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View Full Version : Velvet Drive 71C Transmission Issue


PolarBear
05-29-2009, 08:44 PM
End of last summer my wife was trying to pull me up and it felt like the boat had no power. So I let go (knowing something wasn't right) and got back in the boat. I took it for a spin with no skier and it felt ok. I assumed the transmission slipped. Checked the tranny fluid and it looked like the picture below. On the left is new fluid, right is fluid I took out. Can I safely assume I burned some plates in the tranny?

Another symptom: Before this happened, my boat always went forward (1-2) mph even in nuetral. It had always done this in the 3 years I owned the boat so I figured it was normal. Read in a different thread that can be a sign the transmission plates are burnished.

One last note: First time I took the boat out after purchase, I forgot the darn plug and water got into the bilge. I didn't know it, but water leaked into the tranny through the dipstick and I drove it for a couple hours that day without knowing it got in there. Flushed it thoroughly 4-5 times but might have done damage? Not sure.

Do I even need to bother to check the pressure or are all signs pointing toward a rebuild? Boat, engine, tranny is only a 2001 but I don't know what it was driven like before me. Thoughts?

FlatBoard
05-29-2009, 11:56 PM
I am sure that someone will be along soon. Try doing a thread search for some info.

CantRepeat
05-30-2009, 09:49 AM
I did a rebuild on my 71C myself. With just a press and some feeler gauges you can do the same. There is a good file on the web about doing them.

Yours seems like it's ready now. Does the fluid smell burnt? There are only a few things in the 71C that can go bad. The clutch friction discs, the metal discs that go inbetween the friction disc, and then the seals in the front pump.

In short, fluid that dark that smells burnt is a clear sign the transmission needs a rebuild.

PolarBear
05-30-2009, 01:10 PM
Thanks 92Mstr. Let's put it this way, it didn't smell like new transmission fluid so yeah it probably smelt a bit burnt. I took the picture last fall and can't remember the exact smell. I've got a coworker who has rebuilt ford truck transmissions and he said he has all the tools. I've read just about every single thread ever written on the subject so I know a lot of the good tips already. I also downloaded a 1994 service manual which looks just like the current ones for sale. Can we just follow that and it will have all the necessary info? Any last words of wisdom?

Minny PolarBear

Bellinghamster
06-01-2009, 10:45 AM
Make sure you pay extra attention to the clutch pack retention snap rings - they have a tiny bevel on one side. If you put them in backwards they'll look right but later pop out of the groove, making it possible to have the transmission in forward and reverse at the same time (don't ask how I know that...).

Other than that, replacing the clutch disks is pretty straightforward and doesn't require any overly special tools or skills. You've already replaced the fluid to flush the gunk out. There will probably be more gunk settled/caked in the bottom of the case that'll need wiping/cleaning out. I recommend replacing at least the input and output seals, as well as all o-rings and gaskets you disturb.

The cause of the burned clutch in the first place is the biggest concern. Those BW trannys are really stout, and shouldn't slip unless you're pushing >400 hp and loads of torque. Shift lever not fully reaching the detents is the easy thing to check - it should reach the detent position in both forward and reverse - if not, use a shorter arm hole position (on the tranny, or a longer one on the throttle/shift control). If it was properly adjusted, then you probably lost oil pressure somewhere, most likely spot is one of the o-rings on the "piston" that compresses the clutch plates.

I've got a PDF'd service manual (early 80s) for 71C's. Let me know if you need it "for reference."

I think creeping in neutral is pretty normal. How full was the bilge with water? Water in oil usually looks milky, so unless you changed the oil after the bilge washing, I don't think you got any in the transmission.

CantRepeat
06-01-2009, 12:20 PM
My 71C never did creep either before or after the rebuild I did.

Once my tranny started to slip I changed out the fuild that day. It lasted another 5 or 6 years before I did the rebuild.

The only really special tool I need I made. It was a 5.25 inch tall metal ring used to mount the rear bearing in my press.

PolarBear
06-01-2009, 11:32 PM
My bilge was totally full of water, I mean totally. I'm sure I got water on my starter, because that had to be replaced the next spring (2007), the steering cable is super tight too, so I supposed water got up in there and is now rusting so I'm going to replace that this spring.

I started my boat in the driveway on Saturday and let the boat get up to temp, the prop was spinning as fast as the engine. I then checked the fluid and it was at least 5 notches low. I've been checking it cold every year I've flushed it and didn't fill it properly. Now that I've read all the info here, it is a big no brainer how to check. I've probably ran the fluid low the last 3 years. Guessing that could have done it too? Take a look at my other thread, I've got the transmission off and now I have pictures of the dampner plate. It looks rusty, wondering what to do.