The International Cessna 170 Association

I ordered a brake bleeder kit from Spruce and when it came I just assumed I got what I needed.
For some reason I ordered and received a Hegar Brake Bleeder kit. It uses Chevron ATF fluid! Looked red to me so I bleed my brakes.

Yep you guessed right. ATF fluid all over the place. O rings murdered by the ATF fluid. Oh and no brakes!

So new O rings and 5606 on the way.

I have drained as much ATF fluid from the system as will flow from gravity. Should I flush with something other than new 5606 before replacing the O rings and fresh 5606. The ATF is pretty caustic and I feel I should drive it running from my brake system before something else fails.

Thanks-

Interesting. Bet your not the first to use ATF though you didn't intentionally. My partner claims in his very early days of ownership of 7A, back in the seventies, he used ATF on purpose. Never mentioned any issues. Only changed back to 5606 when some high fluting airplane mech told him not to use ATF. He and I recently visited about this as we had some brake issues requiring 5606 and our supply was dwindling or so he thought.

I suppose if I really wanted to do a thorough job I'd remove the master cylinders and brake cylinders, disassemble and flush with solvent. You are disassembling these items aren't you to replace the rubber? While removed I'd flush the lines with said solvent and some low air pressure.

I wouldn't be surprised you could get away with a good flush of the system with 5606 and be done with it. Likely all my partner did if he flushed the system at all. Others will have to weigh in on this. It's a real pain to remove the master cylinders. If not for the rubber in them which would be suspect if other rubber had issues with ATF, I'd make every effort to leave them in place and flush them.

Hi Bruce, I have been using Dextron 3 ATF in my hydraulics for the wheel skis, 3 years now no issues. I use the approved 5606 for the brakes. The drawings for the skis never really specified the type of hydraulic oil,so I used atf, red makes it easier to find leaks

cfzxo wrote:Hi Bruce, I have been using Dextron 3 ATF in my hydraulics for the wheel skis, 3 years now no issues. I use the approved 5606 for the brakes. The drawings for the skis never really specified the type of hydraulic oil,so I used atf, red makes it easier to find leaks

If I didn't make it clear, I'm surprised Jim had trouble because of the ATF. I've not investigated but believe any seals made for use with 5606 could also be used with ATF. There is of course a possibility the seals that gave him issue where not correct even for 5606. Again I have not investigated the differences in the seals required for each. And I'm not advocating ATF instead of 5606.

There are a number of different fluids used for brakes and hydraulics that can be detrimental to various systems. The OLD ATF known as "Type A" was a petroleum fluid easily substituted for 5606 in some systems other than transmissions (It was used in some manual-assist steering systems) but as Auto-Transmissions became more sophisticated things changed. Ford created a Type "F" which was not interchangeable and often used in power steering systems.
Some automotive brake fluids are glycol/ether and some are synthetic/silicone and some are alcohol based. Obviously, we shouldn't mix them and we should do as LeRoy's Falutin mechanic was correct... Use the correct fluid for the purpose. H5606 (mineral-based) in ours.

Type-A ATF is now Dexron, and as the additive packages have changed, so have the numbers following - pretty much the only type you can find anymore is Dexron III (mostly due to GM licensing/certification), but it works backwards to the old Type-A.

Type-F ATF was used by Ford for use with bronze impregnated clutch disks (which pretty much went away with the old Cruise-O-matics like C4, C6, etc). It is heavier in viscosity, but otherwise largely compatible with Type-A. In fact, before the advent of commonly available racing ATF, racers almost all used Type-F...even in their GM products. The additive packages resulted in firmer shifts with less slippage. Aftermarket B&M Trick Shift is basically Type-F with some other additives and is cleared for use in a wide variety of transmission in a racing application.

In the early '80s, as focus shifted to smooth shifts and NVH (noise, vibration, and harshness) became a focus for the quality engineers, Ford shifted to Mercon. Mercon is essentially the same as Dexron and why you often see it marketed as Dexron/Mercon - Ford just wanted their "own" ATF. Similar to Dexron, they add a letter suffix to denote differences (i.e. Mercon V, LV, SP, etc).

Many of the newer ATFs like Mercon LV are fully synthetic and, as such, should not be mixed with earlier non-synthetic fluids. Some ATFs are synthetic blends, and may be able to be mixed, but it's best not to as it's impossible to tell how much base stock is mineral vs synthetic.

Seal compatibility between ATF types is largely a non-issue - in other words, the seals generally don't care which fluid you use. The fluid additive packages and viscosity which differentiate the various ATF types largely only change shift characteristics or provide different wear packages for newer friction types. Generally speaking, newer fluids are often lower viscosity and run at slightly higher pressures than older, heavier fluids.

Auto manufacturers develop the unique blends of ATF for their specific transmissions as they chase different goals (smoothness, heat resistance, mileage, etc). The primary difference between them is largely additive packages, followed by viscosity and, of course, whether they're synthetic or mineral based. All the old oils (Type A, F, Dexron, Mercon, etc) are mineral based - only the modern ones are synthetic or synthetic blend.

Having worked on hydraulics for several years, it's difficult to ruin seals due to using the wrong fluid. There are exceptions, of course, but the larger problem with contamination is actually cleaning out the old well enough to call it 'clean'. In emergencies, I've run all sorts of things in hydraulic systems - always requiring a thorough cleaning and possibly rebuild - I must hasten to add that none of these systems operate on aircraft!!

The best answer, is, of course, to use the correct fluid for the application. If an error has been made, thorough flushing is called for and that may include complete disassembly. While seal replacement may not be required, with the components apart, it seems foolish not to...unless cost is a large factor...and even then, seals can be damaged during disassembly, often imperceptibly and may cause issues down the road - it is almost always best to replace seals if a component has been disassembled.

Don’t forget about the flex hoses at the base of the master cylinders below the rudder pedals. Not sure the MIL spec standard they are built to but hope no damage to those.

Thanks everyone. I drained the ATF; flushed with mineral spirits till clear; flushed with 5606 and took everything apart. Cleaned everything with mineral spirits and installed new O rings and gaskets. Put it back together under supervision and refilled with brand new 5606. Everything works great and there do not appear to be any leaks. I shall always remember "5606"

Jim Layman
N9534A

Wow Jim fantastic recovery on your part!