I have a new roo with I think Model Mechanic brakes and retracts. It's new, but I got it second hand.
The brakes will barely slow the plane down, even with 120 psi.
I had the O-rings lubed with vaseline, tried removing that and it doesn't seem any better.
I'm using the supplied valve.
Any way to improve the braking on this system?
I'm used to brakes that will lock the wheels if necessary.

Appreciate any ideas on this.

Pete,

If you put 120 PSI directly to the brakes (not through the valve) it should lock the wheels (or close to it) - at least as far as turning them by hand. Does it? I have MM wheels and brakes on my Euro, but I flushed the MM valve and went with the UP-6. The brakes are very positive although I don't think I can actually lock the wheels with the plane on the gear - especially if it has a lot of fuel left on board. Maybe the valve isn't providing the full 120 PSI to the brakes...

Bob

Do the O-rings look very worn?

No, they only have five flights on them.
It does have their proportional brake valve.
Maybe I should try a different valve.
A friend said he had to clean all grease off them with thinner.
I could try pressure straight to the brakes to see if that improves them.
You'd think their valve s/b engineered for their system.

Thanks for the help

OK, I have a mini air guage by the air tanks.
I put another guage on the air line that attaches to the brake.
Both read the same pressure when I apply the brakes hard.
About 2/3 up the guage eguals 110-120 lbs.
The proportional feature workd too, can vary the pressure as I apply the brakes.
Must be the oring against aluminum coefficient of friction is poor.
I was thinking of putting disk of plywood? or something in the rim to improve the friction.
What would work for that?

Pete, putting "something" inbetween won't really work.
My guess is that the o-rings have expanded over time and are now too wide for the nudges they slide in. That way the friction on the brake wall will be so great that the o-ring can hardly open up and accually brake on the wheel rim. My suggestion: excange the o-rings for new ones. They should be about 0,15mm thicker than the actual "nudge".
Brakes are a somewhat tricky and sensitive matter, especially the o-ring type. I'm currently working out a new "concept" which will be running with rubber brakepads, and am also having my share of "problems"....
Regards
Hank

The Vaseline may have caused the orings to swell. It is best to lube them with a silicone based lube like what is available at any swimming pool supply store.

If you use Butyl N rings, Vaseline works very well.

Problem is, I'm sure they're metric O-rings. I've tried to buy metric O-rings in the US before, couldn't find any.
I'll have to try to find The Model Mechanics web site. I'm fairly sure that's who made them.

Thanks for the help guys.

If you're all out of luck, give me the measurements and i'll get you o-rings that fit. Pretty easy to get metric stuff in germany....

Pete,

I have been able to find metric O-rings from McMaster-Carr