Transaxle oil cooler pumps Options

[pcar916]

How many of you are using gear pumps instead of diaphragm types and what filter element (micron) sizes are you using?

[john rogers]

Well the R&P question pops up again as I suspected. In the 20+ years I worked in the Navy as a Nuclear machinist, I baby sat quite a few gear stacks, the largest was on the USS Enterprise (64,000 HP) and the smallest was on an old FRAM WW2 destroyer. Anyways, in all those cases the oil supply squirted right into the gear mesh and provided three basic things: shock absorbing ability, cooling and lubricating the metal surface. We want the same thing in these 40+ year old designed transmissions and the R&P is the weak point. When the oil come into the contact area, any excess is squeezed out the sides of the mesh and some sneaks into the clearance at the bottom of the teeth engagement area. In the 10 years I vintage raced, there were 4 or 5 R&P failures/seizes until all the high RPM 911s and 914s started running pump and cooler setups. This made a 901 last 3 and possibly 4 years with a 2L engine and 2 years with a 3.3L engine before a rebuild would be necessary. Funny thing about the failure was most times the car would be making a grinding noise and once back into the pits and cooled off, it would not move!!

[Richard Casto]

Well the R&P question pops up again as I suspected. In the 20+ years I worked in the Navy as a Nuclear machinist, I baby sat quite a few gear stacks, the largest was on the USS Enterprise (64,000 HP) and the smallest was on an old FRAM WW2 destroyer. Anyways, in all those cases the oil supply squirted right into the gear mesh and provided three basic things: shock absorbing ability, cooling and lubricating the metal surface. We want the same thing in these 40+ year old designed transmissions and the R&P is the weak point. When the oil come into the contact area, any excess is squeezed out the sides of the mesh and some sneaks into the clearance at the bottom of the teeth engagement area. In the 10 years I vintage raced, there were 4 or 5 R&P failures/seizes until all the high RPM 911s and 914s started running pump and cooler setups. This made a 901 last 3 and possibly 4 years with a 2L engine and 2 years with a 3.3L engine before a rebuild would be necessary. Funny thing about the failure was most times the car would be making a grinding noise and once back into the pits and cooled off, it would not move!!

I suspect we are mostly on the same page. I am a big fan of empirical evidence, so if it worked for you and others, I am willing to listen. I do have an open mind. (IMG:style_emoticons/default/wink.gif)

Out of curiosity, I have some questions regarding your Navy experience as well as what you have done with your 914. It sounds like on the Navy solution included some planned shock absorption via the evacuation of oil from the mesh, but in general, I am thinking that this type of spray lubrication system is NOT trying to do the same thing as what we would see with a high pressure oil pump, oil galleries and ultimately hydrodynamic lubrication of bearings (oil under pressure acting as a wedge).

Rather, at least for our Porsche transmission, it relies upon a low/zero pressure splash lubrication system in a stock configuration and that the addition of a sprayer is just an enhancement of that concept? In short, the sprayer is providing additional volume at a targeted location, but at the same time NOT trying to accomplish this extra lubrication via "high pressure induced" hydro-static films (wedge via pressure)? So my question would be for both the Navy ships and in the 914, did the solutions rely more on relatively high volume, but low pressure, or lower volume and high pressure? And a related question is if the "spray" in either (Navy ship or 914) was a "stream" (such as a single jet) or a "spray" (such as a conical spray pattern)?

Richard