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19. Brakes update


danny_galaga

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I put it off for a while but I finally contacted the factory about the brake pedals as they were binding such that when you had full right rudder the brake pedal wouldn't move. They sent out an update kit and I swapped the faulty parts.

 

Last night I finally got around to bleeding the brakes. I had a hell of a time. Couldn't do it 'bottom up' I assumed because of the cheapo oil can I was using. So I decided to bleed them the regular automotive way. Still no joy. Then I started to think maybe I had left mixed with right on the lines. So I had Jo pump a right pedal while I cracked the left bleed nipple. Some oil seemed to come out! Well, I must admit I lost my shit and yelled and carried on so much I scared the dog!

 

When I calmed down we played around with it a bit longer and it occurred to me it was acting more like a blockage than anything. I wonder. .

 

Turned the park brake 'on' and voila! Oil squirted out the bleed nipple! 

 

See attached for my fix !

 

1.thumb.jpg.e0a5de66e03d91593d1dbdc5958b2216.jpg

 

Edit: I haven't checked yet, but it seems likely to me that the park brake is a one way valve, which means my 'fix' won't work- the park brake will be 'off' in both position!

 

so for now I may just put a cover over it. Not all ultralights have a park brake.

 

it also occurred to me that the park brake is assymetrical when it comes to mounting it in the Bushcat. I found a pic from when I was installing it and sure enough there is only one way you can put it in (see pic). This means the park brake was assembled incorrectly at the Matco or Bushcat factory! Grrrr

 

2.thumb.jpg.92eca2e1797e0f59f126cadc9bdd6dae.jpg

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With hydrolic,s a simple valve in the brake line will act as a park brake, brakes on turn park valve & brakes stay on.

spacesailor 

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Good point! I'll test it out once all the lines are bled ?

 

its quite an epic journey to get that floor board off again so fingers crossed!

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It is a simple and straightforward process to bleed the brakes on the BushCat if all has been installed correctly. Use a syringe with a tube attached to bleed nipple on each calliper. 

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"Use a syringe with a tube attached to bleed nipple "

If you reverse the process, Fill syringe with fluid, attach to wheel brake nipple,  push fluid Up the line to the reservoir, just make sure its not over full.

Saves fighting the law of, air bubbles raising to the surface, when pushing fluid down the brake-line.

spacesailor

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First:

You fill them from the bottom by buying a cheap small garden pump spray and attaching a neoprene pipe (which you also buy) to the nipple on the brakes themselves. This gives you, hopefully, a clean fill with no air pockets. Easy. You then stash all that gear in a poly bag for use in future services.

Second, of course the park brake isolates the brakes (from the pedals):

To apply park brake, press on pedals (so applying brakes) while turning on the park brake. Now, when you take your feet off, the pressure remains in the brakes!

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I bleed my matco by sucking through from top to bottom. (Vacuum on nipple and operate brake lever)

I bought a cheap brake suction kit on ebay.

Some caliper nipples are on the bottom of the calipers. I think these are better suited to a push through system. Forcing air through and out the top.

As my matco nipples are on the top of the caliper (and the oil line at the bottom), I prefer to suck through them to remove the air.

 

 

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I tried to bleed them the 'airplane' way before I realised the park brake was faulty. Wasn't working of course So i ended up bleeding them the 'automotive' way. After all, if it's good enough for hundreds of millions of cars...

Edited by danny_galaga
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Usually parking a hydraulic brake is not considered reliable for any real length of time.. What you MUST have is no chance of it NOT releasing in normal use. (Brakes OFF check pre landing). Bubbles always run uphill. If you don't bleed fast enough  and continuous to carry them through  you will never get all the air out. and have spongy brakes. always. A bleed nipple at the highest point may make all the difference. Nev

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On 23/09/2020 at 5:20 PM, spacesailor said:

"Use a syringe with a tube attached to bleed nipple "

If you reverse the process, Fill syringe with fluid, attach to wheel brake nipple,  push fluid Up the line to the reservoir, just make sure its not over full.

Saves fighting the law of, air bubbles raising to the surface, when pushing fluid down the brake-line.

spacesailor

That's what we do these days on mountain bikes. . (Syringe on nipple.) - 

 

Sometimes, if I don't have the syringe handy, (mountain bike)  there is another cleaner way.... I remove the reservoir  cover,  ensure it is topped up. I tap the brake lines over their length with a donger  while pumping the brake lever . You watch the air bubbles come out of the pipe to the surface in the reservoir as you pump and tap  .  Most of those brakes are mineral oil. A few (Avid) are Dot3). IE can get away with not opening the bleed nipple. have done this in a vehicle also... (bleeds air but of course doesnt change out the fluid) (and mountain bike calipers are small pots !) Orientation matters, also.  getting air out of the actual caliper may require re-orientation of the bike or caliper. harder to do on a vehicle or aircraft...

 

Edited by RFguy
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