Changing Cobra compression brake gas strut

Before heading out to the gliderport with tools in hand, does anyone have experience and comments about changing the Cobra trailer's compression brake gas strut? I have the new strut and welcome your guidance.

Raul Boerner
LS6

Bring bandaids.

5Z

Raul-

I did some work on your trailer a few years ago, but I don't remember what model year it is. I have swapped a number of gas dampers, but the ALKO tongue comes in several styles. Text me a photo of the tongue to my mobile number and I will look at it to see if I can give some hints about the procedure. 505 249-0161

And Tom is right. BandAids are often necessary.

On Friday, August 14, 2015 at 8:44:28 AM UTC-6, Mark628CA wrote:
Raul-

I did some work on your trailer a few years ago, but I don't remember what model year it is. I have swapped a number of gas dampers, but the ALKO tongue comes in several styles. Text me a photo of the tongue to my mobile number and I will look at it to see if I can give some hints about the procedure. 505 249-0161

And Tom is right. BandAids are often necessary.

Mark, Photo is on the way. - Raul

My older Cobra has a damper, not a gas strut. Looks almost the same but acts like a shock absorber, not a spring. Do later models have actual gas springs? The damper is a pretty easy swap because it doesn't have to be compressed against a force to be installed.

Chip Bearden
ASW 24 "JB"
U.S.A.

So how do I know that the strut needs replacing?

Drove into town today to replace the tires - just in the nick of time as old ones looked real bad on the inside, but they were over 6 years old and trailer parked in Mojave desert.

Anyway, I noticed that if I come to a stop while driving forward, the tongue remains compressed. When I release the hitch and crank it up, the tongue ever so slowly extends back to full forward. This probably means I need a new strut...

The surge brake is working well and tongue cylinder is reasonably well greased.

Of course, I parked it back at the airport and didn't think to take a look to confirm what might need replacing. It's a 2001 Cobra with square tongue.

DONE!

The "damper" went on with minimal effort. After Chip mentioned that it might be a damper, versus a gas strut, I went out and put pressure on the push rod; it moved with relatively light pressure. So, I used strong string to hold the damper to the correct length. I used wood dowels to keep the internal spacers aligned with the mounting holes: pushing the bolts into the holes then pushed the wood dowels out the other side. The operation took one hour. It would have taken less time had I figured out, earlier, how to keep the spacers in position. The test drive, with test stops, brought a smile to my face.

Raul Boerner

Anyway, I noticed that if I come to a stop while driving forward, the tongue remains compressed. When I release the hitch and crank it up, the tongue ever so slowly extends back to full forward. This probably means I need a new strut...

In my older Cobra trailer, that's normal behavior. The damper just prevents the tongue from slamming the brakes full on in a hard stop. It also prevents the tongue from hitting the stop in fully expanded position in hard acceleration. It is, in fact, very much a shock absorber, not a spring.

That's not to say that later models don't have gas springs; I wouldn't know.. But I would think it would make more sense to use a coil spring with progressively higher force the more the tongue is compressed rather than a gas spring with its nearly linear force/deflection profile. But I'm not an expert.

If you can deflect the strut by hand by slowly compressing it, and if it's about as difficult to expand as to compress, it's a damper. You'll know if it's a spring: lots of force in one direction and if you let it go, it expands quickly to its free length.

The nice thing about the damper, at least in my trailer, is that you just unbolt the tongue, including one end of the damper, and slide out the moving, inner (piston) tube. Bolt in the new damper on one end, then insert the tongue and slowly compress it by hand while peering into the hole in the tongue for the other end of the damper. When it finally comes into view, insert a punch to line everything up, then insert the bolt. It's literally a 5-10 min. operation after you've done it once.

The older Eberle trailers didn't have anything, as I recall. In a hard stop, the trailer brakes would come on suddenly causing the trailer wheels to briefly lock up, especially on uneven pavement when a panic stop would cause the wheels to lock up and bounce, chirping madly every time they touched the ground. Those are also the ones where you had to get out and set the locking lever in the tongue to allow you to back up without actuating the trailer brakes.

Chip Bearden
ASW 24 "JB"
U.S.A.

For the hitch, technique suggested by Cobra:-

http://www.cobratrailer.com/wp-
content/uploads/Kupplungstausch_englisch.pdf

At 04:10 15 August 2015,
wrote:


In my older Cobra trailer, that's normal behavior. The
damper just
prevents=
the tongue from slamming the brakes full on in a
hard stop. It also
preven=
ts the tongue from hitting the stop in fully expanded
position in hard
acce=
leration. It is, in fact, very much a shock absorber,
not a spring.=20

That's not to say that later models don't have gas
springs; I wouldn't
know=
.. But I would think it would make more sense to use
a coil spring with
prog=
ressively higher force the more the tongue is
compressed rather than a gas
=
spring with its nearly linear force/deflection profile.
But I'm not an
expe=
rt.=20

If you can deflect the strut by hand by slowly
compressing it, and if it's
=
about as difficult to expand as to compress, it's a
damper. You'll know if
=
it's a spring: lots of force in one direction and if you
let it go, it
expa=
nds quickly to its free length.=20

The nice thing about the damper, at least in my
trailer, is that you just
u=
nbolt the tongue, including one end of the damper,
and slide out the
moving=
, inner (piston) tube. Bolt in the new damper on one
end, then insert the
t=
ongue and slowly compress it by hand while peering
into the hole in the
ton=
gue for the other end of the damper. When it finally
comes into view,
inser=
t a punch to line everything up, then insert the bolt.
It's literally a
5-1=
0 min. operation after you've done it once.=20

The older Eberle trailers didn't have anything, as I
recall. In a hard
stop=
, the trailer brakes would come on suddenly causing
the trailer wheels to
b=
riefly lock up, especially on uneven pavement when a
panic stop would
cause=
the wheels to lock up and bounce, chirping madly
every time they touched
t=
he ground. Those are also the ones where you had to
get out and set the
loc=
king lever in the tongue to allow you to back up
without actuating the
trai=
ler brakes.

Chip Bearden
ASW 24 "JB"
U.S.A.