Velvet Drive Clunking when shifting into gear

"Hello All,

This past weeke

"Hello All,

This past weekend I was crusing at 3100 RPMs and both engines were knocked out of gear breifly and then back into gear. Now, my starboard side transmission makes a pretty good "clunk sound" when it is shifted into forward or reverse. It seems to run fine when after the clunk, but the clunk has me very nervous. Any thoughts on what may be wrong or how to trouble shoot?"

"As you probably know by now,

"As you probably know by now, that was bad. For the record, the best technique to my knowledge is to bring the throttles back to idle, let the props return to a stop and then reengage the transmissions. I'll be the first to admit that is not the instintive thing to do. Your brain says you need to return it to where it was and your hands instinctively shove the levers back into gear.

Several things might have gone wrong, some of them not so bad.

1. The drive coupling bolts were a little loose and now they are bent/stretched/broken. Look at the couplings and see that they are tight and not damaged.

2. The flex plate between the engine and transmission is broken. These last up to 5000 hours under normal conditions, less if the trans is shifted at higher RPM. A brief description of the flex plate is an outer metal plate bolted to the flywheel and an inner metal plate connected by splines to the transmission. The two plates are connected by a number of springs which absorb the shock of going into gear. When these wear out they normally make a lot of grinding noises as the pieces of spring get caught between the flywheel and the bell housing. The shock of going back into gear at speed may have broken this plate. (my #1 guess) The broken plate may continue to work for days or months. Or it may lock up and stop the engine tomorrow.

3. A crack or break inside the transmission. If you see no leaks, or cracks on the outside of the trans you're probably ok on this one. You should take a good look though.

This is not a complete comprehensive list of everything that may have been damaged, but it's a start.
K"

I vote for Fred's #2. Insp

I vote for Fred's #2. Inspection is the only diagnosis I know of. some installs have inspection plates but using them is impossible in some installations. It is possible one or more springs broke and the clunk is the "pins" (that provide a link between the two 'parts' of the plate) hitting their stops. You want this fixed ASAP as any broken pieces in the area of rotating metal is not good.

another possibility is that you glazed the forward clutch pack. this results in an 'all-or-nothing' engagement of the gear and the resulting thwack.

Thanks guys. I will get up th

Thanks guys. I will get up there this weekend and have a look at the couplings.

How difficult is it to change the flex plate? How available are they?

Is the flex plate something a guy with slightly better than average mechanical ability and knowledge can change on his own?

"Answer to first question - ho

"Answer to first question - how accessible is your gear? it's within your capabilities...The hardest part is just getting to everything. You need to block up the engine and remove the gear (you can set it in the bilge if dry). Once out out the way, the flywheel cover comes off & the flex plate is readily accessible. The plates are readily available and some transmission shops have them, too.

I'd encourage an air compressor and some impact tools and if you're not in Maine, a large portable fan. Once done, verifying the engine alignment is the last item."

"If I decided to have a mechan

"If I decided to have a mechanic in the town where I keep the boat change the flex plate, what would you guys say would be a reasonable price range?

I guess I am trying to decide if I want to take vacation and go up there and do it myself or just pay someone to take care of it and save my vacation for play time.

Thanks again for everyone being so helpful and willing to take the time to give me advice. My hat is off to this site and the experts who cruise it and help guys out."

"depends upon how accessible t

"depends upon how accessible things are- if the engine/gear is out, its about an hour. If you have a day cruiser with 'open' engine compartments, shouldn't take more than a day. If you have them under the cabin floor with no 'head space', it could be a couple days.

I'd suggest calling a few locoal shops and see what they want. If its real old and you snap a couple fasteners, it will add up quick.

If you are inclined to do it, you should be able to get it done in a weekend, worst case."

"The proper name for the flex

"The proper name for the flex plate is "Vibration Dampener" It absorbs the shock when shifting and is also the spline that is bolted to the fly wheel for the Borg Warner to engage. Removing it always means pulling the gear box. Support the engine before removing it as letting it drop to bilge can damage the forward engine mounts and will make it difficult to reassemble. Since the gear box will be out anyway have it serviced. I have seen internal damage at the same time as a damaged dampener from a high rev shift. If you do not have it serviced you may be paying for its removal twice. The Borg Warner C71 or C72 weigh about 155lbs., so you do not want to mess with it twice. Good luck"

"Here is a picture of the plat

"Here is a picture of the plate. Also a link to the rebuild, parts, pdf which is quite useful. Hope this helps.
Cal
www.marineryachts.com/borg_manual.pdf
Damper plate

"I was going to give you a blo

"I was going to give you a blow by blow for changing the "drive damper" (Lehmans official name)for a trawler style boat. Then I reread and saw you were at 3100 rpm and it became obvious that if you had a Lehman at 3100 you had more problems than just a flex plate.

If you decide to do it yourself here are some tips. I've done this in both my 40' Puget Trawler and in my 36' Chris Craft. Both took about 3 hours with hand tools. Depending on your age, your back will heal in 3-4 weeks. ;-)

If the damper springs are shattered and in pieces you should take the flywheel out and make sure to clean behind it. On the lehman the flywheel weighs 87 pounds, it's a bitch to get back on. Buy some longer bolts, cut off the heads and use two of them to align the flywheel going back on.

The same thing can be done for getting the transmission back into the plate and onto the bell housing (transmission adapter).

Hanging the transmission from a cross beam makes it much easier to handle. 4x4 across floor beams, window sills or boat sides, as appropriate for your situation. A small come-a-long or even a twisted rope will work for lifting/holding.

Shop around for the plate. A transmission repair shop, or large marine parts store will have much better prices than West Marine or the like. Under $100 is pretty decent.

If you're pretty handy with tools it is easily within your ability to change. As mentioned by someone above, air tools are worth the hassle of bringing a compressor close to the boat. Especially the flywheel bolts are pretty hard to do by hand. (use a 6 point socket)

Good luck and don't be afraid to tackle it yourself.

k"

"Jim - all I can add to the gr

"Jim - all I can add to the great info above is one last tip. On most all V-8's, supporting the engine is pretty easy to with wood blocks between the stringers and the exhaust manifolds. A 2-ton hydraulic bottle jack is also handy to have around. I had one job where the stringer tops were rounded beasts. Wound up with a pair of big C-clamps holding 2x4's to each side to get some flat areas for the blocks."

I can't thank you guys eno

I can't thank you guys enough for all the helpful info. I still haven't decided if I am going to try myself but it isn't from a lack of very helpful information from you guys! I'll post when I get it straightened out and let you know how things went. Thanks again!

"Believe it or not there doesn

"Believe it or not there doesn't appear to be any damage to the transmission, the dampener, the drive shaft or the prop. Unrelated to the violent shift episode, the boat wasn't idling down into the 600 to 700 RPM range because of problems in the distributor. I didn't realize the RPMs were up around 1000 when I was shifting and that was causing the clunking. We fixed that and now the velvet drive shifts in and out of forward and reverse as quietly as it ever did. All that worry for nothing. It is odd that the timing came so soon after my major shifting mistake. Thanks again to all of those who posted to advise. I learned alot, even though I was looking at the wrong problem.

Jim"

"Glad to hear it was so easy.

"Glad to hear it was so easy. So easy in fact, none of us thought to question you on engine speed when shifting.

Happy cruising,"

"glad to hear you got an easy

"glad to hear you got an easy 'fix'.

Did you go out an run the boat normally? How did she behave, beyond the normal shifting?"

"Mark,

I did take her out a

"Mark,

I did take her out and stretch her legs up to 3200 RPMs. She was top notch. Ran smooth and perfect. I was smiling ear to ear as I pulled back into the harbor on my way to her slip. No problems as far as I can tell."

Jim - glad to hear she's w

Jim - glad to hear she's working right throughout the RPM range.....now give her some fresh oil so she stays that way the rest of the season.