Brake bleeding help needed

[mowog63]

Hi All,

I am having issues getting my brakes back to working condition and need ideas to solve the problem.

This not my first time working on brakes, but it is the first time I have done the brakes on this car: 85 Carerra.

The car is on jackstands with all wheels off and the front end pitched slightly higher.

What I've done:
- rebuilt the front calipers with Ate rebuild kit - there were no issues with the pistons, they came out nicely with some air pressure and had no rust
- reoriented the pistons as per the manual
- all new hard brake lines at the calipers
- all new flexible lines on all four corners - DOT-approve SS
- new Zimmerman rotors, front only
- new Porterfield pads, all four corners
- added new Ate brake fluid

The current situation:
I used a Motive pressure bleeder and Ate brake fluid and pressurized it to around 15 psi and was able to get fluid coming out at each corner successively, working furthest to closest in regard to the MC.

But after doing all four corners twice with the pressure bleed, now when I press on the brake pedal it is soft and the fronts don't operate.

I had my son come and help me do it by the manual process; I say down, he presses the brake down, I open the bleeder valve and the fluid runs into a tube and catch can. I close the valve and say up and he releases the pedal.

Still no change.

If he pumps the brakes up about five or so successive pumps, all of the brakes work and clench the rotors.

Considering I rebuilt the fronts, I'm assuming that they have a lot of air in them still.
Any tips on getting the air out or what the issue is?

Thanks,
Erik.

[Oh Haha]

Did you keep the MC full of fluid when bleeding by hand? You don't sound like a novice but it came to mind anyway.
You may need to bleed them several more times. Tapping the calipers with a rubber mallet can help expel air.

[aj88cab]

Did you put the front calipers on the correct sides when you replaced them?...with the bleed valves facing up.

[CCM911]

It is most likely a combination of things. When you rebuilt the calipers, did you use sil-glide on the new seals? Sometimes, the pistons will try to pull back, creating a difficult to bleed situation. Wayne is correct regarding the rubber mallet method. Also, consider doing an old fashioned "gravity bleed". Do it one caliper at a time. Sounds like you only need to do the fronts. Start by cracking open the bleeder valve on the passenger side. Let it go until it starts flowing fluid. Then repeat for the driver's side.

You'll be fine, you just need to work that leftover air out of the system.

I'll be doing mine this Saturday, so I will be following your progress as well.

[Quicksilver]

It is much easier to get a good bleed by prebleeding the MC by routing a hose from the out-port to dump back in the reservoir. Once that is running pure brake fluid the rest of the process works much better.

New calipers can be a similar situation. If you pre fill them and then push the pistons back it does a pretty effective prebleed of the calipers.

Once it is all together you should be close but in the situation where it is being difficult you can bleed with the caliper pistons extended using old pads or masonite spacers and then press the pistons back to clear out stubborn bubbles.

And as mentioned before: Bleeders must be pointed up.
And if there are deficiencies such as bad flex hoses those must be handled before any realistic chances of success.

[yelcab1]

Upside down calipers. Nipples need to point up.

[CCM911]

Erik, RTR Happy Hour in your town tonight. Hopefully, you'll meet some techy folks that can offer some input.

[mowog63]

Thanks all for the help!

Chris, yes I used Sil-Glyde.
No, I can't make it to the happy hour tonight.....and it's walking distance!

I hope it turns out to be upside down calipers.....this is the downside of "hobby" work after work; dumb things happen.
I can't say for sure that that is the case, but with my luck it is!!!

"I cut this board three times now and its still too short"

Thanks,
Erik.

[OffCamber00]

Whenever I have the brake system apart - like really apart - I have found that the Motive alone does not give me the rock hard pedal I want. This is where the traditional method of pumping the brake pedal to build pressure and agitate the fluid and then cracking the bleeder valves works wonders.

[rusnak]

Erik, there is a brake proportioning valve. You should place a brick or something under the brake pedal so it won't go to the floor.

Have your son pump the pedal fast like ten times, then hold the pedal down like a panic stop - a lot of pressure.

Then open the bleeder valve. It won't matter if it's facing up, down, or sideways. All the air will shoot out. Repeat for all 4 bleeders. You will save brake fluid and time doing this, if the Motive fails to bleed the brakes.

[LakeCleElum]

Did you bench bleed the master cylinder? This can cause problems like you have.

[Jack Stands]

Sometimes it can be very frustrating! When I installed some PMB rebuilt front calipers on my 914-6, we used vacuum, pressure and traditional bleeding, but the pedal was still soft. Took the car out for a drive on some rough, bumpy roads and reeled with a pressure bleeder. Amazed how much of a 'burp' of air we got at the last bleeding! Rock hard pedal now, but it took a lot of effort.

[BK911]

Many have this question when bleeding rebuilt calipers.
Most of the time it is because the caliper pistons start too far from the rotor.
A couple of spirited stops will help put the pistons in their happy spot.

[guli]

Just had the same experience the other day. Cleaned calipers and replaced seals. After bleeding there was no air in the system but the pedal was soft and I had to pump a couple of times to get a firm pedal. Apparently the new seals pulled back the piston when the pressure was released.

Solution. Remove one pad. Put a piece of 4 mm plywood in its place. Press the pedal to push out the piston. Push it pack again with a large screwdriver. Repeat until the piston moves easily. Took me five times.

Repeat for all pistons.

Now the pedal is firm as it should.

/Gustaf

[rusnak]

BK and guli:

Good call on the pistons. I would pull the pads, do a quick tap on the pedal, and use a brake pad spreader to float the calipers with pads back on to the rotor.

[trond]

had similar issues. Finally I just drove it around the block at slow speed and brakes came back. I believe the pistons may be 'hanging' on the new seals and get pulled back. Later I replaced the master cylinder and had no issues, just bled by gravity and perfect brakes immediately

[Quicksilver]

Excessive seal retraction is a common problem. The second to last set of rebuilt calipers I had in my car just wouldn't get a hard petal. Bleeding, swapping rotors, pads, reassembling... Nothing worked and I battled it for over 2500 miles.

I picked up a nice set of PMBs and then put my head into the bench testing of the "problem" calipers and I quickly found that the seal retraction was hugely excessive. Talked to a few people and the problem isn't that uncommon. Insist on ATE seals. They will be better out of the box and will get better as they break in.

Brembo makes a line of "low retraction seals" but they don't list them for our cars. I really wish they did because I would give up a small percentage of brake life for an exceptionally hard brake pedal.

[cabmandone]

I'm having the same trouble with mine after a 4 corner caliper rebuild. I'm going to work on it more this weekend. I'll let you know if I find anything that works for me.

[boyt911sc]

Exercise the four (4) calipers after the rebuild. When I first heard this 'exercise' procedure from an experience Porsche mechanic, I was skeptical. The reason behind this technique is to move the brake piston/s several times back and forth to minimize the piston retraction. The new brake piston seals tend to retract the brake pistons more than old/used seals. Remove the brake pads and insert a thinner piece of plywood and press the brake pedal. Retract the brake pistons and repeat several times. You will have firmer brake pedal after doing the 'exercise' provided the MC is good. Keep us posted.

Tony

[Ronnie's.930]

A friendly FYI for those that have trouble with brake bleeding.

This is my one and only method for bleeding any brake system (motorcycle to motor home) - been doing it for years - extremely fast and efficent, one man operation.

About 15 psi at the reservoir - easy with the 911 reservoir due to the vent nipple (nipples = good, buttofcourse ), but if no vent nip presesnt, just add a hose barb to the reservoir cap . . . all air is quickly fired out of the entire brake system and there is absolutely no need for brake pedal pumping or "finishing" the process with the traditional method.

Of course, you need a compressor, air/water separator, pressure regulator, air gun, etc.


This is nothing new, but I learned it from a Pelican who posts in the Turbo forum . . . I could not get the air out of the brake system on my 17' box truck using the traditional or vacuum methods over the course of 3-4 days, read about this method and had a Viagra-like brake pedal in about 10 minutes.