[DeTomaso] ZF gearbox extra cooling for Candy 2862

[JDeRyke at aol.com]

Several of the original Gr-4s did have add-on trans coolers, judging from 
published photos. All used mechanically driven pumps- one by vee-belt off the rt 
side inner u-joint adapter, the other off a stub-shaft driven by the mainshaft 
thru the rear cover. This may have been due to the unreliability of electric 
pumps 35 years ago. And remember there were two different ZF limited-slips; 
racers tried not to use the street version with LSD clutches 'cause those units 
generate more heat. Instead, they used the earlier, cooler-running 
sprag-clutch type, and rebuilt it after each long race due to rapid wear of the sprags. 
But before you rush out and buy a cooler, I suggest drilling & tapping a hole 
in the ZF case as close to the ring & pinion mesh as possible, for a 0-250 F 
temp sensor. Then try it in practice- if the lube you use does not rise above 
maybe 220F, you probably don't need a cooler. Non-synthetic diff lube is 
stable up to about 250F & synthetic a bit higher, then things start getting 
serious. I did this a few years ago, & the highways with 70W80 non-synthetic lube, 
our '72 at a constant 100 mph rises to barely 180 F and even that takes 
considerable time. 
Thicker 'racing' lubes will  heat more and cool off slower, and you'll 
probably need either a manual valve or an oil thermostat, 'cause the lube when cold 
is thick enough to shear most drive systems or blow out cooler tubes. I would 
not attempt to adapt some other type of cooler for differential lube- get a 
unit designed specifically for this stuff. In the U.S, NASCAR builders run such 
a cooler only in the longer races- just more complication & chances of parts 
failure. 

If you do decide to add a cooler, note there are cast-in undrilled bosses 
inside the ZF cases that were designed for just such a system, from back when the 
trans was used in the LeMans GT-40s with a smallblock engine. The passages 
exited on the rt side in the back, under the shifter cross-shaft extension. I'd 
contact Lloyd Butfoy at <rbttrans.com>; he's likely more familiar than anyone 
else with this. The one example I've seen of an actual air-to-oil cooler was 
small- about 12"x 6", mounted alongside a real GT-40 gearbox on a bracket.  
Good luck, Patrick- J DeRyke
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