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PostPosted: August 28, 2016, 9:24 pm 
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Location: No. Nevada
The BEC build keeps annoying me to figure out the details.
Fairly well determined to use an FJR1300 but want to center it in the chassis more than the shaft drive wants to make easy.
So now thinking to make my own off-set diff carrier with one longer axle to make the drive axles the same length.

Want to use a small - light readily available and hopefully inexpensive IRS center section/R&P that will handle the FJR1300 HP/Torque.
Would like to have several ratios available, may as well also ask that it be easy to change ratios.
Thinking I may have to create my own carrier housing?

Suggestions?

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PostPosted: August 28, 2016, 10:32 pm 
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You can use a CV joint in the driveshaft.

What kind of rear drive? independant or straight axle?

There are lots of choices either way.

Look first at torque loads and packaging (LSD?)
Weight and rotational mass are next.
I have seen Unequal length axles cause breakage issues in dwarf cars.

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PostPosted: August 29, 2016, 12:10 am 
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IRS.
Equal length axles,
unequal length stub-axles.
Need the unequal length stubs to help center the engine.
Want the engine as far forward as possible so the drive-shaft will be very short, which limits the angle.
Want to eliminate the VW trans and axles entirely.

UPDATE:
This might do it for me, particularly if I can just shorten the long side the same distance as the FJR1300 offset?
7.5" ring gear puts it in between Nissan (Datsun) R180 and R200.
The IFS diff in 85-95 Toyota 4X4 pickup and Four-Runner.
It has one short stub axle and one longer one.
For a narrow diff simply mill the side with longer stub 6mm and use same seal as short stub side.
Plug in another short stub and you have a compact narrow,strong IRS unit. I don't know if the 6 bolt pattern is the same as Nissan R200 and R230.
You could use the same type adapter to VW type 2 or Porsche 930 CV.
Very common and cheap in junkyards.
79-95 2WD rear 7.5" straight axles had ratios of 3.15 and 3.36(rare) 3.42 and 3.58 (more common) 3.73,3.91 and 4.10(most common).
Tru-trac Torsen type or 4X4 lockers are available for this diff.

Remembered this from another forum, old post so it was hard to find.
This may help with other BEC's since you could also us it for a middy with the bike trans.
Just flip it to get the rotation you need.
Lets see if I can post a pic of this Toyota part.

Image

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PostPosted: October 16, 2016, 10:06 am 
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The long side could be shortened, at extra cost, but would still be slightly longer. Maybe you could find 2 if you want neither side to be longer than the other.


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PostPosted: October 16, 2016, 2:02 pm 
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Minor machining allows two short axles.
Bike engine probably needs something in between since the engine power output will be off-set to one side or the other.

Post I found this on said they are easy to find but I've not seen any available yet.

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PostPosted: October 16, 2016, 7:59 pm 
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What, you can't find an IFS 4-Runner front diff assembly? How much would you pay for one, not including shipping?


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PostPosted: October 17, 2016, 3:03 am 
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Not a lot for an experiment.
Only cheap source around here is Pick N Pull, none there so far but I need to look more often.

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PostPosted: October 26, 2016, 12:58 pm 
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Other than footwell room, there's no problem with running the driveshaft at an angle front to back. The U-joints don't care.


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PostPosted: October 26, 2016, 8:32 pm 
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Probably should have made it clear that I am building a REAR engine BEC.
So I have pending issues that are rarely addressed here.

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PostPosted: February 21, 2017, 3:23 pm 
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OK, I got two 4Runner diff's at the P&P half-price sale on Sunday.
Should have reviewed my information as both have the ADD I do not need.
Does not matter if I am converting to two short axles but adds extra weight and complexity if I am leaving the long side intact.
So kind of looking for a non ADD long side to swap out.

The GOOD news is that with actual parts in hand it appears this IS the answer for a rear mounted FJR1300 engine!

The FJR output ends up on the right, the diff input is off-set to the right, so the diff assembly and engine both end up very close to centered.
Drive axles will be fairly short with a 50" track but since they use CV's and travel will be limited on a light road car I see no issue.
The 'Reverse" rotation FJR drive is corrected via the 4Runner FRONT axle, the R&P will have the thrust to the correct side of the gears. :mrgreen:

Not sure about the 4.10 ratio but that can be changed if truly necessary.
No need for the car trans so weight will be saved where it really should be minimal.
Never found a true weight for an FJR1300 but I think it should be comparable to the original VW, or even less.

Small but critical progress! :cheers:

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