Brake problem on 73 922 E

[cmcfaul]

The brakes on my 73 911 E (m calipers) drag excessively after a couple hard stops. The peddle gets rock hard to the point of dragging the brakes. It's like they get pressurized during braking but then don't release the pressure. A hard pedal is usually a good thing but this has gone way too far. Not sure if it's a heat issue or master cylinder. I replaced the master cylinder a few year ago. The brakes are otherwise perfect, no pull or unusual bias front to rear.

The fluid is two years old and is the blue racing type. I changed it last exactly two years ago before my last track event. (hoping to do another this year)

I pulled into my garage last night with the brakes dragging and the calipers were evenly (all four) warm to the touch but definitely not hot (I am assuming not hot enough to boil fluid).

I replaced the rear rotors last week and thought the problem might be an e-brake over heating or something wrong inside there. No, everything was perfect.

The pedal gets so hard that I am sure the brake light does not even come on as the pedal moves barely at all when braking with this problem.

I can free the brakes up by pushing hard on the brakes while standing still and releasing the pedal. The car then rolls freely but the pedal is still hard as a rock and the next stop Will cause them to drag. I parked the car with the brakes in the dragging state. This morning they were fine until I did a couple hard brakes and the problem persists.

Thanks in advance,

Chris

73 911 E

[greens]

Check your flexible lines. They often swell shut when they are old and the calipers stick.

[cmcfaul]

The brake lines? They are the braided steel type. Replaced them 7ish years ago. How can I tell if they are bad?

Thanks,

Chris

[911pcars]

What are your brake dragging symptoms again?

If they were dragging abnormally, one or more would be a little warm to the touch - in fact, a dragging brake/wheel will be very hot to the touch. Does the vehicle speed noticeably decrease, then not? If so, the two symptoms don't seem congruous.

Sherwood

[Neunelfer]

It's hard to tell with braided lines where the problem may be. This is why a lot of people try to steer others away from them. If they're DOT lines they should be of good quality and 7 years shouldn't be an issue.

I always say with soft lines; if you don't know when the last time they were changed... change them.

It sounds to me like you may have pistons sticking. A couple of questions:

* How often do you change your brake fluid?
* Does/Did the car sit for a long period of time?

Most of these types of events can be traced to either, soft lines as these guys mentioned (but the comment about being able to free them up by pushing hard may not work here) or stuck pistons.

With the soft lines, the insides swell not allowing the fluid to come back out at the pressurized rate it came in.

With the pistons it's usually caused by what I call brake fluid shellac. This is old fluid that has gathered around the top 1/3rd (where the seal is) of the piston. The fluid, being hydroscopic, will attract water that likes to gather around the seals. This dirty fluid residue can usually be polished right off the pistons in a good rebuild. It is the cause of sticking pistons 99% of the time. This is why changing your fluid annually, racing or not, is a great idea. The brake fluid system is an open system. Water will get in.

One other question that may be relevant; did you change to DOT 5 recently?

[WCB4]

You only installed new rotors? Or did you do new pads as well?. At any rate it sounds like sticky pistons. When you install new pads it pushes the pistons back into that bore where it has not been in awhile. It would be odd if you only replaced the rotors for this to happen. Or if your using new rotors with old pads it might be cocking the piston it the bore as well, I see this all the time on the Honda Gold Wing's and the Valkarie's. I know they are motorcycles but they also have a flat 6 . And yes I did stay at the Holiday Inn Express last night . I really did!!!!!
Regards Bill B.

[pacarguy]

It could also be pedal cluster bushings.

[cmcfaul]

The issue began before I replaced the rear rotors. I did not replace the pads as I replaced them just a month prior. (Hawk blue's to Mintex)

I rebuilt the calipers a few years ago and I change the fluid usualy once a year (for DE events). I did not do a DE (drivers ed) last year so the fluid is two years old (ATE racing blue). The car does not pull at all under regular breaking or when I have this issue. So I don't think it's an individual caliper or line (unless two went bad at the same time).

I drive the car several time per week and thus it never sits. I think when the brakes drag, it's all four dragging (no pull and the temps are all the same on all four calipers) which leads me to believe it might be a master cylinder issue. I do have to stand on the brakes really hard to get close to skidding. I assumed this is because of the street pads I switched to (Mintex). Maybe not?

Chris

73 911 E