GM Volt Forum banner
1 - 18 of 18 Posts

·
Registered
Joined
·
3,439 Posts
Discussion Starter · #1 · (Edited)
I learned/noticed something interesting about the parking brake in my Gen 1 Volt this weekend. We now have a student driver in the family and we were out practice driving on Saturday. He misjudged a stop and nearly hit the car in front of us. After my voice failed to get him to slow more aggressively, I pulled and held up the parking brake button and the car stopped very quickly, avoiding impact.

It is nice that the parking brake switch is located within easy reach of the passenger seat. If we had been in my other car, I would have had no way to reach the parking brake pedal.

It is also interesting that the parking brake stops the car better than I am used to from previous cars. This one activates brakes on all 4 wheels [edit: I think this is true but can't prove it] if you are in motion above 5 mph, so there is less risk of skidding or fishtailing.

So FYI, if you have to give someone driving lessons, this is a nice feature. I guess it could conceivably be useful in other situations as well, like if the driver were to be suddenly incapacitated, etc.
 

·
Registered
Joined
·
626 Posts
I’ve never heard of a Parking/E-brake controlling all 4 wheels before. That’s Interesting! I could see that, If the car had automatic Brake control as a safety package. But if that were the case, you wouldn’t need to touch the E-brake, it would just stop automatically. What year is you Volt?


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
1,488 Posts
Even in Gen 2, if you pull up the switch for the parking brakes while the car is in motion, the car responds immediately (actually jolting) by slowing down and the DIC will warn about engaging the parking brakes and the car chirps about it.
 

·
Registered
Joined
·
3,439 Posts
Discussion Starter · #4 ·
I’ve never heard of a Parking/E-brake controlling all 4 wheels before. That’s Interesting! I could see that, If the car had automatic Brake control as a safety package. But if that were the case, you wouldn’t need to touch the E-brake, it would just stop automatically. What year is you Volt?


Sent from my iPhone using Tapatalk
Mine is 2013. I've never heard of a 4-wheel system like that elsewhere. Not sure how common it is. It has been discussed on this forum a few times.
 

·
Registered
Joined
·
3,439 Posts
Discussion Starter · #6 ·
How do you know it activates all 4?
I don't have a citation for it, but it was discussed on this forum by a member with extensive technical knowledge of Volt engineering, I think it was a user named WopOnTour, but I might be mistaken about that. I also tested it trying to spin the car in an icy parking lot. Activating the parking brake does not help it spin at all, unlike any other car I have owned.
 

·
Registered
Joined
·
2,993 Posts
I don't have a citation for it, but it was discussed on this forum by a member with extensive technical knowledge of Volt engineering, I think it was a user named WopOnTour, but I might be mistaken about that. I also tested it trying to spin the car in an icy parking lot. Activating the parking brake does not help it spin at all, unlike any other car I have owned.
The e Brake has a cable (on either rear wheel, you can see it if you pull a wheel) that is pulled by a motor to activate the mechanism similar to a manual e brake. The front wheels don't although on the auto braking optioned cars there may be another mechanism to apply front brakes. "Above 5 miles per hour" I'm not sure of the details but not being able to spin on ice like a conventional may be a function of traction control electronics rather than e brake acting on all 4wheels.
 

·
Registered
Joined
·
982 Posts
I do know from tire rotations that the parking brake locks only the real wheels at least when stationary.
Pretty cool to hear about that story though with the student driver.
 

·
Registered
Joined
·
2,678 Posts
It's extremely apparent that at low speed, and at a stop, the parking brake only activates the rear wheels. Any other action caused by that button would have to be activated by some electronic mechanism, and I'd be a little skeptical of that.

In your particular situation, there may be several other explanations of what happened. Maybe your student was already applying the brakes (albeit not hard enough) and the parking brake just added to the load. Maybe the regen disengaged (as over bumps) and the parking brake held fast. And a test on ice is not conclusive. If there was no traction at all the parking brake might not have caused a skid. Try in on dry pavement at speeds above 5mph and you'll get a better sense of what's going on. Personally I value my brakes, cable, and tires too much to try it myself :)
 

·
Registered
Joined
·
3,439 Posts
Discussion Starter · #12 · (Edited)
The technical description describes the brakes as being activated through the hydraulic brake system above 5 mph. Since the hydraulic brake system is a 4-wheel system, I assume it operates on all 4 wheels. However, I can't prove this, so I could well be mistaken on that point. I think it would be technically possible to activate only the rear brakes through the hydraulic system via the ABS controller, although I don't see a reason to engineer the system that way.

In my experimentation of using the parking brake with Stabilitrack turned both on and off, I became convinced that it does in fact work on 4 wheels. That is not proof either, and I wouldn't expect something so informal and undocumented to convince anyone but myself.

That is the basis of my assumption. Sorry if I stated it too definitively. I have edited the OP with a disclaimer about this assumption.

I encourage other owners to test their systems in a safe environment to learn the limits of its performance. You never know when you might need it. I was impressed with it compared to the systems on previous vehicles I have owned. I have used other systems that provide very little stopping power and other systems that skid the rear wheels with only moderate braking.
 

·
Registered
Joined
·
1,790 Posts
The technical description describes the brakes as being activated through the hydraulic brake system above 5 mph. Since the hydraulic brake system is a 4-wheel system, I assume it operates on all 4 wheels. However, I can't prove this, so I could well be mistaken on that point. I think it would be technically possible to activate only the rear brakes through the hydraulic system.
But that's just it. The parking brake is NOT hydraulic, it's cable-driven.
 

·
Registered
Joined
·
626 Posts
The way WOT explained it, is that If the EPB button is lifted and held Up at 6 Mph or higher, the ABS will apply hydraulic brake pressure first up to a slowing g force of 0.6. Once the speed drops to 5mph the electro mechanical system is then allowed to engage. It does make sense. Whether the ABS is applying pressure to all 4 wheels is unknown, but I don’t know why it wouldn’t.

I had never thought about the ABS functioning this way, since I always thought of ABS as an Anti-lock system as opposed to the other capability it has to apply pressure under the Traction control side of the system.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
18 Posts
ABS Systems have an electric pump that is between the Brake Master Cylinder and the Brake Calipers. The pump is activated by the computer system and operates regardless of pedal pressure on the brake. As soon as ABS braking systems were introduced to cars, automatic braking has been "possible" but the supporting technology was not available until recently. Sounds like in the Volt, pulling the Emergency brake switch activates the ABS pump to stop the car without causing a skid until the car is going slow enough for the "mechanical" brake to engage. While this is neat feature I will always prefer to a fully manually hand brake (not a foot brake) that goes to a completely separate breaking system than the rear hydraulic brakes. I know Porsche's, Subaru's and most High Performance / Super Cars have separate brakes for the ebrakes. Some are dedicate calipers and others like Porsche and Subaru integrate a Drum Brake inside the disk brake caliper. This is because of those people that will drive well beyond the grinding noise of metal on metal in the brakes where a dual purpose rear caliper will fail because the pad is gone. It also will still work if you have overheated the brakes. Our "special" parking brake makes some emergency situations better but completely ignores others. Either way. Good save with the learning driver.
 

·
Registered
Joined
·
77 Posts
I can confirm on 1st gen Volt the parking brake button does use the hydraulic brake system on all 4 wheels at speeds above a crawl. Did it while turning on ice, the rear end did not flip around so obviously all 4 wheels are braking and it is instant and I do not hear the loud e-brake motor running at all.
My fear with this is the car may not be smart enough to revert to the e-brake motor for the rear wheels in case the hydraulic system fails.
 

·
Registered
Joined
·
277 Posts
I also have a student driver, and also suggest in a panic stop that you can toss the car into reverse and slow down pretty quick too. Since there's no transmission, putting the car in reverse just acts like a regen until you start going backwards. The brake might be faster, but they both will slow things down.
 

·
Registered
Joined
·
41 Posts
Yah. I was trying to rub the rust of the rear rotors on my car (fronts are shiny). I tried applying the e-brake at speed. Would be perfect for the job. But yes it brakes more than just the rear. If e-brake only I would have held it until the rears locked. But the switch isn't connected to the rear brake actuator. It's connected to a computer and the computer decides what it thinks is the best to do. Makes sense that it wouldn't just apply the rear brakes. it is an e-brake (emergency brake) after all.

Want some fun and more proof. while driving try applying the accelerator and then pulling the e-brake switch. The car ignores the accelerator. The controls are just hooked to computers.
 
1 - 18 of 18 Posts
Top