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MG MGB Technical - slow electrics

2 questions about my 77 bgt.

1- the overdrive engages quickly, but takes several seconds to disengage when the car is cold, when its warmed up, there is no problem. Any ideas, or do I have to put up with this?

2- my drivers side indicators are a bit slow, but the passenger ones dont even flash. (the hazards work well, in fact i reckon they are a bit quick). Again, any ideas?

All ideas greatfully received.

John
John Collins

John - I'll let someone more knowlegable answer your question about the O/D unit. Regarding your indicators, start withthe passenger side indicators, start the engine and switch the passenger side indicators on, then look at both front and rear lights. Chances are very good that one of them is not lit at all, while the other is on constantly. The standard flasher unit used for the indicators is current dependent. By that I mean that it requires the current from two light bulbs to flash at the correct rate. If one bulb is burned out or not working due to bad connection, ground, etc. the flasher will not flash. Conversely, if you add a third light bulb to the mix (as in plugging in a set of lights of a trailer, the flasher will flash very quickly and very fast. This set up is used for the flashers so the driver will know if one of hte bulbs is burned out. With this in mind, check first if both of the bulbs are good. If you don't have a burned out bulb, then start checking connections, both power and ground (Note: the sockets for the bulbs are crimped together and sometimes corrosion can bulid up in the crimp, causing the bulbs not to come on. About the only thing you can do about this situation is to replace the sockets). Somewhere in this mix, you should find the offending item and can fix it. Pay particular attention to the ground points on the chassis. These need to be quite clean to insure a good, long lasting ground (see my article on ground point preparation at: http://www.omgtr.ca/technical/General%20Technical/grounding.htm)

On to the driver's side indicator flashing slow, see the above information regarding connections. Additionally, check that both bulbs are the proper type and that one of them is not a really cheap bargin basement bulb.

Finally, "the hazard flashers work properly or perhaps a bit fast". The flasher unit used for hazard is a special unit that is not current dependent. It flashes at a constant rate regardless of how many bulbs are in the circuit (4 in the case of the hazard lights). The flashing rate is set by the flasher unit and by a small amount by the system voltage. Don't be tempted to use a hazard flasher unit for the indicators to cure your porblem, it will only mask the problem (I suppose that if you don't know about a problem, then it doesn't exist does it? - up side down logic used by some).
Good luck - Dave
David DuBois

John - I should have added to the above that for more information on the above subjects, go to Paul Hunt's web site, The Pages of Bee and Vee at: http://www.mgb-stuff.org.uk/ click on Hammer & Spanner, then on Electrics and finaly on Turn and Hazard Signals. There is also a wealth of other information on Paul's web site - it is well worth bookmarking (or adding to your Favorites). Good luck - Dave
David DuBois

Dave

Thanks for that, I will go and clean connectors, I know that all bulbs work, the passenger side ones stay on, they occasionally flash (when they feel like it I guess) if I have lights, heated rear window etc switched on at the same time, then they definitely dont flash.
John Collins

My 73 and 75 OD are the opposite - take a moment to engage but disengage instantly. It *could* be mucky oil or partially blocked passages, a filter clean and oil change preceeded by flushing with ATF might help. Otherwise live with it.

It is quite possible for the flashers to not flash even though both bulbs are glowing, although if one bulb is out the standard flasher will definitely not flash the remaining bulb. Because it is only one side then a bad connection or other problem on that side is, erm, indicated. However you can have several small faults, some in the common part of the flasher circuit and other on one side, that combine to cause non-flashing on that side but not the other, but clearing the *common* fault will allow the 2nd side to flash as well.

Whilst a rubber bumper front indicators usea a wired ground, shared with the headlights and coolig fan, the rears on all cars (and CB fronts) rely on the physical fixings to the body for their ground connection. Any large loads like headlights, cooling fan, heated rear window also cause a drop in system voltage which will also slow flashing or stop in marginal cases. And because of this it is difficult to tell without a voltmeter whether it is the normal system voltage that is causing a flasher to stop or a bad shared ground. If turning on the parking lights causes it then there is a fair chance that the rear cluster that side has a bad ground.

As Dave says the hazard flasher is a different unit and is largely voltage and current independant. The two should flash at about the same rate so if your 'good' side is noticeably slower than that it indicates you have slight problems that side or in the common wiring as well. I would reiterate the warning not to be tempted to use a hazard flasher in place of the indicator to 'solve' this, in that the indicator flasher has this current sensitivity built-in to act as a warning if one bulb has failed. There are also so-called 'heavy duty' flasher units which have the same problem. Modern cars use an electronic 3-pin unit which also doesn't have this sensitivity to bad connections and flashes at double-speed instead if one bulb is out. Some recommend using one of those instead, but it is only masking bad connections, much better to fix them instead. Bad connections anywhere in the brown - ignition relay - white/brown - fusebox - green - hazard warning switch - light-green/brown - indicator switch etc. through the lights to the body can cause this. There are an awful lot of connections in the circuit. Measuring the voltages with a digital instrument at each point will help you track it down, but don't just expect to find one.
Paul Hunt

Thanks for info Paul, Im guessing bad connections at the rear as the carpet below the light is wet (I noticed this today) so Im guessing that water is getting in and causing poor connections.

Need a dry day so that I can sort things like this, but I will order some new light gaskets ready to do the job and seal the lights first and I will clean the connectors at the same time.

As for od, I will try to change the gearbox oil over the christmas hols, and see if that makes any difference.

John
John Collins

This thread was discussed between 20/11/2004 and 21/11/2004

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