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Technical Area => Questions and Answers => B roadsters rubber-bumpered ('75 to '80) => Topic started by: Norman and Diana on March 31, 2008, 04:42:59 PM

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Title: Vacuum advance
Post by: Norman and Diana on March 31, 2008, 04:42:59 PM
Well the "new" car suddenly lost  power.  After much trouble shooting I found that the vacuum advance unit was shot.  I have a new one on the way but have a simple question about it.  Can the advance unit in an MGB C.E.I. unit be replaced with out removing the distributer from the car?  I don't mind removing it if it is necessary or will make the job that much easier, but if I can leave it in and it is just as easy than that is what I will do.

Title: Re: Vacuum advance
Post by: Art on March 31, 2008, 11:44:00 PM
The vacuum advance units on the 45D type distributors can be replaced with the unit in the car, but it makes life difficult.  Especially depending on what position the advance unit was set in when the distributor was installed and if your car still has its AIR pump and emission control gear in place.

There are small screws holding the unit to the distro body that go in sideways and the whole sliding plate and other internal assemblies that have to be removed and reassembled to connect it.  Many small screws and things that might fall into the works and be lost. 

Also, there could be reasons for the failure beyond the diaphragm.  Make sure you check that the sliding plate has not seized, broken or is otherwise stuck in one position.  Also that the upper and lower shafts are not worn and the weights and springs are intact and functioning properly.  While you would definitely have to reset the timing on removing and reinstalling the unit (which would be a good idea and probably necessary anyway even if just replacing the advance unit), removing the distributor gives you an opportunity to properly clean and inspect the workings.

My advice would be to photograph or otherwise mark the advance unit position and wiring so you can reinstall it fairly close to where it came from and take it out to bench inspect and repair it.

Just another note: You already ordered the advance unit.  Lucas distributors for MGB's are completely interchangeable as complete units.  Any of them will fit the engines and drive from 62-80.  Most MG's, for reasons you are now beginning to see, do not have their original distributor anymore.  Early 45DE "Opus" units, as your car should have, were notoriously bad and most have been replaced either with the earlier point-type models, later CEI units or aftermarket conversions.  You mentioned you have a CEI distributor.  Someone might have installed one on your car, but the advance units for the various 45DM (CEI) units are all different.  If you have not already, you might have to check the distributor's Lucas part number to be sure what you ordered is correct.

I hope that helps you.  Good luck.


Title: Re: Vacuum advance
Post by: Norman and Diana on April 01, 2008, 01:48:53 AM
Thanks,  I checked the dist. number so I am pretty sure I have the right one on the way.  The car sat for four years and most of the rubber parts are in need of service.  I can manually advance the plate but applying vacuum will not pull it around and you can hear air drawing through the unit.  I'll just go ahead and pull the dist.  I was hoping to avoid pulling it simply because I don't have ready availability to a bench to work on right now.


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