Engineering a transmission cooler - a working prototype
 

I've been slowed down mechanically due to my injured hand (as an aside, I now suspect I have a fractured metacarpal.)

Anyway, I've been gathering the pieces for my trans cooler setup, and tonight I built a mock-up on the garage floor. My setup consists of such diverse elements as:

• Tilton differential fluid pump
• VW aftermarket remote oil filter housing
• PZ-21 oil filter
• -8 fittings and lines
• Earls oil cooler
• Possibly a small SPAL fan

The point of tonight's exercise was to see if the Tilton pump could develop enough pressure to overcome the anti-siphon valving in the oil filter. It can. To test, I filled a container with used, cold, motor oil and transmission fluid, and rigged some spare line I had laying around to pull the fluid the fluid from the bucket, push it thru the filter and cooler, and into another bucket. It didn't really make much of a mess - the biggest hassle was when I pre-sprayed the driveway, I disturbed a colony of ants, who swarmed all over the equipment in a matter of minutes!

The next step is to actually start mounting the pump, filter, and cooler into the car. The pump will go just aft of the passenger-side rear seat, the filter (probably) just aft of the driver-side rear seat, and the cooler?????

I'm writing this all up at http://vintagebus.com/howto/trans-cooler/

http://vintagebus.com/howto/trans-cooler/test-1.jpg
http://vintagebus.com/howto/trans-cooler/test-2.jpg

Thom

Are you doing a spray bar?

I'm curious why you chose to put in the filter. I change the trans oil annually and it always comes out clean.

No internal spray bar. I'm doing this as a "better than nothing" excercise.

I change my fluid after each track day and it's always icky! That couple probably be due to the advanced state of decomposition of my transmission. I already had the filter housing on-hand, so I figured "why not?"

Thom,
I'm wondering if a test with real (and hot) 80-140 diff. oil might reveal the (engine) oil filter adequate. I'm going to guess the internal bypass valve is going to open and bypass the filtering media due to (1) filter media not designed to pass/filter diff. lube and (2) the viscosity of the diff. lube. This is going to depend on the pump; whether it's designed for pressure or volume. If it's low pressure you might be okay with the bypass valve, but volume might be in question because of that. To verify there isn't too much restriction on the pressure side of the system, you could compare the current draw of the pump with and without the filter; with and without the cooler, then extrapolate.

Not sure where you planned the oil return, but It may not be too difficult to rig up a couple of return paths with one pointing directly to the R&P gears.

The factory mounts their cooler right next to the transaxle. That should be sufficient. A fan may or may not be necessary. Even the smallest Spal fan might be too big for the available space (and somewhat on the other side of inexpensive). How about using an inline blower motor (marine bilge fan) with 2.5" hose on either side of the blower motor leading to the cooler. It's a little smaller package, a little cheaper, configuration allows for directed airflow and probably easier to mount within the chassis. This is the basic setup for the circle track crowd. However, they usually cut a big ole hole in the back seat floor to mount all the differential cooling paraphenalia.

Hope this helps,
Sherwood Lee
http://members.rennlist.org/911pcars

I wonder if turning the transmission into a 'dry-sump' type unit would reduce the internal losses?

-Wayne

Wayne, it wouldn't be a dry sump in this case since most of the lube is still contained in the trans case. As far as losses, I'd bet the reduced friction from cooler oil would be offset by the increased viscosity. I run ATF in my stick shift drag car, just like many of the newer manual gearboxs do in order to reduce drag and speed up shifts but with brass synchros in my old top-loader this is not recommended for sustained driving. Newer trannies use carbor fiber or similar blocking rings to survive with ATF as a lubricant. (Borg-warner T-5, T-56, and Tremec for example)

Now if the tranny could practically be converted to dry sump not having the gears spinning in thick gear lube in the bottom of the case would certainly cut losses but this would require a suction pump, pressure pump and an external resevoir at a minimum and I doubt all that extra weight would be offset by the potential gains.

Just guessing here but I think a "dry-sumped" tranny would at least be a neat conversation piece. :)

Wayne,
Gearboxes are usually designed for splash-lube. If you convert to dry sump it, that means you'll have to provide an adequate supply of gear lube to all the nooks and crannies under pressure via passages, nozzles, etc. Perhaps some efficiencies can be gotten with a build-from scratch tranny. IMHO, not enough ROI for an existing trans. what with all the pressure/scavenge pump, external reservoir, hose, drilled shafts/passages, etc. complexity.

Not that this relates, but have you ever seen an A/T apart? I think they must lock up trans. engineers in a padded cell after designing them. Marvels of drivetrain engineering. A small spec of mung in the oil supply is enough to totally trash one due to the labyrinth of oil passages and rubic's cube parts integration. Cha-ching, "$3000 please. I removed the piece of lint from your dip stick wipe down."

Sherwood
http://members.rennlist.org/911pcars

I share Sherwood reservation about the filter. I think that in principle its a good idea, but wonder about its use w/ transmission fluid.

Splash lurication doesn't do justice to what's going on inside of a 915. There's a hurricane of fluid in there. Hence the need for the spray bar only in the most extreme situations.

As long as the heat exchanger is in a non stagnant area for air flow a fan is not necessary. You've seen where the factory mounts them on the euro 915s. As Jack has pointed out, for street use it's not necessary, at the track there is way too much air under the car any way, might as well use it for something useful.

Are you going to use a manual switch as well as a thermal switch?