BCDD Rebuild Parts

[Captain Obvious]

Are the two diaphragms used inside the BCDD still available?

[Captain Obvious]

24 hrs and not a peep... So, I'm guessing that's a "no"?

[Zed Head]

I'm pretty sure that the FSM (76 and 78 anyway) says "NEVER take the BCDD apart", replace the whole thing. So it would be surprising if the internals were available. Could be wrong, but that's my memory.

[Captain Obvious]

the FSM says "NEVER take the BCDD apart"

Haha! Yeah I saw that too, but... So?

If they didn't want me to take it apart, they wouldn't have put screws on the bottom.

Seriously though, I suspected as much. Most discussion I've seen on the BCDD is people talking about how they have disabled them, not repaired or replaced them. I just figured I would throw the question out there and see what stuck. Was thinking (hoping?) that maybe one of the aftermarket specialists might offer parts.

[240260280z]

I think they are important as they prolong the life of rings and valve seals by preventing high rpm vacuum condition that will suck oil past the seals and rings. Rebuild makes sense.

You may be able to refresh tears in the diaphragms with improvised patches.

3m spray adhesive and paper can patch a ripped up speaker so there should be some way to revive a BCDD.

[ZCurves]

When I went over my BCDD, I just cleaned it out and made sure the magnet valve functioned. But I have never been sure that it was working properly, so I am intrigued by removing it without problems.

[Captain Obvious]

I have verified that my solenoid valve pulls in when I apply power to it, but I'm not convinced that the valve makes a great seal. I can certainly tell a difference in BCDD operation between when the solenoid is pulled in or not, but I've got some internal leakage and I can't tell where it's coming from without taking the BCDD apart.

Problem is that I sincerely doubt that I'll be able to split the BCDD parts apart without completely ruining the diaphragms. In other words, I'm not past the point of no return yet and I didn't want to pass that point until I had a "plan".

Blue, this is your fault by the way... :laugh: It all started by looking into that goofy auxiliary throttle return spring that you pointed out to me and has spiraled out of control from there. I've been trying to figure out why that additional return spring was needed to get the throttle to return to idle and I've discovered a whole host of issues that are contributors. One of the fixes (so far) was to completely disassemble and clean the throttle body. With the exception of the BCDD or course.

[rcb280z]

I'm curious on the "whole host of issues".....what were/are they? I wish I had an extra BCDD laying around. I too have often wondered about that "mysterious" gadget hiding under the throttle body. I know what it does, just have always wanted to crack it open. There has to be something available out there as a replacement for the diaphragms. Probably not a direct replacement but a close replacement. It helps that the BCDD is adjustable. I'm going to talk to my buddy that is a mechanic to see if he has an extra BCDD laying around and would be willing to open it up. Capt. Obvious, what made you start looking at the BCDD in the first place?

[Captain Obvious]

The whole host of issues? I just put some details in my throttle linkage thread

http://www.classiczcars.com/forums/showthread.php?45815-Throttle-Linkage-Improvements&p=395674&posted=1#post395674

But the summary is that I've discovered that my previous owner got overzealous with the bead blaster and sprayed things he should not have. Here's the host I've found so far:

Blasting grit in the throttle body and TPS making the throttle shaft movement grainy.

Blasting grit making all of the throttle linkage ball and socket joints sticky.

Blasting grit in the sleeve bearings where the throttle linkage mounts onto the intake manifold.

Blasting grit inside the plastic spherical bearing where the throttle linkage mounts to the firewall.

Not related to my throttle issues, but I found blasting grit inside my distributor as well.

So what made me start looking at the BCDD? To be honest, I don't have any performance reason to believe there's anything wrong with it, but with all the grit I've found elsewhere, it is impossible for me to believe that it didn't get inside the BCDD as well. But I don't want to open it up without replacement parts first.

If you open one, I'd love to see pics. I think I've got a pretty good idea of what's inside, but without opening one up, it's simply speculation.

I just hope he spared the AFM.....:sick:

[Zed Head]

Only $251.77 brand new! http://www.courtesyparts.com/assy-bcdd-p-261497.html Still have one dot for availability.

[rcb280z]

Capt. Obviuos, my buddy didn't have one and hasn't taken one apart. He said if it was bad, rare, he would replace it. But that was rare as well. Asked him about removing it all together and blocking off the hole, he hasn't done that either. Looks like Zed Head is on to something. If courtesy nissan actually has it. I believe someone is parting out a 77 and 78 280 on zcar.com, it might be worth looking there for a used one. Or even zcarsource.com for that matter. Keep updating on your progress....I'm curious as well.

[rcb280z]

zcarsource has it for 210.00 with the throttle body complete.