WTF is a Hobbs switch???

[Ricko1966]

Okay a while back somebody needed a switch for his kick down on his TH400,he ended up 3d printing a bracket to mount a mechanical switch.I stated I thought a Hobbs switch would be an easier solution than fabbing a bracket. Whether it is or is not the easy route, I'm sure a lot of you don't know what a Hobbs switch is. So I'm putting this up here just to educate and give people options they never even knew they had. A Hobbs switch is a on/off switch controlled by pressure,whether it's vacuum or positive pressure it's still just opens or closes a circuit. A plain Jane on off oil pressure switch is a good example no oil pressure the switch is closed your light comes on. For those that have 700r4s they have a Hobbs switch on the firewall to unlock the converter at wot. So just telling people that didn't know if you want to turn something on or off at WOT or Idle under boost whatever it's as easy as mounting a switch and running a vacuum line or oil pressure line.

 

[Dryriver1]

Okay a while back somebody needed a switch for his kick down on his TH400,he ended up 3d printing a bracket to mount a mechanical switch.I stated I thought a Hobbs switch would be an easier solution than fibbing a bracket. Whether it is or is not the easy route, I'm sure a lot of you don't know what a Hobbs switch is. So I'm putting this up here just to educate and give people options they never even knew they had. A Hobbs switch is a on/off switch controlled by pressure,whether it's vacuum or positive pressure it's still just opens or closes a circuit. A plain Jane on off oil pressure switch is a good example no oil pressure the switch is closed your light comes on. For those that have 700r4s they have a Hobbs switch on the firewall to unlock the converter at wot. So just telling people that didn't know if you want to turn something on or off at WOT or Idle under boost whatever it's as easy as mounting a switch and running a vacuum line or oil pressure line.

Hello Ricko1966. I agree with you.

Hobbs switches are and have been extensiveley used in the industrial field along with adjustable oil and water temperature Murphy Gauges that many Pipeline welders use on their Lincoln welding machine engines and many other insdustrial equipment, such as water well pumps, oil pumps, hydraulic oil pressure pums, etc.

That was a really good suggestion Ricko1966!

Be well and stay safe out there. I hope it is not too HOT in your part of the country. We are burning out here.

Best wishes to you and all of your loved ones always!

Dryriver1

 

[BlazerBill]

Forgive me for my ignorance, but why would you want the converter to un-lock at WOT? I had Monster Transmission build me a custom 700R4 for towing and highway cruising and sold me a torque converter lock up kit to keep it locked up at highway speeds in order to get better mpg. I have not yet installed the trans since I’m nearing the end of my ‘83 K5 Blazer restoration that will also have a brand new GM SP350 385HP/406TQ crate engine.

 

[Matt69olds]

Very few factory style converters have the clutch surface area to allow WOT with the converter locked. That’s why multi disc converters became popular.

Unless the converter is built for it, keeping it locked at WOT will almost certainly smoke it.

The friction band on a typical converter is maybe an inch wide, and 10 inches in diameter not much friction area.

 

[Bextreme04]

Also, the assumption if you are going WOT is that you are trying to go faster. Unlocking the converter lets the RPM jump up higher into the power band and gives a bit more torque multiplication at the same time.

 

[BlazerBill]

I’m not sure I agree. A friction band creates friction heat when it is exposed to friction due to slippage and not while it is fully engaged. At some point, the converter must fully engage to transmit the full torque to the wheels. This “inch wide” friction band is engineered like this as its design is intended to only experience a minimal amount of time it is exposed to frictional heat due to slippage. It’s main function is to allow only enough friction during gear shifting transition for a smooth shift and ease the gear engagement to prevent damage until it fully engages. Please correct me if I’m wrong on my understanding.

 

[Matt69olds]

The problem is the amount of torque that one inch of friction material can handle before it begins to slip. With a torquey engine, it’s pretty easy to slip that clutch, which creates heat, which causes the friction material to glaze and eventually flake off, which begins to clog the filter, starving the trans of fluid, which makes it slip even more….. you get the idea.

 

[Bextreme04]

I’m not sure I agree. A friction band creates friction heat when it is exposed to friction due to slippage and not while it is fully engaged. At some point, the converter must fully engage to transmit the full torque to the wheels. This “inch wide” friction band is engineered like this as its design is intended to only experience a minimal amount of time it is exposed to frictional heat due to slippage. It’s main function is to allow only enough friction during gear shifting transition for a smooth shift and ease the gear engagement to prevent damage until it fully engages. Please correct me if I’m wrong on my understanding.

I think you might be confusing torque converter stall function and the lockup clutch. In a normal unlocked state, the amount of stall and the amount of slippage in the converter is all based on turbulence between a turbine and stator blades and fluid in the converter. It flashes up to the stall and then allows a small amount of slippage afterwards. When the converter lockup clutch engages, it is usually after a shift when the engine is at a steady state cruise condition with minimal load on it. The friction material on the clutch allows it to slip slightly when it engages to provide a soft engagement from several hundred rpm difference to zero once the clutch is fully engaged. As long as the engine torque never exceeds the holding power of the lockup clutch, you will have zero slippage and therefore zero additional heat. As soon as the engine torque exceeds the ability of the clutch to hold... bad things happen quick. Race cars running 4L60's and 4L80's will use a triple disk converter with high line pressures to prevent this slippage and allow the converter to be locked during a pass or under a high load. Even then, the converter gets locked pretty late and at higher speeds usually. The mechanical advantage of the converter slipping is actually beneficial for acceleration as it provides a torque advantage. The downside of that converter slippage is an excess amount of heat being generated.