Jackshaft disc brake??

Dulcijo said:
My jackshaft brake is very sensitive and it would work great but I have a spring loaded chain tensioner and it puts great stress on the chain tensioner.
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Ditch the chain tensioner. I don't understand how the j/s brake could put any stress on the chain tensioner at all?
 
Normally when the bike is pulling it tightens the opposite side of the chain from the chain tensioner but when you brake it pulls the spring loaded chain tensioner side tight.
 
Those tensioners are a joke, I thought it might have been better myself and got one. During it's short period of use it would collapse when trying to start the bike (2 stroke) and also would jam up. Plus they really don't hold much tension in the first place. On another note though the chain would grind out the inside bolt on the tensioner pivot point causing imminent failure. I'm past that and 2 strokes. Had some bad luck with 2 stroke motor's and was lucky to get 28mi before loosing all compression and eating up the rings during break in!!! So over it.
 
All spring loaded tensioners do that when the spring is too weak. Had the same problem with my spring loaded tensiomer on my last build. I personally think if you are going to run one, the chain needs to be as short as it can be first, then the spring loaded tensioner needs a very stiff spring and set only to where it allows the proper amount of slack in the chain, no more and no less.
 
wret said:
Seems to me that a jack-shaft brake and a chain tensioner are incompatible.
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This is another way of looking at it that is opposite of what it seems.....

jack-shaft brake:



chain tensioner:



on the primary chain.
 
Ahhhh, but there would be no tension applied to the primary chain during braking. And if all tensioners were mounted as solidly as yours appears to be, it might withstand the stress.

The rear tensionsers I've seen are not designed to do much more than hold up the weight of the chain not the force of braking.
 
Great thread. I'll be working on a disc brake setup soon. I will be doing a jackshaft plate (Gasbike.net unit) brake or a rear disc/sprocket sandwich combo type.
 
wret said:
Ahhhh, but there would be no tension applied to the primary chain during braking. And if all tensioners were mounted as solidly as yours appears to be, it might withstand the stress.

The rear tensionsers I've seen are not designed to do much more than hold up the weight of the chain not the force of braking.
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I agree.
Tensioners are meant for the return side of a chain force side.
If force can be exerted in both directions (power and braking) you want your chain tight without one.
 
My build (from scratch-frame fabracation) so far has no tensioner. I dont wven think I need one for the motor drive chain. Im running the jackshaft billet plate type from Gasbike.net. I have that motor chain pulled tight. Side note: My pedal chain, which is a custom design has no slack so it worked out evenly. You guys know what Im saying?

Im talking about the issue of the two chains never tightning equally and requires at least one tensioner. Im guessing in my situation I can use a heavy fixed tensioner on the drive chain, but only as a guide, not a slack tensioner. Its the slack in the chain that promotes the stress on the tensioner (with jack shaft brake setup).

The less slack, the less stress on the tensioner, which gives a better function of the jackshaft brake as well. If your running disc brakes we all probably would be better off putting the slack on the pedal side with a tensioner there setup with a freewhee (no coaster brake)l.

Then use a tensioner on the drive chain side as well "only" to keep the chain from bouncing up and down and act as a guide, not for elimating slack. Kind of like a real motorcycle. Im aware some of you have this figured out already, Im just trying to put it out there again so maybe someone can benefit from saying it here in a restated way or add some ideas. everybodys build varies as we all know.
 
I think its important that people know that if your doing a jackshaft brake, a tensioner isnt really supposed to be there Unless its a structured guide type. The ones on the market arent designed for that so you got to get crafty.
 
Where do I get the mini hub with holes for disc? Thinking about drill and tap on existing jack shaft mini hubs. Would also need a spacer to keep disc off chain.
js-assembly_480x480.gif ----------> jackdisc.jpg ?

Maybe a mini hub disc between plate and final output gear.
DiscAdapter.jpg
 
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