14 replies to this topic

[mattbeddow]

Hello

At some point a previous owner has changed the points in my 59D distributor and not put it back together properly.
As a reslut the vacuum advance doesnt function.

I have it on good authority that there is a plate behind the points that should move but as the wrong screw and washer combinations were used when it was reassembled, the plate is locked in place and so it doesnt work, and as such has probably bust the vacuum unit.

So ive been looking about for a diagram or set of instructions that shows how these things are ment to go together so i can fix it, but cant find them.

Any ideas?
Cheers

[tiger99]

There is a diagram here which may help:

http://www.somerford...page=page&id=74

Item 34 consists of the fixed and moving base plates.It is likely that an excessively long points securing screw, item 27, has caused the problem, but I don't think that it will have damaged the vacuum unit, just by preventing it from moving.

[mattbeddow]

Thanks, that does help a bit.

Ive ordered a new set of screws so hopefully they should be ok.

How do i test if the vacuum unit is broken then?

[Ethel]

Sucking on it should show just enough movement to show if the diaphragm is still air tight. You can check its effect with a timing strobe when the engine is running by just disconnecting / reconnecting the vac pipe.

[dklawson]

Just to ease your mind, fixing the breaker plate so that it does not move does not cause damage to the vacuum module. All it does is pull hard against something that won't move. If there is damage to the vacuum module, blame it on age, not the previous owner.

The test method for vacuum modules is easy enough. Make sure those long screws are not installed in the breaker plate. (Make sure the breaker plate can pivot as it is supposed to by pushing it with a screwdriver or similar). Disconnect the vacuum hose from the distributor. Fit a hose temporarily to the vacuum unit and suck on the end of the hose. If air rushes into your mouth, the vacuum unit diaphragm is ruptured. If the breaker plate moves and then returns to rest when you release the hose, the vacuum advance module is fine.

[mattbeddow]

Ok thanks,
the guy at the garage said the vacuum advance was "shot" then discovered this locked plate so i dont know if the vacuum unit is ok or not.

Ive also found some instructions for the 25D distributor by searching for "overhaul" rather than "rebuild" so hopefully i can find one for the 59D

[dklawson]

Study the diagrams and instructions for the 25 series distributor, then dive in. Yes, there are differences but the construction will be similar enough to learn from the 25D instructions.

Your mechanic may have just seen that the breaker plate did not move (no spark advance) when he tried to suck on the vacuum line to the distributor. You may find that with the correct length screws the vacuum module works fine.

Why do you feel the distributor overhaul is needed? If it was based on your mechanic's observations, perhaps fitting the correct length screws will be all that is necessary. Keep in mind that if the vacuum advance is not working this will NOT rob you of power or acceleration. The vacuum advance is there to provide mid-throttle, cruising fuel economy.

[mattbeddow]

He found it when sucking on the pipe it made no difference to the timing, he only later discovered the locked plate.

I decided to give it an overhaul because as well as this the points need replacing (thinking of going to electric points) so i figured while it was apart for that id clean it up a bit (was filthy inside)
ITs not a full overhaul really, i just thought if i could find overhaul instructions then id know roughly how its ment to go together. i dont think im going to take the shaft out or touch the weights if i dont have to.

Ill check the vacuum unit today before making the decision on what to do as im still waiting of the correct screws arriving so cant do much work on it till next weekend.

Edited by mattbeddow, 02 September 2012 - 07:42 AM.

[Ethel]

Search for 45d the 59 is just a minimal revision of it.

http://www.mgb-stuff.org.uk/vacadv.htm

[mattbeddow]

Thats a very interesting website, thanks.

Took the vacuum unit off and it is shot, air would freely flow while sucking and the lever didnt move, so to the internets to find a replacement

As a side note, i have now learnt to check the haynes first, for everything, as it is covered in detail in there *facepalm*
I might put together a short guide when im done, if anyone thinks its worthwhile?

[mattbeddow]

Next question: is it critical that i get a vacuum unit with exactly the same advance characteristics (3 9 8) as very few websites actually quote these details and the ones that do want £60+ for them

[dklawson]

Ideally the vacuum module should be the same as the one shipped with your car's engine. The amount of vacuum advance will have been selected by the factory to be optimal for your engine. However, is this engine original to your car? Is the distributor original to the engine?

Keep in mind my earlier comment. You do not have to have a working vacuum module. It is there for mid-throttle, cruising fuel economy. Your Mini has been operating without vacuum advance since whenever the longer screws were installed in the breaker plate. If you were happy with the car's fuel economy before, leave it alone. Plug the vacuum line connection to the carb and drive the car as it is now.

There is math you can do to determine your payback (from improved fuel economy) by installing the replacement vacuum unit. Since we are NOT talking about doubling your fuel economy... I think it safe to say you would be disappointed in how long you will have to drive your car to receive a payback from improved fuel economy with a new vacuum module.

[mattbeddow]

Ok, i dont know if the distributor is the original one but i hove no reason to suspect either have been replaced.

Ii know its purpose now and i understand what you are saying about the limited improvements in economy for the expense, but im the kinda guy that just like everything to work as it should so im determined to fix it

[dklawson]

That's fine. There is nothing wrong with fixing it just to have it "right". My comments were only to warn you that if the mechanic tells you how much money that vacuum module is going to save you... you would have to drive a long time to earn back its cost.

If you are going to replace the module, my advice is to buy the right one even if it costs more. Though outwardly they appear similar, internally they have different springs which will affect how much advance they can deliver. As I mentioned, the factory will have chosen a vacuum module that was correct for your engine.

[mattbeddow]

Fair enough, ill search around for the correct one, might mean a fair few emails to the different sites asking for the info.

The mechanic is a mini specialist near me who i took my mini to to fix an emissions issue, charged me £12 for his labour and also spent a further 40 mins going through some other things that wernt right with the car and telling me how to fix them, they are all fairly minor things and easy to do so i figured "why not"