A pain in the Diodes? MGB handbrake light / starter
Discussion
Advice please.....
Driving home a couple of days ago (on motorway) some none too healthy sounds started to eminate from under the bonnet. I pulled off at the next opportunity and stopped to investigate. The starter motor refused to work. I could find nothing else amiss so bump started the car (luckily I'd stopped on a slope!) and drove home (nasty noise now occasional).
Having checked all of the (I think) obvious things I removed the starter motor which smells of burnt electric bits and will only turn with a nasty rough mechanical feel.
Now, I have a replacement starter but before I install I want to make sure it doesn't instantly go the same way as the last one. I understand that there's a diode in the hand brake warning light circuit that, in a certian failure mode, causes the starter to run. so:-
1. Is this likely to have happened while I was en-route causing the starter to engage with the engine running thus knackering it? (Obviously the H/B was off at the time).
2. Where is this damn diode anyway? ("Up behind the dash" isn't very helpful!)
3. If I just disconnect it (short term) will this fix the problem?
4. Why should a diode cost £30!!!!!
Driving home a couple of days ago (on motorway) some none too healthy sounds started to eminate from under the bonnet. I pulled off at the next opportunity and stopped to investigate. The starter motor refused to work. I could find nothing else amiss so bump started the car (luckily I'd stopped on a slope!) and drove home (nasty noise now occasional).
Having checked all of the (I think) obvious things I removed the starter motor which smells of burnt electric bits and will only turn with a nasty rough mechanical feel.
Now, I have a replacement starter but before I install I want to make sure it doesn't instantly go the same way as the last one. I understand that there's a diode in the hand brake warning light circuit that, in a certian failure mode, causes the starter to run. so:-
1. Is this likely to have happened while I was en-route causing the starter to engage with the engine running thus knackering it? (Obviously the H/B was off at the time).
2. Where is this damn diode anyway? ("Up behind the dash" isn't very helpful!)
3. If I just disconnect it (short term) will this fix the problem?
4. Why should a diode cost £30!!!!!
I don't know if you've already looked here but in case not Paul Hunt's excellent web site mgb-stuff - http://www.mgb-stuff.org.uk/electricstext2.htm#sta...
I've struck this before, the car wouldn't crank with the key, but would crank when you pulled the hand brake! It turned out to be the diode and from memory it is a black square item with a male spade coming out at each end. I think it was taped in to the loom behind the instruments area. The diode was visible and the loom taped over the connectors on either side of it.
HTH
HTH
Found the problem....
The ignition switch is in the process of failing. Betwen position 2 (ign on) and 3 (start) there's only a hairs bredth. So, what had happened was that while whizzing down the motorway the key moved that fraction and engaged the starter thus 'lunching' it.
Having dismantled the ignition switch (the non-key bit) all seemed ok but, on replacement, the problem remains. Until I can fix properly I now have a switch so I can disable the starter circuit. Not a perfect solution but it gets me out of a hole.
Anyone else had this problem? Solutions?
The ignition switch is in the process of failing. Betwen position 2 (ign on) and 3 (start) there's only a hairs bredth. So, what had happened was that while whizzing down the motorway the key moved that fraction and engaged the starter thus 'lunching' it.
Having dismantled the ignition switch (the non-key bit) all seemed ok but, on replacement, the problem remains. Until I can fix properly I now have a switch so I can disable the starter circuit. Not a perfect solution but it gets me out of a hole.
Anyone else had this problem? Solutions?
ATE399J said:
Found the problem....
The ignition switch is in the process of failing. Betwen position 2 (ign on) and 3 (start) there's only a hairs bredth. So, what had happened was that while whizzing down the motorway the key moved that fraction and engaged the starter thus 'lunching' it.
do you mean ignition key barrel or ignition switch is loose?The ignition switch is in the process of failing. Betwen position 2 (ign on) and 3 (start) there's only a hairs bredth. So, what had happened was that while whizzing down the motorway the key moved that fraction and engaged the starter thus 'lunching' it.
note from Paul's site - 'My starter is cranking all the time! On 76 and later models this can be caused by the 'brake test' diode having gone short-circuit. On all models it can also be caused by failure of the ignition switch, a sticking starter relay (1970-on), sticking solenoid, or chafed wiring.'
ATE399J said:
Having dismantled the ignition switch (the non-key bit) all seemed ok but, on replacement, the problem remains. Until I can fix properly I now have a switch so I can disable the starter circuit. Not a perfect solution but it gets me out of a
sounds like you either need a new ignition (electric) switch in which case be careful to buy a good quality one - or you need a new key barrel and possibly new keys to match - or the key barrel repairing if you can take it apartnta16 said:
sounds like you either need a new ignition (electric) switch in which case be careful to buy a good quality one - or you need a new key barrel and possibly new keys to match - or the key barrel repairing if you can take it apart
Yes, that's the square I'm in at the moment. They seem pretty expensive compared to other MG parts (about £65) so I'll have a look at the one fitted to see if it's 'fixable' first.Incidentally, I changed the track rod ends over the weekend and went to have the tracking checked on Monday. The garage (one of those tyre & exhaust places) couldn't do it because "We don't have MG B on the computer and we can't put the settings in manually". So, Computer said "No". Sign of the times?
ATE399J said:
Yes, that's the square I'm in at the moment. They seem pretty expensive compared to other MG parts (about £65) so I'll have a look at the one fitted to see if it's 'fixable' first.
Incidentally, I changed the track rod ends over the weekend and went to have the tracking checked on Monday. The garage (one of those tyre & exhaust places) couldn't do it because "We don't have MG B on the computer and we can't put the settings in manually". So, Computer said "No". Sign of the times?
My local garage did not charge just to check after I've done some work on the steering, but you have tell them the req toe-in.Incidentally, I changed the track rod ends over the weekend and went to have the tracking checked on Monday. The garage (one of those tyre & exhaust places) couldn't do it because "We don't have MG B on the computer and we can't put the settings in manually". So, Computer said "No". Sign of the times?
DocArbathnot said:
My local garage did not charge just to check after I've done some work on the steering, but you have tell them the req toe-in.
I did tell them but they were unable to get the computer into a mode where it would accept typed-in data - it would only set up to what was in its look up tables. Which, strangely, DID include Spitfires, Heralds and the like but NOT MGBs!nta16 said:
oh dear to the cost of locks/switches and very oh dear for wheel alignment either you need a less 'advanced' computer machine or a more advanced operator to get round what the computer wants
Wheel alignment: Either would do, I was just wishing to raise a communal sigh to the state of modern garages.Price of the switch: I don't want to spend £65 if I don't have to!! I think something has rotated somewhere when it shouldn't have although the whole thing appeared to be 'keyed' so it could only be assembled in one way.
ATE399J said:
Either would do, I was just wishing to raise a communal sigh to the state of modern garages.
I don't think many here would take them to modern garages, many either do it themselves, or the car goes out so rarely so it 'never needs any work doing to it' or they take it to a garage where computers are few and far betweensome garages must still have the old metal rod gauge things or the now old new fanged hang it on your wheel red light things
or you could do as WO put and swat up string and sticks method and then progress to building a pyramid in your back garden, subject to planning permission of course
when I put new I should have perhaps put new to you or replacement as sometimes a good s/h part from a reliable source can be much better than some new made parts
good luck
I replaced the TRE's with new, new (from a reputable supplier) because the rubber boots had split. Although I didn't disturb the lock nuts the replacement TREs are obviously significantly different to the old ones in the thread-on-to-the-rod dimension.
I will either find a "traditional" garage or use a long straight edge / Vernier calipers to sort it out.
P.
I will either find a "traditional" garage or use a long straight edge / Vernier calipers to sort it out.
P.
ATE399J said:
I replaced the TRE's with new, new (from a reputable supplier)
yeah I got TREs and steering rack gaiters from two different reputable suppliers neither lasted more than 6 months and the replacement gaiters have started to craze a worry with the (recently introduced) MoT requirements for next year's MoTATE399J said:
or use a long straight edge / Vernier calipers to sort it out.
don't forget to allow for the moment of the sun and moon 
nta16 said:
yeah I got TREs and steering rack gaiters from two different reputable suppliers neither lasted more than 6 months and the replacement gaiters have started to craze a worry with the (recently introduced) MoT requirements for next year's MoT
Perhaps I should dig the old ones out of the bin then - it was only the rubber seal that'd perished rather than then actually having any play.I will of course allow for the Coriolis component -
http://abyss.uoregon.edu/~js/glossary/coriolis_eff...
and the birth sign of the car when setting the tracking as well.
You really don't need any fine measuring tools.
Measure across the front and rear of the front wheels. If the rear measurement is less than the front then it's toeing out, if it's more then it's toeing in.
Adjust as required. The whole process takes circa 10 mins from start to finish. Do it with the wheels on the floor loaded up.
The tool I use is for want of a better description a long broomstick (it isn't a broomstick as they aren't long enough, but 2 fastened together work) with a pair of blades that stick out at 90 degrees from it |_________________| like so. One of the blades is bent over inwards at the top to meet the wheel rim, the other one has a hole drilled in it and a piece of threaded bar to meet the rim. This allows an accurate measurement to be taken off the wheel rim at the front and rear of the wheel, getting around the tyre and also allowing you to hang the bar down and avoid the chassis. It works well but I still use string when I can't be bothered to get it down.
Measuring camber is equally simple with a plumb bob.
Measure across the front and rear of the front wheels. If the rear measurement is less than the front then it's toeing out, if it's more then it's toeing in.
Adjust as required. The whole process takes circa 10 mins from start to finish. Do it with the wheels on the floor loaded up.
The tool I use is for want of a better description a long broomstick (it isn't a broomstick as they aren't long enough, but 2 fastened together work) with a pair of blades that stick out at 90 degrees from it |_________________| like so. One of the blades is bent over inwards at the top to meet the wheel rim, the other one has a hole drilled in it and a piece of threaded bar to meet the rim. This allows an accurate measurement to be taken off the wheel rim at the front and rear of the wheel, getting around the tyre and also allowing you to hang the bar down and avoid the chassis. It works well but I still use string when I can't be bothered to get it down.
Measuring camber is equally simple with a plumb bob.
nta16 said:
ATE399J said:
it was only the rubber seal that'd perished
that's the bit that'll get you an MoT mention or fail (and possibly crud in there)http://www.balljointboots.co.uk/
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