Safety for Hydraulic handbrakes

[galderdi]

I have two cars in which I compete regularly. Both have hydraulic handbrakes as I use them for motokhanas (kinda like Gymkhana). Recently I had a close call and I fell obliged to share my experience so you don't fall into the same trap.

 

Both my hydraulic handbrakes tap into the hydraulic system for the rear brakes. When not in use the pressure passes straight through from the original foot brake to the rear brakes.

 

Both work really well when used the way they were intended (the handle pulled up). But in the heat of battle half way round a vigerous motorkhana corner I must have leaned on the handle (pushed it down). I don't actually remember but I must have done it. That pressure pulled the circlip out the front of the master cylinder allowing all the hydraulic pressure to be instantly lost. Not realising this issue I accelerated towards the finish garage (a finish line shaped like a garage where competitors need to stop to record their time). I slammed on the brakes for a fast finish but the peddle went straight to the floor and there was no reduction in speed what so ever. I was then hurtling towards trees, pedestrians, cars etc My immediate reaction was to reach for the hydraulic handbrake (in that split second not realising it was the cause of the failure). Of course that didn't help either and I continued hurtling towards obstacles. The distance between me putting my foot on the foot brake and the obstacles was about 30 feet and I was probably travelling about 35 miles per hour. I started to then use my steering to choose the lesser of the available evils. This meant heading directly towards one solitary car rather than all the other grouped cars and people. Just as I approached the car I was going for my third option which was the original cable handbrake which I had left installed just next to the hydraulic handbrake. At that speed the rear brakes alone were not enough to stop me before the car so I turned slightly right and somehow I managed to miss (at the time I thought I must have hit it) the car. I clipped the ramps of a car trailer parked to the side of the car and skidding to the left came to a halt about 15 feet behind the car at right angles to it.

 

You might well say that I should have taken precautions before all this happened. But there are no instructions provided with these devices and it is not common knowledge to take precautions.

 

So if you ever intend to install a hydraulic handbrake my message to you is:

1.Leave the orginal cable handbrake in place as a backup &

2.Add a stopper under the handbrake handle so even if pressure is applied the wrong way on the handle the stopper will take the weight rather than the handbrake popping apart leaving you with no brakes.

 

I have now done both these precautions in both my competition cars and feel a little more at ease.

 

 

Good luck

[Tony D]

Taking this was a single-circuit braking system? The front and rear should be separate systems on most vehicles since the late 60's in most countries. Loss of one circuit should still allow you to stop with the other (in this case the fronts.)

 

Are you saying it caused a total brake failure? Was there other modifications done to the braking system (remove porportioning valve, etc...)

 

I think you may have more than one problem that needs addressing if this was on a car with dual circuits.

 

I had a profound failure going downhill in a California Canyon when a deer para-jumped in front of my 62 Bus, precipitating a panic slam on the brakes and a failing of the master cylinder cups...and total loss of brakes. I had to negotiate the rest of the way to work using only my (thank gawd RECENTLY ADJUSTED) cable hand brake.

 

When I went to replace the bad MC, it was replaced with, and the system modified to 1967 Spec with Dual Circuits.

 

Better to have half-brakes than NO brakes!

 

Good to hear you avoided catastrophe and the spectators none the worse for wear.

[johnc]

Good job not wrecking.  Most folks just panic and stare striaght at the thing theya re going to hit.  Tony's right, if you're brakes were not all just one circuit there may be another problem.

[galderdi]

I think you are both correct. When I got the car it had clamps on the rear brakes to "fool" the MC to send pressure to the front. I think the safety setup of the MC was/is not working correctly. Its fine when there are no weak points but as soon as there is a loss of pressure anywhere in the system the whole system fails. Problem is a new MC costs as much as I paid for the whole car. I did have the old MC reconditioned but obviously that did not solve that particular issue. Looks like I'll need to fork out for a new one anyway.