Flap Pump Questions

[EricJ]

3 hours ago, Barneyw said:

4. I get the point about the O-rings and I reconfirmed that a synthetic ATF was used, to my shock to be honest. Apparently it is common practice mainly to save cost although that's debatable now.

NO, it is NOT common practice to use ATF and it is not an approved part to service any GA aircraft that I'm aware of.   I'd be very wary of whoever told you this.   I've never heard of it being done before, for reasons that are obvious here.

3 hours ago, Barneyw said:

The question is now do I replace both cylinder's O-rings while it's apart and possibly the flap valve and flush the system and replace the oil to a more conventional one or continue with the ATF. I'm leading towards convention.

 

The approved hydraulic fluid is MIL-H-5606, which is the red mil-spec mineral-based stuff that's been around forever.   It gets gooey as it ages, but is otherwise fine to use.   It is very inexpensive.   There are modern synthetic equivalents that are miscible (mixable) with 5606 and specifically formulated to be compatible everywhere 5606 is used, and it doesn't get gooey when it gets old.   It's more expensive, but if it saves you an AOG experience or something like that it can easily pay for itself.    Royco 782 and Aeroshell 31 are synthetic substitutes for 5606 and are available at many aircraft suppliers, like Aircraft Spruce.

3 hours ago, Barneyw said:

This is a job I should be able to do myself, under supervision, and get the mechanic with the gear to bleed the system and I should be on my way. 

If you are mechanically inclined (hopefully moreso than whoever says ATF is okay to use), none of it is super-difficult to do.  However, any o-ring or seal that the ATF has touched is suspect and will at least need to be frequently inspected, including the o-rings in the brake calipers, parking brake, flaps (if you have hydraulic flaps), etc., etc.

Edit:   There are many potential issues with ATF, not the least of which is that there are a zillion different kinds with different formulations for whichever manufacturer wanted to use a particular kind of seal or gasket, or whatever.   Generally ATF has loads of detergents in it as well, since transmissions have a lot actuators with small passageways, etc., and don't get serviced often.    The upshot of all of this is that, depending on which specific ATF was used (or any of them), there can be a number of ingredients that are not friendly to the components in your ancient plebian small aircraft hydraulic system.

Edit 2:   BTW, check the airframe logbook to see if there's an entry for the last time the brakes were serviced/flushed and if it indicates what fluid was used.

[Ragsf15e]

15 hours ago, Barneyw said:

First of all a big note of thanks for all the rapid replies and inputs to my problem. Here are my responses.

1. It was indeed the LH brake master cylinder. See the photo.

2. It dumped the whole reservoir overboard - bone dry. Such a lot of mess for a small reservoir.

3. I do have the two triangular shaped panels and the reservoir is mounted still in its original position in the cockpit.

4. I get the point about the O-rings and I reconfirmed that a synthetic ATF was used, to my shock to be honest. Apparently it is common practice mainly to save cost although that's debatable now.

5. Thank you for the links to the new AMM and IPB - very useful. My manuals have a 197x handle.

The question is now do I replace both cylinder's O-rings while it's apart and possibly the flap valve and flush the system and replace the oil to a more conventional one or continue with the ATF. I'm leading towards convention.

This is a job I should be able to do myself, under supervision, and get the mechanic with the gear to bleed the system and I should be on my way. 

Thanks for the welcome and excellent info.

Next time I post it will be more about me and the aircraft which was to be titled "I bought a Mooney, now what!?"

Cheers

BW  

 

I’m glad you found it and I’m glad the initial fix is relatively easy. Sorry about the atf being used.  Just so you’re aware, refilling and bleeding the hydraulic system on a Mooney isn’t rocket science, but it’s also not exactly easy if you’ve never done it.  There are a few different techniques, but there are several common areas where you can get bubbles and end up with a soft brake or flaps that don’t work.  I’d use google and find one of our many threads on brake bleeding before attempting it.

[Barneyw]

Thanks everyone for your inputs - all very useful

I want to allay all the concerns about this and let you know that I was quite astonished when I heard that ATF was used. So you all know I believe the aircraft is sound and the decision to use ATF was the owner's but the rest of the aircraft is rock solid and the PPI I had arranged for the aircraft before purchasing it confirmed that it was a sound ship. Before conducting the PPI this aircraft underwent a full restoration to a very high standard and a full audit by licenced mechanics (LAME) and signed back into service. It is just unfortunate that the previous owner was led to believe that using ATF was a good alternative but there was no way of knowing prior to purchase. It's just a question you don't tend to ask.

Interestingly enough having gone a little deeper I have discovered that the use of ATF is probably more common than people might think. For example LSA use it (ATF 3) quite commonly and this has most likely spilt over into GA, for whatever reason, confirmed by a couple of  conversations I have recently had with mechanics. So if it's happening here in Australia I'm sure it's happening elsewhere.

Furthermore, I had a discussion with another owner who relayed a story to me that shortly after he purchased his aircraft the hyd fluid had become so thick (aged) that the flaps failed to retract so I'm just wondering if not enough attention is being paid to this aspect of aircraft maintenance and this system. My point here is that the use of ATF is but one problem that can lead to system failure. Moreover, as mentioned, there was no way of knowing what oil was being used and, most likely, two incompatible oils could have been mixed leading to the hyd oil not performing to specification. So this is just another consequence of using non-specified oils and alike.

The good news is that I will be replacing all system o-rings as well as the offending oil with 5606 which is tried and true. The decision to use a non approved alternative never ends well and it is something I would never contemplate. 50 years in aviation has taught me if you try to outsmart aviation it will outsmart you right back with, sometimes, dire consequences. On reflection I feel I have dodged a bullet and count myself fortunate that this happened sometime after shutting down and putting the aircraft to bed and not in flight.

I look forward to further conversations with the group.

Cheers

BW

Edited April 29 by Barneyw

[PT20J]

There is nothing wrong with 5606 and it has the advantage of being universally available. However, it does thicken with age and especially heat from the brakes. I still use it, but I drain some from the wheel cylinder bleeders every year until the discolored fluid is running pure red. Then I top off the reservoir.

[Shadrach]

If one is draining one's hydraulic system for a flush and fill, the cost delta for synthetic vs mineral based hydraulic fluid amounts to anywhere from $0.50 to around $3.00 in the US.  It is readily available in the US, if pricing and availability are similar in Australia, I would insist on filing an empty system with synthetic MIL-PRF-83282 unless I had no other option.

[EricJ]

5 hours ago, Barneyw said:

Interestingly enough having gone a little deeper I have discovered that the use of ATF is probably more common than people might think. For example LSA use it (ATF 3) quite commonly and this has most likely spilt over into GA, for whatever reason, confirmed by a couple of  conversations I have recently had with mechanics. So if it's happening here in Australia I'm sure it's happening elsewhere.

If the system is designed for it initially, which a new system may be, e.g., by using appropriately compatible materials for the seals and gaskets, then there's nothing wrong with it.    This would be reflected in the system Maintenance Manuals and Parts Manuals, though, so that the properly compatible fluid(s) could be used.

Airliners haven't used 5606 or anything remotely like it for decades, because it is flammable under certain conditions (e.g., atomization from a high-pressure leak).   They use some crap called SkyDrol which smells really bad and is actually toxic to your skin, and is very expensive, but it won't burn, so they design everything for it and that's what they use.   IIRC it's blue, so it can't be confused with 5606, which is red.

Our plebian GA brake and flap systems don't make enough pressure to make 5606 a probable fire source, so, very fortunately for us, nobody has proposed using SkyDrol, and we can use the same 5606 that the ancients used long before us.    

5 hours ago, Barneyw said:

The good news is that I will be replacing all system o-rings as well as the offending oil with 5606 which is tried and true. The decision to use a non approved alternative never ends well and it is something I would never contemplate. 50 years in aviation has taught me if you try to outsmart aviation it will outsmart you right back with, sometimes, dire consequences. On reflection I feel I have dodged a bullet and count myself fortunate that this happened sometime after shutting down and putting the aircraft to bed and not in flight.

The main options for us are 5606, and the compatible Royco and Aeroshell synthetics mentioned earlier.

[Barneyw]

Hi All

I just wanted to follow up on the problem I had with a LH master cylinder and happy to report that the aircraft is now serviceable albeit with some controversial discussion points.

The Fix - The fact that would take some time to get a kit out from the US and there I was able to obtain new o-rings locally and decided to just pull out the offending master cylinder as the most expeditious way to solve the issue having in mind that if the o-rings showed any signs of damage and, moreover, swelling then I would be up for a bigger job ie full o-ring replacement on all hydraulic components.

The Problem - With the master cylinder removed it was disassembled and the o-rings were compared to the new o-rings. There were no signs of damage or swelling. the cylinder bore was also inspected revealing no damage. It was soon discovered that the piston shaft had a slight bow in it. To say it was bent would not be correct. This was confirmed on a lathe.

Corrective Action - We managed to nudge the shaft, being held in a chuck of the lathe, at a few locations and managed to get the shaft straightened confirmed by spinning it up and being concentric compared to what it was like. The master cylinder was reassembled, installed and brakes bled and voila the aircraft was back in service. 

Questions - What caused the shaft to bow? Is it possible to put too much foot pressure on a master cylinder especially in a turn? As I have quickly discovered the Mooney has a greater taxi turn radius than a B747 and it's easy to apply a little too much pressure on the pedal to get the aircraft turning a little tighter. What do people think?

Now the controversial bit

I continued using ATF because there was no evidence that the o-rings had been damaged plus the fact the ATF had been used in service already for over two years and there was no evidence of any other leakage. If the o-rings were reactive to ATF it would take a matter of months, if not weeks, for the o-rings to start failing. In fact it seems that synthetic ATF is rather benign and inert having had it on my hands, on a painted surface on the hangar floor and on the aircraft with no evidence of staining or deterioration of the paint etc. Being a dermatitis sufferer I didn't even experience the slightest tingle or irritation.

So I am clear I am not advocating the use of non-approved fluids or parts etc but it seems to me that H-5606 has had it day and apart from Skydrol, which I have had the misfortune of servicing an aircraft using the stuff (not good), and the suggested alternative Royco synthetic oil It would seem to me from some very rudimentary research that the general aviation industry, when it comes to hydraulic fluid has not done much by way of improved products (I might be wrong) whereas, the auto industry has. In fact the synthetic oil I am using meets over 25 - 30 manufacturers standards. This is by no means definitive that suggests tacit approval to use ATF in aircraft but I have had discussions with a number of mechanics who just don't seem to have a problem with it and as mentioned previously it is probably not about cost. I would also like to know, as I have been led to believe, why it is the recommended fluid in LSA braking systems. I would be interested in what the ASTM has to say on the matter and how Royco Synthetic oil standards compares with ATF standards - but that's for another day.

I'd be interested to know, given the scale of general aviation in the US, if people have come across the use of ATF? I fully understand what should happen but would like to know what actually happens.

I look forward to the replies 

Cheers

BW

[Fly Boomer]

9 hours ago, Barneyw said:

I'd be interested to know, given the scale of general aviation in the US, if people have come across the use of ATF?

Never heard of using ATF for brakes, but I am not a mechanic.  I have read that it has a greater affinity for water than 5606 or the synthetics.

[Shadrach]

I do a 180°, max performance turn in between hangar rows every time I put my plane away. Lots of tight turns and full power brake releases at short fields. My brake cylinder shafts have been subjected to whatever hundreds of pounds of pedal pressure delivers to the shaft without bowing.
 I just rebuilt both cylinders and the parking brake valve for the first time this year after 57 years in service. Everything was straight and in good shape save for the o-rings which hardened enough to weep fluid.

I suspect that yours was likely bent during a maintenance event. It would take a tremendous amount of force to bow one of the shafts from compression alone.

I have straightened vintage motorcycle push rods by drilling a hole in a 2x4 slightly larger than the rod. Then affixing the rod in the drill chuck to run it through the hole in the 2x4 with of a slight side load. Takes a few passes, but is an effective way of straightening a slightly bent rod or shaft

I must say that I am disappointed that you did not take the opportunity to correct the unapproved fluid situation during this maintenance event. It may function fine but the industry specified 5606 for a reason.
The approved synthetic replacement for this application is MIL-PRF-83282D and is equal to or superior to 5606 and ATF in every way. Much higher flash point. Superior operating temp range. Resistance to oxidation and gelling.  It is less hygrscopic and more resistant to breakdown while being kind to seals and o-rings. 

I understand the frustration with regulatory inertia and how it can sometimes prevent the use of more modern and superior products.  However, in this case, there is a reasonably priced, modern, approved product that is by all accounts superior to the unapproved product you’re using. A complete system fill with Royco 782 (MIL-PRF-83282D) costs less than $20 USD. Seems like a silly hill on which to plant a flag…
 

 

[EricJ]

10 hours ago, Barneyw said:

I would also like to know, as I have been led to believe, why it is the recommended fluid in LSA braking systems.

Those are new designs that were probably designed from the beginning with that fluid in mind, so it has gaskets and o-rings that are compatible with that fluid by design.     Your system was not designed for that fluid, it was designed for a very different fluid.

ATF is very different from typical hydraulic fluid.   It has a number of detergents and other components that are useful in machinery that experiences high temperatures and high shear loads at high pressure.   It does a very different job.   An old engine cleaning and de-gunking trick is to put a quart of ATF in the oil and run it for a while before an oil change, since the detergents are strong enough that they'll clean out a ton of crap.

You're a test pilot.   It's not even a very useful test, since the appropriate fluids aren't especially difficult to get or overly expensive.

 

[Barneyw]

Hi All

I can't argue a case here because the AMM will win all the time and I'm not trying to plant any flag based on cost - I've never argued that. I'm merely trying to gauge the prevalence of the use of alternatives. At the end of the day there is no evidence of any damage and the systems works well. Interestingly enough I heard from another owner, who had 5606 in his system and the oil gummed up that much the flaps became jammed down. Most likely an overlooked maintenance item but nonetheless a problem caused by 5606. Make me wonder what is more of a problem.

Anyhow I appreciate the feedback. The aircraft is due for an annual in July and that partly the reason why I did not change the fluid. As I need to do some work on the flaps I will most likely change to the Royco 782.

Cheers

BW