ZF68 & ZF80 Series
By Chris, Hale Marine · 40+ years rebuilding Velvet Drive and ZF transmissionsChris thinks ZF increased the pressure on the 630s over time, and now they're the ZF68. Basically, they haven't really changed the inside. The ZF80 is the HSW800, built in both A (in-line) and IV (V-drive) versions. We've had the ZF68IV in 1.6:1 and 2.0:1, the ZF80IV in 1.6:1, and the ZF80A in 2.1:1.
ZF68: same disassembly approach as the ZF63
To tear one down you'll need a 24mm socket and a 3-jaw puller. Chris drills a little hole in the bolt that holds the spacer and coupling in place, and uses it with the puller. That makes pulling the coupling off nice and easy, and you're not getting it off without a 3-jaw puller. On a matching pair of units he opened, both sets of clutches were wiped out, and his guess was the filter had never been changed.
Low pressure isn't always the filter. A ZF68IV came in with a tag saying it was a relatively new model, but it was only reading about 100 psi in every position, even neutral. The filter and O-rings had been replaced in hopes of curing it, and it didn't. A new pump assembly for these is a real expense. Chris also points out that the vent style is a hint to how old a ZF is, even without a tag. That one had the latest style vent ZF is using.
ZF80: what we've found
With the V-drive versions, the shaft comes through the whole transmission, so on the test stand we have to crawl underneath to take a look. On one ZF80IV, the pump key got smushed and burnt, which locked up the pump. And on a ZF80 input shaft, Chris found what looked like silicone inside the transmission. It wasn't. ZF uses plastic cages around the needle bearings that ride inside the clutch drum, and that owner had overheated it enough to melt the cage and liquefy it.
