MCI power steering pump drive coupling

bevans6 · December 16, 2010, 12:02:05 PM

I was pondering the issue of the fiber drive gear for the compressor that Clifford brought up the other day and recalled that the dog drive coupling for my power steering pump is kind of a phenolic substance. It couples the drive dogs on the left bank accessory drive to the dogs on the power steering pump. Is it considered reliable or should I make one out of aluminium or steel?

Thanks, Brian

luvrbus · December 16, 2010, 12:22:52 PM

Brian, the coupling is very reliable design to break if the Vickers pumps freezes up then the gear train chews in up and drops into the pan no harm no foul in the oil pan if the coupling ever breaks

good luck

bevans6 · December 16, 2010, 01:55:57 PM

Thank you very much, that makes a ton of sense!

Brian

papatony · December 18, 2010, 12:29:38 AM

Brian:: Please dont wait until it breaks. Mine broke and locked up the engine. Some one before me had changed the gear and left the nylon chunks in there. I had disamabled every thing on the back of the engine before i found several chunks had fell inth the gears of the crankshaft locking down every thing. So it is not a big deal to pull and change DO IT NOW.

Oonrahnjay · December 18, 2010, 06:23:56 AM

Tony has a good point; also, "where do you want to break down". The engine in a Cessna L-19/O-1 has a "weak link" plastic spider in the drive to the vacuum pump (which handles all the bad-weather flying instruments). The weak link is also to protect the engine if the pump jams up or becomes clogged. It will strip out exactly when you need to go cross-country to get some other maintenance done but the weather's iffy. (Don't ask me how I know.)

bevans6 · December 18, 2010, 07:10:13 AM

Well, seeing as it, the pump, and the whole drive system is currently in a bin on the floor of my shop while I rip the engine apart and transfer all to the new engine I have, changing it would indeed be a simple task at this point...

Sean · December 18, 2010, 10:38:05 AM

Our experience with the fiber disk:

http://ourodyssey.blogspot.com/2008/01/our-moose-is-gone.html

-Sean
http://OurOdyssey.BlogSpot.com

bevans6 · December 18, 2010, 11:31:59 AM

Sean, your note was excellent and it made me realize that since the drive dogs and the driven dogs on the pump are in the same plane, they will of course engage each other if the disc falls out. That means that it really won't act as a fuse in the system to protect against a seized pump, and of course your pump kept working without the disc for some time, potentially leading to it's eventual failure. So now I am back to should I make one out of aluminium? Maybe a stronger synthetic plastic? Well, that is a decision I can put off for a long time...

Cheers, Brian

Sean · December 18, 2010, 01:01:02 PM

Brian,

I would stick with the OEM material.

Even though the dogs are in the same plane and would collide, as they did on our coach, the fiber does serve the purpose of reducing the transmission of vibration from the engine to the pump, and correcting for any slight misalignment of the two shafts. I will tell you subjectively that the steering system got a lot quieter when we replaced the disk. Although we also replace the pump, so that's not conclusive.

We also, as you read, survived the destruction of the disk with no adverse effects. In fact, all the "damage" we had (we ended up throwing a new set of bearings in) was due to the shaft seal failure dumping ATF into the crankcase. If you run motor oil in your steering system, even that would be a non-issue for you (our steering is not happy with motor oil in the cold).

On the follow-up posted a photo of the bits of disk we fished out of the oil pan:

-Sean
http://OurOdyssey.BlogSpot.com