Brake Caliper / Piston Install Leads to Lower Brake Pedal - LotusTalk - The Lotus Cars Community
 
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post #1 of 10 (permalink) Old 10-05-2018, 07:25 AM Thread Starter
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Brake Caliper / Piston Install Leads to Lower Brake Pedal

As the subject says, I installed the stainless steel pistons and new seals into my stock front calipers to keep the fluid from boiling. Also changed the rotors.
Bled the brakes and now the brake pedal starts engaging the brakes much lower than before.

To give you some context I couldn't heel/toe the car because the brake pedal was much higher than the gas (under braking) now under braking the brake pedal is slightly below the gas pedal. Pretty big and concerning difference. Going to the track on Sunday, so I want to make sure.

I could belive theres still some air in there, but we bled them multiple times, and I did a pretty exhaustive bedding process.

Any thoughts, I already had a brake failure last track day, so I don't want to repeat that situation
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post #2 of 10 (permalink) Old 10-05-2018, 09:02 AM
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I'd guess some air as well. Did you also bleed the clutch and rear calipers?
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post #3 of 10 (permalink) Old 10-05-2018, 09:32 AM
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One surprise (to me at least) was the extent to which sealant around the bleeder threads makes a difference. As those threads get sloppy from bleeding the brakes, they start to let air in. If you are seeing brake fluid seep through the bleeder nipple threads, then you can expect some air to be getting in, too, especially if you are using a one-man bleeder setup. You can buy new thread sealant from speedbleeder.com, but you might as well get their bleeders, too, while on the website. That's what I did, and it helped a ton. Prior to that, I had the same long pedal no how many times I bled the brakes with a bottle with a check valve.

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post #4 of 10 (permalink) Old 10-05-2018, 10:27 AM Thread Starter
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I'd guess some air as well. Did you also bleed the clutch and rear calipers?
Not the clutch but we did do the rear calipers. I think I'm goign to try the power bleeder next, but yeah a bit concerning before a track day
I thought I had heard someone mention flipping the calipers upside down when bleeding them because air gets stuck in the stock calipers easily.
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post #5 of 10 (permalink) Old 10-05-2018, 10:32 AM
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Originally Posted by Ls1Rx7 View Post
Not the clutch but we did do the rear calipers. I think I'm goign to try the power bleeder next, but yeah a bit concerning before a track day
I thought I had heard someone mention flipping the calipers upside down when bleeding them because air gets stuck in the stock calipers easily.
There are a few mentions of removing the caliper and turning it over to get all of the air out if air has been introduced into the caliper. This has to do with the location of the bleed screws and crossover tubes. BOE can add a different brake line input and then you can turn the normal input into another bleeder to help with this issue.

I'm guessing this would not be the result of air in the clutch line, but I'd be checking everything before a track day.
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post #6 of 10 (permalink) Old 10-05-2018, 11:10 AM
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As alluded to above, if you have the stock calipers you have to take them off and bleed. There is a high spot on the inside that will collect air.

I use a hand pump vacuum bleeder in one hand and the unbolted caliper in the other hand to do this. I would also close the bleed niple and lightly tap the caliper body with the wooden handle of a hammer to make sure air bubble could not cling to the inside of the caliper. Then pump up the vacuum and open the bleed nipple.

Once the inside half is bled, turn it right side up and finish bleeding.
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post #7 of 10 (permalink) Old 10-05-2018, 12:16 PM
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Originally Posted by cyow5 View Post
. . .
If you are seeing brake fluid seep through the bleeder nipple threads, then you can expect some air to be getting in, too, especially if you are using a one-man bleeder setup.
. . .
. . . unless you are using a pressure bleeder, in which case leaky threads just leak a little fluid. Air won’t run counter to the pressurized fluid, so no air will be admitted via the threads. I also use the thread sealant from Speed Bleeders to avoid the mess.

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As alluded to above, if you have the stock calipers you have to take them off and bleed.
I’ve done this with dry calipers several times . . . works well.

Glen

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Last edited by Glen; 10-05-2018 at 12:23 PM. Reason: Add second quote
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post #8 of 10 (permalink) Old 10-05-2018, 01:17 PM
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Yes, you probably have air trapped in the top of the inside piston (which has no bleeder screw), or in the brake line between the ABS control unit and the caliper. You will have the do the "caliper dance":

- Unbolt the caliper from the hub assembly. Push the pistons all the way into the caliper. If you are using a pressure bleeder, like a Powerbleeder, place a piece of wood between the brake pads and/or pistons before pressuring the master cylinder reservoir so that the pistons don't pop out.

- Try to hold to hold the caliper higher than the ABS control unit (inboard of the left front fender, above the left front shock mount) for the whole procedure.

- Hold the caliper so that the cross-over tube from the inboard piston to the outboard piston is at the top (basically upside-down). Bleed a little fluid out of the outboard bleeder.

- Rotate the caliper outboard side up so that any air in the cross-over tube can make its way to the outboard piston (the air will always try to rise up on top of the fluid). Bleed a little more fluid out.

- Finally rotate the caliper so that it is right side up (with the bleeder screw on top) and bleed it again. At some point in this dance, air bubbles should have come out in your bleeder outlet tube.

After introducing air into the system, it can easily get trapped on the inboard side, so the goal is to work the air out by letting it rise to the top in each step. The intermediate bleeding is to encourage the air to move towards the outside piston, where it can be expelled via the bleeder screw.

This should make things better. You might have to do it a couple of times if you don't get back to your previous pedal level on the first try.

For those who are about to change their caliper pistons, the best way to minimize this problem is to pull the old pistons out one at a time, facing up so that no brake fluid comes out, and then completely fill the cylinder bore with brake fluid before pressing the new piston in. The goal is to try not to introduce any air into the caliper. Yes, it will be a bit messy when the excess fluid runs onto your hands, but it could save you from having to do a lot of "caliper dancing"...

p.s. If you are going to bleed the clutch, you have to be EXTRA CAREFUL and make sure to overfill the master cylinder reservoir, because the fluid supply nipple for the clutch system is very close to the "FULL" level on the reservoir. If you let the fluid level get too low, bleeding the clutch will suck AIR into the clutch line instead of fluid...

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post #9 of 10 (permalink) Old 10-05-2018, 02:11 PM
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I did a ton of brake work recently. All the regular method of bleeding and use of the power bleeder didn't help.

Had to dismount calipers. Turn upside down and tap. And then bleed. Having the power bleeder and constant pressure helps.

I also lost so much fluid during my brake work that i had air in my abs system. Had to engage abs as many times i could and then re-bleed.

Let me know if you need to borrow my power bleeder. I'm in the Watertown waltham area.

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post #10 of 10 (permalink) Old 10-05-2018, 08:54 PM
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If you pump the pedal and it comes up, but with constant pressure sinks again, it is air.

(If pedal doesn't sink, brakes are too worn.)


See below.

I have never had to move calipers, even after replacing all 4 brakes lines.

05 elise (BOE Rev300 supercharged, SSRs, shift tower mods, Multivex; HID hi/low beams); 05 Corolla XRS. Past '72 Elan Sprint (I restored), Lotus 7 w/X-flow, TT Supra, Bugeye Sprite, BMW 2002 & 2002tii, '65 GTO.

Driving Tips-https://www.lotustalk.com/forums/f10...art-1-a-49665/
Moss Emergency Line-https://www.lotustalk.com/forums/f10...cy-line-36631/
Bleeding Brakes- https://www.lotustalk.com/forums/f10...-brakes-241138
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