Brake cylinder rebuild and bleeding

Well that was fun.. and educational I suppose.

While doing other wiring work I had noticed fluid on the floor under Left side pedals.

Ordered Matco rebuild kits from Aircraft Spruce and rebuilt the Cylinders (easy)

Reinstalled cylinders into airplane and purchased blake bleed kit from Harbor Freight (Vacuum system bleeding).

4 hours of bleeding and finally got the sequence that seemed to work -- ugh.

Reservoir is so small it doesn't stay full long... but here are the steps I believe finally worked:

*Fill Reservoir
*Pump Right seat right pedal 5-10 times
*Refill Reservoir
*Bleed Right side slightly cracked bleeder valve
*Pump Right seat right pedal while bleeding
*Refill Reservoir
*pump Left seat Right pedal to fill cylinder
*Continue bleeding until no bubbles or pressure holds for 3-5 seconds on bleeder vaccum gage. -- Keep Reservoir from going empty
*Close bleeder valve and check brake firmness on right pedal
*repeat until firm and repeat on left pedals
*refill reservoir

One key thing you see in this is 'fill reservoir' -- the reservoir is so small it is quick to empty when trying to refill the brake cylinders.

Now - had I purchased a pressure bleed system instead of a vacuum bleed system, I suppose I could have saved myself a lot of pumping of pedals and refilling of reservoir?? Pressure system 'fills' the system from bottom up and fills the cylinders until fluid comes out of reservoir? Perform this on both sides and brakes should be good?

Soooo much easier doing it from the bottom. Do a search and you can find lots of good advice.
When you rebuilt your cylinders, did you replace the rods? They wear due to the poor symmetry of Vans design. That is what compromises the seal.

I did bleed from bottom but I guess really the key is moving the fluid from bottom to top.. not top to bottom

No I did not replace the Rod. It looked in good condition. The installation in the airplane has a spacer between the pedal and the rod to keep the more inline. But I have read on this and will be adding the brake cylinders to a more periodic inspection.

pump from the bottom

Just did mine following the "pump it up from the bottom" advice I got on the VAF and it worked perfectly. I can't really test the brake effectiveness since there's not a lot of room to pick up speed in my garage, but the pedals are very firm - no mush at all.

I just used a standard oil can with a hose on it - if you don't already have an oil can, get a big one so that you can put all the brake fluid that you will need to fill the system in one go. This reduces the chances you'll get air in the system if you have to stop to refill the can.

FYI...unless you polish the bore it will leak again.

rocketbob said:

FYI...unless you polish the bore it will leak again.

Click to expand...

I did, but it was very obvious where the piston rod had worn and compromised the seal. Perhaps there is more than one issue that can cause these to leak.

I rebuilt mine and still ended up with a slow leak after 6 months so i ended up just putting new masters in.