Avid MK4 braking effect


35 posts in this topic

Posted

After rebuilding the right caliper that was leaking and rebuilding the right master cylinder I just could not get all the bubbles out of my left double puck system. 

I filling fron the lower nipple using and oil can with a feed trigger that would then fill the reservour. I tried bleeding it like we do autos by having someone presson the pedal while I open the bleed nipple.

Nothing would move the bubbles pout of the tube that connects the top caliper to the lower caliper.

Finally, my friend brought over the system he uses to bleed his brakes on his Kitfox and RV. It is a small garden sprayer. 

I set it up so any excess on the reservour would go into a recovery bottle. He opened the nipple and pushed the trigger on the sprayer and the fluid moved so fast that the bubbles were moved up and out of the system. This ended several hours of trying to get rid of the bubbles.

The brakes are now solid.

I HATE bleeding brakes. 

John M

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Posted

I just measured the clearance between the top of the  brake pedal and the cross bar on the firewall structure on my Avid MK4 (1 inch) and a friend's Kitfox 7 (3.25 inches).

I have good geometry on my brake pedals (3:1) but the clearance issue does not allow my foot to be high enough on the pedal to get good pressure. I actually push with the toes on the top of the pedal. 

I had a situation where on landing I applied brakes and my toe got caught between the toe and the firewall crossbar. She almost nosed over. WHEW!

John M

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Posted

Even f you have the pedal geometry correct it is hard to get good braking due to the lack of toe clearance caused by the firewall crossbar.

On my MK4 and the same on the Model B I had, you can't raise your foot high enough on the pedal to get the ball of your foot on the pedal.

I only  wear a size 9 and have this issue. 

On a trip to the Idaho back country last year the shoes I wore were wearing out and the soles coming off. So I flew into McCall and bough new Sketchers shoes.

Trouble is, the material on the heel extended behind the heel so much that it raised my foot to the point where the toe could get caught on the firewall crossbar. So I had to fly in my stocking feet. And by the way, I had much better feel and braking effect in my stocking feet.

John M

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Posted

If anybody wants to make their own bleeder they can do it for around 10 bucks or less. I make them for a lot of people. Take a 4" heavy wall sewer pipe about 1' in length, 2 flat end caps or curved, a 1/4" brass barb fitting, shut off valve, (old fuel valve) and a tire pressure valve.  Drill and tap the bottom cap for the barb fitting. add a length of fuel line with the shut off valve in the middle, drill the top cap for the tire valve and its also used as the filler hole so don't glue it in.  Glue everything together, fill halfway with 5606, Add about 20-25 lbs air pressure to the air valve then remove air hose, attach line to brake bleeder, open valve, bleed, and shut valve. For a new brake system you might have to refill before going to the other side. The thick wall caps will thread for the fittings, thin wall will not. Add 3 legs w/hose clamp for the pipe and its a one person operation. Hope this was clear, if you've built an aircraft you can figure it out. Don't let the "tank" run out of 5606 or you'll start all over again.

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Posted

Great idea Allen! So you are using ABS pipe, right? Is that because you know hydraulic fluid does not affect it? Do you know if the fluid affects PVC? I can research, but if you already know that's easiest :-)

Chris

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Posted

I really wasn't too concerned whether it was compatible or not. I made the original for a quick in field repair when a brake line got torn off. But its still holding up good after a year or more. But you could drain out the fluid after using if concerned. Its not something one uses everyday unless there is a bunch of you and then everybody could chip in and pay 100+ for a good one that does the same thing. As an A&P , I rarely bled the brakes but a few times a year on different birds. Cessna's have a habit of the flexible lines under the floorboard going bad after 20 years and nobody checks till one blows.  And they are a PITA to replace.(confined area)

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Posted

A garden weed sprayer (the type with a flexible hose )is the perfect cheap solution for bleeding brakes.

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Posted

My system has to be the lowest tech of all.  I took a clean mustard bottle, cut the end of the spout off so the hose fit into it but was really tight.  Fill the bottle with fluid, hold bottle up side down, push out all the air out of the hose and even let some fluid come out as you hook it onto the bleeder so you aren't adding any air into the system.  Turn the bleeder open, and squeeze the bottle.  I do like Allen's idea though, it would be easier then trying to squeeze the bottle and keep everything in place.  JImChuk

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Posted

For my single caliper Avid MKIV, I tried everything, even the power re-fill systems that blast clean fluid up from the calipers to the reservior. The ONLY thing that works for me, and it really works, is grandpa's old fashioned tube in the glass jar method, were the tube, pushed over the bleed fitting, is under fluid in a jar. Then you open the bleed while pushing on the brakes and the bubbles come out. It works well, costs nothing, and gets the brakes to feel solid. 

I think is works best because the air-trapping corners in the claiper as best cleaned out that way.

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Posted

Nick, your method will work a lot better on a system with the remote reservoir then the original style brake cylinders.  They are a bit of a pain to add fluid to.  I used your method when I changed a brake line on my pickup last fall.  JImChuk

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