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Wednesday, July 17, 2019

Hydraulic Throwout Bearing

1974 MGB GT
MG's are a little small and cramped for my taste, but this one is pretty and since someone has replaced the original L4 engine with a V8, it is probably a real tiger.

Howe Racing hydraulic throw-out bearing
The story mentions that they employed a "Howe Racing hydraulic throw-out bearing", which got me to wondering why you would bother with such a contraption. I mean the standard mechanical fork was good enough for the umpteen zillion clutches installed in cars with manual transmissions, why do we need to change? But then I thought about it and realized that the mechanical fork requires either:
  • a complicated mechanical linkage,
  • a stout flexible cable (like bicycle handbrake cables, but stouter), or
  • hydraulic master and slave cylinders and their associated lines.
Hooking up these mechanisms is complicated by the location. The floor pan, the firewall and the bell housing all come together in one spot. The bell housing (which houses the clutch, called a bell because of it's shape) is generally right next to your right foot. I am sure there have been some very slick designs that managed to fit all the required pieces into the available space. I am also sure there have been some truly horrible designs that required a mechanic to have the skills of Houdini to work on them.

The hydraulic throw-out bearing is conceptually simple. It replaces the slave cylinder and the clutch release fork so it gets rid of some parts and frees up some space. But if it ever fails, you have to pull the transmission to replace it. On the other hand, a well made version of this part should last forever, so it should never need to be replaced.

I went looking for a picture that would illustrate the clutch release mechanism, but after poking around for a good long while, I failed to find one that was clear and simple enough for my purposes. It's a relatively simple mechanism, but all the illustrations I found assume a certain level of familiarity with automotive machinery.

Via Engine Swap Depot

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