Velvet Drive 71C slip in fwd below 1200 rpm

[Marko]

Anyone experience this issue? VD slip in fwd below 1100-1200 rpm:

Velvet Drive 71C slips (weak engage) below 1200 rpm when at normal op temp. No slip in reverse ever. No slip in fwd when cold. Slip is only below ~1200 rpm when at normal temp.

DexIII fluid is new, several changes/flushes, correct level (check hot immediately after shutoff). Cooler is 9” on port side stringer, new lines (correct inside diameter), 1981 318 single in a 261 (F26) w/ straight 1:1 drive. Tranny few years old, but did over heat couple years ago go before installed strainer for raw water cooling (fresh water seaweed clogged tranny cooler).

Have disconnected tranny Morse cable to shift by hand, same slip in fwd below 1200 rpm. Any suggestions before pull tranny at fall haul out?

[prowlersfish]

Slip below 1200? Does it suddenly engage when you are above? I would get a photo tach and compare the engine speed with the prop shaft speed. Make sure you us it on both the engine and the shaft, don't trust the dash tach.

I'm just wondering if it's something on the prop?

[Marko]

Thx! When cold (startup), no slip engaging fwd. As warms up to normal VD op temp (>140) slip begins slight slip below 1000 rpm. Just before normal VD op temp slip is intermittent about 1000 rpm (slip-engage-slip-engage), once at op temp slip is consistent not grab until about 1100-1200 rpm. Essentially, once VD at temp, consistent slip until 1200 rpm.

Good idea photo rpm compare since prop/shaft turns at slip but not enough to move boat noticeably.

[prowlersfish]

Interesting, I have seen the "in and out of gear" but it was due to low fluid level. I would assume it would not go away at high rpm but did not try. Have you checked the transmission temperature with a temperature gun? If its a lot higher, check the temperature of the fluid hoses going in and out.

[Marko]

Good call to check hose temps will do this weekend. Expect out to cooler same as VD, curious what return from cooler will be.