Transmission Rebuild

[csuggs]

Here I'm starting yet another service and repair thread for my beloved Sunsport. :(

Ever since I broke the flexplate (damper plate - see my thread titled "transmission failure"), I've been chasing a vibration in the drive line. I removed the new prop shaft and found that there's a "rub" mark on half of the shaft where it goes through the stern tube or shaft log. There's a mating "rub" mark on the i.d. of the stern tube. So I checked the shaft to be sure that it's straight using about 5 dial indicators all down the shaft. The shaft is only out .001" at one location. Next I measured the output flange from the transmission to find that the face of it is out .0035" and the outer edge is out .005". Then I removed the output flange and measured the output shaft and found the culprit. The output shaft itself is out .005" causing a "wobble" effect on the shaft. So now a transmission rebuild is in order . . .

I will document with pics as I go.

Rub marks on the prop shaft.

http://i887.photobucket.com/albums/ac71/csuggs/DSC03021.jpg

http://i887.photobucket.com/albums/ac71/csuggs/DSC03024.jpg

Looking into the shaft log from inside the boat

http://i887.photobucket.com/albums/ac71/csuggs/DSC03014.jpg

[csuggs]

Close-up of rub marks at back end of shaft log or stern tube.

http://i887.photobucket.com/albums/ac71/csuggs/DSC03019.jpg

http://i887.photobucket.com/albums/ac71/csuggs/DSC03006.jpg

http://i887.photobucket.com/albums/ac71/csuggs/DSC03008.jpg

[Okie Boarder]

Bummer! Does it seem like there was a misalignment at the strut or just the shaft log? Are you going to do the rebuild yourself?

[csuggs]

The only place the shaft was rubbing anything was at the shaft log, but not all the time - that's the really weird thing. The really bad vibration seems to come and go, and is worse under higher rpms and heavier loads. I would have sworn the shaft was bent because the rub mark is only around half of the shaft, but not according to the gauges . . .

[Sluggo]

Is is possible the shaft has weakened over time and is flexing under load? Not sure how that would happen with this type of material without a visable crack or fracture, but just throwing it out there.

[csuggs]

Sluggo - that thought crossed my mind. But if the shaft was flexing under load, then the rub mark should go all the way around the shaft, not just half-way. That's why I would have sworn the shaft is bent. Also, the shaft is new, only run about 2 hours. With the output shaft of the tranny being out .005", I gotta believe that's my problem.

[Okie Boarder]

If you want some good information on the transmission, there's a guy that does it for a living on one of the other forums I'm on that I could put you in touch with.

Have you bounced this off Supra or Jim?

[csuggs]

If you want some good information on the transmission, there's a guy that does it for a living on one of the other forums I'm on that I could put you in touch with.

Have you bounced this off Supra or Jim?

Okie - I'm always up for ideas and would welcome input from an experienced transmission guy. I talk to Jim frequently and when I called him yesterday, he happened to be at a marine show of some sort in Louisville so he was going to talk to some tech guys at the show about my problem. A simple trans rebuild doesn't scare me, but my concern is that if my output shaft is bent in some way, then are the pinion gears and carrier also fouled-up? If so, I might be getting into more money than I want to spend on a rebuild. A new trans with warranty is $1600 and a reman is $1400 (no reason to buy a rebuild in my opinion); my general rule of thumb is that if I'm going to have to spend more than 50% of a new part to rebuild the original, then I'll seriously consider the new part. At this point I don't the price of the parts so I need to do some research. I know that I can get a rebuild kit with seals and clutches for around $300.

[Okie Boarder]

Clint,

Sent ya a PM with his contact info.

[csuggs]

Got the motor and transmission out of the boat on Saturday. I washed the boat and cleaned the interior and put it away for the winter in the garage. The engine and trans are mounted to a couple of 4x's on the floor of the garage. I will probably start taking the transmission apart soon so that I can get parts ordered. Not sure yet if I'll do anything with the motor - I mean my philosophy is usually "if it ain't broke, leave it alone". On the other hand, I have a good buddy that builds and drag races Fords, so he's after me to let him "tinker" with my 351 over the winter. The stock trans is only good for 310HP so there's not much I can do with the motor unless I also change to a heavier transmission. Hmmmm . . . . .

[csuggs]

The motor and transmission have been out for a couple of weeks. Today I picked up an engine stand, and this weekend I will seperate the motor and trans, then mount the engine on the stand and finish winterizing it. Also, I will start taking the transmission apart - with pics.

[csuggs]

Gonna disassemble the tranny this weekend. I will post pics and document as best I can . . .

[csuggs]

Clint,
If the 351 was rated at 245 hp and the tranny at 310 hp, then wouldn't you have some room for increased hp in the motor? What would your friend do to better the output? New heads? New manifold? You could always put a big block in it?
Well, I think it sux you have to go through all this after your major re-do. Was it improper alignment or something internal to the tranny?
Best of future luck to ya.

I don't know for sure when the problem started. It became an issue last August when the flex plate broke. When I replaced it, I thought I could improve the alignment, and maybe I made it worse. I don't know . . . I just had a vibration that I couldn't seem to make go away and I chased it all the way down to the output shaft on the tranny. In all honesty though, the vibration may have been there for years and I never noticed it so much because my stringers were wet, thereby absorbing vibrations. Now since they are rigid again, the vibration is noticed.
I hope I can find something wrong in the trans. . . .
Oh yeah - we could bump the HP a little and still be ok. Maybe 50hp

[csuggs]

I have run nothing but a 13x13 which is the oem prop. I have tried 3-blade and 4-blade, but I have never had anything new, just refurbished. I think I am going to purchase a 3-blade ACME CNC prop this spring.

I talked to a guy in Cleveland yesterday that came highly recommended as a Velvet Drive "specialist" and I think he has talked me out of rebuilding the transmission for now. He tells me (and I've heard others say this as well) that the 71C is pretty rugged and it will usually either work or not work, and that he has never seen a driveline vibration that was caused by the tranny. My transmission shifts in and out just fine, no slippage and the oil smells and looks good. So I think that I'm going to concentrate on the vibration possibilities beginning at the other end of the shaft, with the prop. I already have a new prop shaft and coupling, along with new strut bearings. So I think a new prop is in order and a really good alignment to go with . . then we shall see!

In the meantime, since I've got the motor out we are going to remove the oil pan and inspect the bearings, etc. Maybe replace the oil pump while we're in there. That way when the motor is back in the boat, the bottom-end is good to go and if I have any trouble down the road it should be on the top-end - which I can access with the motor installed. So that's the plan. :smile:

[TitanTn]

Very nice. You're not scared to jump in there and do it right. I'll be curious to hear if this solves your vibration issue.