View Full Version : Tri Pacer Brakes

02-16-2009, 07:12 PM
I noticed that the brake shoes on my Pa22-20 are marked "R" and "L". According to the parts catalog this stands for R hand and L hand. When I took the shoes off there was a R and L on each wheel. There appears to be a slight offset in the alignment of the shoes when either 2 lefts or 2 rights are assembled on the same torque plate. When placing a right and a left on the same torque plate the shoes are aligned. What is the correct assembly and why the difference? I hope this isn't confusing. Thanks for your help.
Dick Miller Pacer15P.

Glen Geller
02-17-2009, 12:10 AM
I have wondered about this too, if you put two "L" shoes on the left side, one on top and one below, they are not mirror images of each other if there is an offset to the center rib or lining placement. How does a dumb old Tri-Pacer know what is correct?

Steve Pierce
02-17-2009, 06:48 AM
My daughter just took 3 sets off their associated gear legs. I will check it out and get back to you.

02-17-2009, 08:52 AM
Working on ONE brake only (drum style. Discs are NOT the same at all), as you hold (or "imagine yourself holding") the brake "body" in your hand, AND you are looking at the inboard side of the drum out "away from the airplane"... On the side OPPOSITE the side you are looking directly at, the "R" shoe goes on the right side of the drum and the "L" shoe goes on the left side of center.

The brake ASSEMBLIES are the same for either side. Each assembly uses one "R" and one "L" shoe assembly (casting, with lining attached). When viewed "outboard --> in", each individual brake "body" has the brake cylinder and shoe pivot point NOT on a straight "diameter line" through the center of the axle it goes on to. It is "offset", and this makes one shoe longer than the other. When viewed outboard --> in, each brake has the longer "R" shoe on the LEFT.

This has NOTHING to do with the "side-to-side location of the airplane". Their nomenclature may be somewhat confusing, but always remember that in order to work on an airplane, it is necessary to be at a bare minimum 1% smarter than what you are working on in order for there to be a successful outcome. It is ALSO why even a certificated mechanic is required to have someone that has experience "work with him" if he is taking on a task he has never done before. Books do NOT always tell the whole story; experience is invaluable.

02-17-2009, 10:00 AM
Thanks John for the info. In automotive the rear lining is the longer brake shoe, is that the case in this situation? If I got your explanation correct, the right shoe (aft) on the right side....is it the longer shoe?

02-17-2009, 10:53 AM
Thanks for the replies, still not sure what is being said regarding the L and R, my shoes are of equal length, and are not assembled left and right , but rather top and bottom on the torque plate as assembled to the landing gear/axle. And the pivot bolts and cylinder both appear to be on the centerline of the axle. The question now becomes when looking at the assembly, ( shoes attached) , will you see a shoe with the R or a shoe with the L? (one of the shoes is reversed and the part no. can't be seen.)

Thanks, Dick

02-17-2009, 11:47 AM
I currently own a 57 Tri-pacer with original brakes. I prevoiusly owned 53 Tri-pacer that you could pull out on the runway, set the parking brake and go to takeoff power push in the knob and go........ This bird you set the parking brake at idle she will roll off after about 30 sec. It tells me I have a leak downstream of the parking brake valve but i have not been able to find it. I really can't go to Clevelands and Steve's Brake Booster at this time so... I have all the O-rings and a new diaphram and plan to tear into the brake system when it gets a little warmer here. My question is What to look for in order to get a Fair Braking system, adjustments, bleeding ect. I'm sure these things had decent brakes when they were new and I may be missing somthing that maybe somebody else has come across........
Thanks for a Great Website Mike

02-17-2009, 12:45 PM
Dick; I guess you ARE indeed correct...the shoes are the SAME LENGTH and the associated parts ARE located straight across the centerline. How they are "handed" is because of the way they are cast. There is an offset cast into the shoes to properly space them away from the backing plate. That is, the WIDER SIDE of each shoe ass'y being closest to the backing plate. Incorrectly installed, the brake cylinder bars will not match up to the tangs on the shoes correctly and the shoes will scrub on the drum (They sometimes do anyway!). If I had correctly mentioned that I was referring to "left and right" while assuming "straight up" (12:00 position on each side) as the reference, I would have been "acceptably clear" (I think!). Mea culpa. This explains naming them "Rt and Lt" as to which way the casting is "offline" when viewed from the "outside". [Hmmm. I wonder if I am going to reget saying that???]

So, When the brakes are installed on the gearleg so that the inlet fitting for each brake line is in the extreme-most "aft" position...on the RIGHT SIDE Brake, the "R" shoe is DOWN (or RIGHT OF -CLOCKWISE TO- the pivot); on the LEFT SIDE Brake, the "L" shoe is DOWN.

On a correctly installed setup with original Piper shoes, BOTH the shoes have the part numbers readable from the "wheel and tire" side of the brake (got a complete setup right here in my fat hand). If later Piper castings and/or aftermarket replacement part shoes are different, then I am unaware of that!

If you are assembling the shoes to the backplates on the bench, view with the pivot at 12:00 and the "R" shoe goes on the left, and the "L" shoe on the right...for both brakes. Then when they are installed on the gearleg in the original Piper positions (straight AFT of the axle), the shoes are correct as described two paragraphs up.

So sorry for the confusion. Strictly MY fault! BTW, all these brakes work perfectly well no matter HOW the units are "timed" to the axle. Piper used "straight back" as the brake line inlet position to best protect the "plumbing" from ground damage by hiding everything behind the relatively "massive" axle structure, but you can occasionally find them installed in different positions (sometimes to clean up a non-standard wheelpant installation, sometimes because they were just installed wrong, and anything -logical or not- in between).

Mike; Don't overlook that the "leak downstream of the parking brake" may actually be IN the parking brake itself. There were two different makes of P. Brake valves originally, and they use different O-rings internally (fortunately, you only waste a couple bucks if you buy both kinds!). In a LOT of cases, you also can spot a cracked flare somewhere under a B-nut. Why these so many times do not leak enough to readily spot where the problem is, is beyond me. Also, its not uncommon to find that you MAY have old, old rubber brake lines up inside the belly to allow the brake lines to flex at the gear attach points, that "balloon" when you mash on the brakes. That will cause similar "creep away" issues. Them puppies are about 70 bux per side.

MANY PEOPLE do their runups "on the move", steering with feet, braking with one hand and "checking" with the other.

02-17-2009, 01:01 PM
Thanks for the input, I hadn't thought of the Hoses as I'm sure mine are very old! I did get the o-rings for the parking brake Valve just haven't Put them in yet. I have learned to do a run up crossarmed yankin on the brake lever with my arm stuck throuh the control wheel on the mag switch but my intent is to get everything working normal so maybe my wife, who has expressed a desire to learn to fly can jump into it with a low experience instructor(nee 172 driver) and not have any weird stuff to deal with. Again thanks for the input lookin forward to more info on bleedin tricks too.
Thanks Mike

Steve Pierce
02-17-2009, 02:52 PM
Remember the adjustment cams on the brake drums as well. Thanks for the great information John.

02-17-2009, 05:18 PM
Thanks again John, I had ended up assembling as you now describe. Very simply the part nos. go to the outside, readable as you noted, leaving the extra clearance between the shoe and torque plate due to the slight offset in the shoe casting.

Thanks, Dick

02-17-2009, 10:21 PM

If you've riveted new pads on your shoes you should also think about checking, and if necessary, making them the same radius as your drums. Put the shoes in the drums and determine if they make contact through their whole length. Do they just rub on their ends, maybe just the middle of the shoe hits. You can check by pinching a paper strip or two between the shoe and the drum and try pulling it out.

In the old days brake shops would radius the new shoes after a quick drum measure to make sure things were as best they could be. If yours need a little attention, they might not, rough sandpaper cuts shoe pads fairly easily. I've always scuffed off the glaze in the drums with 80 or so paper before assembly too.

I've been using the stock drum brakes for 27 years and every now and then, can't explain why, they seem to work just fine. I did convert to the pedals when I did the conversion back then though.

The heat sinks around the drums are important too. Don't be fooled by somebody saying you can glue them on with JB Weld, it's a heat sink that needs intimate contact, not just free of rattling noises. There are several ways of dealing with loose heat sinks, do a real fix if need be. Drums brakes need everything going for them to work acceptably well, you'll not want surprises later on.

02-26-2009, 08:34 AM
Hey there,
Looking to get into my brake system and researching Brake hose P/N's in the IPC and i noticed my PA-22-150 has a return spring on the brake pedal/arm under the seat and the IPC doesn't ??? Is this suppossed to be there? or has someboby else added it ??? Thanks, Great Resource

Steve Pierce
02-26-2009, 10:23 AM
I think it is original. From memory all the 150 hp Tri-Pacers had this spring.

02-26-2009, 01:27 PM
Thanks for the Picture,I just found my SWPC CD and the drawing shows the spring. Guess i should have looked a little deeper. Thanks for the quick response-Now if I can find the correct fittings to make my gear leg hoses without spending a bunch of gas money (Univair) Mike