Saturday, 12 October 2019

One completed and another started

The coffee tables have been varnished and are now beside our recliner chairs.


I’m reasonably pleased with the way the colour and grain of the Jarrah turned out.


The amusing thing is we’re not using the tables and chairs as we are waiting on the delivery of the internal shutter blinds for the bay window.  At the moment the room is almost empty which means any noise echoes rather loudly.

A start has been made on the next project.  If you’ve been reading this blog over the last 15 months you may recall my first serious outback trip and how the suspension on the loaned camper trailer broke on the second day. 


All four shock absorbers had totally failed.

Our ‘new’ Chinese camper trailer has exactly the same shock absorbers.  They do come with a 12 month warranty and if they did fail the trailer supplier would probably provide replacements.  Which would then also fail.  I’m not a suspension engineer but I do want to understand what the problem is and how it might be rectified. 

So under the trailer I went with a jack and tape measure.  I measured and marked one of the shock absorbers when the trailer was both empty and partially loaded.  Then I removed the shock.


The black line is the shock fully compressed.  With the trailer half loaded the shock has 35mm of movement before it ‘bottom outs’.  The maximum extension of the shock is 180mm.  Now the role of the shock is to counter (dampen) the upwards movement of the spring to keep the tyre in contact with the road.  As you can see from the photo; if the trailer wheel hits a bump in the road then the shock only has 35mm of upwards movement.  The spring has significantly more upwards movement before striking the bump stop.  I assume this is why the shocks in the loan trailer failed.  Another issue is the poor manufacturing quality of the shock.  After being compressed the shock should start to extend when the pressure is released.  But this one doesn’t!   end result is I have four cheap and useless shock absorbers.  Which raises another question….. Why four shocks? (two each side).  The 4x4 only has one shock each side.  My assumption is the Chinese manufacturer believes doubling the number of shock compensates for the poor quality.  Of course the shocks would probably be satisfactory on a relatively smooth bitumen sealed road.  But outback tracks are going to kill them very quickly

A trip to the local suspension supplier proved to be interesting.  The parts storeman confirmed the quality of the shock was shocking <sorry couldn’t help myself>.  After measuring the shock he consulted their database to identify a compatible replacement.  I nearly had a full litter of kittens when he informed me each shock would cost $227.  That’s $900!!!  However he went on to explain the shock he was recommending was one of their “upmarket” nitrogen foam models which would probably outlast the life of the trailer.

All this leaves me searching for another solution!


Davidss said...

"After measuring the shock he consulted their database to identify a compatible replacement.".
If by compatible you mean the same size (and the same ends) that is surely what you do not need?
As you have explained, the shocker only has 35mm of compression movement, thus bottoming out before the chassis bump stop is troubled. Surely you need to go back to the trailer, measuring the distance between the shock absorber mountings on the axle and the chassis, both with the axle on full droop and with the axle touching the bump stop (or even compressing it). A ratchet strap or two might be handy here, to go around the axle to enable full spring compression.
Then you can go looking for shock absorbers that actually fit. You may find it difficult to get ones short enough.
Another point to consider is that if you fit the best that money can buy (with internal bump stops) you can justify fitting only one per side.
Another option if there isn't a shock absorber short enough is to fit double or triple bellow rubber springs as long bump stops, as these will come into effect before a better sized shock absorber bottoms out.


Tom and Jan said...

Hi David

I did explain the problem and the offered shocks have an additional 10mm of movement before they bottom out. I also should have mentioned I've measured the distance when the suspension spring fully compressed and fully extended (410mm). Yes, I'm thinking of modifing the suspension so there will only be one shock each side. I'm also considering airbags.