Soft pedal after caliper rebuild, ideas?
 

I just rebuilt my calipers (2000 S) with new Centric seals and new silicon dust boots from racing brake (supposed to be more high temp resistant, but can fail if brake fluid gets on them. We'll see if it was a good idea or not :) ). It wasn't too bad, and after I got the calipers back on the car I bled them twice: 1 time all the way around the car with the motive bleeder (and with the pistons fully retracted), and then I pumped the brakes to seat the pistons on the pads, and then did another bleed with the motive, accompanied by a few pedal pumps.

I got a lot of air out the first time, as expected, and I got some out the second time too.

Then I took a drive, and got the following behavior: braking power is the same as it ever was, except the pedal travel is a little longer than it used to be, like I have to push the pedal down a little further before I get to the actual braking.

Doing a few searches has led me to some theories:

1. I still have some air in the calipers.
2. The new seals are pulling the pistons back into the caliper, and that extra pedal travel is moving the piston onto the brake pad, and when I release the pedal, the seal is pulling the piston back. If so, this should resolve itself after some driving.

I'm going to another bleed, this time the "old fashioned" way with 2 people, and using the brake pedal to push out the fluid. This will generate a lot more force than the motive and may help to dislodge bubble. Also I worked the brakes pretty good when I was on my test drive, and activated ABS a couple times, so maybe that dislodged the bubbles to the top. I may also tap the calipers with a rubber mallet to dislodge any air bubbles...

If this doesn't resolve it, I am not that excited about "waiting" for it to solve itself in regard to the pistons seating on the brake pad and not getting pulled back by the seals, since I am going to Roebling this weekend.

Just wondering if anyone has ever seen this, as I know a few folks have rebuilt their calipers.

Thanks

Steve

#2 is the issue. Pump bleed with a thinner block of wood in there instead of the pad. K

I'll check that out, I have some old pads I can use if I can't find some wood.

Suppose the issue is several air bubbles - it may take a bit of time for them to coalesce .When they do ,they will be easier to bleed out.
If you bleed the old fashioned way, is it a good idea to pressurize slightly with the Motive Bleeder at the same time?
Anyone in favor of using automatic bleeder valves - to make it easier ,not to magically eliminate bubbles?

You'd feel an empty moment, possibly scary moment also, no? You think longer pistons would solve your issue?... name your preferred SS type material (304 ok?) ;)

Long pedals r not welcome at the track, got to be fixed :/

edit: isee, you haven't changed the pistons. Strange behavior in that case.... +1 to Gelbster. Air, what else

+1,000 to that, I have had only 1 long pedal at the track, and that was after sitting for a while due to a red flag, once we got going again, the first time I pressed the brakes the pedal went waaaay down (I guess because the brake fluid got so hot sitting in one spot with hot rotors and calipers and no cooling air), they came right back though.

stay alive Steve! Get the first athletic kid you can find and get him to pump those 4x wheels for you. Mech bleeders, magic valves, sucktion, zero-gravity-vacuum... whatever its labeled the "old fashioned" way is the way. Its those violent kicks that really dislodge those trapped bubbles ;)

Egyptians invented that techniqueI think lolll

My son is going to help me :)

Do you have PSM? It could also be air in the ABS and/or PSM circuits.

Hi,

i suspect air bubbles.

Don't use the old fashion way if you have an ABS/ESP system in your car.

Make shure you have always min 1 bar and max 2 bar pressure in your over pressure system (motive bleeder). I recommend 1 - 1.5 bar, because the brake reservoirs are min. approx. 15 years old now.

Don't forget to bleed the clutch line, as it is connected to the brake system. It can affect also brakes if you have air in the clutch line.

Start from the longest line to the brake cylinder and go stepwise to the shortest.

If you have an S brake, don't forget to bleed both brake cylinders in the front calipers.

Seals won't affect any brake travel.

Regards, Markus

The clutch slave bleed valve is a PITA to get at and turn. It is located at the top front left of the transmission and the easiest way to get decent access to it is to put the rear on jack stands and remove the left rear wheel.

Have fun!

I'm going to bleed it again after work today, I bet I am going to find some big bubbles.

I think I am ok with regard to ABS/TC because:

• I never let the fluid get below min in the master cylinder
• I blocked the brake pedal down a little before I removed the calipers, this kept the brake fluid from draining out, and also I put a bleed cap on the end of each hard line. This way I lost almost no brake fluid out of the lines when the calipers were off. Hopefully this kept air from floating up and getting into the ABS/TC system

Edit - yeah the clutch is a hassle to bleed :) I have done it recently, and so I didn't plan on doing it this time. My understanding is that the clutch runs its own line off the master cylinder, so unless I were to empty the master cylinder too much when bleeding I shouldn't introduce any air into the clutch line. And the clutch line doesn't get pressurized when I apply the brakes so even if it had air, I wouldn't think it would affect the brakes.

I will tell a story though - the very first time I flushed my brake fluid it was with ATE Super blue, and I paid a shop to do it. They didn't do the clutch, and I think they only did the outer bleed screw (I don't even think they took the wheels off, I think they just put a tube on the nipple, opened it up and let it drain out "gravity" style). Shortly after that I got the Motive bleeder and when it was time to flush the brake fluid again, I did it myself, and I noticed the following this:

• When bleeding from the inner bleed screw on the brakes, I got a short slug of the original amber brake fluid before the blue came out. It was all blue from the outer screw.
• When I bed the clutch, it came out totally blue. Somehow the blue got mixed in with the original amber, I guess due to the brake fluid going in and out at the master cylinder end when the clutch was applied. Odd :)

So I may be way off with my thoughts above about how the clutch and brake interact...

Hello,

a brake system with ABS has an ABS regulator block (don't know the right english term for that part). The conventional bleeding method by just hitting the brake pedal while sombody else opens and closes the bleeder valve doesn't work with that. So i recommend to use a pressure system to bleed brakes and clutch.

http://cdn4.pelicanparts.com/techart...small/Pic3.jpg

Regards, Markus

Another bleed got no air from RR caliper, little air from RL, lot of air from FR, tiny air from FL, brake is firm right away and all good :) my driving and abs actvations must have vibrated loose some air :)

Glad to hear that! After major work it is a good idea to activate ABS and PSM after bleeding and then re-bleeding.

Porsche and the indies have the tools to open the ABS and PSM circuits during bleeding, but that's not available to us home wrenchers.

I have a durametric and it has a command for activating the TC/ABS/PSM, I tried it once and it did nothing, I emailed durametric and they were like "oh well, not everything works on every model..." :)

There is a hilly spot in my neighborhood where sand seems to collect, always good for manually activating abs :)

If I ever got air in those systems I'm not sure how I would get it out..

The air will come out when you activate them. The reservoirs are small and the amount of fluid required to activate the systems is larger.