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furgo
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 Posted: Fri Jun 02, 2017 6:58 am Post subject: Stuck vacuum advance on distributor |
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I probably won't have time to work on the bus today, so I'm looking at a couple of parts that just arrived.
One of them is the distributor, a SVDA (VW 022 905 205 S, Bosch 0 231 170 093):
Note the Compu-Fire module: a nice addition as it gives me the choice to use either electronic ignition or points, but I was mostly interested in the distributor itself.
IIRC the seller said it was in working order (I need to double-check that), but what I've actually found out is that the vacuum advance is stuck.
I'm not an expert on distributors, so I might be wrong here. Essentially, I sucked air from the vacuum can nipple and I could clearly hear the diaphragm moving. However, the plate and the connecting arm that goes into the can remained unmoved. Trying to gently push the arm manually has no effect either.
Does this effectively mean that the vacuum advance mechanism is shot? If so, is there any way to fix it, short of getting a replacement vacuum can?
Here are some close-ups:
Notice the solder here. Looks like someone had either been soldering something in there (I couldn't think what or why), or someone was soldering something else nearby.
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Wildthings
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| Posted: Fri Jun 02, 2017 7:36 am Post subject: Re: Stuck vacuum advance on distributor |
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| Sometimes wasp or orchard bees will build their nest up in the mechanism and fill the area with mud. A blast of some kind of cleaner followed by something like WD40 might get things to move. |
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busdaddy
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| Posted: Fri Jun 02, 2017 7:39 am Post subject: Re: Stuck vacuum advance on distributor |
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My first step would be to remove that Compufire module, a long screw or something touching the side could be jamming up the works.
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Glenn 
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| Posted: Fri Jun 02, 2017 7:44 am Post subject: Re: Stuck vacuum advance on distributor |
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You need to determine if its the vacuum canister or the breaker pate. Remove the canister and test it. Then see if the breaker plate moves freely without it connected.
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Glenn
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aerosurfer
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| Posted: Fri Jun 02, 2017 7:52 am Post subject: Re: Stuck vacuum advance on distributor |
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Removing the advance plate is easy enough, pull it out to get a look at the weights below and get a real clear view of all the dirt and grime to clean out, then you can separate the advance plate and clean that, lube the pivot point and ball.
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furgo
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| Posted: Fri Jun 02, 2017 8:26 am Post subject: Re: Stuck vacuum advance on distributor |
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Thanks everyone for the suggestions.
| Glenn wrote: |
| You need to determine if its the vacuum canister or the breaker pate. Remove the canister and test it. Then see if the breaker plate moves freely without it connected. |
I think the answer is... both. The good news is that I got the plate somehow unstuck, though.
I initially removed the Compu-Fire module, but it wasn't the culprit. Then I removed the vacuum can. The plate was still stuck, but applying quite a lot of force with my fingers I managed it to move it from end to end. It's still sticky, but at least it moves. It appears to have been a thick mass of dried up oil.
- What's the best way to remove the oil residue there? Simply spray brake or carb cleaner underneath the plate?
- Once I've cleaned it up, is a particular type of lubricant required in that area?
Now for the not so good news: the arm in the vacuum can won't move. I'm tempted to wiggle it a bit, but I'm always weary of forcing NLA parts. As I said, the diaphragm moves when I either suck or blow air into the can, but the arm won't move, not even when gently pushing it with the hand.
I can't visualize how the arm is actually attached to the inner part of the can, so I'm not sure if it's something fixable (i.e. just stuck) or not (detached from the diaphragm?)
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lil-jinx
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hazetguy
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| Posted: Fri Jun 02, 2017 8:58 am Post subject: Re: Stuck vacuum advance on distributor |
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can you hold a vaccum on the canister "pipe" with your tongue when you suck on it? If you can't, the diaphragm is bad.
your third pic in the first post looks like the pipe is not seated properly into the canister housing, a.k.a. broken.
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Glenn
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| Posted: Fri Jun 02, 2017 9:29 am Post subject: Re: Stuck vacuum advance on distributor |
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It needs to come apart, cleaned, fresh lube and parts and then tested to ensure its working correctly.
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Glenn
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wcfvw69
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| Posted: Fri Jun 02, 2017 9:53 am Post subject: Re: Stuck vacuum advance on distributor |
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Agree with Glenn-
After 40 years plus, the original grease is hard and like peanut butter. Ad in dust and dirt and corrosion as well and you have sticky plates.
When I restore those distributors, they are completely disassembled, inspected and if the parts pass inspection they are polished and then re lubricated. Make sure you have two Bosch fiber washers on hand as they need to be changed as well.
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raygreenwood
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| Posted: Fri Jun 02, 2017 10:32 am Post subject: Re: Stuck vacuum advance on distributor |
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| busdaddy wrote: |
| My first step would be to remove that Compufire module, a long screw or something touching the side could be jamming up the works. |
^^^ this...is a common problem. Look carefully. If you were not careful about which screw went back into what hole....one of the screws that go through the body can commonly impinge on either the mofule or plate.
Also...most common...is that the screw that comes with the compufire unit to hold the module down.... is too long. It goes through the top plate and contacts the bottom plate on the glide ring. It effectively locks the top plate to the bottom plate.
In my many comment threads on compufire and pertronix....I have noted this before.
Ray |
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furgo
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| Posted: Fri Jun 02, 2017 10:48 am Post subject: Re: Stuck vacuum advance on distributor |
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That was exactly what I needed, thanks!
I had done a search on "distributor disassembly" on the forum before writing the initial post, but hadn't found this one.
| hazetguy wrote: |
can you hold a vaccum on the canister "pipe" with your tongue when you suck on it? If you can't, the diaphragm is bad.
your third pic in the first post looks like the pipe is not seated properly into the canister housing, a.k.a. broken. |
The pipe is fine, that is probably a visual effect on the picture. But the diaphragm might well be bad. I say might as this is the first distributor that I've taken apart, so I do not yet have a feel for how exactly each part is supposed to work.
I now also understand that to properly clean it, it needs to be done thoroughly and the distributor disassembled. That's fine, the only issue I have is with the parts I cannot take apart (and put back together), as with the vacuum can.
I can push the arm into the vacuum can with my fingers, although it does require quite a bit of pressure. The tension is probably the one it's supposed to have, and the mechanism is not sticking.
I can suck air and the arm moves into the vacuum can. It does require quite a lot of suction, and I don't manage to apply enough to make it travel to the end. I can hear the diaphragm moving and see the arm traveling, but it is probably leaking, as I believe it's not holding the vacuum and the arm creeps back into position.
It might be a case of me not being able to apply enough vacuum (also I'm doing it directly from the nipple atm). As I said, I don't have a prior reference to compare.
How do vacuum cans usually fail? Perforated diaphragms? Detachment from arm?
What I've got seems to be a case of a perforated diaphragm, as it does move the arm with a lot of suction, but it does not seem to hold it.
Assuming worst case with a non-repairable bad vacuum can, what are the options? Live with a mechanical-advance-only distributor? Paper weight? Are single vacuum cans as NLA as the distributor themselves?
Update: I just found the vacuum can discussion thread, I'm going to do some reading to better understand these things. The person who started it helpfully posted a picture of a disassembled vacuum can, which I found quite useful to have a visual picture of how they are supposed to work:
Thanks.
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hazetguy
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| Posted: Fri Jun 02, 2017 12:42 pm Post subject: Re: Stuck vacuum advance on distributor |
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| furgo wrote: |
I can suck air and the arm moves into the vacuum can. It does require quite a lot of suction, and I don't manage to apply enough to make it travel to the end. I can hear the diaphragm moving and see the arm traveling, but it is probably leaking, as I believe it's not holding the vacuum and the arm creeps back into position.
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if this is the case, then the canister is bad. when you suck, place your tongue over the end of the pipe. it should hold vacuum. if the arm returns/"creeps bacK" it's no good.
replace it. if it's got a 581 on the arm and you need one, let me know. i have a good tested one available.
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wcfvw69
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| Posted: Fri Jun 02, 2017 1:52 pm Post subject: Re: Stuck vacuum advance on distributor |
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You can't really check a vacuum advance can with your tongue or mouth 
Yes, it will move the arm but it will not show you if the can is leaking down or how rapidly.
Get a hand vacuum pump w/gauge for $20 bucks. Pump it up and see if the vacuum can will hold w/out leaking down at all..
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furgo
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| Posted: Fri Jun 02, 2017 2:45 pm Post subject: Re: Stuck vacuum advance on distributor |
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| hazetguy wrote: |
if this is the case, then the canister is bad. when you suck, place your tongue over the end of the pipe. it should hold vacuum. if the arm returns/"creeps bacK" it's no good.
replace it. if it's got a 581 on the arm and you need one, let me know. i have a good tested one available. |
Yes, it's got a "581" stamped along the length of the arm, on both sides. On the upper side it has a smaller "110" stamped across two. I'm not sure if these markings have a particular meaning or can be used to identify this vacuum can. They can be seen in pictures #3 and #4 on the first post of the thread.
I just started playing with distributors today, so I'll see if I can gather some more knowledge first, but my hunch is that I'll need a new can. I appreciate the offer and I'll PM you if I decide to get it.
| wcfvw69 wrote: |
You can't really check a vacuum advance can with your tongue or mouth
Yes, it will move the arm but it will not show you if the can is leaking down or how rapidly.
Get a hand vacuum pump w/gauge for $20 bucks. Pump it up and see if the vacuum can will hold w/out leaking down at all.. |
I just went with what I had in hand and with what others suggested in this thread (for which I'm extremely thankful!).
Given the little experience with distributors, it's difficult for me in this case to judge what to believe when opinions from two experts diverge as in here. I.e. someone says the tongue test works, someone else says it doesn't.
Generally I favour using measuring devices, but I'd be just doing a one off pass/fail test for this one, which I'm not sure justifies getting a vacuum pump for. But perhaps it can come in handy for other jobs too  .
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Glenn
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| Posted: Fri Jun 02, 2017 2:53 pm Post subject: Re: Stuck vacuum advance on distributor |
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| furgo wrote: |
| Yes, it's got a "581" stamped along the length of the arm, on both sides. On the upper side it has a smaller "110" stamped across two. |
581 is the part number, 110 is the date stamp.
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Glenn
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Tcash
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| Posted: Fri Jun 02, 2017 2:54 pm Post subject: Re: Stuck vacuum advance on distributor |
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For the uninitiated, thanks to Rob.
Link
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furgo
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| Posted: Fri Jun 02, 2017 3:16 pm Post subject: Re: Stuck vacuum advance on distributor |
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| Tcash wrote: |
| For the uninitiated, thanks to Rob. |
That's the first place where I saw this test, yes.
| Glenn wrote: |
| 581 is the part number, 110 is the date stamp. |
Thanks again.
I found the part number for the vacuum can from the Bosch - VW distributor information list. According to it, the can is:
• VW 021 905 271 F
• Bosch 1 237 121 581
Also, just for the fun of it, I looked up the stamped dates on the date codes chart in that PDF:
• Distributor: 831 - Nov 1978
• Vacuum can: 110 - Oct 2011 - would mean it's been replaced once at least? According to Bosch, these were produced until April 2014.
Anyway, I now know the part number I need to look for, and a potential source from Hazetguy. As per the previous posts, I suspect mine is broken.
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Wildthings
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| Posted: Fri Jun 02, 2017 3:40 pm Post subject: Re: Stuck vacuum advance on distributor |
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| wcfvw69 wrote: |
You can't really check a vacuum advance can with your tongue or mouth
Yes, it will move the arm but it will not show you if the can is leaking down or how rapidly.
Get a hand vacuum pump w/gauge for $20 bucks. Pump it up and see if the vacuum can will hold w/out leaking down at all.. |
Why not? You suck on the hose until the arm moves and then close the hose off with your tongue. You can hold the vacuum this way for as long as you want. If the arm doesn't return until you get tired of looking a bit weird the can is not leaking. |
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wcfvw69
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| Posted: Fri Jun 02, 2017 4:09 pm Post subject: Re: Stuck vacuum advance on distributor |
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| Wildthings wrote: |
| wcfvw69 wrote: |
You can't really check a vacuum advance can with your tongue or mouth
Yes, it will move the arm but it will not show you if the can is leaking down or how rapidly.
Get a hand vacuum pump w/gauge for $20 bucks. Pump it up and see if the vacuum can will hold w/out leaking down at all.. |
Why not? You suck on the hose until the arm moves and then close the hose off with your tongue. You can hold the vacuum this way for as long as you want. If the arm doesn't return until you get tired of looking a bit weird the can is not leaking. |
Why do it half ass? I guess I'd rather spend $20 on a tool to insure I'm getting an accurate assessment of the parts I'm inspecting.
I really enjoy folks telling me at swap meets that the vacuum can on a used distributor I'm looking at is good "cuz they checked it with their mouth and tongue". It brings me lots of pleasure to pull out my hand vacuum pump with a gauge, hook it up and watch the can leak down right in front of them.
So, the vacuum can is good huh? Right...
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Follow me on instagram @sparxwerksllc
Decades of VW and VW parts restoration experience.
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**Now rebuilding throttle bodies for VW's and Porsche's**
**Restored German Bosch distributors for sale or I can restore yours**
**Restored German Pierburg fuel pumps for sale or I can restore yours**
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