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Poor Braking - Help Required


jwill214

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Howdy,

 

I'm rebuilding a 76 02 and working on the braking system but having a tough time. 

 

My current symptoms are excessive pedal travel and poor braking performance. I have new lines (hard and flexible), calipers, master cylinder and rear wheel cylinders and can only get a firm pedal if my rear drums are adjusted so that the shoes are locked against the drums. Even then, the pedal travels nearly to the floor before getting firm. When I press the pedal in, it feels like it is firming up for a short part of the stroke and then a noise sounding like a puff of air occurs and the pedal goes to the floor.

 

Things I have tried so far:

Bled entire system multiple times (>1 liter of fluid)  using power bleeder and RR, LR, RF, LF method. I also cracked the fittings at the master cylinder open to see if any air was trapped in the master cylinder.

I replaced my booster check valve

Adjusted the rear drum brakes according to the Haynes Manual, No change.

Checked for leaks at all fittings and end points, none were found

Replaced the rear brake line with a plug at the master cylinder. I got a firm pedal  when the pedal was nearly to the fire wall but the air puff issue still remained. Same thing happened when I adjusted the shoes to their maximum adjustment so they were locking the drums.

Searched here and bimmerforums for people experiencing similar issues as me

 

Things I am going to try again:

More brake bleeding

More rear drum adjustment

 

Questions:

Are there multiple sizes of drums/shoes for these cars? Do I have shoes that go with a smaller drum or vise versa?

The puff of air I am hearing sounds like its coming from the booster. The booster is original. Could that be causing an issue? Everything I have read about a failed booster is that the pedal feels too firm, not too soft.

 

Has anyone experience this or know what the issue could be. Any tips/tricks/hints/prayers are appreciated. 

 

Signed,

Jacob, Frustrated First Time 2002 Restorer

 

 

 

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Hi Jacob,

 

One thing you might try is to check the brand & compound of your linings.  I don't think it will help in your situation but a really quality pad is a great place to start & work your way back to the problem.

 

This gives a bit of moral support + lends itself to an ultimate solution.

 

Cleaning everything from the pedal to your pad is also a great place to start....& the more time you put in the better will be your understanding of the system & thus results.

 

Not the golden answer but hopefully more information will follow this post.

 

Best of luck,

 

Mo

Edited by mo02

73 sunroof 2002 (past)  |  73 CSi (present)  |  FAQ Member #2538

 

2002 decals (mofaraz.com)     |     eBay

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The more I trouble shoot the more it seems like a booster problem. It sounds like the "puff" of air is coming from the rear of the booster. Is there a seal that could be not seated right allowing air to blow by the booster? When I got a new master cylinder, it came with a new front seal for the booster. 

Edited by jwill214
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You didn't mention new drums... perhaps the drums are worn, so that there is excessive distance between shoe and drum surface. These cars are very sensitive to rear shoe adjustment.

 

Also - use high quality pads and make sure there's no glaze or ugliness on the rotors. 

 

My mantra for bleeding calipers: "UPPER, INNER, OUTER" on the bleed screws, per caliper. 

Paul Wegweiser

Wegweiser Classic BMW Services

Nationwide vehicle transport available

NEW WEBSITE! www.zenwrench.com

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From your description, it is not the rear.  You have air in the front half.    The booster has no effect if the engine is not running. You should get a firm pedal if the booster is working or not.  

 

Concentrate your debugging on the fronts.  Ignore booster and rear brakes for now.    Have you tried manual bleeding with a helper pumping the brake pedal?  Remote chance.  I always use a pressure bleeder and have no issues, but it is worth a try.

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Thanks for the replies everyone! I should have clarified that everything involved with the braking system is new including the drums. 

 

After doing some more digging I saw a picture showing me I had the calipers swapped. I have swapped them to the correct side and will bleed them after a food break. Hopefully that solves my problems. I feel like a dummy.

 

Still unsure if it will solve the strange air puff noise. We shall see. 

Edited by jwill214
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Bled the system three times after switching the calipers. Only the first round gave me any air bubbles, only solid fluid on the last two rounds. Pedal feels better but still has quite a bit of travel. The air puff sound is still there also.

 

I'll try more bleeding tomorrow to see if it improves further. 

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Where did you source your parts?

 

Yes there are multiple size drums and rear wheel cylinders. 

 

You might want to look carefully at those parts as well as the master cylinder to ensure that they are 2002-specific.

 

What brake fluid are you using?

 

Good luck, you'll get it sorted!

 

Cheers,

Edited by ray_

Ray

Stop reading this! Don't you have anything better to do?? :P
Two running things. Two broken things.

 

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Are you certain you installed the booster check valve in the proper orientation?

 

Was the booster itself an issue prior?

 

Double check that you were sent the parts you ordered ;-)

 

 

Ray

Stop reading this! Don't you have anything better to do?? :P
Two running things. Two broken things.

 

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Closely inspect the bleeder screw threads. Some rebuilt calipers have subpar quality bleeders. When bleeding the front, have a helper tap lightly on the calipers with a rubber hammer to try and expel any trapped air. Jack the front end up as well.

Jim Gerock

 

Riviera 69 2002 built 5/30/69 "Oscar"

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Had some bad info and had the booster check valve installed backwards. After correcting that the air puff sound is no more. One issue down! Yay! Thanks ray_ for that tip!

 

Image result for Yay meme

 

Going to spend today bleeding, starting with the master cylinder. 

Plan is as follows:

1. Jack up the front of the car so that the master cylinder is level or slightly nose up.

2. Pressurize the system using the power bleeder

3. Crack open the lines as the master cylinder starting with the line furthest away from the booster and working my way back.

4. Do a standard bleed with the pressure bleeder with the added tip of tapping on the calipers from jgerock

5. Press the brakes and find that I have solved my issues haha

 

If anyone has anything else they think I should try, let me know!

 

Jacob

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