Brake problems

PeterD

Newbie
Joined
Jul 13, 2012
Messages
19
Location
Alameda, CA & Waiheke Island, NZ
Aircraft
Xenon RST, AirBorne 912-XT, Samson Switchblade
I've had ongoing brake issues.

Changed o-rings in original master cylinder (quite a search to find correct rubber compound for DOT-4 in metric sizes) twice (including honing cylinder itself), before replacing altogether. Now the new cylinder appears to be tango uniform.

Never used other than DOT-4 fluid. About ready to change to something like the Matco MC-7, but then there's the problem of fluid which would be compatible with both it and the calipers...

Has anyone else been having problems? If so, what have you done?
 
fluid type

fluid type

HI flush every thing out.. replace with silicone brake fluid its compatible with regular o rings plus this type fluid wont hurt painted things. also trans fluid can be used either or works good....hope this helps ya..
 
I had a similar problem...

I had a similar problem...

Combining the standard brake calipers with Matco master cylinders when I switched to differential braking. The DOT 3/4 ate up the Matco seals. The only dual compatible fluid is DOT 5. Flush with methanol, replace the seals, and be careful not to agitate DOT 5 before installation. Here's some down-to-earth info that I found on a blog. No guarantee that it's entirely accurate.


Here's some good info on DOT 5 silicone based, DOT 4, and DOT 3 glycol based fluids.

DOT3 Brake Fluid Grade - Min dry boiling point=205degC or 401degF. Min wet
(saturated w/water) boiling pt = 140degC or 284degF. Aliphatic
polyether-based. Can be mixed with DOT4 and if so, characteristics will be
(linearly) in between DOT3/DOT4 parameters. Cheap, most widely used, eats
paint, absorbs water easily, eats natural rubber seals (this is bad). 1%
moisture can lower the boiling pt to 369degF, 2% to 320degF, 3% to 293degF.

DOT4 Brake Fluid Grade - Min dry boiling pt=230degC or 446degF. Min wet
boiling pt = 155degC or 311degF. Borate ester-based. Can be mixed with DOT3
and if so, characteristics will be (linearly) in between DOT3/DOT4
parameters, 50% more expensive than DOT3, eats paint, significantly increased resistance to moisture absorption compared to DOT3 (but still absorbs water), does not eat natural rubber seals (this is good). Most DOT4 fluids actually start out with a 509degF dry boiling point.

DOT5 Brake Fluid Grade - Min dry boiling pt=260degC or 500degF. Min wet
boiling pt = 180degC or 356degF. Silicone-based. Cannot mix with other
fluids, turns to jelly if done so; colored purple. Used mostly for antique
cars and some motorcycles. Contains more dissolved air than glycol-based
fluids, aerates more easily when pumped rapidly through small orifices ala
ABS. Is more compressible than DOT3/4. Twice as expensive as DOT4 (and thus
3 times as expensive as DOT3) and has limited availability. Does not damage
paint. Has low lubricity, which increases the wear on sliding surfaces and may cause galling. Becomes corrosive toward brake seals when hot, more specifically, leaches the plasticizers out of nitrile rubber seals (which are very common in brake systems) and causes them to become brittle. Doesn't absorb water but also, doesn't stop it from getting into the system. It then collects in the low
points of the brake system. Absorbs air the way other brake fluids absorb
water, and releases the air at temps well below the rated boiling point
(fluid itself isn't boiling, but it's giving off air bubbles and giving you
a spongy pedal just the same). Viscosity at room temperature causes it to
entrain air when you pour it, which means you're going to be pouring air
bubbles into your brake system. See SRF.

DOT5.1 Brake Fluid Grade - Min dry boiling pt=260degC or 500degF. Min wet
boiling pt = 180degC or 356degF. It's a stupid name (the 5.x bit) as it's
synthetic & glycol-based (borate ester) like DOT3/4 but has NO silicone.
Named in the 5.x series as it beats the DOT5 performance criteria. Absorbs
water, eats paint, more expensive than DOT4, difficult to locate.


Joe
 
Thanks, guys.

My problems to date should not have been caused by brake fluid type, as I've continued to use DOT-4 with 99.9% Xenon (or Zen :)) supplied parts (0.1% = replacement o-rings, no longer in use).

Bill - I did remember your problems, which is why I've been careful to stick with only the DOT-4.

Interestingly, Matco recommends aircraft hydraulic fluid (not brake fluid at all!).

Well, aside from fluid compatibility, has anybody had this sort of problem with their Xenon brakes?
 
Hi Peter,

What issues have you had ?

Maybe I missed it but I don't see where you explained what the probem was.

Perhaps more info will give everyone a better chance of helping you out.
 
Karl -

Good point.

First let me point out that none of this occurred during taxi or flight. Further it played out over weeks, and I've condensed this somewhat (for example, I dismantled the master cylinder 2 or 3 times).

Here's the sequence of events:

1. Brakes working fine. So firm that it nearly took both hands to lock the handle in the 1st parking brake position.

2. My brakes got very "soft" - that is, the handle got spongy and nearly bottomed out on the stick before the brakes applied.

3. Bled the brakes. Back to firm brakes.

4. Shortly thereafter, I lose the brakes altogether.

5. Bled the brakes. No improvement.

6. Dismantle master cylinder. Source new o-rings. Hone & reassemble cylinder.

7. Bleed, bleed, bleed... Still no brakes.

8. Order new master cylinder and wait weeks for delivery from Poland.

9. Bled the brakes. Back to firm brakes.

10. Weeks later... No brakes.

11. Bleed, bleed, bleed... Still no brakes.

12. Facepalm in despair! :(
 
Uh, I had to....

Uh, I had to....

Wore my shoes out. The Flintstone theme song kept echo'ing through my head.
 
....
8. Order new master cylinder and wait weeks for delivery from Poland.
....
12. Facepalm in despair! :(

You probably ordered by CA sp. z o.o.
No wonder you were waiting for so long.

In the future you should contact Aviation Artur Trendak,
the factory in Jaktorów, that manufactured your machine,
not the new PLC company, that since over a year has
manufactured noting.

AAT is continuously manufacturing the machine (25 units in 2012),
has made a lot of improvements in the meantime.
 
Last edited:
Paul / Michal -

I got the master cylinder through Mike Bantum. I have no doubt he ordered from AAT. Things just take time to get to us here in the US. Had to wait while back-ordered, then deal with wire transfers, customs, etc.

I contrast this with my other aircraft - a trike from AirBorne in Australia. Every part is clearly listed by part number and illustrated in exploded CAD diagrams which I can download online. One phone call and I can give my credit card and have something shipped immediately.

Don't get me wrong, I love my Xenon. And, I know AAT is earnest in their efforts to improve the aircraft and the manufacturing. But I use AirBorne as an example of what I hope they will strive for...

Meanwhile.... Still hoping to hear whether I'm the only one to have such bad luck with my brakes (I'm not counting Bill, since his situation involves customization of the brake system).
 
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