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.

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.

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.

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

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.

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.

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:
Click to view attachment

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

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)

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.

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)

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


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


As I mentioned, my cables are new.

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

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....

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.

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.


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.


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.


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


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.


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


Cables are seated fine.


Rebuilt calipers. (Thanks, Eric.)


Factory routing.


Clamps were removed.


No need. I already found the problem.

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....

Paul, you need to read my original post. My post didn't request help; it offered guidance to others who might have the same problem. And if you'll read the responses, you'll see that at least three other 914 drivers have EXACTLY the same issue. I'm glad you're not one of them, but when you blindly extrapolate your success to every 914 on the road, then you do the community and others who might have this problem a disservice.

I don't need to build a better system. I've already solved the problem with the OE system. I lubricated the cable. Others should consider doing the same.

Dave,
First off, Thanks, I know if you were able to explain this without the crux of the internet everyone would listen.

I am still fighting the problem that you originally had where the drivers side clamps first and then the passengers side. Right now my car could probably not be held on a hill from the ebrake alone. I really haven't worked on it since I originally adjusted everything, and I mean everything last winter. I did attempt to lubricate the cables with wurth penetrating oil and although it did get better it never fixed the problem. Its wierd because you can literally watch the friction of the passenger side cable put more tension on the yoke. Looks like I just need to bite the bullet and buy new cables and make sure to lubricate them first, then readjust everything.

kyle

This is not a design flaw/issue it is an expectation of design- flaw.

And is a quite common one …

only because I can’t get over this one....

The "E-brake" as you call it is not an "E" brake, it is a PARKING Brake, designed to HOLD the car in a standing position.

The design intent with the Equalizer is to distribute equal force to both sides of the car. Left wheel Right wheel ONCE engaged.
It is not designed to work the same a your speed reducing brakes with equal engagement at the same time, as this is not a concern of a Parking brake.

Once the first set of pads make contact with the rotor.. if all is adjusted properly force will then begin to be distributed to the other set that has not made contact yet by using the equalizer bar. Once equalization of force is established additional travel by the hand lever will apply approximately the same value of force to both sides.

Were this gets tricky is if the (equalizer) = cable lengths are too far out of adjustment and an equilibrium between cannot be reached before tension from the main cable is all applied to one side, on our 914s this is usually the Right side wheel that receives little force.

Expecting “first contact” of both sides is not the intent of this design.

If you have improved the timing of contact with lubrication /adjustment, ….fantastic! No harm…

Kyle, you've got the exact problem that I've been chasing for the past year. My ebrake wouldn't stop my 914 on a hill. (Thankfully, I never needed to use the brake in an emergency, because it undoubtedly would have been ineffective.)

The yoke behavior that you describe is typical of the high friction cable. Pulling on the handle, you can watch the driver's cable move while the passenger's cable remains stationary and the force balance yoke resultingly changes angle. Very obvious.

As I mentioned, I saw a dramatic improvement after I lubricated the cable. I noted that most of the cable friction is due to the first bend in the cable, at the firewall. This is conveniently just about the only place that you'll be able to wipe grease onto the cable. I can't recommend penetrating oil as a lubricant -- these oils largely evaporate away over time. I'd suggest a good grease.

I'm also beginning to suspect that I might have a non-OE cable. Given that other 914 owners don't have seem to have the problem, it is likely that my new cable has a higher friction level than others. I'd recommend trying to get the OE cable, if it's still available. I'm going to pursue an OE cable purchase today.

Yeah, I'm aware how the force balance works. But it can only equalize forces at the firewall. Forces at the caliper will be reduced by the cable friction. That's the whole problem.

And in fact, the mechanical brake IS intended as an emergency brake. It's a backup for hydraulic system failure.

Dear Dave,

I really don't think that you are qualified to doubt the complex engineering of porsche's design of the "parking brake/emergency brake" system.
If you are having trouble with servicing it you clearly have no business working on any automobile let alone a porsche.
so please just step away from these cars. you should just stick with the more simple stuff.......
your friend troy

quite simply adjust the cables so the RR makes contact first and your system shold work fine....

oh and find me any manufactuere that Today will call it an Emergency brake

Of course. This works in theory. But it fails when we have high cable friction. That's the whole problem. The force balance is equalizing forces at the wrong point in the system.



I call the system an "emergency brake" as a reference to its design intent and function. The manufacturers' choice of name is irrelevant in that context.

Thanks for the support, Troy.

Now take your perfect ebrake and go join the other haters.

You can call it all you want.

At the end of the day, it's still a PARKING brake ...
Andy

From the owners manual:

Sure. That's one of its functions.

Its other function is as an EMERGENCY brake.

Setting aside the semantics, lube your BRAKE cable, dammit.

Maybe in Texas it isn't, but around here, the parking brake is commonly refered to as an "E brake."

I presume by the same people that call the fog lights "running lights" and leave them on even when there's not a speckle of fog in a 100 mile radius?

Other people say it so it must be true.
Andy

First, do you have any credible source to back up that claim?

Second, have you ever actually used your handbrake to slow your car down in an emergency?


I had the pleasure of that experience when my master cylinder decided to blow up when i had to do a hard brake after a guy cut me off at about 70mph.

I stomp on the brakes, *POP* it said and the pedal went to the floor in an instant!

So i pull on the HANDBRAKE lever as hard as i could. And yes, my handbrake was adjusted and working just fine.

Care to guess how much "emergency" braking i got out of that?
Andy

So you used your parking brake in an EMERGENCY?

Yes. I tried just that ...

Did you also read my question? I'll ask again:
"Care to guess how much "emergency" braking i got out of that?"

Andy

that happened to me on an old hunting truck we had... top of the hill, no brakes... emergency brake my ass... it did almost nothing... we had to use a tree to stop

guys i am glad we can all give each other a hard time about this...
i worked at a brake shop during college and spent a considerable amount of time getting "corporate Educated" to NEVER NEVER call it an E brake....
for the reasons stated.......
and of course the legal ramifications.

glad you could see the sarcasm!

now how hyjacked can this thread get on semantics?!

Maybe you shoulda lubed your cable.

A+ for your lubrication skills
D- for not answering my questions

Andy

Don't the brake lines travel through the tunnel? This could go right next to the heater lever. You'll be done in an hour. Uh, this is DEFINITELY not for emergencies. However, if your system is in good shape, these work really well for about $200 and no more cables. I hooked one up to the front of my Samurai so I could have front and rear parking brakes. Fancy units for about $400 are electric and will work on all 4 wheels. You can put the switch right on the gear shifter.

Hehe. You told him to lube his cable


Worst Semantic Debate EVER....

Kyle

bad idea to use a hydro lock for any but short intervals. manufactures will not put those on manlift trucks any more.

http://wtanaka.com/node/7745