Why doesn't my right ebrake work?, It's the asymmetric cables, dummy. Options

[davesprinkle]

Here's why most modern cars have the ebrake handle in the middle of the car -- it's so the cables running to the wheels have identical length and path. How do I know? Here's the anecdote:
For the last year, I've been struggling with my ebrake system. The right caliper just wouldn't clamp as tightly as the left. I've got rebuilt calipers, new pads, new cables, proper clearance, but no worky.

Finally found out why. It's the internal drag of the actuation cables. The passenger-side cable is substantially longer than the driver side. Also, the right-side cable has 3 right-angle bends vs the left-side cable with none. This results in so much internal friction that the cable just binds solid when it's pulled.

I was able to improve the situation somewhat by lubricating the cable. Still not perfect, but much better.

[jim_hoyland]

I have the same issue.....where did you lube the cable ?

I heard, years ago, of a 914 using a pair of mini hydraulic actuators to pull the E-brakes. I believe they were mounted on the fire wall with a straight line shot to the calipers. Any thoughts on this ?

[davesprinkle]

I have the same issue.....where did you lube the cable ?

I heard, years ago, of a 914 using a pair of mini hydraulic actuators to pull the E-brakes. I believe they were mounted on the fire wall with a straight line shot to the calipers. Any thoughts on this ?

Yeah, hydraulics would definitely solve the cable friction issue. Cons of such a setup:
1. extensive engineering and fab effort
2. another hydraulic system to service
3. some might be philosophically opposed to abandoning a mechanical backup

It's tough to do a good job lubricating the cable. I used two approaches:
1. First, I used some lightweight mineral oil (bicycle chain lube) and allowed it to wick down the cable. (Working at the interior end of the cable.) The oil was thin enough that capillary action pulled it down the cable.
2. Next, I wiped some grease on the inner cable and worked the cable back and forth.

I noted that most of the cable's friction is due to the first 90 degree bend, the one immediately at the firewall. Conveniently, this is the area most easily lubricated.

[tat2dphreak]

dunno about OR, or CA, but a hydraulic Parking brake is not legal in TX.

if the cable is binding, get a new one, imo. I replaced both of mine years ago, no problems with it working so far

[davesprinkle]

dunno about OR, or CA, but a hydraulic Parking brake is not legal in TX.

if the cable is binding, get a new one, imo. I replaced both of mine years ago, no problems with it working so far

The cables are brand new. They still bind.

[tat2dphreak]

new cables should not bind, perhaps it was bent before you got it?

[Shade Tree]

I've been considering just putting a line lock in place like I have on my Samurai. It just goes in line with the existing brake lines where they exit the master cylinder. Has a switch that turns on a one way valve. Flip the switch, give the brakes one good pump and all 4 wheels are locked.

[davesprinkle]

new cables should not bind, perhaps it was bent before you got it?

Wayne, even new cables aren't free of friction. But don't take my word for it. Set aside your skepticism and try it yourself.

Pull off your cable. Stretch it out straight. See how easily the inner cable slides. Nice.

Now bend the cable through 90 degrees. It doesn't have to be a sharp radius bend, 4" will do. Now when you move the inner cable, you'll note substantially higher force is required.

The thing is, you're going to have 3 of these bends in the cable when it's installed in the car.

[JJ914GT]

That's exactly why my car has the handbrake in the middle ( old type VW Golf style handbrake.) Works like a charm.

Not the best picture ( pretty old picture now), but you can see it here:

[tat2dphreak]

new cables should not bind, perhaps it was bent before you got it?

Wayne, even new cables aren't free of friction. But don't take my word for it. Set aside your skepticism and try it yourself.

Pull off your cable. Stretch it out straight. See how easily the inner cable slides. Nice.

Now bend the cable through 90 degrees. It doesn't have to be a sharp radius bend, 4" will do. Now when you move the inner cable, you'll note substantially higher force is required.

The thing is, you're going to have 3 of these bends in the cable when it's installed in the car.

I understand what you mean, but when I installed my new one, I did not get these issues... maybe I got lucky?



JJ-how did you set that up? that's great, imo. I hate how the seat interferes with the e-brake

[JJ914GT]

The PO installed it before I got the car, so didn't do the fabricationwork myself. It's a handbrake setup from a MK2 VW Golf ( Rabbit), which uses cables of the same length to overcome the exact problem as described above :-) I plan on using a MK2 plastic handbrake cover instead of the leather thing that's you can see in the picture. This would make it look close to factory made I think.

These's many MK2 Golf parts on my car; the front grill ( water cooled car, you can see the ugly pipes in my interior,.. not part of a rollcage,.. they are gone now.), VDO guages, Handbrake and even the engine that was in was VW Golf ( 16valve 1.8L ) ( Now I'm doing a ej20 Subaru conversion)

[McMark]

Dave, did you try adjusting the ebrake cables? And while adjusting them, did you keep an eye on the 'yoke' in the cabin to make sure it stays perpendicular?

Just curious. (IMG:style_emoticons/default/cool.gif)

[PRS914-6]

The length of the cable should not effect it. The cable has a T yoke that will equalize the pull. Of course if you have cables that need lubing they should probably be replaced after 30 years of grit and grime. I have stock cables and handle with 911 rears and they work perfectly (new cables and everything clean)

[davesprinkle]

The length of the cable should not effect it.

A longer cable will have more of the inner cable in contact with the outer cable, so the length WILL affect the friction.

The cable has a T yoke that will equalize the pull.

Yes, the mechanism has a force balance. But it cannot compensate for friction mismatch.

Of course if you have cables that need lubing they should probably be replaced after 30 years of grit and grime.

As I mentioned, my cables are new.

[davesprinkle]

Dave, did you try adjusting the ebrake cables? And while adjusting them, did you keep an eye on the 'yoke' in the cabin to make sure it stays perpendicular?

Just curious. (IMG:style_emoticons/default/cool.gif)

Yeah, Mark, I was careful to set up the cables so that the force balance was perpendicular to the cable.

[PRS914-6]

The length of the cable should not effect it.

A longer cable will have more of the inner cable in contact with the outer cable, so the length WILL affect the friction.

The cable has a T yoke that will equalize the pull.

Yes, the mechanism has a force balance. But it cannot compensate for friction mismatch.

Of course if you have cables that need lubing they should probably be replaced after 30 years of grit and grime.

As I mentioned, my cables are new.

Sorry, the friction difference between two new cables, installed properly would be very minimal. The problem is elsewhere. While you might feel a slight difference by hand, the amount of leverage applied with the handle is a lot. Crawl underneath a pickup and you will see tons of vehicles with one side WAY longer than the other without issue. Most cables are teflon lined and have minimal friction if routed smoothly. Mine slide easlily with the bends. The problem lies somewhere else.....not cable length

Disconnect them at the caliper and have someone pull the handle. Do the cables come back easily?

Cheap aftermarket cables?
Cables not seated properly on the tube?
Calipers not working properly?
Cables kinked somewhere?
Clamps on the cables too tight?

Keep looking....

[914Mike]

My cars both grab the driver's side rotor first, and let the passenger side slip. I just figure it's designed in difference. That's how I rotate the engine while the car is in the air, just put it in fifth and rotate the passenger side rear wheel, there's even timing marks on the bottom of the flywheel for this.

[davesprinkle]

My cars both grab the driver's side rotor first, and let the passenger side slip. I just figure it's designed in difference. That's how I rotate the engine while the car is in the air, just put it in fifth and rotate the passenger side rear wheel, there's even timing marks on the bottom of the flywheel for this.

Mike, this is exactly the problem that I fixed when I lubricated the cable. Both brakes should grab equally.

[davesprinkle]

Sorry, the friction difference between two new cables, installed properly would be very minimal. The problem is elsewhere.

Well, you're wrong about that. The problem was in the cable. Period. I didn't arrive at this conclusion lightly. I chased this problem for the better part of a year. I went through every piece of the brake system. New cables, new pads, rebuilt calipers, close attention to pad clearance, cable routing, and force balance position. The problem was only resolved after I lubricated the cable.

While you might feel a slight difference by hand, the amount of leverage applied with the handle is a lot.

At least here you're correct -- the handle has a large mechanical advantage and can generate large tension force in the cable. But that's exactly the problem -- tension force in a straight cable turns into a normal force when the cable is bent, loading the inner cable against the housing. Refer back to any high school physics text -- friction force is proportional to normal force.

Crawl underneath a pickup and you will see tons of vehicles with one side WAY longer than the other without issue. Most cables are teflon lined and have minimal friction if routed smoothly. Mine slide easlily with the bends.

The debate is not whether the asymmetric cables have dissimilar friction. They do. The debate here is really whether the force mismatch is large enough to cause actuation problems.

In my system, the friction force caused actuation problems. Lubricating the cable reduced the friction enough for acceptable actuation. It'll never be perfect as long as the cables differ, but it's a substantial improvement.

I'm glad you don't have any actuation problems, but I'll bet your system doesn't work as well as you think it does.

The problem lies somewhere else.....not cable length

Again, you're wrong. To the extent that cable length increases internal friction, then it DOES play a role.

Disconnect them at the caliper and have someone pull the handle. Do the cables come back easily?

Yeah, I've been through this. Disconnecting the cable removes the tension force, thus removing the normal force and reducing friction. Sorry, but this is not a valid test for a loaded system.

Cheap aftermarket cables?

Maybe? Purchased from Pelican. I don't recall if they're OE or not.

Cables not seated properly on the tube?

Cables are seated fine.

Calipers not working properly?

Rebuilt calipers. (Thanks, Eric.)

Cables kinked somewhere?

Factory routing.

Clamps on the cables too tight?

Clamps were removed.

Keep looking....

No need. I already found the problem.

[PRS914-6]

It cracks me up when people get on a forum and ask for help and then get pissy with those that are trying to help them.

I'm not saying that there is not more friction in a longer cable because of course there is. I'm saying that if you have two quality new cables in this application not working there is something wrong. Just because YOUR cables are high in friction does not mean that ALL cables are that way and it's a defective design. Car manufacturers have been using cable systems since Barny Rubble was driving. Not the best system but they were required to have a mechanical backup.

I don't want this thread to give out the idea that there is something wrong with the 914 cable setup since it works fine for most people.

As for my cable system on my car, just ask others who have seen it.....It works great.

If you are satisfied that Porsche and other manufacturers are using a bad design you should build a better system....