93 K75S Master Cylinder Seepage

[GasStation]

After stripping the threads of my last front brake master cylinder with a careless over-torque of the hollow bolt, I purchased and installed a brand new front brake master cylinder. Since then, I have installed Spiegler brake lines but continue to fight some seepage of hydraulic fluid at the junction of the bayonet hose line and the hollow bolt under the master cylinder reservoir.

There is no evidence of fluid from the reservoir. It appears to come from the lower crush washer junction of the bayonet and hollow bolt. I have replaced aluminium crush washers for new ones; still no change. My next option is to change crush washers from aluminium to copper. Then it will be to change the hollow bolt. After that, it will have to be a faulty bayonet brake hose line.

Anyone else ever have this kind of problem?

[motodude]

I just added a Spiegler brake line to the front of my '90 K75RT.  No fluid issues (so far--knock wood) but I used copper washers for the banjo bolt.  When I removed the original hose, that particular connection had copper washers, so I replaced w/ copper.

Tom

[frankenduck]

Did you use NEW washers?

Did you use a torque wrench?  If so, how much torque did you use?

[wmax351]

You can also anneal the washers. Heat to cherry red hot, then allow to cool.

[GasStation]

Did you use NEW washers?

Did you use a torque wrench?  If so, how much torque did you use?

Absolutely, new aluminium crush washers. It is painful enough to have to bleed the brakes at every change of washers, I cherish my time more than the cost of two crush washers.

As for the hollow bolt torque, you bet that I used a torque wrench up to the appropriate value. I have three shop manuals, BMW, Haynes and Clymer. I am not at home right now so I can't confirm precisely, but I know I cross referenced the service manual before doing the job. I do remember it is not much; if memory serves me correct, I convert the Neuton Meters into lbs per square inch and it was < 80 inch/lbs.

[frankenduck]

I convert the Neuton Meters into lbs per square inch and it was < 80 inch/lbs.

Um, pressure(psi) and torque(in-lbs) are completety different concepts. One is force per square area and the other is force times distance.  I hope that was a typo. :dunno

I recently redid the lines on my RS.  The K1100 manual had 18 N-m for the banjo bolts which is equivalent to 159 in-lbs.  I think we may have found your problem.

[GasStation]

I convert the Neuton Meters into lbs per square inch and it was < 80 inch/lbs.

Um, pressure(psi) and torque(in-lbs) are completety different concepts. One is force per square area and the other is force times distance.  I hope that was a typo. :dunno

I recently redid the lines on my RS.  The K1100 manual had 18 N-m for the banjo bolts which is equivalent to 159 in-lbs.  I think we may have found your problem.

Maybe I am not expressing myself correctly and it wouldn't be the first time.  :laugh

What does "NM" in the BMW manual torque section of each chapter mean to you?

[frankenduck]

Maybe I am not expressing myself correctly and it wouldn't be the first time.  :laugh

What does "NM" in the BMW manual torque section of each chapter mean to you?

Newton-meters:  Force times distance - torque.

PSI(pounds per square inch): Force per area - pressure.

The correct conversion factor for N-m to in-lbs is approximately 8.85 so 18 N-m converts to 159 in-lbs.

Newtons are a measure of force:  1 N = 0.225 lbs
Meters are a measure of distance: 1 m = 39.37 inches

0.225 x 39.37 = 8.85 (with some rounding taking into account)

[GasStation]

Maybe I am not expressing myself correctly and it wouldn't be the first time.  :laugh

What does "NM" in the BMW manual torque section of each chapter mean to you?

Newton-meters:  Force times distance - torque.

PSI(pounds per square inch): Force per area - pressure.

The correct conversion factor for N-m to in-lbs is approximately 8.85 so 18 N-m converts to 159 in-lbs.

Newtons are a measure of force:  1 N = 0.225 lbs
Meters are a measure of distance: 1 m = 39.37 inches

0.225 x 39.37 = 8.85 (with some rounding taking into account)

We are saying the same thing. There is a brain fart in my post above. At the end, I actually referred to 80 inch/lbs which probably equates to 9 NM. All is well with conversion. My torque wrench gaffe stems from being unfamiliar with a new torque wrench; a mistake which cost me $250.00.