rbuswell

Here's the story:

Replaced front and rear shocks on my 1982 911 SC and needed to detach the brake hoses to get at the front struts properly. After I put everything back together and bled the brakes, they felt mushy. Decided that it was a good time to replace the brake hoses with braided ones and flush the system. Given how dark and dirty the old fluid was, it was probably a good idea. Bought a Motive Power Bleeder and one way speed bleeder valves. Put everything together, pressure-flushed about one and one-half quarts of fresh fluid (old dirty color changed to the new clean, clear color very nicely) and bled the system until I got no more bubbles and the pedal felt very firm with no leaks. Took it for a test drive and the pedal stayed firm and the car seemed to stop OK and kept getting better with each additional test stop but they didn't feel all that great. I was eventually able to get the brakes to lock up but not what I expected after fresh fluid and bleeding. By the way, tires are brand new (but not good ones put on by the PO) and the pads checked out OK in the PPI when I bought the car in March. Only put about 2k miles on it since then with very little town driving so I doubt that the pads are bad since then.

Am I imagining things or do I need to keep running more fluid through the system and bleeding it more? It really seems like I got all fresh fluid with no bubbles, so I'm perplexed.

PS: I had to use a big pipe wrench to tighten the pump lid on the Motive tank before it stopped leaking air. Anyone else have that problem? There was not a rubber seal at the pump lid end which seemed odd.

PPS: The Motive system seemed to work very well otherwise. It didn't overfill the reservoir like some other Rennlisters have mentioned it can do.

autobonrun

When you placed your brake pads back in the calipers, did they slide in easily or was it a tight fit?

Edward

Pipe wrench?!!! You need to get a hold of the vendor who sold that to you and get them to send you a gasket. The top screws on hand tight ...that's it!

If your brakes still don't feel as hard as they were before the hose replacement, you still have air in there. Tap the caliper pistons lightly to loosen any bubbles and keep at it. If you went through 1.5 qts of fluid, use the other .5 and see if that improves. Otherwise, buy another can and go at it again. It's a bit of a pain I know, but at least it isn't difficult

Edward

rbuswell

autobonrun: I didn't replace pads since it didn't appear to need them. I thought it would be a good idea to replace the hoses and fluid however.

Edward: I suspected the Motive unit should have had a gasket but there was no parts list in the box so I gave the benefit of the doubt. As far as the pedal feeling hard, it does feel at least as hard as before if not more so ... I'm just not sure that it is stopping as well. Frankly, I didn't really press the car in braking that hard before I did the work but am pushing it pretty hard now since I'm testing and focusing on the brakes. That's why I was hoping there would be some way of knowing that at least the work I've done on the hoses and new fluid and flushing/bleeding isn't the cause. But I'll certainly try the caliper tapping technique and see if I get more bubbles.

g-50cab

They should be rock hard after a flushing/bleeding.

Edward

If the pedal feels just as firm as before, and you never even removed the pads, you're brakes are probably fine. Find a clean stretch of empty road w/o cross traffic and get to speed, say about 75-85 or so, and *firmly* clamp down on the brakes, just short of lock up (you don't want to flat-spot your tires), but release the brakes just before coming to a complete stop (so that you're rolling, never coming to an actual stop). Do this a few times, and on the last time come back up to speed if you can and stay off the brakes for a while --you're trying to cool them off now. This works best if that empty road you're on leads to a fwy or hwy where you could loaf at speed and get some air into the brakes for a few miles. After this cool down, your brakes should feel solid and normal braking should feel, um, normal

Edward

autobonrun

Rbuswell, the reason I asked is that I found out that if the distance between the pads and the rotor surface is excessive, then even after the bed in exercise the brakes would not work optimally. When you insert the pads, they should be a tight fit. All this time I thought when I pressed the brake pedal, any play would be taken up so I would just make life easy for myself and drop them in place. It was brought to my attention by a very knowledgable board member that the brake pad fit should be tight initially.

Like you I completed a bleed, flush, and brake hose change only to find my brakes difficult to lock up and very spongy. I repulled the wheels, removed the pads, inserted a thin piece of wood, then had someone press the brake and take up the play. Then I pressed the piston slowly back in until the brake pad would barely fit down into the slot. I did this for both sides and the sponginess disapeared. I then did the bed in exercise Edward mentioned and my SC brakes were extremely powerful. They drag the car down with just enough force that I can control the point where they lockup; but they will lock up now if I need them to.

It could be that there is excessive play between your pads and the rotors after your flushing exercise even though you never removed them. You may want to check.

Daniel Dudley

Classic test for well bled brake is a very firm pedal, and both front wheels locking up at the same time. Glazed rotors or contaminated pads will cause uneven braking as well.

It is an axiom that you can never over bleed brakes, only underbleed them. As has been said, tapping the calipers smartly, and pumping the brakes as in an old fashioned bleed, can dislodge air bubbles. It is possible that you have sticking pistons in your calipers, if so, often one pad will show up as more worn than the other as it drags on the rotor. I would be surprised if you have this problem, but it does happen with older cars.LOL

rbuswell

You guys are the greatest.

I've got a lot of leads to follow up on. It's snowing here now so I can't go blasting around to see if Edward's idea helps but I think there's tons of stuff to try. I'll let you know what I find out.

rbuswell

Took it out yesterday and did the 80 to zero check and they seemed quite good. See my thread on why I bought this car.

dsmith

I always manually bleed the brakes after flushing (I use a vacuum unit). Gives a much better pedal feel IMO. Shouldn't this take up any slack in the pads/pistons?

David

psalt

Hello David,

Yes, modern hydraulic brake calipers are self adjusting, the idea that pads need to be tightly fitted is nonsense. Just the opposite is true, the pads need to float freely in the caliper. The pistons need to be retracted to fit new pads and the proper procedure is to apply the brakes several times before bleeding to move the pistons forward. Early disc brake systems, Dunlops used in Jaguars in the 1950's for example, used retractor mechanisms, but they learned that this could be accomplished by the seal design. I agree, some systems will not firm up with power or vacuum bleeding, often because of the caliper or bleed screw design. I also manually bleed if the pedal feel isn't firm.

Paul

autobonrun

Add IMO after your statement and it is correct.

There is only so much slack the "self adjustment" can take up. I followed the recommendations of another group of members and it worked perfectly for me. The gentleman asked for additional ideas. That's all that can offered. If someone chooses not to try it that is their option. He stated in his original post that he had already bled them. Assuming that was done correctly, he was looking for other options to consider.

By the way, after I use a pressure system to add new fluid, I always manually bleed them as well.

psalt

"There is only so much slack the "self adjustment" can take up"

This is also incorrect and suggests a complete lack of understanding of brake systems. Every automotive disc brake system since the 1950's is designed with a minimum pad thickness and the caliper is self adjusting within that limit. There is no cause and effect to the situation described, you simply did not correctly bleed the system on your first attempt. To suggest that calipers need to be "adjusted" by removing the pads and inserting a block of wood is beyond "silly" to anyone with experience with hydraulic systems.

autobonrun

IYO. FWIW.

Actually "adjusted" is your word, not mine. The wood was just used as a stop to keep the piston from being pressured all the way out. A used brake pad works as well. I'm not the only one that has done this successfully by the way. I offered an opinion as he says he has already bled it well. It worked for me in a similar situation where I bled the brakes multiple times and the brakes would not firm up until well into the travel.

As you have offered your opinion and I have offered a suggestion if the countinued bleeding failed, I'm done. I promised myself years ago I would not flame anyone. I've made it 5 years without doing so and won't start now. It's way too easy; more difficult not to.

I respect your differing opinion. Enjoy your Porsche.

Cheers