Distributor vacuum advance diaphragm adventures

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Mark
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Distributor vacuum advance diaphragm adventures

Post by Mark »

I had one of my distributors out of one of my Tercels lately and I found that the vacuum advance diaphragm wasn't holding a vacuum at all. I decided to take it apart and see what the diaphragm looked like and how it failed. I used a pair of vise-grips to bend out and "unroll" the crimp holding the 2 halves of the housing together:
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The diaphragm was a rubberized fabric. I didn't see any obvious holes or tears in the diaphragm until I held it up to a light and I saw it was full of pinholes. This was in areas where the rubber coating had worn off the fabric:
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I used a flexible urethane sealant (Seamgrip, but another popular brand is Aquaseal) to coat the diaphragm on both sides. There are probably lots of products that could be used, but in years of repairing dive gear, I've found that this urethane stuff bonds the best and lasts the longest. Plus it's what I had lying around. I gently wiped off the diaphragm with Toluene first to remove any oils. That stuff is liquid birth defects so I wore gloves. I like to think that since it changes DNA, there's a slight chance that I might end up as a superhero. I also thinned the urethane sealant with a bit of the Toluene to make a thinner coating and to help it dry faster.
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While I was waiting for it to dry I took apart the rest of the distributor to clean out any oil and dust and lube the centrifugal advance system:
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I let the diaphragm dry overnight.
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I coated the rims of the housing with a bit of the urethane sealant to help the diaphragm seat better and I gently clamped it all together in a vise:
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helipilot77
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Re: Distributor vacuum advance diaphragm adventures

Post by helipilot77 »

Very nice fix. I can see this being useful to me in the near future on my AAP diaphragm.
. / TOYOTA
./_| |/|/ |]
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Mark
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Re: Distributor vacuum advance diaphragm adventures

Post by Mark »

I then used the vise-grips to roll/bend/clamp the crimp back together:
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It didn't look pretty, but I put a vacuum hose on it and sucked and it worked fine. I tried to put the assembly back in the distributor and I realized that I had put it back together wrong and the arm coming out was oriented the wrong way.
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I bent back the crimp again, opened up the housing, removed the diaphragm and rotated it 90 degrees to the proper orientation. I then put it all back together and re-crimped it. It really looked ugly now, but I was feeling proud that it still worked when I applied a vacuum. I then noticed a spring sitting on the table and realized that I had forgotten to put it in the housing before I crimped it back together.
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I took it apart again, put the spring back in and put it back together, but by now the crimp was so shredded that the diaphragm didn't seal anymore.
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Mark
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Re: Distributor vacuum advance diaphragm adventures

Post by Mark »

I was too stubborn to give up now so I ground off the shredded crimp all around the housing and clamped them together using 2 steel rings held together by small bolts. I also used a bunch of that silicone gasket maker before tightening everything down. This ended up being pretty ridiculous, but it worked again so I put it in the re-assembled distributor and attached a vacuum hose from my wagon while the engine was running at idle. It advanced the mechanism as it should. A couple of people asked me why I didn't cut down the long bolts I used, but I figured if it's going to look stupid, it might as well look really stupid. I'll just say it's Steam Punk.
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Anyways, the moral is, it is sort-of possible to repair these things as long as you're not an idiot like me and do it wrong twice in a row and ruin it.
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Mark
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Re: Distributor vacuum advance diaphragm adventures

Post by Mark »

helipilot77 wrote:Very nice fix. I can see this being useful to me in the near future on my AAP diaphragm.
I've never had a AAP that worked. I just disconnect/cap the vacuum hose to disable them. I don't know what kind of product you could use to re-seal an AAP diaphragm that would be resistant to fuel.
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Petros
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Re: Distributor vacuum advance diaphragm adventures

Post by Petros »

actually you made a vacuum advance that is now serviceable, you can take it apart to replace the rubber part any time you want. now if we can find a source of think rubber sheet to use as a replacement diaphragm.
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helipilot77
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Re: Distributor vacuum advance diaphragm adventures

Post by helipilot77 »

McClendons hardware sells rubber sheet in diferent thicknesses. I would think polyurethane would be fuel resistant. I'll have to do a test sample.
. / TOYOTA
./_| |/|/ |]
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Mark
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Re: Distributor vacuum advance diaphragm adventures

Post by Mark »

I don't know if regular rubber sheet thin enough would be strong enough. These diaphragms are made of rubberized fabric. I think you can actually buy sheets of this diaphragm stuff somewhere. I wonder if Hypalon or whatever inflatable boats like Zodiacs are made of would work. I think I read somewhere that for small automotive diaphragms, nylon-reinforced nitrile rubber is the stuff to use.
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helipilot77
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Re: Distributor vacuum advance diaphragm adventures

Post by helipilot77 »

Maybe a patch kit for a zodiac could be had for cheap. I might look into that.
. / TOYOTA
./_| |/|/ |]
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dlb
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Re: Distributor vacuum advance diaphragm adventures

Post by dlb »

Mark, I'm about to try this myself. I have the vacuum advance out and ran out of time trying to unroll the crimped edges. The little bit of unrolling I tried went dreadfully -- on a scale of 0-10, how difficult/irritating did you find undoing the crimp? Just wanna know how much patience I should force myself to have with this process.
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Mark
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Re: Distributor vacuum advance diaphragm adventures

Post by Mark »

Man, that was so long ago, I forgot all about it. I think I maybe used a needle-nose vise grip. At least that's what I'd use now. I'd probably use some kind of very fine-tipped flat head screwdriver to help pry it up. I'm not sure what happened eventually with that distributor vacuum advance. I do remember making a new housing from aluminum on a lathe and making a diaphragm from a Zodiac boat patch which is a rubberized fabric. I did a search on this forum and couldn't find any posts about it so I must not have taken pictures. I'm not using that home-made vacuum advance housing on either of my Tercels at the moment so I must have eventually replaced it with a working one from another 2nd gen tercel that I had. Now I'm curious myself as to what happened to those vacuum advance housings. I'll have to look around and see if I still have them somewhere.
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dlb
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Re: Distributor vacuum advance diaphragm adventures

Post by dlb »

Ha, funny that you forgot about this. I'm really glad you did this write-up though, it took a while but I got mine apart, gooped both diaphragms up with Shoo Goo (I couldn't find Seam Grip, Aqua Seal, or any similar products so I just went with something rubbery and tough), and am letting it cure for 24 hrs now. I hope to put it back together tomorrow.

My advance unit has two diaphragms. The upper diaphragm looked like yours, worn out fabric with pinholes, but the lower one was in good shape except for one hole. Each diaphragm has its own spring, and they are different sizes so I took pics along the way to keep track of what goes where (and in what orientation), I'll post all those once I'm done.
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dlb
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Re: Distributor vacuum advance diaphragm adventures

Post by dlb »

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The lip of the lower diaphragm was harder to peel back because it's so tight against the raised portion in the center. I pried at it with a small flat screwdriver until it came up just enough for the vice grips to grab and start peeling. Once I got each one started it went quickly. The upper one was much easier to get started.
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Nordical25
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Re: Distributor vacuum advance diaphragm adventures

Post by Nordical25 »

Good job. These vaduum advances are getting older and more expensive so that is a very good idea. By the way, some Tercel 4wd fuel pumps are also built similarly. You could fix them in similar way if they start to fail.
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dlb
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Re: Distributor vacuum advance diaphragm adventures

Post by dlb »

Yeah I saw some new vac advance units on ebay but they are $180 CAD -- steep! So I figured this was worth a shot first. I'll post my results once I get it reassembled.
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