Brake heat!

prkaye · #1 08-22-2011, 09:09 AM

I've had an issue with my left brake squealing loudly just as the wheel is about to stop, and also with weak brake effectiveness on that side. So this weekend I took the brakes apart on that side, cleaned the pads (including a light sanding and beveling the edges), reinstalled, re-bled and then I did the brake re-conditioning procedure (taxing at low speed with 1700RPM). Must have overdone it because when I got out and looked at the brakes, that side was SMOKING! It appeared to be the glue on the label attached to the brake caliper that was burning off. The other side wasn't as hot. Anyway, appears no harm was done, and after letting them cool down and re-testing, the brakes worked much better and were much quieter.
But wow, it was a lesson to me - brakes can get unbelievable HOT when you drag them. Makes me glad I use Ryco 782 fluid and have SS brake lines!

Question - could my light sanding of the brake pad during the cleaning have left some residue that burned off causing more of the smoking? I sanded the pads because I could feel some irregularities and rough bumps when I ran my finger over them.

TS Flightlines · #2 08-22-2011, 09:35 AM

the piston in the caliper is sticking and its keeping the pads against the rotor. Not only can you heat crack the pad and warp the rotor, but you can, if severe enough, overheat the piston seal causing a fluid leak. Fluid leak in one side means a really hard time slowing your RV down after landing.
Tom

LifeofReiley · #3 08-22-2011, 09:46 AM

I'm with Tom... the piston in the caliper is probably sticking. If you take the caliper down for a rebuild inspect the piston closely and replace the oring with a Viton oring. Use of brakes with the "A" models can be reduced by using a little more speed when taxing and letting the rudder do the work. Also, roll out... don't try and exit the first opportunity, you can bleed off some speed and take the next exit. I've got 240 hrs on the brakes and no issues using this method. Also, make sure the brakes are not sticking at the pedals.

prkaye · #4 08-22-2011, 09:48 AM

Quote:

sounds like the piston in the caliper is sticking and its keeping the pads against the rotor.

Hmmm... maybe you misunderstood, I wasn't describing a problem with the brakes sticking or the pads dragging on their own during normal use ... I was INTENTIONALLY applying brake pressure throughout a slow taxi with high RPM, keeping the pads on the rotor, to RECONDITION the pads (as described in the instructions, except I did it more aggressively than the instructions say). The instructions say that this procedure is intended to generate heat to create a glazing on the pads. The process worked - the brakes are more effective now, but the amount of heat generated, and the smoke, was surprising to me. It was also interesting to me that one side was much hotter than the other (and it was smoking).

frazitl · #5 08-22-2011, 09:54 AM

the pedals themselves. Lots of info on the site, but in summary, the return springs on the master cylinders are marginal. If they don't fully return to the fully open position, fluid under pressure is trapped applying continuous pressure to the brake pad.

The two fixes that worked well for me are a single long bolt at the pedal pivot point, and "helper springs" on top of the master cylinders. Ryco fluid too just in case...

gereed75 · #6 08-22-2011, 09:56 AM

I think that you mis-understood. The responses are intended as an explanation as to why that brake overheated. There is nothing in your procedure (sanding etc) that should have caused an overheat more than the right brake, so... it would appear that your left brake is dragging (and maybe has been for some time , thus causing the original squealing and need for attention).

Brake dragging can be caused by two things - piston hanging up (not retracting after brake application) or the master cylinder not retracting fully.

The fix for a piston hang up is to clean the piston bore and replace the seal, the fix for the brake pedal hang up is as Terry said.

Fly safe

prkaye · #7 08-22-2011, 10:01 AM

Ah, ok, i see.
I actually do hear the brakes dragging a bit when I push the airplane around by hand. Hmmm. I do have springs on the master cylinders.

Quote:

The fix for a piston hang up is to clean the piston bore and replace the seal

Hmmm... So I have to take the caliper apart? Is this to easy to do? Are there instructions (with diagram) available? Where can the seal be purchased?

Russ McCutcheon · #8 08-22-2011, 10:05 AM

Quote:

Originally Posted by prkaye

Hmmm... maybe you misunderstood, I wasn't describing a problem with the brakes sticking or the pads dragging on their own during normal use ... I was INTENTIONALLY applying brake pressure throughout a slow taxi with high RPM, keeping the pads on the rotor, to RECONDITION the pads (as described in the instructions, except I did it more aggressively than the instructions say). The instructions say that this procedure is intended to generate heat to create a glazing on the pads. The process worked - the brakes are more effective now, but the amount of heat generated, and the smoke, was surprising to me. It was also interesting to me that one side was much hotter than the other (and it was smoking).

Hi Phil,
I never do that pad break-in procedure; I just go out and do a couple of full stop landings, usually there good after the first one. At any rate if the label on the caliper was smoking I would disassemble it and replace the O ring, it is very possibly somewhat melted and problems could occur in the near future.

LifeofReiley · #9 08-22-2011, 10:05 AM

Got my Viton orings at Grainger.

prkaye · #10 08-22-2011, 10:07 AM

Quote:

Got my Viton orings at Grainger.

Thanks!! I'll PM you my mailing address!
Could you let me know the specific part number too, in case I have to get more in the future?
Also, do you know where I can find instructions on how to disassemble the caliper to remove teh piston and replace the o-ring?