another cruise install question

[Fred W]

The spring is there, but only to force the vacuum cup out. The cable isn't pushed out byt the spring, though. The cable is free to slide into the servo unit, or you couldn't move the throttle with the cruise disengaged, or grab a little extra gas when it is engaged.

Not really. The whole point of the beaded chain is that the cable is free to flex around if you open the throttle further than the servo is calling for. In the opposite direction, when trying to close the throttle while the cruise is active you would actually be moving that diaphragm against the vacuum suction.

Eventually the servo senses the speed error and disengages, but it will allow you to pull against the vacuum pressure somewhat first. It's one of the downsides to having these cruise controls. If you lean on the twist grip while riding you can influence the speed outside what the CC is shooting for somewhat.

 

[rfulcher]

The spring is there, but only to force the vacuum cup out. The cable isn't pushed out byt the spring, though. The cable is free to slide into the servo unit, or you couldn't move the throttle with the cruise disengaged, or grab a little extra gas when it is engaged.

Not really. The whole point of the beaded chain is that the cable is free to flex around if you open the throttle further than the servo is calling for. In the opposite direction, when trying to close the throttle while the cruise is active you would actually be moving that diaphragm against the vacuum suction.

Eventually the servo senses the speed error and disengages, but it will allow you to pull against the vacuum pressure somewhat first. It's one of the downsides to having these cruise controls. If you lean on the twist grip while riding you can influence the speed outside what the CC is shooting for somewhat.

Oh cool I get to screw up a thread with tiny detail no one cares about. The ball chain and the cable sliding inside of the servo cable attachment both allow for the servo to only pull, they are actually redundent. There was actually an install on the old Concours 1000 site where the installer omitted the ball chain and depended only on the cable being pushed into the servo to allow for cable movement. It was a very clean install but I worried to much about cable binding to omit the ballchain.

 

[wfooshee]

True. Posting when sleepy.

But consider the generic-ness of the system, and think of an installation with less, or maybe even no bead chain at the throttle.

Basically, if the rider is operating the throttle the chain is slack and the cable is free to slide into the servo. (If there were any situation where the throttle tang could contact the cable, you want the cable free to move out of the way.)

When the cruise is operating the throttle the cable is tight. If the bead chain is too tight when the throttle is closed, the bike won't settle down to idle. If the bead chain is too slack, cruise engagement is delayed or even prevented.

 

[str8]

I can see clearly now.

When I ordered the kit from Murph's, I also ordered the vacuum cannister. I'm impressed with this unit. I has 2 ports and has an internal check valve (nice feature). The unit appears to have a Ford part number on it.

Here it is on the bike where I intend to put. The fit is *tight*, like it was made to go there. Changing the air filter will require a removal of the cannister. Not a big deal.

 

[fljab]

When I ordered the kit from Murph's, I also ordered the vacuum cannister. I'm impressed with this unit. I has 2 ports and has an internal check valve (nice feature). The unit appears to have a Ford part number on it.
Here it is on the bike where I intend to put. The fit is *tight*, like it was made to go there. Changing the air filter will require a removal of the cannister. Not a big deal.

If you're not too far into this - what is the Ford p/n? I made my own out of PVC and mounted it under the seat directly behind the servo.

My bike is different in that I have "a lot" of farkles including the AVCC (now on my 2nd servo); point being is I have a fairly large wiring harness going up that side past the air cleaner opening. Changing my air filter now is a exercise in patience to make sure everything is seated right and sealed. I can't imagine putting another obstruction in front of the a/f.

I've been going to take my old servo and do some surgery to see what's inside "just because" but haven't really had the extra garage time with all my projects backed up.

Good luck on the build! A real cruise is the way to go IMO; throttle locks are OK I guess and I have one for backup (good thing too after mine crapped out @ CFO last yr), but it's no replacement for a true cruise.

 

[Constant Mesh]

"The cable moves slowly, it does not snatch to where the device thinks it should be. It pulls a little, then a little more, then a little more, regardless of resistance or lack of resistance. It doesn't know when it actually starts moving the throttle, so if there's too much slack, it takes longer to get the throttle engaged."

I haven't tested this operating response but I'm a bit skeptical of how it operates when the cable is slack. I don't see any position feedback sensor which tells the servo's brain where the diaphragm is located in its range of movement.

If there's no tension on the cable it would seem that the diaphragm would move until the vacuum generated force equaled the cable tension force. It's hard to see how the diaphragm inches methodically along when there's no tension on the cable. There would have to be a position indicator in the loop to get that level of control.

You may be right about this but I'm skeptical.

 

[wfooshee]

Its ONLY feedback is engine speed. As for moving the cable, it pops the vacuum solenoid, checks what happened, pops it again, checks what happened, until either something does happen and it knows it has throttle control, or enough attempts go by and nothing happens, at which point it gives up and disengages.

It doesn't just hold open vacuum into the chamber until it sees a response. Such a response could be sudden, abrupt, and unmanageable. That "level of control" comes from bleeding vacuum a little bit at a time

The switches that set vehicle weight vs engine power adjust how much vacuum bleed happens during those cycles.

The statement that too much slack delays or inhibits engagement is not speculation. That's exactly how it acts. With proper chain slack (i.e. almost none) the engagement is effectively instantaneous. With too much slack, the bike will coast before the cruise has throttle control, which poeple describe as "it drops a couple of mph before pulling." They complain that it hunts speed after engaging, but what's actually happening is that it's not engaging at all until the slack is eventually pulled out.

 

[Constant Mesh]

You may be right but my cable has quite a bit of slack and there's no significant time lag in the start of servo control. With just one momentary opening of the vacuum control valve at start-up how can the servo know how far the diaphragm moved? It doesn't know anything except the engine speed versus the setpoint. The cable is verified taut only when the engine speed stops falling after servo start-up.

With one momentary opening of the vacuum valve the cable/diaphragm will move that distance where the forces are in equilibrium.

Obviously too much slack will limit the maximum opening of the throttle. But it's not apparent that different amounts of slack will appreciably affect how quickly servo control begins. It doesn't take much force to pull a slack cable.

 

[wfooshee]

There is no force feedback. It has no idea how much tension is on the cable. A little blip of vacuum doesn't move the diaphragm until it has throttle, it moves it enough to make up for the reduced pressure in the chamber. It has nothing to do with force, but with volume of air being bled off. Understand that it doesn't just dump vacuum into the chamber until it sees the throttle move. It hits it a little, then again, then again, then again, in short quick increments.

The switch settings can affect engagement, too. Some folks feel the engagement is a bit gentle, and will change from the high-hp-low-weight settings, which will increase the amount of pulse with each vacuum bleed.

I've been installing this unit on cars, and now bikes, since the late '70s. I'm not guessing about the slack thing. I know that's what it does because I've seen it numerous times, and the correction is always to reduce the slack present when throttle is at idle and cruise is disengaged.

 

[reaction57]

Any info to which way the arrows go on the check valves? Toward motor or away?

 

[mcatrophy]

Any info to which way the arrows go on the check valves? Toward motor or away?

Try sucking (or blowing) in one of its orifices. It will go one way, not the other. You need air to be able to flow TO the engine FROM the actuator.
I'd guess the arrow points to the engine, but I'm not sure. The suck/blow will guarantee correct orientation.

 

[Fred W]

Yes, arrow shows direction of flow. You want that to point at the engine.