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Discussion in 'Airheads' started by Box'a'bits, Oct 25, 2012.
Discuss. Not mine, so I won't be offended
Make it a heavy monolever. Nice. I'd have concerns about that weld pulling a chunk of the swingarm wall out the bottom as it definitely was not designed for that. How much that would help the u-joints, I don't think anybody can really say. I think the main problem facing those u-joints is that they don't run in an oil bath. That would solve all of it. Second, problem is the angles they're pushed to and this might reduce that a little bit. Overall though, I wouldn't do this to my own bike. I still think someone should try developing a sealed cv joint driveshaft for the paralever GSs. That application begs for a cv joint.
+1 - I also don't think the sidewall of the swingarm is set up to take the loads that the welded bracket is now applying to it. Quite a bush league set up in my view.
That's not a bad idea! Not sure if anything is small enough, but perhaps something from a really small car. I'll take a look at the CVs from my buddies Tercel/Paseo. What's the diameter of the available space on either end, and what's the distance it takes to get to the smaller diameter of the shaft (and what's that too while we're there)? How much distance is there for the larger diameter before it starts getting smaller? Anyone have a paralever driveshaft apart?
I have thought about doing that. This is probably been covered before, but the joint that usually fails ... is it the one connected to the final drive?
EDIT: Also ... you could add a longer tab to the swingarm so it would connect more of the swingarm ... but even then ... I'll bet the weight is not that bad ... it's aluminum.
It defeats the benefit of the paralever design, doesn't eliminate the U joints and likely weighs more than a monolever.
Why not just install a monolever swingarm ?
I bet these guys could do it:
Oh hell yeah! 68.35mm is their smallest? I bet that would work. And if it costs less than the $550 it costs for the fully rebuildable upgraded shaft, which I suspect it probably does (or even if it is slightly more), this would be a great deal! I smell a group buy. Although, I remain fairly skeptical that we can get the enormous amount of space needed for a CV joint inside a paralever housing.
The other cheap option to adapt would be an ATV CV axle. They're fairly small diameter and not very long. They're probably designed for similar torque too. A CV joint would handle sharper angles much better, run smoother also and might actually improve gas mileage a little bit.
1. Becasue it's 4"longer than a Monolever.
2. Monolever rear ends with a spoke wheel are uber rare. They only exist for the ST and G/S bikes and you know how expensive those are.
3. Many people are turned off of BMW Paralever Airheads due to them being prone to shaft failure. If this little trick solves that problem ... Then the only weakness of the paralever bikes is solved.
Just my opinion of course.
CV shafts wear and fail too .. typically about 95-125k miles for front wheel drive Honda, Nissan, etc.
as does any sealed bearings. after XX miles all bearings need maintenance. roller bearings that live in an oil bath gets continuous lube and typically will last life of vehicle.
this apply to all sorts of applications. for instance rear wheel bearings on a FJ-60 Landcruiser is bathed in oil and typically never need replacement.
CV joints themselves can last a VERY long time if they remain well sealed. It's typically the boot that fails around 100k, letting in all manner of contamination and from that point on the CV joint eats itself quite quickly. No it's not something you could fix quickly and easily on the side of the road, but if it used two off-the-shelf CV joints from a common car then a repair could be as close as the nearest NAPA.
You're right. The real solution would be an oil bath. The 1st gen paralevers were designed to run in an oil bath, but at some point immediately before release to the public they changed over to a dry swingarm. Plenty of publicity and sales photos of the bikes show drain and fill plugs on the swingarm. So does the parts fiche. The '88 and '89 paralevers still have the flat on the casting for the drain and fill plugs, but they never had the hole cut and threaded. It seems that the lower boot just wasn't up to the task for reliably keeping all that oil from dumping onto the rear wheel and represented too much of a liability.
...and here (#15,16):
Here's an 88/89 with the flat visible on the swingarm casting:
I'm intrigued by this idea, but let's start a new thread about it, this doesn't really pertain to the OP.
In regards to the OP, aren't you reinventing the wheel a bit. You could achieve the exact same thing with less weight by cutting off the entire control arm bracket and installing two bolts through the top and bottom of the housings, which would also keep pressure off of the comparably weaker middle of the housing. Probably would need some sort of spacer to run parrallel to the shaft and go in between the two housings to prevent torsional force from ripping out the bolts, but that could work actually. Like someone else mentioned though, you'd be obfuscating the point of the paralever design that keeps the suspension from compressing under hard accelleration, but it worked for the mono and all the chain driven bikes in the world, so why not if you're so inclined.
there was an airhead (oak i think) that had a prototype cv joint airhead driveshaft built for a gs years ago. i never heard the output of the testing but i gathered from a lack of feedback that it didn't go well.
my 88 and 94 swingarms both have the flat spot where the parts fiche shows the fill and drains for shaft oil.
Thanks all for your input. A good discussion. I am not intending to follow this example.
My question & curiousity arose because:
I came across this picture again, &;
I am thinking about a shortened torque arm as a means to raise the back end, to get some more ground clearance (following Redboots example).That won't happen yet though (a few other issues to address 1st)
Re the more extreme angles resulting from the potentially taller suspension, I am looking at the aftermarket driveshaft, & a higher maintenance schedule. The bearings / cruciform seem cheap enough to treat as consumables.
I had thought about a mono conversion, but the cost & hassle of that seem...
I had enough of them failed/failing BMW driveshafts.A few on my bench still....!:eek1 Yes the angle of operation is critical on them lasting longer. That's from the specialist up here, good driveshaft at 125,000(?) Kms on his personal GS. Do not crank up the preload too much he told me.
Don't know how "consumable" them repleacable U-joints are. Sure not cheap for that later driveshaft I just had rebuilt ,but yes cheaper than a new driveshaft that's for sure.So now I also can treat the U-joints as consumables but still will be greasing them up every year.
And from someone from Wanaka that was just up here, helped me set my suspension for that....angle of operation vs sag, no more than 16 Degree operation on any U-joint will make them last a lot longer. BTW 16 degree is pretty close to where BMW sets them on the newer bikes, altough I still have to measure my K-bike properly, me and the Kiwi got pretty close to that by eye only. Sorry can't measure the GS, all in pieces/boxes but for the bad driveshaft kicking around the bench somewhere with the other ones.:huh
I'd heard Oak's CV project didn't go well. I think there were a couple crashes or dramatic failures and the company designing them wasn't willing to invest more free energy into the project.
Something sure needs to be done about these things - and CV joints certainly seem like the better approach!
BTW, the first thing I saw in the OP's pic was the brake cable not attached and wondered what sort of solution that could be?
I sent an email to Oak about it. We'll see what he says.