My ZF6 + cold start = no reverse
 

Yes I know 97's didn't come with a ZF6, but mine has one as it was swapped in. If it is around 20° or so it grinds and won't go in to reverse. I need to check my Master Cylinder fluid level as there seems to be almost no travel before the clutch is engaging. So if it isn't just fluid, what else should I think about?

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If the slave cylinder is dry, I would suspect the master cylinder. The slave cylinder leaks if it fades and you would see a loss of fluid. The master cylinder can fade without losing fluid because it backs into the reservoir. It can also leak, though. If you can see the slave cylinder, it might be good to have someone hold the clutch down while you watch the slave cylinder to see if it slowly returns while the clutch is fully depressed.

If none of those possibilities pan out, the next thing I would suspect is the pilot shaft binding in the pilot bushing/bearing. Sometimes when transmissions are swapped, a bell housing alignment needs to be done. Without that, the pilot shaft can bind and cause the synchros to wear prematurely or even prevent the transmission from going into lower gears, especially reverse since that gear doesn't have a synchro.

Thanks.. I will check into it. The two days after I posted it went into reverse without issue. :what:

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matts156 is on the right track. I ran it by a Ford guy who helped me a ton with my powerstroke. He owns a ZF6 towtruck.

but. . .I wouldn't wanna perpetuate any rumours, without knowing it myself. :w2:
FYI: My ZF5 did the same thing if it hadn't come right down off high idle, when I first bought the truck.
Was the master cyl. I replaced it when I did the clutch. suddenly I had nice early engagement and no issues into reverse in the cold.