The Stovebolt Site Forums The Parking Lot Big Bolts Clutch Booster or what ?

anybody know what this is?

It looks to be a vacuum diaphragm hooked up to the clutch pedal.

Why?


pictures...
http://sdrv.ms/17M5q2V

That's a hydrovac unit,and it BETTER be hooked up to your brakes. Check your pedals,but I'm sure that the linkage will be actuated by the brake pedal. Clutches are all mechanical,(as far as I know). Looks like the origional rod got replaced with a length of cable. I'd replace that with a correct chunk of threaded rod. There's a turnbuckle on one end,for fine-tuning. Hope this helps.

That ain't no Hydrovac! It's a simple vacuum-assist canister. It's got a one-way check valve in the feed line. Looks like a vacuum tank on the outside of the frame-rail as well. And it COULD be attached to the clutch.

What was this truck in a former life? Fire trucks, and I'm guessing other construction and work trucks, often used a vacuum assist to pull the truck out of gear from a remote location. For example, on a fire truck that drives the pump through the transmission (usually direct gear), with the drive shaft taken out of line, the vacuum assist allows the pump operator to disengage the pump by turning a knob on the pump panel, thus stopping the pump.

The hydrovac is on the other frame rail. It looks like they may have shared a vacuum line.

-Michael

I agree with Mikestem...

Mike B

It was a Fire Dept truck, 1947. It had a big water tank on it and I suppose a pump. It was all gone when I got the truck.

I'm still not sure how it worked. What do you mean by "often used a vacuum assist to pull the truck out of gear from a remote location."

Fire trucks operated their pumps by disengaging the rear wheels from the transmission, and engaging the fire pump to the transmission. In other words, the drive shaft went through the pump transmission. When they drove, the transfer was in "Road", and when they pumped, the transfer was in "Pump". When the fire truck got to a fire, the driver would put it in neutral, push the clutch in, shift from Road to Pump, then shift into 4th or 5th gear, before letting the clutch out. The pump operated through the transmission, usually in whichever gear was "direct".

However, all the pump controls on a fire truck are usually on the side. So after putting the pump in gear and getting out of the truck, the engineer needs a way to disengage the pump, without having to climb back into the cab.

By flipping a switch on the pump panel, vacuum would be allowed into the canister, which, acting on the piston inside, would pull that cable attached to the bottom of the clutch pedal, thereby disengaging the clutch. In this case, that would allow the pump to stop pumping, or "shut down". There is also a remote throttle control on the panel for adjusting the speed of the engine. If they weren't going to pump for a while, the driver could then climb back into the cab, take the transmission out of gear, and idle the engine.

If you aren't going to return this truck to a fire truck, I can't imagine what use the vacuum clutch control would be to you. It doesn't have any effect on your driving the truck. No reason not to remove it and the associated plumbing - just be sure to plug it at the source, to avoid a big sucking vacuum leak!

-Michael

aft of the check valve is a tee with a line that is cut does that go or did it go to the vacuum tank on the outside of the frame? where does the line thats going aft go to? since this is a wrecker i bet spanky would know.

Thanks Michael, great explanation.

51 ashton - this is not the '49 wrecker frame. This is a '47 donor truck.

Hmmm, my 1950 Gmc 450 firetruck didn't have one of these, it has a mechanical linkage to the clutch. Had to look after that discussion. Thanks. Jim