Refurb'ing a dizzy two diaphragm vacuum advance

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wimberosa

wimberosa

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Nov 8, 2017
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Durango Colorado
@NeverGiveUpYota @62Cruiser @duffontap @ducktapeguy @65swb45 @4Cruisers

I'm standing on the shoulders of giants here (see above members) ... but would like to close the loop on definitively how best to fix the diaphragms in vacuum advances. In this case I have a vacuum advance with both carb port and HAC port. I have split both port sides at the lip (which btw is actually pretty simple and took less than an hour opening both sides). I have two types of diaphragm materials on the way but am willing to try others until I nail it with proper material thickness:
  • mcmaster carr: 8610K61 Weather-Resistant EPDM Rubber Sheet, 12" x 12", 1/64" Thick
  • DCI Equipment (from american dental associates): Dimensions: 11" X 8.5" X .013" thick sheet
Now I have a couple of questions based on the following pic attached below:

  1. This slotted coupling connects to an advancer pin on the inside of the dizzy. It has a clip on one side and a spring on the other. Seems like with the clip and the spring on either side it should be able to move slightly...otherwise why the spring? My slotted coupler seems to be almost pressed on and does not move. Thoughts?
  2. The second diaphram for the HAC port doesn't seem like it removes as easily from the metal hub it's sandwiched between, whereas the primary diaphragm does easily remove. Anyone got this diaphragm apart for replacement with new material? Luckily this one is in pretty good shape and I may just plasti-dip it...but it would be super cool if I could figure out how to replace the material completely in case someone opens up their advance in the future and that diaphragm is torn.
Here is the photo with components laid out in order of removal.
IMG_4298.webp
 
Here are some close-ups of those pieces that I'm asking questions about. Does that diaphragm look like a "compressed on" assembly?
When I put these diaphragms back together I'll silicone them into the housing. I was considering not using the metal lip as a fold-over and instead either clamping the housing together or gluing it together with an epoxy. Fundamentally I'm thinking it could become more easily serviceable if assembled differently.

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Yep. That HAC diaphragm has to be pressed on between two tight "cups" and then hammered / embossed into each other. Those little dimples and the absence of any screw threads tells me that this little unit is going to be very very hard to swap out any diaphragm sandwiched between it. The tech is beyond my current capability. I'll have to butter this HAC diaphragm up with a little plasti-dip and call it good. If you open your vac advance up in the future and figure out how to replace that HAC diaphragm please tell me.

I'll still be posting about the material I eventually use in the other main diaphragm. That seems to be the one to predominantly fail since its used the most.

I also do not know what the inside of a single diaphragm vacuum advance looks like (world market) and would sincerely hope those diaphragms are replaceable. I know people are doing without these vacuum units and/or you can get the world market dizzy with only carb advance port that originally appeared sometime around 77-78 ... but if you want to keep your rig looking somewhat oem ... what I just attempted may be our future in lots of areas due to NLA.
 
numby said:
Maybe sandwiching a thin rubber diaphragm to the original with something more flexible than Plasti-Dip like Flex Seal?
Click to expand...
I think this is the answer for the second diaphragm that cannot be fully replaced with new material. If that diaphragm gets torn then the answer may be to trim that diaphragm .. but leave a portion to overlap and glue/connect to new material. Flex-seal may flex better (unsure) but it gobs on as opposed to the more paint like spray-on plasti-dip. I've been somewhat concerned about changing the overall thickness and flexibility of the material I replace these with. If you look at the way these diaphragms are connected...there is a small amount of slack linkage between the two diaphragms but they are paired in the sense that additional vacuum at the HAC port "stretches" the main diaphragm more than the stretch that would otherwise be present from the carb ported vacuum alone.

To further attempt to clarify/muddy this.... The outer diaphram is engaged when the system is closed at the HAC port and vacuum is generated (3000+ feet). i.e. a relatively constant vacuum starts coming thru the manifold-HAC-advancer portion of the system. That HAC advance is small because the amount of movement available in that advance chamber is smaller. But when the HAC diaphram moves it also pushes on the carb port diaphram it is paired with and the advance rod moves. Then when the carb port starts generating vacuum above idle, the carb port diapham moves the advancer rod even further. To me this looks like a somewhat delicate balance of material strength, spring strength, and advancer chamber volume to "do the right thing".

I live above 7000', so I'm seeing that hac advance that lots of people would never see.
 
Are you sure that the amount of vacuum applied to the HAC diaphragm is the the same as that applied to the main advance diaphragm? There are all sorts of vacuum-limiting orifices in smog era 2F ignition systems. As you've found the amount of advance that can be applied via the HAC system is not limited by the diaphragm material itself or by the space within the cannister because the standard advance can override the amount applied by the HAC. Total advance available is ultimately limited mechanically.

I wouldn't attribute very much advanced math or heavy lab time to the designing of the advance cannisters. It just doesn't fit with the sensibilities of the time period. It's probably only a single causative factor like controlling the recoil on a 1911 .45acp pistol which is mainly done via spring strength.
 
Don't think I said (HAC vacuum == Carb port vacuum). Doubt it is...but its more constant at the HAC port since its directly off the manifold. There is some variability there which is why there is a check valve in that line. The carb port is generating vacuum that increases as the throttle opens.

I "perhaps" see what you are saying though. How would the HAC "overcome" and pull the main advance diaphragm further than it already is at when above idle...bringing yet more vacuum advance into the total advance. In order for it to do that, the HAC vacuum has to be higher than the main advance vacuum...but still limited to a smaller advance on the HAC side because the chamber is smaller....i think.

The more I continue to edit and add to this post...the more I'm starting to think I don't know how these work in tandem ;-)
 
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I don't think I read your explanation of the system correctly. Let me see if I have it correct now.

Anytime you're above 3K' the HAC delivers a set amount of manifold vacuum to the corresponding side of the cannister. Are you certain that the amount of vacuum supplied does not vary by altitude - i.e. - it's all or nothing?

Since the HAC comes in at idle are you certain that it adds additional advance to the total ported carb vacuum advance or is there a limit to the total number of advance degrees that the entire system can deliver regardless the source? You've indicated it might be cumulative. Have you done a simple test at idle by applying vacuum to the cannister ports in different combinations and recording the advance in distributor degrees?

If you find that there is a limit to the total advance degrees applied whether or not the HAC is in play and the HAC is an "all or nothing" system that supplies a set amount of distributor advance degrees when above the 3000' mark (and mainly at idle/low RPM), then you need the HAC for idle/low RPM running and you'd need to keep the HAC working when at altitude.

If it's cumulative then you could (in theory) ignore the HAC side of the cannister and just dial in the appropriate number of advance degrees into your base timing as long as you're staying above 3K'. This is one use of the adjustable timing control knob on the 19100-61080 ROW points distributors I think.

Also, I'm not certain the HAC vacuum would have to be higher than that delivered by the advance port on the carb to get it to move the advance lever even more than with just the ported vacuum signal alone because the two vacuum signals are additional to each other with separate chambers in the cannister. Every little bit helps though. I'm not sure it would matter if they were included in one chamber with a single diaphragm but that might behave like a vacuum leak as the two sources try to equalize with each other. Again, every little bit helps - maybe. Advance port vacuum is variable by throttle plate position but there's certainly an "all in" point. Without pics I'm guessing that HAC port on the manifold is larger but that may just be convenience.

You might need to start monitoring vacuum advance degrees from inside the cab while driving to know what really comes in and when but that can be problematic because of any additional mechanical advance as RPMs increase.
 
numby said:
Anytime you're above 3K' the HAC delivers a set amount of manifold vacuum to the corresponding side of the cannister. Are you certain that the amount of vacuum supplied does not vary by altitude - i.e. - it's all or nothing?
Click to expand...
It's all or nothing.
numby said:
Since the HAC comes in at idle are you certain that it adds additional advance to the total ported carb vacuum advance or is there a limit to the total number of advance degrees that the entire system can deliver regardless the source?
Click to expand...
It adds advance of about 5 degrees. It would add 5 degrees at idle or 5 degrees at max carb advance. It kicks in at around 3930' of elevation. The prior answer and this answer are in the Emission Control Repair Manual (for the 1979 its on page 4-42)

Regarding total advance limit... My dizzy has a double nut adjustment on the advancer rod. So you can restrict or expand the total advance if the system is over or underachieving.

I cannot fully test the system yet as my main advance would not hold vacuum. My HAC advance will hold. This is why I'm rebuilding the thing.


numby said:
If it's cumulative then you could (in theory) ignore the HAC side of the cannister and just dial in the appropriate number of advance degrees into your base timing as long as you're staying above 3K'.
Click to expand...
Yes. This is what many people do if you are not crossing that elevation threshold. I on the other hand cross that elevation threshold all the time as I'm in the 4 corners and go places.

Curiously the HAC is basically a designed vacuum leak at both high and low altitude. At high altitude, its also directing air into the main carb nozzles...so its doing more than just advancing the timing. At low altitude it hasn't closed that loop used by the HAC vac advance on the dizzy...so air is getting sucked into the manifold thru the HAC module itself.
 
Wow, it's been a while since I looked at my vacuum advance, I almost forgot I repaired it. I had to go look through my old thread to remember what I did.

My memory is pretty fuzzy after 15 years so I can't answer all your questions, but from what I do remember

1. That slotted coupling I think is supposed to slide. Mine had a knurled adjustment knob to allow timing adjustment of a few degrees without moving the distributor. The spring just keeps it pressed against the knob. The double jam nuts control the overall range of adjustment. In my old thread you can see what mine looked like, yours looks different so I'm not sure how it's supposed to function.
Vacuum advance repair - https://forum.ih8mud.com/threads/vacuum-advance-repair.281609/

2. That second diaphragm probably isn't going to be easy to replace. You could possibly grind off the staked sections very carefully and attempt to re-stake it, but in the end a non-destructive repair like plasti-dip is just a lot easier. Mines been working fine for the last 8 years or so since I posted. Or it's more accurate to say that it hasn't given me any trouble where I've needed to even look at it again in the last 8 years. The first one I repaired in 2009 might still be working too, but I don't know it's buried in a box in the garage somewhere.

From what I remember, the 2 vacuum advance diaphragms work in series and are additive, so they basically act independently of each other. So the HAC doesn't necessarily need to "overcome" the vacuum in the main advance, it just adds to the total advance. Think of it as 2 air pistons connected in series. The movement of each piston is independent of each other, but the location of the first one is dependent on the movement of the second.

The advance is mostly dependent on the vacuum reading and spring force, the stiffness of the diaphragm material plays a minor role. As long as it's flexible enough to allow full range of adjustment, and strong enough to overcome the spring stiffness, that's all that really matters. Volume also doesn't matter, just surface area, so the 2 advance diaphragms being the same diameter basically function identically, just with a different range of adjustment and spring constants.

It had been so long I had to go back out and look in the engine compartment to remember what I did, and it looks like I took out the HAC diaphragm completely and converted the dual chamber vacuum advance into a single chamber unit. I don't vary in elevation that often where I thought I needed it, and I can always just compensate with base timing.

EDIT: After seeing pigheads post maybe I just bought an advance unit from 4 cruisers. It's been so long I honestly don't even remember what I did.

Around the time I was messing around with these vacuum advance units, I thought about making an electronic advance mechanism. Basically a vacuum sensor at the carb controlling a linear motor at the dizzy where you could customize the advance curves. But in the end it just wasn't worth the effort for very little benefit.
 
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aging fleet said:
I run a big cap FJ60 distributor, my vacuum advance diaphragm failed so I'm running ported vacuum to the HAC port at the suggestion of FJ40Jim. Apparently it's not able to provide as much advance, but something is better than nothing.
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I replaced the dual diaphragm advance mechanism on my FJ60 dizzy with a single diaphragm unit I got from @4Cruisers. Single vacuum line to ported vacuum and it seems to work

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Pighead said:
I replaced the dual diaphragm advance mechanism on my FJ60 dizzy with a single diaphragm unit I got from @4Cruisers. Single vacuum line to ported vacuum and it seems to work
Click to expand...

I didn't even know that was an option, thanks @Pighead. @4Cruisers are you still selling these?
 
I had an expensive electric fuel pump in the late 80's. It went bad. I used a hack saw to cut the roll can crimp in 5 or 6 places. Next I used a big pair of water pump pliers to peel each section of the can crimp open. Took the guts out and released one of the brushes that got stuck in the holder. Used some needle nose to do some chiropractic work on both brush holders. Put Aviation Permatex on the rubber seal and in the grove of the can crimp. Squeezed the can crimp segments in place with the water pump pliers, then used a hammer to pound the segments down tight. No leaks and lasted another 5 or so years.
 
wimberosa said:
Regarding total advance limit... My dizzy has a double nut adjustment on the advancer rod. So you can restrict or expand the total advance if the system is over or underachieving.
Click to expand...

That's interesting. I'd have to think about other uses for the adjustment. Hmmm

wimberosa said:
Curiously the HAC is basically a designed vacuum leak at both high and low altitude. At high altitude, its also directing air into the main carb nozzles...so its doing more than just advancing the timing. At low altitude it hasn't closed that loop used by the HAC vac advance on the dizzy...so air is getting sucked into the manifold thru the HAC module itself.
Click to expand...

I'm not sure that's correct. I broke out my '79 2F Emission Manual. Looking on 4-42 the air source for reducing the fuel concentration at the primary and secondary high speed circuits is from the top of the HAC valve - not the intake manifold. Both of those circuits feed into the carb above the throttle plates so no vacuum leak as far as I can tell.

When below the 3930' mark it does seem like there could be air entering the manifold below the throttle plates if it's getting sourced from the bottom of the HAC but it doesn't indicate that specifically. Additionally there are other things that run off that vacuum cicuit via one of the BVSVs at the thermostat housing (EGR/Evap or choke breaker) plus there's an orofice at the check valve dampening everything down so the signal wouldn't be that strong - at least not right off the bat.

What I'm not getting is why pinching off the vacuum supply between the HAC and sub-diaphragm when below the altitude threshold causes an increase in timing advance. That does appear like you'd be closing off a vacuum leak from the bottom of the HAC. I doubt the HACs are particularly accurate but good enough for a Cruiser I guess. Still, the manifold vacuum from the gas filter source is also used elsewhere so that doesn't seem controllable even with the check valve metering orofice.

I thought I recently saw an advert for spray cans of FlexSeal. I might have been drunk so...
 
numby said:
What I'm not getting is why pinching off the vacuum supply between the HAC and sub-diaphragm when below the altitude threshold causes an increase in timing advance.
Click to expand...
you're talking about the check procedure in fig 4-105 (inspection at low altitude). You are pinching off the port in the HAC valve that is open below 3900'. By pinching off the "leak" you have now closed the previously open loop and caused a closed circuit vacuum. That sucks the HAC diaphragm in the dizzy advance module and moves the advance the prescribed 5 degrees.

This diagram that @Output Shaft (who is now apparently gone) posted...is particularly useful for understanding the inside of the HAC.
Output Shaft

Post in thread 'High Altitude Comp (HAC) Valve'

I believe the HAC valve uses a spring loaded poppet to seal and close passages inside the valve. So I think it's actuation is either on or off.

>>>>

High Altitude:
  1. Bellows expand and seal off port A inside valve.
  2. Vacuum increases below spring loaded poppet and pulls poppet down, port(s) B open allowing carb to suck in extra air.
  3. Vacuum on lower black pipe nipple is now sealed (port A is closed) so secondary vacuum advancer on the dissy is now actuated.
image.webp



Low Altitude:
  1. Bellows contract and open port A inside valve
  2. Vacuum releases below...
  • Like
 
wimberosa said:
you're talking about the check procedure in fig 4-105 (inspection at low altitude). You are pinching off the port in the HAC valve that is open below 3900'. By pinching off the "leak" you have now closed the previously open loop and caused a closed circuit vacuum. That sucks the HAC diaphragm in the dizzy advance module and moves the advance the prescribed 5 degrees.
Click to expand...

Thanks, I see it now. As long as you'e pinching off the line close to the HAC (like it says) then that should cause the 5º advance.

If you ran some kind of timing controller and had an altimeter you could just hit a switch when you crossed the 4000' mark for the extra advance and run a 4Cruisers single diapram canister on the dstributor but where's the fun in that? I hope you get the main diaphram repaired. Post up if you do. I have at least one 60 dizzy and a few '78s that have dual advance/retard canisters where only one side works.

Edit - Just saw @ducktapeguy's post above.
 
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Yes. Will post up soon. I have a planned methodology to compress the halves of the vac advance together without crimping and a few bolts for clamping are on order. I also will be using RTV grey on those diaphrams to seal their perimeters . It'll look odd but become semi-serviceable if it turns out like planned.
 
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