Transmission issue

Discussion in 'DIY Marinizing' started by crowsridge, Mar 30, 2012.

  1. crowsridge
    Joined: Apr 2010
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    Location: Eugene, Oregon

    crowsridge Senior Member

    Hello again!

    I was excited to be making headway on my drive system. Yesterday I went to the driveline shop where they were happy to help with an out of the ordinary project.

    But then! Apparently wanting to use one side of the transaxle wont work? They said it needs to have equal load on both sides? Or, some way to lock up the other side.

    Ideas and input would be greatly appreciated

    Thanks! Chris
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    What are you building and why? Transaxles are designed to have transverse engines, the opposite you usually need on a boat. Also, they don't have thrust bearings and a differential which causes huge power losses.
     
  3. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Yes, a automotive transaxle includes a differential to allow relative rotation between the two drive wheels. If you didn't, you would break the axles because the outside wheel has to rotate more than the inner wheel. See the follwing animations.... http://auto.howstuffworks.com/differential2.htm

    If you hold one of the output shafts fixed, the other will turn, but the pinion gears would wear out quickly because the are relatively small, highly loaded, and generally not designed to operate at high slip for long periods of time.
     
  4. crowsridge
    Joined: Apr 2010
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    Location: Eugene, Oregon

    crowsridge Senior Member

    It is a version of trimmable surface drive. I have a thrust bearing in line. Now Im working on the u joint section between the prop shaft/thrust bearing and the transmission.
     
  5. crowsridge
    Joined: Apr 2010
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    Location: Eugene, Oregon

    crowsridge Senior Member

    Hmmm. Guess I need to figure out what marine trans fits behind the vw diesel the. That sucks!

    Now the driveline guys did say there is a group that take these and insert/replace somethng in the transaxle the addresses the issue. I didnt know enough yet to understand it. Will research that modification.
     
  6. Frosty

    Frosty Previous Member

    Weld the diff together.

    The carrier bearings on the diff will take thrust very well as they are taper roller, but you will need a stop on the drive shaft, it will work and good Idea.

    Don't forget diff reduction --will be about 3 to 4 to one.

    Also any thrust you generate will transmit to the engine to the boat, you will need to address this.
     
  7. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    Another issue if one axle is fixed is that the opposite axle will turn twice as fast as it normally would at a given input RPM, effectively halving the gear ratio.
     
  8. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    The off road guys weld the spider gears to accomplish this. Doing it this way won't affect the gear ratio.
    Don't be the guy that welds the ring to the pinion gear!
     
  9. crowsridge
    Joined: Apr 2010
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    Location: Eugene, Oregon

    crowsridge Senior Member

    Frosty, Transaxle is the differential all in one as opposed to rear wheel drive separate, correct?. The motor sits in line with the prop shaft and I wanted to use one side of the axle. I have to use a LH prop, but thats okay. The way it sits, the trans is in the front and much lower than the top of the engine. I plan on the pilot chair in this spot. Its low, and can easilly reach tiller steer and enen the trolling motor if I can get it to go to plan:)

    The DL comes off the trans. Then double u joints with slip. This connects to the prop shaft in a flange thrust bearing. Im pretty sure this photo is from Tom Kane.
     

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  10. crowsridge
    Joined: Apr 2010
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    Location: Eugene, Oregon

    crowsridge Senior Member

    So would that make it 2 to one? Thats why I have the standard transmission first. I can play with the ratios. 4th gear is basically 1 to 1 so 3rd would be about the ratio for the SD. It will need tweaking, but its a starting point. So if half, 4th would be 2 to one?
     
  11. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    If one axle is fixed the output of a differential with 4.00:1 gearing (example; 15 tooth pinion and 60 tooth ring gear) will become 2.00:1 at the axle that is allowed to turn. As jehardiman said the differential will not stand this abuse for long. I wouldn't do it.
    When the spider gears are welded the ouput ratio is not affected. This avoids the problems of finding a way to immobilize one axle and burning up your spider gears.
    I have no experience with this sort of thing in marine applications, just off road rigs. Take this advise at your own risk.
    There are plenty of off road shops in your area that have experience with welded spider gears.
     
  12. crowsridge
    Joined: Apr 2010
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    Location: Eugene, Oregon

    crowsridge Senior Member

    So is the simple fix to weld the spider gears then? I can weld, but will have someone else do it:eek:
     
  13. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The simple fix is to get a marine transmission. A transaxle will put the weight of the engine to one side and make the boat list.
     
  14. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    Good point, gonzo. Depending on the boat some weight could be offset with batteries, machinery, ect.
    Crowsridge, tell us more about the boat!
     

  15. crowsridge
    Joined: Apr 2010
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    Location: Eugene, Oregon

    crowsridge Senior Member

    Milehog,

    It is a 20' long 7' wide military aluminum sled. Gonzo is right about the offset, but its not much, if any more than 8". Since its only 235lbs and it had an Olds 455 in it before, weight shouldnt be a problem.

    As you said, with the closed cooling equipment, seating configuration, battery and fuel placement I should be able to make up the balance issue. Just the placement of the trolling motor can make that up Im pretty sure.

    Gonzo, do you know what marine trans would fit this 82 vw diesel from a rabbit p/u?
     
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