Weakest part of a transmission
 

Does anyone know what the weakest part of a ZF 85A?
They are rated at 671HP @4500 rpm. Will they hold up at 650 to 700HP at 5500? If I understand the weakness maybe I could make some changes. The only reason I want to use these is because you can run in forward or reverse so you can counter rotate your drives and get a drop that is needed to run Arneson drives.

I did notice that the max TQ was 800LBS

We've used them up there. There was a high speed pump option at one time.

So did they hold up? 700HP-750HP?

It was actually more like 875 or so. Big heavy boat.

http://go-fast.com/48_express_cat.htm

Good trans. overall, the only problem weve seen is the 3 sealing rings on input shaft cutting into the alum. pump housing and dropping pressure, but only in commercial applications.Does not tolerate fast shifting though, a couple of times of that and you got a slipped/warped clutch module.

How about the Merc Bellhousings are the SAE 2 or SAE 3?
Also will this trans bolt on a bell housing with dual coolers?

Merc bell housings are "GM" engine pattern w/ bolt pattern for Velvet drive/ZF 45/63/63V trans. A ZF 85A will bolt to Merc bell housing but will need a spacer between trans. and bell housing,the input shaft is longer. Can get SAE 1-5 housings w/ Velvet Drive/ZF pattern usually for diesel/industrial apps.Will fit dual bell housing w/ spacer for longer input shaft.

So the ZF 85A will fit with a spacer nice. Do you know if Merc or ZF makes the spacer? Or will this be a custom deal?
Thanks