Vacuum Brakes

Vacuum Brakes
Vacuum brakes on petrol engines with high manifold vacuum were and are to this day very effective because as you have to take your foot of the accelerator to brake you automatically induce high manifold vacuum. There is however one catch. There is no manifold vacuum on a diesel engine. These engines have to be fitted with a vac pump. I don

They were still around when I got a licence for trailers, but thank goodness they were on the way out, as Air over hydraulic had become very popular. Then that lot went the way of the dinosaurs as well, all air came in, oh bliss, put the foot on the stop pedal and now it did what you wanted it to do. Had to drive a few vehicles with vacuum, but they were mainly tray trucks, these tray trucks belonged to none other than the FOX and can remember some of them were fitted with the old vacuum trailer brake handle.
Chocs father would remember driving these over powered road monsters !

A fella who I knew in the early 70's, had an old AB Inter semi that was full vacuum and he used to do Melbourne to Adelaide every week. He just used to drive it accordingly and didn't do anything stupid, made him enough money over the years to be able to buy a house and a newer truck.

regards greenie [smiley=vrolijk_1.gif]

Yes it was rare to see an air system in those days, mostly V8 petrols with vacuum brakes.
I go back to the single line air and vacuum systems too which were real slow waiting for the trailer brakes to come on. Westinghouse hand piece the size of something from a train.
Can remember one bloke starting her up to move under the bin and he noticed she wasn't stopping too well.
She'd done the usual big back fire on engine start so we popped the bonnet.
They had an in-line vacuum filter with a wire loop to hold the metal cannister on.
The backfire had beaten the non-return valve and blown the canister off.
Who remembers reading about the tipper operator living up a steep side street on Kingsford Smith Drive?
An old Leyland ?? with no air and flat batteries so he did a hill start.
Didn't make enough air in time and ended up hanging the front over the river bank.
Got into big trouble, guess the traffic must have been light.

And the warning sign on the rear of trailers.



Caution air brakes.

Most of these vacuum brakes would be in reality "vacuum boosted" hydraulics. A lot of trucks had large vacuum storage tanks to help prolong their cycle. Brakes still work without vacuum, but you might need a strong leg. :-X Modern light diesel 4WDs have a mechanical exhauster to provide vacuum.

I have a 1940 Leyland which has a straight vacuum system. A big cylinder (like a maxi) on each front wheel hub with linkages to the drums. A servo on the the side of the chassis with rods and linkages to the rear wheels. Loose vacuum here and you need a paddle. >

I think the best thing to happen for modern diesel cars and 4x's is the electro hydraulic brake master cylinder.
I first came across one on a Toyota Aristo, electric booster and ABS all in the one unit.
Key on and you've got power brakes.

Trouble with electronic jobbos is that when the battery drops in voltage (such as v cold or just off colour battery) they shut down with no power anything.

Back in the 60s i drove a Federal with pole jinker around Sydney. Vaccum trailer brakes. Prime mover and trailer had no brake connection. You had a hand control for the trailer and foot brake for the truck. We carted 40ft flitches of oregon with that. By the way the truck had no doors fitted so was fully air conditioned.
Ah for the good old days.
Cheers kevin.

Foot and hand control became the standard sometime in the 60's in Qld.
All our trucks had trailer brakes which operated separately from the prime mover, prior to the foot and hand control regs.
Single line brakes were the go too before trailer break-away valves were introduced.
Became 2nd nature to grab a few notches of trailer brake (waiting, waiting, waiting) before even thinking of lifting the right foot to the brake.
Then with foot and hand control, we got lazy.
Forget to wind back the percentage of trailer brake when empty so lots of tyre smoke until the brain got into gear.
Always checking, now did I set the percentage for empty or loaded?

I forgot to mention that every cloud has a silver lining. When the starter motor burnt out or the batteries went flat you could always tow it to start it because there was no deadman on vacuum mechanical systems. There had to be something good about them!