Secondary Actuators, Upside down or Not

[A26B]

Ideally, if the actuator arm was a rod, connected straight through the center of the diaphram and perfectly aligned with the linkage bellcrank, then there would be no controversy, but it's not.

As it is, the actuator arm is an "L" bar and the linkage arm is offset from its connection at the center of the diaphram. when the actuator arm is aligned with the bellcrank, the center of the actuator diaphram is not aligned. As such, the pull is angular when vacuum is applied to the actuator.

As Bearly Flying observed, when the arm is "angled" to the bellcrank, the center of the actuator diaphram is in alignment and the pull is straight when vacuum is applied to the actuator.

When the actuator is installed with the linkage arm "straight," you can see the diaphram move angular in the housing as vacuum is applied. This is evidenced by the need to grind & remove metal from the arm to clear the actuator housing when vacuum is applied.

Scott, Your analysis would be correct IF the linkage arm fitment to the bellcrank shaft was such that it forced the arm to remain perpendicular to the bellcrank attachment pin. It is not however, as it fits loosely enough that it works more like a flexible ball chain than a connecting rod.

On my 60K mile 94, I tested the actuators as they were installed "angular" and reversed "straight." "Angular" operated smoothly and quickly, "straight" was jerky & took slightly more vacuum to open fully.

I consider Gorden Killebrew a good friend and a true genius on the C4 Corvette from bumper to bumper, but he was responsible for propagating the "installed backwards at the factory" myth. He is incorrect in this assumption.

The angular linkage arm does look "wrong" but in reality it is not installed upside down and it works perfectly in that configuration. Most importantly, it was purposely designed & installed that way.

[scottfab]

Originally Posted by A26B

Ideally, if the actuator arm was a rod, connected straight through the center of the diaphram and perfectly aligned with the linkage bellcrank, then there would be no controversy, but it's not.

Yes most likely. This approach would have been a proper design.

Originally Posted by A26B

As it is, the actuator arm is an "L" bar and the linkage arm is offset from its connection at the center of the diaphram. when the actuator arm is aligned with the bellcrank, the center of the actuator diaphram is not aligned. As such, the pull is angular when vacuum is applied to the actuator.

Only if the top of the L where it connects tot he linkage is left unbent. Read on.

Originally Posted by A26B

As Bearly Flying observed, when the arm is "angled" to the bellcrank, the center of the actuator diaphram is in alignment and the pull is straight when vacuum is applied to the actuator.

Not my observation. As the pull occurs from this noticeably off center angle. the ball travel is interrupted toward the end of the travel. This puts a lateral stress on the diaphragm. It's really hard to imagine anyone thinking this was engineered this way. More like it was overlooked this way.

Originally Posted by A26B

When the actuator is installed with the linkage arm "straight," you can see the diaphram move angular in the housing as vacuum is applied. This is evidenced by the need to grind & remove metal from the arm to clear the actuator housing when vacuum is applied.

Not my observation. The metal would need to be ground down even if the off center pull was left in because the actuator is upside down.
It simply makes contact with the side of the actuator regardless of the angle.

Originally Posted by A26B

Scott, Your analysis would be correct IF the linkage arm fitment to the bellcrank shaft was such that it forced the arm to remain perpendicular to the bellcrank attachment pin. It is not however, as it fits loosely enough that it works more like a flexible ball chain than a connecting rod.

Ah but you missed the fact the the angular travel eventually is severe enough to run to the end of the ball travel. That is where the sticking can occur. (video is needed here)

Also the perfect L has to be altered to a more acute angle when the
actuator is installed right side up (so pull is straight looking)
This puts the top of the L in alignment with the center of the diaphragm. (THIS IS THE KEY POINT)
I must admit I forgot about this bend until now. I remember bending a part but could not remember which.

Originally Posted by A26B

On my 60K mile 94, I tested the actuators as they were installed "angular" and reversed "straight." "Angular" operated smoothly and quickly, "straight" was jerky & took slightly more vacuum to open fully.

On my 90 I tested the actuators installed upside down and found at the end of the travel the assembly would stick. Once I had the part out I could see the rubbing of the L bracket and concluded it was because the actuator was upside down. I reversed it and noted as you that the pull was jerky. I then bent the L bracket and walla. A straight pull and straight appearance. Complete root cause analysis AND fix.

Originally Posted by A26B

I consider Gorden Killebrew a good friend and a true genius on the C4 Corvette from bumper to bumper, but he was responsible for propagating the "installed backwards at the factory" myth. He is incorrect in this assumption.

He is absolutely correct but incomplete on the fix. The offset angle caused binding toward the end and is also visually upsetting. Poor fix at best to leave such a crappy looking assembly in place. AND I just know it was not designed that way. (original drawings) It was, even by your story, a problem area whose solutions was questionable (put the actuator in upside down) at best. That is not design or engineering. That is expediting a possible fix on the assembly line. Somebody's good idea.

Originally Posted by A26B

The angular linkage arm does look "wrong" but in reality it is not installed upside down and it works perfectly in that configuration. Most importantly, it was purposely designed & installed that way.

Not my understanding of the word "perfectly". The ball runs out of angular travel when the actuator is installed upside down.
I do agree is was purposely installed that way.
I do not agree it was designed that way. I think it was left that way.
Lack of time or ? to do a proper fix.

In summary:
This discussion has brought back to memory the step by step approach I took in resolving what at the time, seemed to be an assembly error. Little did I know at the time that the fix I made would lead to:
1. 10yrs of reliabiliy
2. aesthetically NOT upsetting appearance that will confound future owners.

I recommend that everyone leave the actuator looking crooked (upside down) unless you are willing to at least bend the L bracket such that the top end of the L be aligned with the center of the diaphragm.
If you do so you'll have a visually pleasing appearance AND reliable operation.

[Dynomite]

Originally Posted by A26B

Ideally, if the actuator arm was a rod, connected straight through the center of the diaphram and perfectly aligned with the linkage bellcrank, then there would be no controversy, but it's not.

As it is, the actuator arm is an "L" bar and the linkage arm is offset from its connection at the center of the diaphram. when the actuator arm is aligned with the bellcrank, the center of the actuator diaphram is not aligned. As such, the pull is angular when vacuum is applied to the actuator.

As Bearly Flying observed, when the arm is "angled" to the bellcrank, the center of the actuator diaphram is in alignment and the pull is straight when vacuum is applied to the actuator.

When the actuator is installed with the linkage arm "straight," you can see the diaphram move angular in the housing as vacuum is applied. This is evidenced by the need to grind & remove metal from the arm to clear the actuator housing when vacuum is applied.

The angular linkage arm does look "wrong" but in reality it is not installed upside down and it works perfectly in that configuration. Most importantly, it was purposely designed & installed that way.

Great Description and explanation Jerry

I (because I am a Pirate) install the canisters with straight link back to the pivot linkage. I file the canister link arm if I notice it is even close to touching the canister opening.

I install the link straight back to eliminate any sidewase thrust on that little link keeper on the pivot linkage shaft. That is the Pirates way

Cliff

1990 LT5


1991 LT5

[scottfab]

Here is a diagram to better show how the straight pull is accomplished
by bending the L bracket after putting the actuator in right side up..
Note as so many have noted (not just Gordon Killebrew) the upside down
actuators are visually upsetting. The bent L bracket is less so as well as
fixing the problem of hitting the end of the travel on the ball socket.

[A26B]

Scott, if you're happy, I'm happy and I will respect your EE skills and hope you can respect the ME skills which are a portion of my PE skills.

Out of respect for a significant volume of empirical data (6,000+ LT5 engines with "angled" actuator arms) the angled actuator arms work just fine.

if the "angled arm" visually bugs anyone, then by all means, rotate the actuator, increase the right angle on the linkage arm to an acute angle but don't forget to straighten it at the end so it is perpendicular to the bellcrank pin. BTW, there is no ball socket at the attachment to the bellcrank.

[scottfab]

Originally Posted by A26B

Scott, if you're happy, I'm happy and I will respect your EE skills and hope you can respect the ME skills which are a portion of my PE skills.

not sure skills come into play only facts should.

Originally Posted by A26B

Out of respect for a significant volume of empirical data (6,000+ LT5 engines with "angled" actuator arms) the angled actuator arms work just fine.

I totally agree. That is why on a previous post I recommended leaving it as is if one was not willing to modify the L bracket.
The upside down actuators work but they are problematic both visually and functionally (end of throw binding)
As with other design issues on the car. They can be and have been improved (fixed) by many of us.

Originally Posted by A26B

if the "angled arm" visually bugs anyone, then by all means, rotate the actuator, increase the right angle on the linkage arm to an acute angle but don't forget to straighten it at the end so it is perpendicular to the bellcrank pin. BTW, there is no ball socket at the attachment to the bellcrank.

Yes, I mostly agree however, the angle on the L bracket needs to decreased (accute) not increased (obtuse).
A bellcrank is composed of several components. the L bracket connects to the bellcrank through a "king pin" or "ball socket". A bellcrank is the arm part. On many bellcranks there is a shaft connection point. In our cars a king pin is used at the "moving pivot" point.
See this figure for info:
http://myweb.tiscali.co.uk/technologyweb/bellcrank.gif
This is all getting off topic so I think we're beating a dead horse.


Suffice it to say there are reliability issues with the 6000 plus cars with secondaries that work so well with the actuators "purposely" installed upside down. To fix the original design flaws there are those feed up with the reliability of the secondary system so much so that they rip them out.
Not that even a major component of these failures are at the actuator but I submit that it contributes to this reliability issue. In so far that that is true I offer the correction to the weird looking upside down issue for the betterment of the car and it's survival.
I'm now done with this thread.
I must need something at the store. It's nice out and I need to go see if my secondary actuators still work ok.

[Blue Flame Restorations]

I'd suggest ripping them out.....no more troubles...

[Bearly Flying]

Yes, I have read several of the threads on that. Still haven't came to a conclusion on that subject.

[Blue Flame Restorations]

Originally Posted by Bearly Flying

Yes, I have read several of the threads on that. Still haven't came to a conclusion on that subject.

For me, it made perfect sense. Less parts to fail and less vac lines to leak. I've never looked back....

[Dynomite]

Originally Posted by Bearly Flying

Yes, I have read several of the threads on that. Still haven't came to a conclusion on that subject.

1990 LT5 with Secondaries (Non Kludged)


1991 LT5 No Secondaries (Kludged)