Air in Rear Brakes

[Neelskit]

Got an interesting one for you... I have a 1999 LeSabre Limited with 151k miles. The drivers side rear brake seems to keep getting air in the line. However, it is not losing fluid. (level in resevior is constant) You can feel as you drive the car that the rear brakes aren't doing much (car tips forward during all breaking conditions) and the pedal feels "spungy". If I bleed that brake, the brakes feel normal for a few days, then are spongy again, as well as increased stopping distance. Is it possible for a leaking wheel cylinder seal to allow air in when the brake pedal is released, but not allow fluid to escape when the pedal is depressed. I have pulled the drum and the shoes/springs/drum all look good and no evidence of fluid leaking from the cylinder seals...or I am going about this all wrong and the problem lies elsewhere?

[HotZ28]

Welcome to AF!

Well, one thing for sure, if your system were leaking, there would be some evidence of fluid on the outside, either in the lines, connections, bleeder valve, wheel cylinders or calipers. When you release the brake pedal, you are simply releasing hydraulic pressure from the calipers or wheel cylinder, the system does not create a vacuum to pull air back in. BTW, your problem could also indicate a leaking master cylinder piston seal.

Now, with that said, have you checked the drum to shoe clearance? The auto adjuster on these cars, are notorious for not keeping the rear brakes in proper adjustment. It takes several reverse stops from a higher speed to engage the auto adjuster. Every few months, I put my car in reverse, then accelerate to about 20 MPH and hit the brakes hard. I execute this procedure three or four times on each occasion, to keep them in adjustment. In fact, I just did this today!

Normal stopping in reverse will not keep them adjusted. Unfortunately, this is how the system works. If you prefer, you can pull the drums and manually adjust the shoes until the drum fits snuggly on the shoes and start from there.

[Neelskit]

I think the rear brakes are adjusted properly- the parking brake is tight (2-3 clicks before it engages) and the drums fit snug on the shoes, but don't prevent wheel movement.

How do you think air keeps getting into the rear drivers brake line without leaking fluid. Would a failed Master Cylinder Piston Seal cause this? Could there be a problem with the ABS/TCS?

Thanks for your help!

[LeSabre97mint]

Hello

How is the problem with the brakes coming? How are you bleeding the brakes? I would try using a length of clear tubing and bleed into a clear container. Watch what comes through the hose. Are you having a helper push and hold the brake pedal while you open and close the bleeder? After you close the bleeder the helper then releases the pedel and then pushes it down again for the next air/fluid release.

I hope this helps.

Regards

Dan

[Neelskit]

Still having the problem- I've been bleeding the brakes with a vacuum pump on the bleeder screw. I get all the air out of the rear drivers (rear passenger does not accumulate air) wheel cylinder and close the screw. The car brakes great for about a week, then mysteriously there is air in the rear drivers brake again. Again- no noticable fluid loss in resivoir.

Puzzling.

Thanks again for any suggestions.

[HotZ28]

Click Here for the "Basic Operating Principles" of hydraulic brakes.

[LeSabre97mint]

Hello again,

I would try bleeding with using the brake pedel as I described in the above post. I've had problems using a vacuum pump because I've pulled air around the bleeder screw and not pulled a full vacuum. It might make a difference.

Regards

Dan

[speedbullet2]

Well i seem to be having this same problem and been to les schwab quite a few times im in 300 bucks so far in reapirs new master clyinder and rear wheel cylinders new brake lines etc etc etc and still get air in my system as well only in the passenger side on mine though rear anyways the guys i keep having work on mine are thinking its the abs unit creating air