How many times did you bleed till it felt "right"?

[chrisbruck]

OK, got my brake system all back together (new MC, new reservoir, rebuilt calipers, new pads)... bled a whole bunch (1+ ltr of fluid) with a Motive Power bleeder at 12-15 psi myself. Banged on the calipers to jar out any bubbles. Didn't see any more bubbles so out for a test.

First test drive = Took 1 full pedal pump to stop with a nice firm feel. Didn't drop all they way to the floor but had way more travel than I wanted. Had to pump each time to stop with confidence. Not very pleasant. Drove maybe 40 miles.

So I bled again = A few stray bubbles from the rear only but not as many as I expected. Drove again and pedal feel improved. You could stop on one pedal push but lots more travel than I'd like. Pumping helped but not required as in the first test drive. Drove another 40-50 miles or so.

So I bled again = A few more stray bubbles this time from the front. Drove again and pedal felt better. Still not quite "there" yet but I think I've matched or improved on the old system feel.

Plan on bleeding again this coming weekend. Will probably drive another 30-50 miles depending on weather.

How many times do I need to plan on bleeding this darn thing?

(Plus, I'm good enough now to where I can jack her up, pull the wheels, bleed, and be back on the road within an hour.)

[KFC911]

When I replaced my complete system (930 setup), it only took one "session" of bleeding, going around to each caliper 2 (maybe 3, I don't recall), before I had no pedal travel and a STOP RIGHT NOW system...hmmm? Did you also replace your rubber lines along with everything else? Maybe one of the "experts" will chime in with some suggestions, but something does seem amiss imo. Good luck!

[chrisbruck]

I didn't replace the lines but I'm kicking myself for not doing them when i had it apart. I was concerned about breaking the hard lines.

[KFC911]

Originally Posted by chrisbruck

I didn't replace the lines but I'm kicking myself for not doing them when i had it apart. I was concerned about breaking the hard lines.

How old are they? I'm betting that may very well be your issue as it does sound as if you've gotten the air out of the system. Waiting for an expert to chime in...

[Hodgey]

Chris,

What was the feel like before you replaced the listed parts?

Could be the hoses are expanding under braking.....

[KFC911]

Originally Posted by chrisbruck

I didn't replace the lines but I'm kicking myself for not doing them when i had it apart. I was concerned about breaking the hard lines.

You know what you need to do don't cha ? Get the proper wrenches, put one on the hard line, one on the rubber line, and squeeze them together like you're using scissors. Sorry to give ya the bad news...good luck!

[Halm]

I may be confusing pedals, but isn't there an adjustment screw in the cluster that allows you to move the engagement point? Move it so there is almost immediate engagement when you press the brake pedal. Just understand that this changing where on the arc of travel it hooks up and does not firm up the pedal.

[mreid]

Did you bench bleed the mc? I never do, but I also use a pressure bleeder. It connects to the top of the mc and allows me to apply 15 lbs of pressure which pushes fluid through the system. All I do is open bleeders (rr, lr, rf, lf). If you don't use a pressure bleeder and replace the mc, you will have the problem you describe.

[KFC911]

...and you did bleed the clutch during this pocess too?

[redstrosekNic]

I have had many cars take up to 6-8 times of bleeding before having a rock-hard pedal. It can be extremely frustrating, but I think you'll get there. The fact that air continues to come out tells me that you still have some in there.

Good luck

[MotoSook]

It shouldn't take you more than a couple times to bleed.

One of the often forgotten aspect of rebuilding calipers is that the new seals will hold the pistons out until they have set up. This happens when you install new pads sometimes too, but more often with new piston seals. What happens is the seals hold the pistons off the rotors just enough to induce more travel than when they all set up together.

Try removing the pads and putting a paint stick or some other blocking spacer that is narrower than the new pads, then pump the pedal to move the calipers in, the spread the pistons out, just so the pads fit over the rotors. You want it tight. You'll want to do this with all calipers.

Try this and report back.

[ivangene]

Originally Posted by KC911

...and you did bleed the clutch during this pocess too?

+1 !

and you asked so my answer is

2

it took me two times with new (long list of parts - complete different calipers, hard lines, and flex lines)

I have found the bleeder can be too forceful sometimes so I like to just open a bleeder and let it gravity bleed for a while - not sure on the 87 if that works or not, but works magic on air for the 86' (and older)

but I have 964 calipers, so the Q relates more to the MC and the hydraulic clutch set up

[gsxrken]

Just grit yout teeth and go back in to redo the flex lines. If the fittings are not yielding even with the proper flare wrenches, you can cut the flex lines and use some heat on the female side of the union. (Heat with fluid in the line will take forever and probably burst the line.)

I use a motive pressure for fluid renewal, but always need to follow up with an assistant. The movement of the pistons in the MC and calipers seems to dislodge the last bit of air. It takes very little air to kill your pedal feel.

[chrisbruck]

I'll bleed them a few mores times and if it's still not quite there I'll bite the bullet and replace the flex lines.... dang it I'm just kicking myself for not doing those as well..... oh well, live and learn.

Maybe there is just that last little bit of stubborn air bubble somewhere.....

[MotoSook]

I doubt the stock lines are causing your problem, but that doesn't mean you shouldn't replace them, even with new ones. They really do not flex as much as people think.

[Tom '74 911]

Originally Posted by MotoSook

One of the often forgotten aspect of rebuilding calipers is that the new seals will hold the pistons out until they have set up. This happens when you install new pads sometimes too, but more often with new piston seals. What happens is the seals hold the pistons off the rotors just enough to induce more travel than when they all set up together.

This. If you put new seals in the calipers, just as Sook said, they will take a few miles to break in. When you release the pedal, the new seals retract the pistons away from the disk, so the next time you apply the brakes, the pistons have further to travel before they start applying pressure to the rotor. The result is a longer pedal until everything gets broken in and the pistons aren't pulled away by the new seals.

This has been my experience at least - so take that for what it's worth. If you do a search on rebuilt calipers, you should be able to find a few threads on this.

As long as it feels safe, put some more miles on it and do another bleed or two too. . . Seems like every time I bleed my brakes, I can always get a few tiny bubbles out. . .

[chrisbruck]

Interesting about the caliper seals.... being an engineer I can totally understand the logic there. Perhaps I'll pull the new pads out and put the worn, old pads in place and pump the pedal to extend the calipers past their current position and then reset them and put the new pads back in place. I lubed the seals pretty well so the pistons did slide in pretty easy.

Great advice.

[DRACO A5OG]

Check all brake lines not just at the calipers:



behind the stone guard, there is an elbow and a T connectors.

[Bob Kontak]

Originally Posted by MotoSook

It shouldn't take you more than a couple times to bleed.

+1

Drive it, re-bleed. You will know when it is free of air. Amazing when you clear the lines out. You won't hit that "step" you are feeling now.

[Reiver]

twice around, just right.