Brake issue

[dberman]

On my 85 911, I rebuilt the front and rear calipers and installed new brake lines. After putting it back together and flushing the brakes, the brake pedal travels further than I expect before it engages the brakes. That is, the brake pedal goes a little past the gas pedal with moderate pressure. At first I thought I had air in the lines so I flushed the fluid again but this didn't help. After looking more closely, I can believe the problem is that when I take my foot off the brake, the front pads are retracting further than they should. If I look at the rear brakes when my foot is off the brake, I can't even see a gap between the rotor and the pad. However, in the front, there is approximately an 1/8 inch gap. This is true for both pads on the left and right side of the car.

Does this gap seem larger than I should expect and if so, does anyone have an idea of what might be causing this? My understanding is the 0 ring in the caliper is what pulls the caliper piston back to cause the gap.

Thanks for your help.

[eauboy]

Were the brake bleeders pointing up on the calipers? If not, you have them installed on the opposite sides and trapped air will not flow out. Also, it helps to rap on the calipers gently during the bleeding to encourage all the air to flow out.

[dberman]

Yes, the bleeders are on top. I don't think the problem is air in the lines. I think it is the gap between the pads and the rotor.

[cashman]

1/8 inch gap is too much. I would remove the pads, insert a small piece of wood that is slightly smaller than the pad thickness. Press the brake pedal to remove the gap. Open the space just large enough to fit the pads. It should be a tight fit. You should almost have to tap them in place.

This is most likely your issue. Make sure you have the bleeder valves on top of the caliper. If not, the calipers are upside down.

[cashman]

Man, you guys type fast. Disregard the bleeder issue. Remove the gap.

[DRACO A5OG]

Okay same issue here on my 85, what a coincedence.

According to Marc at Redline Technic, you and I should have done the fronts first then after broken in tackle the rears.

In the meantime, you will need to bleed and bleed and bleed again.

I have a 3rd round coming up soon. After every bleed it is getting better and better. I have tried all methods including reverse bleeding, vacuum, 2 man and even the one man gravity bleed.

My buddy with his 87 couple is going thru this as well.

Jim

We three must be the real unlucky guys

[dberman]

Jim,

Why do you think the problem is air in the lines? What's the theory about doing the fronts and rear seperately?

Thanks,

Dave

[jlr69s]

You can add me to that "unlucky" list. Ive had an issue with my '84 for a while now. Rebuilt the fronts and replaced all pads. Even installed a rebuilt master cylinder. Now when I push the brake pedal I feel resistance and its stopping, it just isn't firm. At slow speeds I can press all the way down till the pedal hits a "stop." Not to hijack by any means. Are you hitting this point of "stop" in your brake pedal travel?

[DRACO A5OG]

Hey Dave,

I did everything properly, evn placed a 2X4 on the pedal as I removed teh calipers to insure no air in the system. But lucky me it did not help.

Marc asked if I used lube on the pistons, unfortunately I did not. I just used new brake fluid, like most do and my 87 buddy did.

I agree, I don't think it is air in the lines because I swear all air is out but every time I bleed it gets better.

Marc explained, after the fronts are done. One should break it in for about 500 miles or so to insure they are biting perfectly then the rears.

I really do not understand why it needs to be broken in but he is one of the repected wrenches here and I am going thru what he has described to the letter.

Question I have for you is, when at rest is the gap still there? If so that is definitely not normal, It could be the piston may be binding. Yes, that means a "re-do"

Jim

P.S. Thank goodness for over engineered PAG brakes, she stops on a dime but the pedal feel is soft at first the it bites like crazy

[DRACO A5OG]

Joe, down to the floor board really? Whoa, that is not good.

Mine never hit the floor board, just a bit soft at top.

May want to consider bleeding again.

I found a very good method using a catch bottle placed on a garbage can which is higher than the caliper and long piece of clear tubing from HD. I fill the tube with fluid, attach to the bleeder valve, then open the valve and leave it open and start pumping away at the pedal until all air is out. Very easy and quick, found it to be the BEST METHOD of All methods, uses the least amount of new fluid to boot.

The only thing is to insure the valves are not leaking when you turn out 1/4 to open the valve.

Jim

[dberman]

Jim,

Yes, the gap is still there when the car is at rest and no pressure on the pedal. I actually used silicon brake lube on the pistons too.

One thing that I was concerned about. Since half of the piston has is higher than the other half, this probably accounts for some of the gap. But it still seems like too much of a gap and I don't see the same thing in the rears.

The pedal moves freely until it gets down to about the gap pedal height and then it engages. I can watch this when my wife presses the pedal. Once it travels to the height of the gas pedal the pad is fully engaged against the rotor and the brakes feel normal. So, the problem I believe is just the distance the pedal travels. Once engaged it doesn't feel soft.

Glad to hear I'm not the only one with this problem.

Dave

[dberman]

Joe,

No, my pedal doesn't go down the floor. It just goes further than I expect.

Dave

[DRACO A5OG]

Gap? Oh my, that is not correct. I hate to write this but you may need to re-do.

When you were doing the work, did you remove all the carbon deposits? It sounds like it is binding where it will not seat properly at rest.

I did not use lube because ATE instructions did not call for it or would have. I did not want to add any other fluids to the system other than brake fluid.

[dberman]

Jim,

I don't think it is binding. I can watch the pads as the brake pedal is pushed and the piston slides towards the rotor. When the pressure is removed from the pedal, the piston slides back. The problem seems to be that it slides further than I think is reasonable. My understanding is the rubber seal in the piston is what makes the piston retract. That is, it deforms as the piston moves out and this deformation is what pushes the piston back in.

I probably will try what Cashman suggests and see if that helps.

Dave

[DRACO A5OG]

That is interesting and I can visualize what he is writing. Maybe that is my issue too. But I know I don't have a gap but I will check mine just in case.

Keep us posted for us un-luckies

Jim

[dberman]

Cashman was right - thank you!

I pulled out my new front brake pads, installed my old pads and stepped on the pedal a few times to firm it up. The brakes felt tight. I then reintalled my new ones and the brakes again feel tight. So, I think I am all set. I guess it has to do with the position the rubber seal in the caliper is in when everything is installed since it is this seal that pulls back on the piston.

Jim - I would check the gap between the pads and the rotor. If it is anything more than 1/16 i think you have the same problem as I do.

I appreciate all the help.

Dave

[DRACO A5OG]

Whoa! Really? Damn, learn something every day.

Congrats Brother Congrats!

[dberman]

Jim, I'm curious if your problem is the same as mine. Let us know. Thanks.

[DRACO A5OG]

Hey Dave,

Not yet, working on putting my son's car back together after cylinder head re-build . Plat is Full

I will definitely post if this cures my issue, bot if it is the same my buddy will be very happy

So, how are the brakes so far? Back to normal?

[dberman]

Yes, the brakes feel exactly as I expected. I put a few miles on the car yesterday and everything feels great.