172 brake caliper play

[172pilot]

How much play is normal for a 172sp brake caliper?

Should it be tight, and wiggle 1 or 2mm, or is it ok to easily much more than that?

Thank you.

[kilpicki]

You're having your maintenance done on a public forum? Please nobody answer this question, thats what manuals are for. Send me your log book and I'll sign out your annual.

[cgzro]

Give me a break, it is perfectly reasonable for an owner or even a renter to wonder what is a normal amount of brake movement so that they know when maintanance is required. Infact most decent mechanics will help an owner know what is normal and what is not.

[GyvAir]

There's nothing wrong with an owner knowing and being shown what's good/bad, normal/abnormal, worn/worn out, etc. I encourage owners to take an interest in such knowledge. However, trying to relate something so tactile as determining acceptable "wiggle" in a component via an online forum is bound to result in poor communication.
In what direction or axis is the play? How much resistance is there to the movement? What version of the component happens to be installed on the aircraft in question? I.e. standard versus optional or STC'd. Simply too many variables to try to cover properly.
Ask the AME that's doing your maintenance to have a look at it and show you what to look for. If you're on the owner maintenance program, find an AME that's willing to give you some pointers.

[172pilot]

You're having your maintenance done on a public forum? Please nobody answer this question, thats what manuals are for. Send me your log book and I'll sign out your annual.

I'm not having my or any maintenance done on a public forum. I dont own an airplane or even know anyone that does. I'm trying to gain some knowledge as a renter.

I ask because when doing a walk around, on a 172sp, some brake calipers are tight and have very little movement, then there are others with lots of movement (~5mm), in all axis, side to side, and up/down, with very little resistance.

Kilpicki, I was looking for some friendly conversation is all.

[GyvAir]

Well.. that amount of play does sound a tad excessive.
I hope you bring it to the attention of the owner and that they in turn will have it looked at and assessed. I understand that brakes can be fairly important during some phases of flight.

[groncher]

172pilot,
I don't think anyone is getting offended. GyvAir hit the nail on the head with his comments, there are too many variables sometimes to be answered on an internet forum. I have always taken time in my career for pilots who take an interest in learning about their aircraft, but you're always going to be better off asking in person, with the aircraft there.
I assume you rent from a school or club? They most likely have an AME on staff, please ask him or her if they have a minute to have a look at something that concerns you. If it were me I would gladly take some time to take a look.
There are no stupid questions when it comes to your safety.

[cgzro]

I ask because when doing a walk around, on a 172sp, some brake calipers are tight and have very little movement, then there are others with lots of movement (~5mm), in all axis, side to side, and up/down, with very little resistance.

The following is generic disk brake stuff, not specific to any type of plane or car. For stuff specific to your plane of course check with your mechanic.

In general, a disk brake's calipers slide freely for and aft on greased pins so that when the pads are squeezed the force is even on both sides of the disk (because often the force is only directly applied on one pad). So play in the direction that the pads squeeze is normal and infact necessary (no play means frozen pins and the brakes are only 1/2 as effective). Play in any other direction should be minimal. For example kneeling facing the wheel it is normal to be able to pull/push the caliper in/out a bit but it should not rotate or move up and down or sideways...much.

The more worn the pads are the more play there will be (in that single direction). Some pads have witness marks on them so that you can tell when its time to replace them. Often its a little U shaped indent in the edge of the pad which will eventually disappear when the pads reach their life limit.

It is very smart to ask questions when you see differences between otherwise identical planes because there are very few things that should be loose on a plane. The other one that comes to mind are some mufflers which have loose slip joints that tighten up when the mufler heats up. Those planes you grab the muffler and it will rattle .. normally ... and if it does not it risks cracking.

[172pilot]

I have always taken time in my career for pilots who take an interest in learning about their aircraft, but you're always going to be better off asking in person, with the aircraft there. I assume you rent from a school or club? They most likely have an AME on staff, please ask him or her if they have a minute to have a look at something that concerns you.

Thanks Groncher. Correct, the school has an AME on staff, but I'm always there afterhours, or on weekends when he is not around, which led me asking the question on this forum. Just noticed this caliper movement and wanted some insight as I have no idea if it's normal or not. But I will do as you mention and talk to him in person tomorrow when i pop in.

In general, a disk brake's calipers slide freely for and aft on greased pins so that when the pads are squeezed the force is even on both sides of the disk (because often the force is only directly applied on one pad). So play in the direction that the pads squeeze is normal and infact necessary (no play means frozen pins and the brakes are only 1/2 as effective). Play in any other direction should be minimal. For example kneeling facing the wheel it is normal to be able to pull/push the caliper in/out a bit but it should not rotate or move up and down or sideways...much.

It is very smart to ask questions when you see differences between otherwise identical planes because there are very few things that should be loose on a plane.

cgzro, thanks for the explanation. These (on both sides of the ac) had a lot of up/down movmement versus a couple similar a/c on the ramp. But now i understand side to side movement along the pins you are talking about being normal - thanks for that. I'll find out tomorrow morning if everything ok or not. Even if everything checks out fine, I've learnt something in the mean time.

[GyvAir]

Kudos to all pilots that actually take the time not just to look and wiggle (some can't be bothered even that far), but to learn what normal looks and feels like.