Brake Pedal Supposed To Be HARD?

fangthorpe · 11-26-2003, 06:15 PM

I'm chasing good pedal pressure in a '92 Airstream MH with hydroboost. I have a high pedal that activates the brakes in the right place, but at rest, motor on, the pedal will travel 2" - 3" past where the brakes go on. Is the pedal at some point supposed to be HARD or is what I've got right?

Thanks

PeterH-79MH · 11-26-2003, 07:34 PM

Sounds like Master cylinder fading.
If you get a hard pedal at the normal location but it continues to fade further down, you need a new master cylinder.

swebster · 11-26-2003, 08:13 PM

I had the same problem with mine. Replaced the Master Cylinder in a under two hours and things are back to normal now. If you install this yourself make sure you bench bleed the master cylinder and take you time.

I had an over zealous assistant who immeadiately stomped the pedal to the floor and we spent then ext two hours gravity bleeding and pushing air out of the lines.

87MH · 11-27-2003, 09:57 AM

It's probably safe to assume the brake fluid has never been changed on your unit.

I would recommend bleeding the entire system in order to change out all of the brake fluid while you are messing with it.

Brake fluid absorbs water, especially with Motor Homes usually sitting idle for long periods. The water that is absorbed becomes highly acidic, and this encourages corrosion in the steel lines.

fangthorpe · 11-27-2003, 10:11 AM

I think that's where the problem came from. I bought it with a one-pump bubble in the brakes, although they worked fine. Sucked out the reservoir, gravity bled the new fluid out the fronts and had the "weird "pedal. Can't seem to get at the rear bleeders without removing the wheels, so I'll go back at it another time, but I can't for the life of me remember if the pedal - once pumped - was actually HARD. I posted this on open roads forum and got 10 responses from P30 owners saying they all had soft pedals and good brakes.
I will pull wheels, suck out all 4, smack the high spots in the rear and check the hoses, but should the pedal be "two feet stand on it racecar hard" or does the hydroboost bypass and let the pedal go down some past the engagement point?

87MH · 11-27-2003, 10:23 AM

Mine has about 3" total pedal travel from engagement to full lock up.

No bleedoff thereafter.

PeterH-79MH · 11-27-2003, 11:05 AM

same here, 3" travel, rock hard thereafter, with or without Hydroboost.
Back to my first reply: bad master cylinder.

fangthorpe · 11-29-2003, 12:48 PM

OK, last post on brakes, I promise. I gravity bled new fluid for 1 hour to all 4 wheels. Took 1 1/4 quarts until clean. Got no bubbles I could see. '92 has discs in rear - found no proportioning valve. Pedal with motor OFF is 1/3 down and HARD. Won't pump up, won't fall under steady pressure and stays the same after a 1 min. wait and another hard hit. I like this. However, with the motor/hydroboost on, the pedal is high when the brakes go on, lock and skid on gravel, but the pedal will go down another 2"- 3" past that point and it feels a little like the hydroboost is pushing back. Pedal never gets hard with motor on. Steering is OK, fluid is clean and full, all hoses on steering and brakes relatively fresh. I'm starting to think this is how it's supposed to be. Maybe I just never pushed the pedal past the engagement point before. It really doesn't feel like a bad MC or an internal bypass, as the pedal is hard and won't fall with the motor off. Any comment?

Also, I can only find 1 fuel filter, in the frame rail under the door. I thought there were supposed to be 2. This has F.I. remember.

Thanks.

PeterH-79MH · 11-29-2003, 01:10 PM

What you describe is exactly how the brakes on my 2003 GMC 3500 work, except the 2-3" you mention after lock-up. Also, the pedal does feel spongy and does come up after the motor is started.