Vacuum advance repair

[ducktapeguy]

I was having a lot of trouble getting my engine running right. It was running ok, but every once in a while when turning off the ignition I would get a kickback as the engine stopped. I assumed it was a timing problem (I had previously timed it with a vacuum gauge) so I broke out the timing light and adjusted it exactly to 7 degrees. However, it ran like crap and had no power when set to spec. After some quick tests, I figured out that the vacuum advance wasn't working properly. Unfortunately, I can't find a replacement assembly anywhere, everyplace sells it with the distributor. Since I eventually plan to upgrade to later model electronic distributor, I didn't want to spend the $300+ to get a replacement, so I decided to try and fix the old one. After all, it's broken anyway I can't really can't screw it up any worse

Here's a pic of the assembly. The hardest part was undoing the roll crimp holding the two halves together. I used a small chisel tipped punch and hammer and just worked my way around. Once you get the hang of it, it goes rather quickly.

 

[ducktapeguy]

Here's a picture of all the components inside. Nothing too surprising.

 

[ducktapeguy]

And here's a closeup of the problem.

 

[ducktapeguy]

I used an old secondary carb diaphragm as a patch for the hole. I was going to use a bicycle inner tube patch kit but I couldn't find it. It actually turned out better than expected because the shape of the diaphragm conforms pretty well with the one on the advance. Just remember to roughen up the patch area with some sandpaper then clean it well. I also put the patch on the non-vacuum side of things, so vacuum pressure will tend to suck it tighter. Actually, I also put a small patch on the backside but i don't think it's really necessary. To hold it together I used superglue, which I've found glues rubber better than anything else

 

[ducktapeguy]

The finished product. The only thing left to do is reassemble then re-crimp the housing by tapping it with a hammer all the way around the edge. It's easier to use some pliers at a few points around the edge to start the crimp and hold everything in place first, then finish it up with the hammer.

I'm not sure how long it'll last, but it's only meant to be semi-temporary. I still plan on replacing the whole distributor when I get a chance (when I have money). At least the car runs way, way better now, my mileage has gone up, I have more power on the freeways, and I'm not in a desperate rush to find new parts. Hopefully this will help if anyone else runs into the same problem.

 

[Coolerman]

I guess they don't call you duct tape guy for nothing?

Good thinking!

 

[breckbone]

I was having a lot of trouble getting my engine running right. It was running ok, but every once in a while when turning off the ignition I would get a kickback as the engine stopped. I assumed it was a timing problem (I had previously timed it with a vacuum gauge) so I broke out the timing light and adjusted it exactly to 7 degrees. However, it ran like crap and had no power when set to spec. After some quick tests, I figured out that the vacuum advance wasn't working properly.

Just curious what your "quick tests" were to diagnose vac advance problems? I'm going through a checklist of items to diagnose some cold-start problems I'm having and vacuum advance is next.

Thanks for any info!

Craig

 

[91 4runner]

I still plan on replacing the whole distributor when I get a chance (when I have money). At least the car runs way, way better now, my mileage has gone up

Car Parts

two accounts?

 

[Pighead]

spamtard. been reported

 

[ducktapeguy]

Update:

I upgraded my distributor a few years ago to the FJ60 dizzy, but as far as I know the patch I did earlier to the FJ40 vacuum advance was still holding. However, after a few years I ran into the same problem with the 60 vacuum advance, and repaired it the same way. Duffontap gave me the idea of using plasti-dip to repair the diapragm in this thread. As long as there's no tear in the diaphragm, it seems to work very well.

Opening the advance mechanism. The 60 advance was much harder than I remembered the 40 one to be, either the metal is thicker or it's a different material. The crimp ring is part of the vacuum advance, not a separate ring like on the 40.

Once opened it looked like this

After multiple coats of plasti-dip on both sides the diapragm is good as new. I couldn't find any obvious source of vacuum leak, but it was a fairly small leak so it could have either been from where the actuator rod goes through or the material itself. That's why I coated the entire center disc up to the rod.

Didn't get any pictures of reassembly, it was getting late and I wanted to finish. But just start crimping the outer ring with pliers until it looks like a pie-crust, then gently shrink the metal back with a small hammer. I also added some sealant to the inside lip to ensure a leak free seal. Installed it back on the dizzy and feels like a whole different engine now. Idle is rock solid and the engine purrs smoothly.