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Master cylinder help

P51DACE

Registered User
Covington La.
I know you guys consider anything Husky to be associated with the mark of the beast. But I was hoping for a little compassion on this one (and I own a PA-12).

The left brake is dragging on our 1987 Husky, S/N 10.

A few landings prior to the noticeable dragging I had the left brake pedal go all the way to the stop. After I got the plane stopped, I reached down and pulled the pedal back to the rear and then pumped it a few times, all seemed normal.This certainly got my attention as it was on a short strip. I then flew home and cleaned,lubed, checked tire clearance, changed caliper O-rings and bled the system. Also at the same time I did this servicing we installed some '26 Bushwheels. I went up for a flight and when I landed the left brake felt normal but it is now dragging. There is no tire rubbing and clearance is not an issue. The caliper definitely is not fully releasing. Checked clearance again, bled the system, same results, still dragging.

I then pulled the master cylinder apart and it looks good with nothing obvious. But who knows? I decided maybe I could get an overhaul kit for it as they were all original. I've been an A&P for quite awhile but have never seen a master cylinder quite like this. It has Scott stamped on it and "A3Q86" or "A3086" lettered on the side. I couldn't find a reference for it anywhere. I called the friendly (not) lady at Aviat and she said they no longer used this type master cylinder. Cool, so what is the Scott part number I asked? Don't know. Seriously? Yes. Unbelievable.

It kinda looks like a Gerdes and Matco cross pollination. Any help,suggestions or insight is appreciated. Thanks.
Brake.JPGBrake-2.JPG
 

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If you don't mind a little extra work, try interchanging the master cylinders to isolate the fault - master cylinder or downstream?
 
There was a Bonanza Master cylinder that got acting goofy. It would bypass half the time. An old A&P changed every O-ring in it. It still was goofy. While they, the owner and the A&P, went to lunch, I took it apart again. There was one harmless looking washer with rubber on one side that looked like it acted as a one way valve. That washer didn't get changed. We studied the parts manuals until we found a parts kit with the mentioned valve washer, ordered it, changed all the stuff out again, and the master cylinder worked OK. jrh
 
Husky now uses a Grove cylinder, if that helps. Did you carefully check your parking brake setup? Those things have a way of failing in the wrong position. We had a Stinson that would self-actuate on a bouncy landing. Pulled those suckers off, and never looked back.
 
the other drag issue is that washer mention above with o ring in it, it must NOT be engaged when pedal is not in use...
 
Looks like a Scott 4408 Master Cylinder. The A3Q86 is most likely the cure date of the o-rings installed at time of assembly, third quarter 1986.
Here is a parts break down. Good Luck, Jim

View attachment scott 4408.pdf
 

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Looks like a Scott 4408 Master Cylinder. The A3Q86 is most likely the cure date of the o-rings installed at time of assembly, third quarter 1986.
Here is a parts break down. Good Luck, Jim

View attachment 19593

Jim,
Thank you for the schematic. It really made the difference.
Here is the latest and its not good news for me. Talked with the very nice folks at Grove. They have direct replacement cylinders for $499.00 each. I also to talked to a nice guy at Burls'. They both gave me the same story. Scott was purchased by a French company, Zodiac. Zodiac wanted the oxygen division of Scott and have no interest in supporting the brake division. Burl and Grove both tried to buy the brake division but to no avail. The parts, evidently, in the 4408B-1 cylinder which is in a lot of aircraft, are no longer available. Burls said to try Univair, they may have some parts.

To me, a 1987 aircraft is like brand new. I never thought I would have this kind of issue.
This could get painful.
 
Husky now uses a Grove cylinder, if that helps. Did you carefully check your parking brake setup? Those things have a way of failing in the wrong position. We had a Stinson that would self-actuate on a bouncy landing. Pulled those suckers off, and never looked back.

Yes sir you are correct. I called Aviat and they sell the new Groves, direct replacement, no extra paperwork for $383.50 each. Substantially less than Grove.
Thank you for the help.
David
 
I went around and round with with Aviat and Zodiac. Piss poor support from Aviat and Zodiac. With persistance I got my parts but Aviat was absolutley no help and Zodiac can KMA. I had a couple of the special seals but not sure if I still do. I will look. Glad Robie picked this up and ran with it.

Be sure and lubricate the torque plate bushings and pins with silicone spray periodically.
 
If you sell $2-300K airplanes and can't help someone get a rod end for the end of a master cylinder you want to tell them to KYA as well. But my attitude towards Avia goes back almost 20 years. They don't give a $hit and that is apparent almost every time I have to deal with them.
 
After much $$ consternation, I opted to go with the Grove cylinders. We've had this plane for ten years after buying it from an insurance company. The owner had flipped it over in a field and we did a rebuild. I justified the Groves by hoping we will not sell it for many, many years. Thanks again for the help.
 
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Scott 4473A Master Cylinders

I have an early Husky with Scott 4473A master cylinders. One was leaking down internally so I pulled/disassembled and found what I believe is a seal missing. I know Scott is out of business and I can't find much info on the internet. Does anyone have a parts diagram of this or a similar Scott Master? Anyone have a lead on where to get the appropriate seals/cup/o-ring?

v/r
Bryan
 
Call Grove Aircraft. They are now OEM suppliers to Aviat. Their entire master cylinder is probably less than the cost of your part. I have their master cylinders on two Cubs and an Aeronca - bulletproof.
 
I merged your thread with an older thread on the same subject with some links to seals. Read some of the previous posts and hopefully they have the parts you need. As you can tell from my previous posts on this subject I was pretty PO'd at Aviat and Zodiac (owns Scott).
 
Update: they are model 4408 brakes, 4473A was the reservoir part number. Univair has the parts in their Stinson interactive catalog. Parts needed are:
MS28775-113, O-ring for the bottom of the reservoir
4014, Seal piston stem
18051 U cup (linear)
$60 for 2 sets.
Thanks Steve!

Bryan
 
Installed the new seals. Now I can't fill/bleed the brakes from below with a squirt can as I normally do. It is building up pressure. I checked my pics and installed the cup seal as it was previously. The cup is facing down on the piston assemble so the stroke pushes the open end of the cup downward. Could it be installed backwards? I tried with the pedal in various positions.
 
I always had to stick a toothpick in the vent on the top of the master cylinder to keep from pissing fluid all over. I would disassemble and inspect.
 
I know you guys consider anything Husky to be associated with the mark of the beast. But I was hoping for a little compassion on this one (and I own a PA-12).

The left brake is dragging on our 1987 Husky, S/N 10.

A few landings prior to the noticeable dragging I had the left brake pedal go all the way to the stop. After I got the plane stopped, I reached down and pulled the pedal back to the rear and then pumped it a few times, all seemed normal.This certainly got my attention as it was on a short strip. I then flew home and cleaned,lubed, checked tire clearance, changed caliper O-rings and bled the system. Also at the same time I did this servicing we installed some '26 Bushwheels. I went up for a flight and when I landed the left brake felt normal but it is now dragging. There is no tire rubbing and clearance is not an issue. The caliper definitely is not fully releasing. Checked clearance again, bled the system, same results, still dragging.

I then pulled the master cylinder apart and it looks good with nothing obvious. But who knows? I decided maybe I could get an overhaul kit for it as they were all original. I've been an A&P for quite awhile but have never seen a master cylinder quite like this. It has Scott stamped on it and "A3Q86" or "A3086" lettered on the side. I couldn't find a reference for it anywhere. I called the friendly (not) lady at Aviat and she said they no longer used this type master cylinder. Cool, so what is the Scott part number I asked? Don't know. Seriously? Yes. Unbelievable.

It kinda looks like a Gerdes and Matco cross pollination. Any help,suggestions or insight is appreciated. Thanks.
View attachment 19562View attachment 19563
How do you take this apart please?
 
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