Hard Brake Pedal on SWB

mickey356 · 08-28-2016, 11:59 AM

I have a hard brake pedal on my 1968 912. I thought it had something to do with the master cylinder so I replaced it because it was leaking. The new one seems to be leaking a bit as well….I still need to get in there a inspect but replacing the master had no affect on the pedal.
I plan to redo the system with refurbished calipers from PMB and stainless brake hoses. Is it recommended to replace the lines with new as well? How much of a PITA is it to replace the lines?

Walt Fricke · 08-28-2016, 04:30 PM

Mickey
Leaking brake hydraulic parts usually result in a soft pedal, not a hard one, so I am not surprised that replacing your MC didn't change this.

Are you sure that the difference here is really the change from the boosted brakes of the SC and 996 to the plain vanilla brakes of the 912?

If your steel brake lines have not rusted internally (or externally other than superficially, I don't see why you would need to replace them. It is rather a PITA to fish the one for the rears through the tunnel, although replacing the other shorter parts is easy, and those are the ones most likely to have some external corrosion. My '68 912 (for a long time converted to six cylinders and a race car) has the long line original. I may have replaced some of the shorter ones, since I have a dual MC setup.

I can't tell from the parts catalog if the '68 only came with the single MC setup (just one pressure chamber for all four brakes), or the tandem cylinder (one chamber for the fronts, one for the rear, so if one system fails you have some braking from the other). If a single cylinder, be good to replace with the tandem.

The early 914s came with a 17mm MC. Switching to a 19mm MC will stiffen the pedal. I don't know what MC your car came with, but if a 17 and it now has the 19 (I think all the dual circuit ones are 19s, but not sure), that would make the pedal harder.

mickey356 · 08-28-2016, 07:00 PM

Thanks Walt. You make a good point about about the difference with boosted brakes, it's been a long time since I've driven anything otherwise. I used to have a 356 replica but the brake pedal wasn't near as hard as the one on the 912. It's been that way since I bought it in december (haven't driven it much since as it's been getting some rust repair done). The brakes do work well, so maybe it is just what you imply. I still plan on doing the caliper swap, rotors, and obvious bleeding that goes along, so we'll see what comes of that.
If I recall the mc on that was on my car was a single circuit but my friend ( a tech) did the install of the new and it was a dual circuit. Not sure why it's leaking. Possibly just from sitting for 6 months but I don't think thats a normal mc thing.

Walt Fricke · 08-30-2016, 09:08 PM

Where is it leaking? Where is fluid showing up where it doesn't belong?

mickey356 · 08-30-2016, 09:16 PM

Initially it was leaking on to the floor area by the pedal cluster, and the mc was covered in fluid.
Now that it's been replaced I noticed some fluid collecting under the mc, there is also a very light residue on the floor near pedals but I'm not sure if its leftover from before. I'll get a closer look tomorrow and report back

givory · 08-31-2016, 04:35 AM

Do you mean "hard" as in the pedal engages very quickly? Thinking you have the same setup as me have you adjusted the rod between the brake pedal and MC?

mickey356 · 09-01-2016, 04:21 PM

Givory, not hard as in engages quickly, more of just a firmness to it, there is no "smoosh". Feels very basic and mechanical, if that makes sense.

mickey356 · 09-01-2016, 04:39 PM

Here's a pic of the mc that was put in January this year. It made no difference in the pedal feel or the braking.
I didn't get up under the car enough but from the look of the pic maybe it's not leaking and it's a glossy finish on the mc.?

Sent from my iPad using Tapatalk

Morrie · 09-02-2016, 11:47 AM

Hi, Mickey,

Since I also have a 68 912, and have had others... I can be somewhat of a real world reference. In response to Walt's wondering if the 68 MY came with a dual MC or single ckt, it was the first year of the dual. This also did away with the pressure switch on the MC for the brake lights, and went to the mechanical switch on the pedal cluster that continued on well beyond the demise of the 912.

The comment about a "Hard" pedal is confusing to me. It is possible you are bottoming out in the master cylinder. There are two different lengths of actuator rods used. The pre-68 actuator rod for the single circuit master cylinder is longer than the one for the dual master cylinder. Something to search out as you "might" have the wrong one.

Also, I have heard bad things about the non-ATE master cylinders and early life failures from them. Do you happen to know if your replacement was an original ATE or not?

The pedal on these cars is not rock solid hard stop. There is some give, or "sponge" feel that is not present in a power brake car. If your pedal feels like a modern car with the ignition off and booster not operating, then you definately have something amiss.

All this aside, how is the actual stopping capability of the car? Does it stop quickly when firm pressure is applied? You have to sort of stomp the pedal to lock up brakes on these, but that too is dependent on other factors, such as your brake pad compound, but I digress....

mickey356 · 09-02-2016, 06:19 PM

Thanks Morrie!
I have not attempted to stomp the pedal yet. The car has basically been in some state of disrepair since I got it in December last year so I haven't driven it much. It currently sits with no glass in it and no interior except a seat to move it around, it does run though and can be driven, but not legally.
I'm hoping to get the glass back in next week and then start on the rest of the mechanicals. Brakes and suspension are first up. I was planning on PMB rebuilds and SS lines, pads, rotors, etc… I will check the actuator rod next week, how do I tell if it's the proper one?
The car seems to stop adequately but I haven't been forced to apply the brakes firmly or suddenly. My definition of "hard" pedal is the pedal doesn't depress much when it's pushed, maybe gives an inch or so, not the traditional feel at all. I've driven lots of old VWs and never had as hard a pedal as this. Even though the brakes are working I get the feeling there is definitely something off.
This car came with no history at all. The guy I bought it from really didn't know much about it, or cars in general it seems (though he talked like he did). Someone has done a lot of work on this car along the way (some not so bad, some…..well..), but I don't think they really knew what they were working on aside from an "old porsche", so it's quite possible they just "guesstimated" on year when sourcing parts, or assumed it didn't make much difference. It's mainly for that reason I'm replacing everything in the braking system, and refreshing the suspension bushings…new shocks…tires…etc…

I'm almost positive the replacement mc was NOT original ATE as it was acquired from an non-porsche specific parts wholesaler like worldpac or another part supplier for auto repair shops.

Walt Fricke · 09-02-2016, 11:52 PM

Mickey - I see from the picture why you wondered about replacing the brake lines, though surface rust on the fitting nuts doesn't mean they are going to leak. The front lines are easy enough to replace in terms of access, as is the short line to the fitting by the tunnel for the rears, as well as the hard lines at the rear from the fitting where the line in the tunnel emerges. The line in the tunnel is a lot more sheltered from the environment.

And once I oriented the picture correctly in my heard it looks like the proper MC now that Morrie noted when the dual circuit came in. The switch in the middle, with no wire attached, is for the brake system warning light.

zedsn · 09-03-2016, 03:45 AM

I would try and replace the rubber lines right before each caliper next. That may solve your hard pedal feel.

09-03-2016, 05:44 AM

With no history of the maintenance by the previous owner, I would invest in a proper braking system: upgrade/convert to dual MBC, with all new lines, cleaning/rebuilding calipers. For me it's basic safety for myself, my wife and co-driver, and last but not least other people on the road.

BTW Feeding the hard brake line through the tunnel isn't very difficult, just takes some time. Remove one of the front seats, the shifter mechanism and the cover behind the front seats. The brake line is fixed with clips to the tunnel wall. And ... if you are in there, check/replace the shifter bushings, if worn, resulting in a more precise shifting.

Otto

mickey356 · 09-03-2016, 03:16 PM

Yeah, I'm all about being able to stop

The plan is PMB calipers, new lines throughout, pads & rotors, and a new MC (again).

Can anyone advise on how to tell the proper length actuator rod?

mickey356 · 09-19-2016, 10:34 AM

Well I had a chance to drive my car the other day and I gave the pedal a good stomp doing about 35mph. It stopped quickly (no lock up) but when taking off again the car kinda dragged a bit like the feeling you get when you forget to release the ebrake. Once rolling a bit it freed up fine and drove normally. Hard to explain but I t just doesn't feel right.

Still unclear in the actuator rod length or how to determine if it's the correct length, though I don't think that is the sole issue here.

Morrie · 09-19-2016, 12:13 PM

Quote:

Originally Posted by mickey356

Well I had a chance to drive my car the other day and I gave the pedal a good stomp doing about 35mph. It stopped quickly (no lock up) but when taking off again the car kinda dragged a bit like the feeling you get when you forget to release the ebrake. Once rolling a bit it freed up fine and drove normally. Hard to explain but I t just doesn't feel right.

Still unclear in the actuator rod length or how to determine if it's the correct length, though I don't think that is the sole issue here.

Hi, Mickey,

I stopped commenting when you listed the known condition of components. From above it sounds like you have caliper pistons sticking. I think before you go into anymore bit by bit attempts to diagnose, based on what you have told us, you need to do all of the following.

1. Remove all calipers. Either replace with PMB parts as you have mentioned, or disassemble and reseal all of the pistons. Insure that the pistons all move freely with no binding, A block of wood between them thick enough to prevent pistons from popping out, and air pressure applied from the brake line connection should allow you to see both pistons moving out smoothly in each caliper.

2. Replace all the flex lines. For a driver non track car, rubber lines are fine. This is disputable by some vs braided lines, but for your purposes here DOT rubber will be fine.

3. Replace the master cylinder with a genuine ATE part.

To get a firm pedal after bleeding the air out, you will probably have to install thin/worn pads and allow the pistons to push out, then compress them back just far enough to allow your new pads to fit. This is related to the kick back mechanism in these early calipers.

Let us know if the problem persists after rebuilding and bleeding system. I suspect that your problems will go away at that point but if not, we can diagnose from there. I have a friend doing the single to dual MC conversion now, and we can get measurements on the brake MC actuating pin then.

Kind regards,
Morrie

mickey356 · 09-19-2016, 02:02 PM

Thank you, Morrie!
I already purchased braided lines, so I guess a little extra integrity can't hurt

I will update when the brakes are done. As I mentioned, I am planning on PMBs and new pads and rotors. I will go ahead and get the dual ATE MC as well. Does anyone have a part number on that?

And do I want the one with a booster, or no booster?

mickey356 · 09-19-2016, 02:13 PM

Zims has this kit.
356 Dual Stage Master Cylinder Conversion Kit

Morrie · 09-19-2016, 06:42 PM

Quote:

Originally Posted by mickey356

Zims has this kit.
356 Dual Stage Master Cylinder Conversion Kit

You don't need this.

Morrie · 09-19-2016, 06:44 PM

Quote:

Originally Posted by mickey356

Thank you, Morrie!
I already purchased braided lines, so I guess a little extra integrity can't hurt

I will update when the brakes are done. As I mentioned, I am planning on PMBs and new pads and rotors. I will go ahead and get the dual ATE MC as well. Does anyone have a part number on that?

And do I want the one with a booster, or no booster?

You want the dual master cylinder for 68-76. No, your car does not have power brakes so you don't need one compatible with a booster. I think you can probably find one with our host, or do a catalog search.