Sunday, 25 March 2012

How to Set Up a Slackline

Setting up a slackline is pretty easy.  Unless you're going for one of those Gibbon gucci slacklines with the thick webbing and ratcheting come-along, your entire setup can be purchased for $50 or $60 (probably less in the USA).


Here's what you need (clockwise in above photo):
  • 1" Tubular webbing - The rolled, blue tubular webbing above is 15 m of climbing-strength webbing, rated for 17 kN.  MEC sells it for $1.30/meter here.  This is obviously the main part of your setup and should be good quality.  15 - 20 m should be good.
  • 1" flat webbing (anchors) - Above I have 2x rolls of 4 m (8 m total) flat webbing.  You need something like this to wrap around your trees.  The larger the tree trunk, the longer the anchor must be.  The webbing above is accessory webbing and is not intended for climbing.  It's only rated for about 11-12 kN and is sold for $1.00/meter at MEC.  This should be fine, but if you want something of a higher grade, try MEC's flat climbing webbing.
  • 4x oval carabiners - Do they have to be oval?  No, D-carabiners would work too.... BUT, Ds are more expensive to purchase and they don't hold webbing as nicely.  The Black Diamond biners above are $5.25 ea. at MEC and work great.
  • 2x descending rings (optional) - Optional because they're not required for the setup, BUT they will ensure you do not need to tie knots in your webbing.  Knots weaken the webbing and distort its strength ratings.  Plus, I don't want to spend their time tying and untying knots.  MEC says they carry descending rings but my location does not stock them.  Wilderness Supply stepped up to bat and sold me the above rings (20 kN) for less than $4 ea.  Line lockers or padded chain links would work just as well.

Set Up

  1. Find two trees (~ 25+ cm diameter) between which to set up your line.  Ensure you have about 5 m more webbing than distance.  
  2. Wrap your anchors around the trees, several times if necessary (doubled if possible).  I sewed loops in both ends of my anchors for easy set up (if you do this, make sure you know how to sew the correct patterns for max breaking strength).  If no loops, use a water knot to connect the ends of the webbing together (see below)
  1. Connect an oval carabiner to one anchor and fix your main line (tubular webbing) to it using the descending ring and a bight + line locker.  If you're not sure how to do this, check out these instructional steps.  If you didn't buy descending rings, you'll need to tie your main line to the carabiner.
  2. Bring your main line to the other anchor (ensure no twists).  Add another carabiner + descending ring to the main line about 1 m from the anchor when taut, or about 20% of the total distance.
  3. Steps 5 thru 8 will give a 3:1 mechanical advantage to tighten the slackline.  Add two carabiners to the anchor webbing and feed the main line through one of them.  If the top one, feed the line top to bottom.  If the bottom, feed it bottom to top.
  4. Bring the main line back to the biner/descending ring combo and feed it through the carabiner the same way you did in step 5 (top to bottom or bottom to top).  
  5. Bring the line back to the anchor and feed it through the other ring, the opposite way from step 5.
  6. Feed the main line back to the the carabiner in step 6 and bring it under the webbing from step 6.  You should now have a tension lock and the line should hold itself up.  It should look something like this:
  1. Finally, grab that loose end and pull!  Keep pulling until you tighten to the desired amount of 'slack'.  You may want to enlist the help of a friend.  The line is under a tension lock and will hold itself... BUT just to be safe, tie off that extra webbing in a knot as a backup.
Happy slacklining!

Wednesday, 21 March 2012

Replace Rear Seal in a Volvo 240

The car is a 1990 Volvo 240 DL with ~310,000 km and an AW70 automatic transmission.  The problem is a leaky rear seal in the transmission shaft.  I did this job last week because of three problems:

  1. I leave puddles (about 3-4 Tbsp) of transmission fluid every time I park
  2. I need to constantly top of my transmission fluid, costing $$
  3. The transmission has to work overtime with so little fluid and ends up costing in fuel economy.
There are a few suggested methods (see here and here) but I took a slightly different route outlined below.  But before that, a word about parts.... I spoke with a handful of suppliers and only one could locate the part I needed.  I heard people call it the 'output seal', the 'rear output seal', the 'rear shaft seal', the 'rear transmission seal', and the 'output shaft seal'.  Make sure you get the correct part.  If you have access to a spare car you might be able to pull the seal out and take it to a supplier to get an exact match.  But if you're like me and prefer having all the parts on hand to complete the job, get it before you start.  I ended up ordering the ALTROM Rear Seal 2116020 from Napa, which looks like this:
This looks a bit different than some other seals you'll find on the market (and from the one I took out of the car).  They look like this:

I suppose they perform the same.  Here's the complete parts list:
  • ALTROM Rear Seal no. 2116020 from Napa ($13)
  • Transmission Kit FK-162 from PartSource ($15) *this isn't necessary, but might as well do it*
  • 4L Mobil ATF D/M 598368 from PartSource ($16)
With parts in hand, here's the procedure.  Note that I estimated 3 hours and it took 4-5:

  1. Jack up the car and put it on jackstands.  Do not ride up on ramps as the wheels must be free to rotate
  2. Shift car into N.
  3. Drain transmission fluid.  It doesn't have to be done now but it must be done before Step 12
  4. Mark/score the rear flange and remove the 4 driveshaft bolts from the flange (near rear wheels).  You may need to rotate the driveshaft to get at all 4 bolts, and the flange may need a whack with a rubber mallet to come free.  Impact wrench on the bolt heat and hand wrench on the nut.  
  5. Mark/score the front flange and remove the 4 driveshaft bolts from the flange (near tailshaft housing).  May also need a rubber mallet.  (Note: some guides advocate removing the tailshaft housing.  Not a bad idea, but much more work and not entirely necessary if you have a socket the exact diameter of the new seal)
  6. Remove the 4 bolts on the crossmember bracket and prepare the lower the entire driveshaft to the floor for later usage.  You will need to replace one or two of the bracket bolts to keep some sheathing from falling down. You should now see the centre bolt inside the front flange.  
  7. Shift the car into Park.
  8. Remove the centre bolt from the flange.  Impact wrench ok.
  9. Pull off the flange and remove the rear seal.  I used a flathead screwdriver and broke the seal while getting it out.  No matter, it was leaking anyway.
  10. If you have a socket in the correct size, gently tap the new seal into the housing.  Be careful not to press in too far.  If you don't have a socket this size, borrow one!  It's way easier.  If you must, remove the entire tailshaft housing and press the new bushing in.
  11. You can now reverse steps 4-11 to reinstall the driveshaft assembly.  Make sure to shift back to Neutral after installing the centre transmission bolt.  Also make sure not to overtighten if using impact wrenches.
  12. The remaining steps are to change the transmission filter and gasket.  It's not necessary but is probably a good idea if you've been running low on transmission fluid.  If you didn't do so before, drain transmission fluid.  
  13. Pull off the 14 bolts on the transmission pan.  Remove the pan gasket from the pan and clean thoroughly (esp. if it was an old cork gasket.  The new kit comes with a silicone version).
  14. Pull off the 5 bolts for the transmission filter.  Have a look at the new filter to make sure you're loosening the right bolts.  You may need to pull off a steel line or two (they're just tension fitted)
  15. With the pan and filter out of the way, spray the entire assembly with brake clean.  Get all the fluid out of there so it's not dripping on you when you replace the filter and pan.
  16. Clean the pan and magnet in a parts washer or with brake clean.  Get all the grime out of there.  
  17. Bolt the new filter (with gasket).  Use torque settings if you have them.
  18. Replace the pan and pan gasket, and add some RTV to make that gasket stick well.  14 bolts and you're done the hard stuff.
  19. Now, add as much fluid as you removed (possibly more if you were running really low).  I believe it is around 3 L, maybe a bit more.
  20. Start the car in Park and slowly cycle through all gears.  Check for leaks and go grab a beer.

Tuesday, 20 March 2012

How many kg in a kN?

Quick physics lesson today.  Often we see carabiners, rings, rope, etc. rated for a certain number of kilo Newtons (kN).  What does that number mean and how does it affect me?

The quick and dirty answer, working with normal gravity, is that 1 kN = 101 kg = 224 lbs.  These are conservative masses, meaning I have rounded down.  To convert kg to kN, multiply by 0.00981, to convert kN to kg, multiply by 101.97.

Why is this so?  Glad you asked.  While a kg is a unit of mass, a kN is a unit of force.  The unit of measurement for kN is the Newton, defined as the force of earth's gravity required to move 100g (0.1 kg).   Since force is defined as mass multiplied by acceleration, we must apply some sort of acceleration to our unit of mass (kg) in order to get kN.  Usually, this acceleration is gravity (9.81 m/s).  With this in mind, we can see that a 1 kg mass under gravity is equal to:

  • F = m * a
  • F = 1 kg * (9.81 m/s)
  • F = 1000 g * 9.81 m/s
  • F = 9.81 N
  • F = 0.00981 kN
So, as an example, that climbing item you have rated for 20 kN would not be able to take more than 2039 kg under gravity. 

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