Hydraulic handbrake (+)

[Dirtylouie]

Its an electromagnetic thing - also fitted to some recent Audis... From about 2004 or thereabouts. There must be same way that is declared OK for MOT and such cos I would have thought a good old metal cable is fundamentally safer. I presume the E-brake mechanism must be locked ON somehow if there is an electrical fault - it must fail safe - don't you think ?

BTW i'm not that sure about electro-magnetic principle =) EM to my mind works like 1-0 (On\off)
with these things it's more like it has a range of pressure to stop the car smoothly, gradually. When stationery you can also hear the sound of the electromotor, standing outside of the car near the trunk, once you engage the parking brake.

[stiglet]

The whole point of a handbrake is that it will not fail and release. Hydraulics can leak, release pressure as the fluid cools, etc, which is why they are illegal in the UK. The electro mechanic devices (I think) use a corkscrew design, which means that if the electronic device fails whilst it's on, the mechanical part will not move and hence it will stay on. you just won't be able to turn it off!

Of course if it fails off, you won't be able to put it on, but the same can be true of regular handbrakes too.

In a nutshell, the whole point is that if you leave the car with the handbrake on unnatended, there is no way that a well maintained handbrake can fail AND RELEASE. Hydraulic handbrakes can fail, and when they do they release.

[90/90qs]

I have been contemplating this issue as well. I have Boxster S calipers on front and rear, and I'd like to add an emergency brake (I like being able to stop in emergencies . The K-Sport model looks nice and appears to fit well, but I can't come up with a method for running an isolated fluid path. It seems to me that no matter what you do, if you loose line pressure you can not divert that pressure to a different line. You'd have to shut off the flow at the caliper, from the leaking line and switch to the non leaking line. A leak anywhere would affect the entire system otherwise.
I can't figure out a way to overcome that issue; then again I don't know a whole heck of a lot about hydraulic systems and available components.

One item I have thought about is a separate mechanical caliper with a rotor on the center driveshaft, in front of the diff. Certainly a less than perfect solution, because with the size of the rotor (space constraints) and heat dissipation your rotor would last for maybe 1 sudden stop (hopefully). This could also be moved to the rear inner driveshafts, but space is tight there as well, and then you're looking a lots of expensive custom components...............

[S2central.net]

So - this is a good thread... Allow me to ask some stupid questions.

Can the hydraulic handbrake be rigged up in such a way that it can do its thing hydraulically whilst at the same time maintaining a traditional cable mechanism for MOT and safety.... I'm thinking about an elaborate dual purpose handbrake lever here - or a 2nd smaller lever could be added for fly-off hydraulic hbrake... Not something you need everyday on the S2 of course, but hey...

[s2driveruk]

see my link Paul.....exactly that

[stiglet]

Not something you need everyday on the S2 of course, but hey...

If I had a hydraulic handbrake, I would probably use it everyday

[S2central.net]

Totally missed your link Dave - good find... Love it when a plan comes together

[kritis17]

The whole point of a handbrake is that it will not fail and release. Hydraulics can leak, release pressure as the fluid cools, etc, which is why they are illegal in the UK. The electro mechanic devices (I think) use a corkscrew design, which means that if the electronic device fails whilst it's on, the mechanical part will not move and hence it will stay on. you just won't be able to turn it off!

Of course if it fails off, you won't be able to put it on, but the same can be true of regular handbrakes too.

In a nutshell, the whole point is that if you leave the car with the handbrake on unnatended, there is no way that a well maintained handbrake can fail AND RELEASE. Hydraulic handbrakes can fail, and when they do they release.

Actually, the whole point of the handbrake depends on HOW you want to use it.

For every day use, just to park the car, it's not worth it to install the hydraulic BUT if you want to slide the car with 5 people inside on the tarmac, hydraulic is your best choice.

[anton]

i think stiglet was meaning from a legat standpoint, as mentioned, in the UK it is illegal to replace an electric or cable handbrake with a hydraulic one for the safety reasons mentioned.

Ant

[Markarina]

The whole point of a handbrake is that it will not fail and release. Hydraulics can leak, release pressure as the fluid cools, etc, which is why they are illegal in the UK. The electro mechanic devices (I think) use a corkscrew design, which means that if the electronic device fails whilst it's on, the mechanical part will not move and hence it will stay on. you just won't be able to turn it off!

Of course if it fails off, you won't be able to put it on, but the same can be true of regular handbrakes too.

In a nutshell, the whole point is that if you leave the car with the handbrake on unnatended, there is no way that a well maintained handbrake can fail AND RELEASE. Hydraulic handbrakes can fail, and when they do they release.

Guess it depends which angle you are looking at it from, my POV as somebody who has written ECU software for similar things then the last thing you want to happen is for the brake to engage at speed, not being able to put the brake on when stationary is nuisance and work roundable.

[S2central.net]

Not such a nuisance / work roundable if the thing fails while parked on a hill... The VWAudi ebrake must fail safe somehow - it just wouldn't be viable othewise, and there must be other mechanisms which stop it from being applied above a certain speed.

[90/90qs]

I see it specifically as an emergency stopping mechanism. a 3200 lb (sorry don't know the metric translation) vehicle traveling down the road at any speed with no brakes can be a real sticky situation. The handbrake is a fail-safe in the event of loss of hydraulic pressure, and is used secondarily as a parking brake, or drift / rally accoutrement. There's not much that can stop that amount of rolling weight aside from a tree, house, car, lori or river .
Since I've been fudging around with my brakes, and making my car stupidly fast (for a street car), I don't want to leave it to chance that I did everything right the first time. There has been much to remember over the last couple years on this project!
I'll still plan to go with an isolated hydraulic system, but I was just looking around and found "line locks" which could be used to close off the main hydraulic system in the event of failure.
Anyone done this?

[S2central.net]

I have heard of line locks alright... can't recall the application.

I think the hybrid is the right answer with hydraulic assistance a la rally / gravel / snow accoutrement, plus a cable as backup and confidence parked up on a slope for prolonged periods. Plus the cable guarantees MOT pass in UK.

[John B]

996 rear calipers

Hey 90/90qs, interesting that you have Boxter rear calipers....I note that you have custom caliper brackets. Do you have the exact dimensions for these?

The Brembo has 130mm spacing and the rear coupe strut spacing is 90mm but it's the offsets that I'm interested in. Unfortunately the RS2 front brackets have a 94mm spacing in standard form.

Oh and what discs do you use?

Cheers,

JB

[Dirtylouie]

Hey, kind of discussion goes on here, I should have asked about K-sport before
To cut it short let me post this long message))))))))

Using typical mechanic parking brake (like an S2) system, no ABS, to stop the vehicle in emergency can bring you a in a deeper trouble (rear lock-oversteer-roll over) than trying to steer and avoid an obstacle. Usnig it solely to park the vehicle is also not reliable as the whole mechanism releases if one component fails. (lever lock, spring, cable or cable mount) It looses tension - it fails. I would always engage the gear together with the hanbrake. Moreover in winter or at the mountains using a hanbrake to park a front wheel drive may freeze-lock your rear till it gets warmer, if there's no tarmac nearby))
Quite the other story with that funky e-brake - Stiglet is absolutely right here - it's an electro mechanic device and it does not fail-release. the electric motor rotates a corkscrew similar mechanism which attaches the pads. you then need to apply power again to unwind it and release. In case your battery is dead you read manual and then use special tool to release it, or just call your dealer =))))))) It also uses ABS if you activate it when driving and does not lock your rear wheels, which is dangerous, and therefore it is a secondary stopping mechanism in case hydraulics fail. that is the main advantage of it in terms of safety.
Now hydraulics:
Hydraulic handbrake in no circumstancies should be installed to be used as a parking prake or an auxillary means of stopping the vehicle. It looses pressure when parked and locks rear when driving (it is the only reason to have it =D ) Typical hydraulic handbrake does not even have this clicking lock mechanism, meant for fixing the lever. Talking about rally: handbrake is also not that widely used. It fits best for the hairpins on a front wheel drive and a "not very experienced" driver. Most experienced can pass a hairpin quick and without putting their hands away from 3 and 9 positions on the wheel =)))))) Engaging a HB in the race always means loosing speed. In most situations it is used to correct the mistake, therefore most of rally cars have it. In front wheel drive though this is less noticeble, as you use it without cutting torque to the wheels. with 4wheel drive it's more complicated - you can ruin BMW xDrive on an automatic transmission if not in N for example if utilize a handbreak =)