at will from either end, what a strange problem !  I think I'll buy a new reservoir, hopefully that will work !

Thanks,

  Steve.

Answer
Steve, the reservoir should fit very tight in the grommets and the pins are there only to keep the reservoir from coming out of the grommets. If yours are loose you have a miss-match of either the reservoir, the grommets or the cylinder. When removing the reservoir from the cylinder it often requires that you pry the reservoir up because it should be that tight.

I may have some used cylinders around so I will search to see if I can get you some measurements to check against yours.

If you have a crack in that area, you should be able to see it with the reservoir off. The only place I found some leaking was at the seam where the reservoir top was attached to the body of the reservoir and usually at the front where that seam is below the fluid level.

I will dig through my parts to see if I can find one to measure so you will know which is wrong.

Howard