Hello fellow Maximites, I am in the process of preparing my 2000 SE Betsy for sale. She's in mighty fine shape for her 14 years (ten of which with me), but there's one persistent problem that I'd like to get sorted before her lucky new owner steps forward.
The issue is with the brakes, specifically an odd problem with losing hydraulic pressure. Any time I go up a long grade at freeway speeds, I lose pressure after and end up with a mushy pedal. It doesn't drop to the floor, but it's pretty close. Two swift pumps and it's back to normal never to happen in in-town driving nor during typical freeway driving. It's only when I go up a long grade.
The history is that I've dealt with this problem before and presumed to solve it. About two years ago, the brakes turned to total mush at which point I replaced the master cylinder, pumped out the old fluid and bled the system using the prescribed methods. Everything was good for about two weeks until it happened again. Light pressure at a stoplight and the pedal would slowly sink to the floor. I figured I got a crummy reman so I returned it and got a new OEM MC. Same process again, install, bleed brakes. Everything seemed good, no leaks no problems. Over the course of a few months, my rear calipers started hanging, so I replaced them both (fronts were replaced about a year before). No leaky calipers, no fluid on the discs. However, now the problem I've described still persists despite mostly new brake hardware. I did notice that the lower MC connector had a lone drip on it and a spot the size of a half-dollar on the garage floor, so I tightened it up, but the problem has not gone away.
So if anyone out there has experienced a similar load-induced loss of hydraulic pressure and managed to sort it out, I'd certainly be appreciative if you would be willing to share the solution. I am a craptastic mechanic and I am both stumped and bummed that I'm stumped.

Thanks all!

 

Make sure all the lines are tight and do a full bleed on all your calipers in the proper order making sure your master never goes dry during.

 

Sounds like there's air in the lines...


Make sure brake master cylinder reservoir is full. Start car and have someone press up and down the brakes, look underneath the car and the same time if you have a leak somewhere you will hear and sit it

 

I have bled it many, many times, but the problem persists. Also if there were air in the lines, woulnd't the pedal be mushy all the time instead of just after an uphill run?

 

The problem might be the hydroback. You can test it. While the engine is off pump the foot brake until it reach the limit that you can no longet pump it down. Then hold the foot brake and start the engine, the foot brake should release and goes
down , means the hydroback is working. If the foot brake still stiff, you need to replace the hydroback.

 

Air is in the system for sure....Bleed starting at right rear> left rear> right front> left front!

 

Have you checked the power brake booster? If there is a small leak in the diaphram, it could cause the symptoms you are discribing

 

I have had this same issue, it was actually wheel bearings, they were loose and when you would go up hill you would never use your brakes and you would turn left to right so the hub would flop side to side in the bearing and the rotor would start pushing the brake pads out, then you would have to squeeze them back tight to the brake rotor to get the hard pedal.

im confident that this is your issue, jack the car up so the front wheel are off the ground and grab the tire at 12 and 6 and give it a shake, there should be no play.