Stiff brakes, gelled fluid

[Flyler]

I just wanted to add this post with some search terms in hopes that it helps someone out in the future.  Possibly myself when I forget in 10 years!

The brakes on my 201 had felt "weird" since delivery.  They did not feel like they had air in them, if anything it was the opposite.  It felt like I was pushing fluid through a very small hole, and I could feel the pressure release slowly as well.  Brakes seemed to hang on for a second or two after releasing the pedal.  It also felt sort of like glazed pads, where increased brake pressure didn't have a big affect on braking performance.  Just had to push really hard.

The temperature dropped a good 20 degrees between flights, and on landing I was absolutely standing on the brakes. They went from "feeling stiff" to being an obvious problem. Fortunately, with plenty of runway left.

At first I suspected the parking brake was not fully releasing.  Visual inspection showed that was rigged and operating properly.

Next, I cracked the bleeder at the bottom of the caliper and nothing happened for a while.  Eventually, some goo slowly "slimed" itself out- a long, gooey booger.  If you've ever made Strawberry Jell-O and were too eager, and pulled out of the fridge too early... That's the consistency. Not quite a liquid, not quite a solid. It was turning to gel or jelly, and I'm glad it hadn't gotten worse.

Fluid was still clean and red/pink color. Fluid in reservoir looked fine.  Flushed a full quart of new 5606 through and now have felt proper Mooney brakes, and they are good.  I plan to flush again when the temps increase.

I let the old fluid sit in a jar for a while because I wanted to be sure the gel would "thin out" with the new fluid, and it appears to do so after a while.  Temperature was below 30F at the time so things moved slow.

[PT20J]

5606 does that with age. Many have switched to a newer synthetic MIL-PRF-83282 fluid such as Royco 782 which doesn't seem to do this.

 

[cliffy]

You may still have gelled fluid inside your wheel pucks if you didn't remove them and clean out the puck cavity.

In fact I'd bet on it.   I've seen this before several times when the pucks haven't been out of the calipers for a decade or more.

[Flyler]

Thank you both. I think checking the pucks is a good idea for sure.  I almost pulled the trigger on the 83282 but for some reason became convinced it would cause my seals to leak.  I think I will wait for warmer weather to make the fluid change, just in case.  It isn't much fun working in the cold.

I intend to take a look at the old jelly jar next time I am at the hangar to see if it has dissolved more.  You know, for science.

[PT20J]

The o-rings leak with 5606, too. I just had to rebuild my master cylinders last year. I've replaced piston o-rings in both sides. So, be sure to put in a new o-ring when you take the piston out of the caliper to clean it. If you do eventually have a master cylinder leak, it's a good time to replace the brake hoses.

[DCarlton]

16 hours ago, Flyler said:

I just wanted to add this post with some search terms in hopes that it helps someone out in the future.  Possibly myself when I forget in 10 years!

The brakes on my 201 had felt "weird" since delivery.  They did not feel like they had air in them, if anything it was the opposite.  It felt like I was pushing fluid through a very small hole, and I could feel the pressure release slowly as well.  Brakes seemed to hang on for a second or two after releasing the pedal.  It also felt sort of like glazed pads, where increased brake pressure didn't have a big affect on braking performance.  Just had to push really hard.

The temperature dropped a good 20 degrees between flights, and on landing I was absolutely standing on the brakes. They went from "feeling stiff" to being an obvious problem. Fortunately, with plenty of runway left.

At first I suspected the parking brake was not fully releasing.  Visual inspection showed that was rigged and operating properly.

Next, I cracked the bleeder at the bottom of the caliper and nothing happened for a while.  Eventually, some goo slowly "slimed" itself out- a long, gooey booger.  If you've ever made Strawberry Jell-O and were too eager, and pulled out of the fridge too early... That's the consistency. Not quite a liquid, not quite a solid. It was turning to gel or jelly, and I'm glad it hadn't gotten worse.

Fluid was still clean and red/pink color. Fluid in reservoir looked fine.  Flushed a full quart of new 5606 through and now have felt proper Mooney brakes, and they are good.  I plan to flush again when the temps increase.

I let the old fluid sit in a jar for a while because I wanted to be sure the gel would "thin out" with the new fluid, and it appears to do so after a while.  Temperature was below 30F at the time so things moved slow.

Same thing happened to me 10+ years ago.  One brake locked up landing.  Gelled brake fluid in the lines.  Mechanic flushed and replaced the fluid.  Then all good.