Overheating transmissions

By Chris, Hale Marine · 40+ years rebuilding Velvet Drive and ZF transmissions

Short answer: Overheating leaves signs: bluing, burnt or welded clutch plates, graphite in the clutch drum, a melted baffle, a brittle washer. If a cast-iron Velvet Drive overheats, disassemble it and check the baffle.

1018-106 1.88 lots of problems

What Chris sees on the bench

The case and ring gear clutch assembly getting a little blue, and clutch plates starting to show overheating, on a transmission that was over-torqued.
In severe cases, clutch pack plates welded together.
Graphite material building up inside the clutch drum, and an overheated clutch hub with teeth marks and discoloration.
A melted baffle in a cast-iron 1018 with the 1.88 gears.
A phenolic or plastic washer that's gone brittle. If it was overheated, it'll snap.
On a 5000, an overheated drum and clutch carrier and burnt-out clutch plates. Usually when things overheat, the thrust washer goes brittle, but on that one it still had a lot of pliability to it.
A 1017-008 with the forward and reverse clutches, steels and pressure plates all burnt. Chris said he hadn't seen steels burnt like that in a long time.

What causes it

Here's what Chris has pointed to in the videos:

Running it too hard. The plastic baffles will melt and goo will go everywhere if you run it too hard.
Water in the fluid. The strawberry milkshake makes a thick goo in the sump that makes the pump work harder and the transmission overheat.
The 2.10:1 design. Nothing binds the reverse planetary to the case, so it generates a lot of heat.
Running reverse for forward. On the cast-iron units it smokes the planetaries.
An impact or a high-speed shift. On one ZF63IV where the owner overheated the clutches, that's what Chris wondered about.

Fix and prevention

If a cast-iron transmission overheats, take it apart and check for a melted baffle instead of just running it again. On the ZF 63s and 80s, pretty much that whole family, look inside the clutch drum. The clutch plates will cut grooves in the drum itself, and grease marks on the drum show you where that's headed.

When to call

If your transmission has overheated, call (804) 333-3677, Monday through Friday 9 to 3 Eastern, or email sales@halemarine.com.