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Jim Kelly
 
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Default B-W Velvet Drive clunking

There are no U-joints, bleed holes or built in delays.

When you move the selector to forward or reverse, the spool valve directs the
fluid to the proper clutch. There should be at least 120 PSI present at the
spool valve in all selector positions. The internal pump is actually capable of
much higher pressure but it is regulated by a relief valve built into the end of
the spool valve. The relief valve directs fluid to the heat exchanger. There
are test ports for checking the pressure. Remove the 3/8 plug on the top of the
case next to the port leading out to the heat exchanger. Warm and idling you
should read at least 120 PSI in all selector positions.

To check reverse pressure, there is a smaller plug either next to the 3/8 plug
or on the front adapter on the top of the case depending on the vintage (some
models have both plugs in which case you can use either). Warm and idling in
reverse, you should again read a minimum of 120 PSI. This verifies that the
reverse clutches in the front of the transmission are receiving full apply
pressure.

There is no separate test port for forward apply pressure since the hydraulic
circuit for forward is through the center of the shafts and not the case as it
is in reverse. If you have the specified pressure at the 3/8 test port while in
forward, it is pretty safe to assume that the forward clutches are receiving
full apply pressure due to the design of the circuit.

"Charles T. Low" wrote:

I've had my 1978 Trojan 26 for three seasons now, and can't for the life of
me decide for sure whether the transmission has always done this or not. My
mechanic thinks it's OK. The AT lubricant is full and looks crystal clear to
the naked eye, and I do change it (rarely). It's a Borg-Warner Velvet Drive,
original with the boat, to my knowledge.

When put into gear, there is a slight pause, a fraction of a second only,
but easily visible that the prop tranny/shaft does not start turning
immediately - then it catches and away it goes. (Idling just above 600 rpm
indicated.) It does so with a very soft audible clunk, and I seem to
remember it being noiseless when "new" (to me).

I have shifted it into gear at above idle speed, very infrequently, count on
one hand, etc., because I'm kind of clumsy. Other than that, I can't think
of anything that might be considered abusive.

It is still so much smoother than the Bravo II I/O I used to own, which
itself was so much smoother than the Alpha 1 before that. Passengers have
never noticed or commented - it's quite a subtle clunk. I think I may just
be listening too hard.

What is normal behaviour for these transmissions? Thanks.

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Charles T. Low
- remove "UN"
www.boatdocking.com/BDPhoto.html - Photo Contest
www.boatdocking.com
www.ctlow.ca/Trojan26 - my boat

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