Odd battery/starting problem

If the headlamps dim then the neede should drop unless you've not connected it the way you think you have.

Yeah but it doesn't. Voltmeter connected across battery.

I'm wondering if the immobiliser might have got confused. Doesn't explain why it started fine on a jump last night but might explain the complete under bonnet silence. There's not even a click when I turn the key

Tim

I doubt that the immobiliser would be configured to inhibit the starter. With no volt drop at the battery, the dimming of the lights when you turn the key suggests excessive supply resistance.

When you're sure the battery connections are OK, check for volt drop under load between (a) Battery negative terminal and the chassis/body. (b) Battery positive and the feed to the starter solenoid. By that I mean the thin wire that energises the solenoid, not the thick lead from the battery.

If it's too awkward to get to the starter area, it may be easier to monitor the voltage reaching the fuse box.

Is this one where the clutch must be pressed down when starting?

Funny you should mention that..... DOH!

One week driving a crappy old hire car and I completely forget how to start mine! Fereling very stupid.

Our hire car incidentally was a 20 year old Nissan Sentra

(B13 model) which apart from knackered suspension, bald tyres, and leaking windows, still looks like a remarkably contemporary car. Funny how timeless some designs are.

Tim

[...]

I'll bet that if the worry about the battery hadn't distracted you, it wouldn't have been forgotten.

Yet again a problem solved by Mr C's 'think of the basics first' method!

Chris

OK,if the headlamps are dimming but the battery voltage is good then you've got a duff earth bond, try metering battery + to the engine block & if that drops when you crank it then check all the large bonds starting with the battery terminal

I first came across this 'fault' many years ago, my father had bought a 'foreign' car and asked me to come and look at it as it would not start. I got in and it immediately started OK. Dad got in and it wouldn't !!

Much head scratching and I realised it had a clutch pedal interlock.

It had worked for me because I always press the clutch down and hold it down when trying to start a car (or bike), not because of the interlock (which I had not encountered at that time) but purely to aid starting (less drag) and because I always leave (my) cars in gear (pressing the clutch reduces undesirable forces on everything when you put it back to neutral (if it has moved at all) Particularly important as I have always lived on a hill and driven many old wrecks, both my own and my dad's. I guess dad had lost that habit by then as he was starting to lose it in general (dementia)

I always leave customers cars in neutral because most drivers do not check before starting up.

The funny thing is, I've done that for years too! I think the fact that the hire car was an auto "undid" my normal starting routine.

Tim

I drive both all the time so it remains second nature, but it is amazing how fast you can forget something, good job it wasn't something dangerous! The other thing that can throw out your starting routine is if you just sit in the driver's seat sideways with your legs out, just to start it to see if it is OK. I know I have done that.

Years ago I was trained to never hold the clutch down while starting because the friction of the clutch release bearing was greater than the viscous drag of the gearbox in neutral.

Presumably clutch release bearings have improved since then ...

I doubt whether the drag would be more than the gearbox gives, even with carbon block bearings, BUT there may be some mileage in the idea regarding the crankshaft thrust bearings. On some old engines they sometimes wore so badly they fell out because pushing the clutch down shoves the crank quite hard forwards and that could give quite a bit of drag, especially with older type thicker oil.

*If* you are sticking the voltmeter prods into the battery *terminal post* rather than clipping it to the connector, resistance between the post and the connector will give this symptom

The conventional rwd car 3 or 4 on the floor box has the whole layshaft stuck in cold oil driven by the drop gear from the input shaft which is splined into the clutch hub. Only the output shaft that sits clear of the oil is decoupled from the clutch by selecting neutral. So the idea that a single row ball bearing could have more drag is quite odd. Unless it had failed quite badly on the car you were taught on.

Modern FWD gearboxes have some gears fixed to input and some to output. Some RWD ones are also doing this as gears that run at output speed only incur high oil drag at high road speed.

I was taught the opposite for cork lined motorcycle clutches. Some bikes could develop stuck plates quite quickly. Ignition off, put it in gear, pull the clutch and kick it over to free the plates. Then select neutral, pull the clutch and kick it with ignition on. If the plates had stuck and weren't freed off, once running putting it in gear means damage to the 1st gear dogs and possible unintended motion. Of course there was always the story about the bike departing without rider that resulted from forgetting to cut the ignition and it (quite unbelievably) catching on first prod with stuck plates. "it leapt out of my hands and climbed a wall, then went though . glass house .. and fence . and . pond ".

On some cars that is certainly correct, whereas on others the opposite applies, so it's wrong to make a general rule.

Clutch down and it doesn't matter if it has been left in gear (and you haven't checked) also covers you in case of a clutch switch being fitted.

I can see a potential hazard with that system, but on some cars having the clutch down does increase the starter load. Any connoisseur of the Hillman Hunter will attest to that.

Given there's thousands as times as many vehicles with clutch switches as hunters left that's arguably true but fundamentally misleading.

The explanation I was given was that the clutch release bearing was a carbon block.

The only two car gearboxes I've ever taken apart were:

1) a mini, which swims totally in engine oil 2) a Vauxhall Viva HA. From memory the layshaft was alongside the mainshaft - but it's a long time ago now ....