Clutch safety switch purpose?

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On the British car forum I'm on, somebody had some trouble during a safety inspection because his car wasn't equipped with a clutch safety switch, and apparently the regulations didn't account for the fact that they weren't mandated until 1980 or so. I usually don't clutch my MG when starting because it's kinder to the weak thrust bearings, and it never had a clutch safety switch either.
 

ZeeOSix

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I usually don't clutch my MG when starting because it's kinder to the weak thrust bearings, and it never had a clutch safety switch either.
One clutch in start-up, then driving it many miles and depressing the clutch pedal 100+ of times to shift. Don't think doing 1 clutch out start-up per 100+ additional clutch cycles will ever matter.
 
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It's one nanny feature I never gave much thought to. I park in first, when I get in to drive I depress the clutch, I shift to neutral, and start the engine. If it's a cold start I let off the clutch and idle until the rpms get to 1,000, then it's clutch in and into first or reverse and go.
 
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One clutch in start-up, then driving it many miles and depressing the clutch pedal 100+ of times to shift. Don't think doing 1 clutch out start-up per 100+ additional clutch cycles will ever matter.
Except there's no oil pressure when starting it versus while it's running.
 

Pew

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I'm also dumb enough to have started a manual in gear with the clutch disengaged just to dump it and stall the engine 🤦‍♂️
I've done that more than I'd like to admit. Also did that in a drive thru cause I thought I was in neutral instead of first.
 
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How would that affect a throw out bearing, which was the concern stated…
Who stated that? I was talking about the THRUST bearings in the engine, not the throwout bearing. Triumph 1500 (used on the 75-79 MG Midgets) and TR6 engines use the same troublesome crankshaft thrust bearings, so one recommendation to help them last longer is to avoid clutching when starting the engine if you can because the rear thrust bearing has to take all the force from the clutch springs and there's no oil pressure yet.
 

Astro14

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Who stated that? I was talking about the THRUST bearings in the engine, not the throwout bearing. Triumph 1500 (used on the 75-79 MG Midgets) and TR6 engines use the same troublesome crankshaft thrust bearings, so one recommendation to help them last longer is to avoid clutching when starting the engine if you can because the rear thrust bearing has to take all the force from the clutch springs and there's no oil pressure yet.
Then I misunderstood what was meant in your first post. I appreciate the clarification.

I don't have this concern with either of my manual cars, or I never considered it, and I've not worn out a thrust bearing.
 

ZeeOSix

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Who stated that? I was talking about the THRUST bearings in the engine, not the throwout bearing. Triumph 1500 (used on the 75-79 MG Midgets) and TR6 engines use the same troublesome crankshaft thrust bearings, so one recommendation to help them last longer is to avoid clutching when starting the engine if you can because the rear thrust bearing has to take all the force from the clutch springs and there's no oil pressure yet.
I missed the thrust bearing focus too. But IMO the thrust bearing should have a residual oil film on it during start-up, just like any journal bearing in the engine has.

I'd bet the load on the crank thrust bearing with the clutch pedal depressed is less force than the force on a rod bearings when the engine first fires up. There would have to be a large lack of oil flow (constant zero oil pressure) to start causing damage. How does anyone know the rear thrust bearing is designed well and getting adequate lubrication while it's always running? Is the oil supply really pressure fed, or is it splash fed? Maybe they just wear out early from normal engine running due to design issues on that specific engine.

Doing a cold start-up in millions of cars all over the globe doesn't cause their journal bearings or crank thrust bearings to fail - meaning the residual oil film seems adequate for a second or two until oil flow starts moving.
 

Avery4

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I missed the thrust bearing focus too. But IMO the thrust bearing should have a residual oil film on it during start-up, just like any journal bearing in the engine has.

I'd bet the load on the crank thrust bearing with the clutch pedal depressed is less force than the force on a rod bearings when the engine first fires up. There would have to be a large lack of oil flow (constant zero oil pressure) to start causing damage. How does anyone know the rear thrust bearing is designed well and getting adequate lubrication while it's always running? Is the oil supply really pressure fed, or is it splash fed? Maybe they just wear out early from normal engine running due to design issues on that specific engine.

Doing a cold start-up in millions of cars all over the globe doesn't cause their journal bearings or crank thrust bearings to fail - meaning the residual oil film seems adequate for a second or two until oil flow starts moving.
Assuming decent maintenance, a properly designed engine, and a stock clutch, I wouldn't expect thrust bearing wear to be a problem for the reasonably expected life of the vehicle. However, as you said, specific engines can have issues with premature wear from design issues.

Aftermarket clutches with more than stock spring tension can cause issues too since it could put more force on the thrust bearings than they were designed to tolerate. Any bearing will fail prematurely if overloaded. I know in the high performance Honda community it's pretty common for people to bypass the clutch switch when a heavier than stock clutch is used to prevent unnecessary thrust bearing wear.
 
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