Rear Wheel Cylinder Leak

[BigWhiteDog]

So replaced both rear cylinders (5/8") a few months ago with new as a result of left rear leaking. Spent the extra money to avoid potential problems with reproduction cylinders. Got 'em from MM.

Discovered left rear leaking again last night after really not many miles of use. So I'll be back under the car tomorrow putting the old right rear cylinder that I saved and was still OK on the left rear. But I'd like to procure some spares to have on hand for future problems.

Any conventional wisdom about this? Did I waste my money on the non-reproduction cylinder? Or did I perhaps just get a bad part. Is there something else that might be going on? Used DOT 4 fluid. Antbody?

[Mark]

Hi Jerry,
I'm headed down the road of the pipe / taper / flare connection, but I have "heard of" both the reproduction and had the orig lockheed leaking way too soon.
Sometimes, when the new cyl is installed, the 'way to soon' leak is the pipe / threaded fitting connection is what is leaking. Is it for sure the cyl itself?
I've been able to get the flare tip - which meets the "bottom of the threaded bore" when threaded in; to re-seat down there if it has been rubbed down with emery cloth a little bit, ferociously cleaned, snugged down well, and had a couple of wraps of teflon tape way out near the opening of the threaded bore. ( you wouldn't allow any teflon tape down in the taper in the bottom of the cyl's threaded hole, it would just act as a backup way out on the threads, in case the compression of the flare / taper's connection is not perfect. )

I'll be in MLT tomorrow afternoon, and could stop around if you are accepting visitors / club members to stand around with hands in pockets - drinking your beer - yapping too much, etc. during that time.

Best of luck, and let me know,
Best regards,
MSH

[BigWhiteDog]

No I don't yet know that the cylinder itself is the source of the leak as I have taken nothing apart yet. I merely observed all 4 corners to see whether there was a noticeable leak after it sitting in the garage for 24 hours, and sure enough there was the telltale drippage of brake fluid in the left rear.
Thanks for the heads up on the fitting thread being a possible source. I will definitely have my forensic glasses on when I jack up the car and start to disassemble things. Perhaps that will turn out to be the source. Although I will admit that I felt the brakes go soft towards the end of a 20+ mile drive, and it just felt more like the cylinder seal gave way (if one can have a feel for that).
I have other "non-Mini related" chores I will be doing during the course of the day, so I'm not sure exactly my timeframe to jack it up and fix this. Because of that I wouldn't "encourage" a visit, but I wouldn't turn you away if you swing by. I do have a committment for Sat PM so I'll be closing up shop by about 3PM-ish or so regardless.

[Cheleker]

It is not unheard of for a new cylinder to leak, but it is rare -- rare enough that I've not had one.

My first thought was the same as Mark's: pipe leaking. Flare may be bad or it just isn't snugged down enough.

[skip]

I would also bet that it is the pipe flare, could be a minute bit of grit or just plain persnickety fit up. Another possibility may be a nicked, cut or stripped thread on the flare nut.

What is the brake pedal doing? Is it mushy or pretty firm not feeling any different than normal? If there is a leak from the brake cylinder bore there might be some indication at the pedal, (not as dramatic as a failing master cylinder but not really solid either.)

When you installed the new cylinder did you tighten it down then attach the brake pipe? I have found it easier to start the nuts leaving the cylinder sort of float while attaching the pipe. (Had a gray whiskered mechanic friend tell me that trick years ago after watching me fight to attach a brake pipe.)

Not sure how good the hardness of the fittings is on Minis but on some of the early Japanese imports it was slightly less than heat treated Silly Putty as in instant strip! The loose cylinder trick lessens the possibility of stripping the threads on the flare nut.

I have never tried this, only read it suggesting how to find a brake cylinder leak on a '50's Chevrolet. I cannot vouch for it's safety either. To test where the actual leak is take the brake drum off. Next take a nylon cargo strap and band it around the brake shoes snugly. Have a partner pump the brakes two or three times. If there is a leak in the hydraulic system you should be able to see it weeping.

Good Luck

[Cheleker]

Skip: rear cylinder, so no nuts to leave loose; however, the same idea applies (and the way I do it) is to get the pipe started into the wheel cylinder before I put the e-clip on.
The club, in the loaner tools, has a brake drum made specifically for checking brake action -- has the mounting face removed.
Not really necessary in this case. A leaking pipe is easy to see and removal of the drum and pealing back the wheel cylinder rubber covers will make it obvious if the w/c is bad.

[BigWhiteDog]

So it seems like the armchair assessment was correct. Leaking appeared to be from the brake line fitting, possibly at the bleed nipple fitting. I did clean out some debris from the cylinder threads and also "smoothed" up the taper on the fitting. Then reinstalled with just a little teflon tape out at the end of the threads.
The cylinder seemed like it was OK, seals looked good. Maybe some minor indication of scoring on one of the bores, but I don't think the cylinder was bad, except...
Left rear circuit acted a little funny when I was bleeding the system. Got air out, but didn't get much fluid through the nipple. It seemed like the left rear cylinder was not actuating while I was bleeding the system, as opposed to right rear where could hear/feel it actuating.
Overall brake pedal pressure (and brakes) restored to the previous feel before the issue. But I have a suspicion that all is not right yet. Gonna look at it again later in the week/next weekend and verify no leaking present. Is it possible that the brakes can feel OK even without left rear cylinder working?
Jerry