Soft brakes on 77 911

[DelPico]

Hi,

After driving along distance my brakes have become soft. I can't lock the wheels if I wanted to. Anyways a friend of mine recommended checking the pads and then the fluid. The fluid is probably at least five years old. Anyways, if I measure the pads what width am I looking for. Also, what brake fluid do I need?

Thanks,

David

[jbrand540]

Have you checked for leaks anywhere in the lines and cylinder. If you were picking up air in the lines the pedal can have a soft (spongy) feel to it.

[DelPico]

The fluid level has never dropped. It is the same it has always been.

[jbrand540]

I would bleed the brakes first as it is easy to do with a brake bleeder and the least expensive.

If you question the quality of the fluid then have the fluid flushed, replaced, and bleed.

[tonythetarga]

Five years in MA without changing fluid is too long. You most certainly have some water in there from the winter condensation cycles you've seen even if you haven't driven the car that much. I just helped a buddy flush his system after he bought a roller and got it running with a new engine. The brake system was almost 25% water and the normally clear fluid was brown.
Get yourself some good brake fluid, ATE Blue or Gold and flush your old lines completely. Try and avoid using the pedal push method unless you only use the normal brake pedal travel during the flush process. You could damage the m/c by pushing the full stroke. A Power bleeder is better in my opinion.
Once you flush and bleed, bleed again in a couple days after driving it.
Your pads should be about a 1/4" or more of pad material on each side not counting the metal backing.

[ChrisBennet]

David,
For brake fluids I use the Castrol LMA (Low Moisture Affinity) or the the big silver bottles of Valvoline Syn Power. The Valvoline synthetic stuff is not silicone and its boiling point is/was (the boiling point has varied) 500 degrees - only 36 less than the ATE Racing blue stuff I used to use.
-Chris

[Shaun @ Tru6]

Check:
Rotor thickness (specs are in the Pelican online catalog)
Pad thickness

Replace as needed.

Bleed system completely (I have a Motive power bleeder if you want to borrow it)

Since it's a "whole system" feeling, look to the M/C if the above isn't helpful.

[DelPico]

Thanks everyone for your help. I will try bleeding the system first.

Thanks,

David

[T77911S]

as the pads wear, the pistons in the calipers extend out further which in turn can reduce breaking. the moister in breakfluid will cause pitting on the caliper pistons, and combined with worn pads will cause the reduced breaking. i just put pads on my 77 and found i had a "frozen" piston in each caliper. i did not have time to rebuild them, which they need it desperately, but i cant believe how incredible my brakes are with all pistons working. with the age of your car, you might want to consider rebuilding yours too.

[Paulporsche]

In addition to the above, how old are your brake lines? They can expand over time, adding to the sponginess.

[DelPico]

Not sure how old the brake lines are. They are not original's for sure. The one I looked at last night looked pretty good. I'll start with bleeding and then try pads, then lines, then MC. I bet the brake fluid is bad.

Thanks,

David

[Gunter]

Originally posted by DelPico
Not sure how old the brake lines are. They are not original's for sure. The one I looked at last night looked pretty good. I'll start with bleeding and then try pads, then lines, then MC. I bet the brake fluid is bad.
Thanks,
David

Sounds to me that the pistons in the calipers are frozen.
They don't retract like they should and keep the pads against the rotors which builds up heat after long driving.
The heat boils the old fluid and the brakes get spongy.
Just changing to new fluid may not solve your problem; a rebuild of the calipers is in order if it hasn't been done for many years.
Force the pistons back into the calipers using the old pads and you'll see if they are frozen.

[DelPico]

Change of fluid I believe worked. Now alternator light is fairly lit. I wonder the connection. I am hoping it is that I just parked outside last night and the heavy rain dampened something that will dry. Otherwise, it drove like a champ.

Thanks again,

David

[unclebilly]

I live in bone dry Alberta (except for this spring...).

I rebuilt my calipers on my 911 3 or 4 years ago and changed brake fluid. While at the track earlier this year, I was getting horrible brake fade. I finally got around to changing my brake fluid per the recommendations on this board (I put in Dot 5.1) and was totally amazed at how much water was in the old stuff. I'll bet there was 100 mL of water in there - it comes out looking like oil and vinegar salad dressing

From here on in, I'll be changing it out every year. At the end of the day, I probably didn't need DOT 5.1, just replacing with DOT 4 would have been ok, the big thing was removing the water. I used a vacuum bleeder to change the fluid.

[dm36415]

David,

Oddly enough, I just redid my rear brakes, and my alternator light has come on. It's humid here, but I haven't driven in the rain. I found your posting while doing an alternator light search. Have you solved that problem?